Building Bulletin 93, Acoustic design of schools

Bui lding Bul let in 93

ACOUSTIC DESIGNOF SCHOOLS

A DESIGN GUIDE

BUILDING BULLETIN 93

Acoustic Design ofSchools

Architects and Building Branch

London : The Stationery Office

DfES Project TeamRichard Daniels Building Services Engineer, School Buildings & Design UnitAlex Freemantle Architect, Formerly of School Buildings & Design UnitMukund Patel Head of School Buildings & Design Unit

AcknowledgementsDfES would like to thank the following:

Editors:Bridget Shield, London South Bank UniversityCarl Hopkins, BRE Acoustics, Building Research Establishment Ltd (BRE)

Principal authors:Carl Hopkins & Robin Hall, BRE Acoustics, Building Research Establishment Ltd (BRE)Adrian James, Adrian James Acoustics, NorwichRaf Orlowski & Sam Wise, Arup AcousticsDavid Canning, City University

Other authors and advisors:Stephen Chiles University of BathDavid Dennis London Borough of NewhamNigel Cogger The English Cogger PartnershipJohn Miller & Theodoros Niaounakis Bickerdike Allen and PartnersLes Fothergill Building Regulations Division, Office of the

Deputy Prime MinisterGuy Shackle Barron and Smith ArchitectsJulie Dockrell Institute of Education, University of LondonMindy Hadi Building Research Establishment Ltd (BRE)Matthew Ling Formerly of Building Research Establishment Ltd (BRE)Russell Brett British Association of Teachers of the DeafRichard Vaughan National Deaf Children's SocietyRoz Comins Voice Care Network UKThomas Wulfrank Arup AcousticsDavid Coley & Andrew Mitchell Centre for Energy and the Environment, Exeter University. Derek Poole Formerly of University of Wales, College of CardiffJohn Lloyd & Tom Cecil Faber MaunsellPeter Brailey Hawksmoor Engineering Ltd.Andrew Parkin RW Gregory LLPTerry Payne Monodraught LtdWayne Aston PassiventTim Spencer Rockwool Rockfon LtdDavid Whittingham Formerly of Ecophon Ltd

Photographer: Philip Locker, Photo Graphic Design, Bolton

Design & Mac file: Malcolm Ward, Malcolm Studio, Croydon.

ISBN 0 11 271105 7

Introduction 1

Scope of Building Bulletin 93Overview of contents of Building Bulletin 93

Section 1: Specification of acoustic performance 7

1.1 Performance standards 81.1.1 Indoor ambient noise levels in unoccupied spaces1.1.2 Airborne sound insulation between spaces1.1.3 Airborne sound insulation between circulation spaces and

other spaces used by students1.1.4 Impact sound insulation of floors1.1.5 Reverberation in teaching and study spaces1.1.6 Sound absorption in corridors, entrance halls and stairwells1.1.7 Speech intelligibility in open-plan spaces

1.2 Demonstrating compliance to the Building Control Body 161.2.1 Alternative performance standards

1.3 Demonstrating compliance to the client 171.3.1 Timetabling of acoustic testing1.3.2 Remedial treatments1.3.3 Indoor ambient noise levels in unoccupied spaces1.3.4 Airborne sound insulation between spaces1.3.5 Airborne sound insulation between circulation spaces and

other spaces used by students1.3.6 Impact sound insulation1.3.7 Reverberation in teaching and study spaces1.3.8 Sound absorption in corridors, entrance halls and stairwells1.3.9 Speech intelligibility in open-plan spacesReferences

Section 2: Noise control 21

2.1 Choosing a site 212.2 Recommendations for external noise levels outside school buildings 212.3 Noise survey 222.4 Road and rail noise 232.5 Aircraft noise 232.6 Vibration 232.7 Noise barriers 242.8 Noise from schools to surrounding areas 242.9 Planning and layout 242.10 Limiting indoor ambient noise levels 252.11 Impact noise 252.12 Corridors, entrance halls and stairwells 252.13 Masking noise 262.14 Low frequency noise and hearing impaired pupils 26

References

Contents

1

2

Page

Section 3: Insulation from external noise 27

3.1 Roofs 273.1.1 Rain noise

3.2 External walls 283.3 Ventilation 28

3.3.1 Ventilators3.4 External windows 303.5 External doors 31

Sound insulation of the building envelope 323.6 Subjective characteristics of noise 323.7 Variation of noise incident on different facades 323.8 Calculations 323.9 Test Method 32

3.9.1 Conditions for similar constructions3.9.2 Conditions for similar sources

Sound insulation between rooms 333.10 Specification of the airborne sound insulation between rooms using Rw 33

3.10.1 Flanking details3.10.2 Examples of problematic flanking details3.10.3 Junction between ceilings and internal walls3.10.4 Flanking transmission through windows

3.11 Specification of the impact sound insulation between rooms using Ln,w 363.12 Internal walls and partitions 37

3.12.1 General principles3.12.2 Sound insulation of common constructions3.12.3 Flanking transmission3.12.4 High performance constructions – flanking transmission3.12.5 Corridor walls and doors

3.13 Internal doors, glazing, windows and folding partitions 413.13.1 Doors3.13.2 Lobbies3.13.3 Folding walls and operable partitions3.13.4 Roller shutters

3.14 Floors and ceilings 453.14.1 Impact sound insulation3.14.2 Voids above suspended ceilings3.14.3 Upgrading existing wooden floors using suspended plasterboard ceilings3.14.4 Upgrading existing wooden floors using platform and ribbed floors3.14.5 Concrete floors

3.15 Design and detailing of building elements 50References

Section 4: The design of rooms for speech 53

4.1 Approach to acoustic design 534.2 Internal ambient noise levels and speech clarity 534.3 Reverberation times 544.4 Amount of acoustic absorption required 544.5 Distribution of absorbent materials 544.6 Room geometry 544.7 Classrooms 55

Contents

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3 Page

4.8 Assembly halls, auditoria and lecture theatres 554.8.1 Room geometry4.8.2 Sound reinforcement

4.9 Open-plan teaching and learning areas 584.10 Practical spaces 59

4.10.1 Design and Technology spaces4.10.2 Art rooms4.10.3 Floor finishes in practical spaces

4.11 Drama rooms 604.12 Multi-purpose halls 614.13 Other large spaces 624.14 Dining areas 62

References

Section 5: The design of rooms for music 63

5.1 Aspects of acoustic design 635.2 Ambient noise 635.3 Sound insulation

5.3.1 Sound insulation between music rooms5.4 Room acoustics 64

5.4.1 Reverberation time, loudness and room volume5.4.2 Distribution of acoustic absorption5.4.3 Room geometry5.4.4 Diffusion

5.5 Types of room 675.5.1 Music classrooms5.5.2 Music classroom/recital room5.5.3 Practice rooms/group rooms5.5.4 Ensemble rooms5.5.5 Control rooms for recording5.5.6 Recording studios5.5.7 Audio equipment

5.6 Acoustic design of large halls for music performance 735.6.1 Shape and size5.6.2 Surface finishes

5.7 Design of large auditoria for music and speech 75References

Section 6: Acoustic design and equipment for pupils with specialhearing requirements 77

6.1 Children with listening difficulties 776.2 Children with hearing impairments and the acoustic environment 776.3 Hearing impairment and hearing aids 786.4 The speech signal and hearing aids 786.5 Listening demands within the classroom 796.6 Strategies developed to assist children with hearing and listening difficulties 796.7 Individual technology 80

6.7.1 Radio aids6.7.2 Auditory trainers and hard-wired systems

6.8 Whole class technology 826.8.1 Whole classroom soundfield systems6.8.2 System overview

Contents

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6

Page

6.8.3 Personal soundfield systems 6.8.4 Infra red technology6.8.5 Induction loop systems6.8.6 Audio-visual equipment6.8.7 Other assistive devices

6.9 Special teaching accommodation 876.10 Beyond the classroom 89

References

Section 7: Case studies 91

7.1 Remedial work to a multi-purpose hall in a county primary school 93 7.2 An investigation into the acoustic conditions in three open-plan primary schools 977.3 Remedial work to an open-plan teaching area in a primary school 1077.4 Conversion of a design and technology space to music accommodation 1137.5 A purpose built music suite 1177.6 A junior school with resource provision for deaf children 1237.7 An all-age special school for hearing impaired children 129 7.8 Acoustic design of building envelope and classrooms at a new secondary school 1397.9 Acoustically attenuated passive stack ventilation of an extension to an inner city

secondary school 1437.10 An investigation into acoustic conditions in open-plan learning spaces in

a secondary school 147

Appendices 159

Introduction to appendices 1591 Basic concepts and units 1612 Basic principles of room acoustics 1653 Basic principles of sound insulation 1674 Classroom sound insulation – sample calculations 1715 Sound insulation of the building envelope 1756 Calculation of room reverberation times 1777 Calculation of sound absorption required in corridors,

entrance halls and stairwells 1818 Equipment specifications for sound field systems in schools 1859 Noise at Work Regulations relating to teachers 19110 Example submission to Building Control Body 193

Bibliography 203

List of organisations 207

Contents

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Page

1

The constructional standards for acousticsfor new school buildings, as given inSection 1 of this document, are requiredto be achieved under the BuildingRegulations. This represents a significanttightening of the regulation of acousticdesign in schools, to reflect a generalrecognition, supported by research, thatteaching and learning are acousticallydemanding activities. In particular, thereis a consensus that low ambient noiselevels are required, particularly in view ofthe requirements of the SpecialEducational Needs and Disability Act20011 for integration of children withspecial needs in mainstream schools.

Unfortunately, a large number ofclassrooms in the UK currently sufferfrom poor acoustics. The most seriousacoustic problems are due to noisetransfer between rooms and/or excessivereverberation in rooms. There are manyreasons for the poor acoustics, for example:• The acoustics of the stock of oldVictorian schools are often unsuitable formodern teaching methods. • Modern constructions do not alwaysprovide adequate sound insulation andmay need special treatment. • Open plan, or semi-open plan layouts,designed to accommodate a number ofdifferent activities, are areas wherebackground noise and sound intrusionoften cause problems. • The acoustics of multi-purpose rooms,such as halls, have to be suitable for avariety of activities, for example music(which requires a long reverberationtime) and speech (which requires shorterreverberation times).

• Many activities, such as music anddesign technology lessons, can be noisyand will cause problems if there isinadequate sound insulation betweenareas for these activities and thoserequiring quieter conditions.

Poor acoustic conditions in theclassroom increase the strain on teachers’voices as most teachers find it difficult tocope with high noise levels. This oftenleads to voice problems due to prolongeduse of the voice and the need to shout tokeep control. Recent surveys in the UKand elsewhere show that teachers form adisproportionate percentage of voice clinicpatients.

Historically, there have been a numberof factors preventing good acoustic designand this Building Bulletin addresses theseissues.• Before 2003, Part E of the BuildingRegulations did not apply to schools. Itnow includes schools within its scope. • Although the constructional standardsfor schools previously quoted BuildingBulletin 87[2] as the standard foracoustics in schools, many designers wereunaware of the requirements of BB87 andthe standards were rarely enforced. Thesestandards have been updated to reflectcurrent research and the relevantrequirements of the DisabilityDiscrimination Act, and are included inthe compliance section, Section 1, of thisbulletin.• The pressure on finances has meant inthe past that acoustics came low on thelist of design priorities. The acousticdesign will now have a higher priority as itwill be subject to building control

Introduction

1. Now incorporated asSection IV of the DisabilityDiscrimination Act[1]

Building Bulletin 93 aims to:• provide a regulatory framework for the acoustic design of schools in support

of the Building Regulations• give supporting advice and recommendations for planning and design of

schools• provide a comprehensive guide for architects, acousticians, building control

officers, building services engineers, clients, and others involved in the design of new school buildings.

2

approval procedures.• There has been little guidance availablein the past on how to achieve the rightbalance of acoustics in the complex anddynamic environment of a school.Architects and designers have had adifficult time finding information to makedesign easy and, in particular, to helpthem choose the correct target values ofappropriate parameters.

Overall, Building Bulletin 93recommends a structured approach toacoustic design at each stage of theplanning and design process, as shown inthe table below.

Introduction

A structured approach to acoustic design at each stage of the planning and design process

Feasibility/Sketch Design ■ Selection of the site■ Noise survey to establish external noise levels■ Orientation of buildings■ Massing and form of the buildings■ Consideration of need for external noise barriers using the buildings, fences and screens and

landscape features■ Preliminary calculation of sound insulation provided by building envelope including the effect of

ventilation openings

Detailed Design ■ Determine appropriate noise levels and reverberation times for the various activities and room types

■ Consider the special educational needs of the pupils ■ Consider the design of music, drama and other specialist spaces separately from that of

normal classrooms as the design criteria are very different.■ Provide the necessary façade sound insulation whilst providing adequate ventilation,

particularly in the case of spaces such as classrooms and science laboratories which require high ventilation rates

■ Architectural/acoustic zoning: plan the disposition of 'quiet' and 'noisy' spaces, separating them wherever possible by distance, external areas or neutral 'buffer' spaces such as storerooms or corridors

■ Consider sound insulation separately from other aspects of room acoustics using walls, floors and partitions to provide adequate sound insulation

■ Design the acoustics of the rooms by considering their volume and shape, and the acoustic properties of their surfaces

■ Specify the acoustic performance of doors, windows and ventilation openings ■ Specify any amplification systems

Building Control Approval ■ Submit plans, including specific details of the acoustic design, for approval by Building Control Body

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SCOPE of Building Bulletin 93

Section 1 of Building Bulletin 93supersedes Section A of Building Bulletin87[2] as the constructional standard foracoustics for new school buildings.

In addition, Part E of the BuildingRegulations includes schools within itsscope and Approved Document E[3]

gives the following guidance: “In theSecretary of State’s view the normal way ofsatisfying Requirement E4 will be to meetthe values for sound insulation,reverberation time and internal ambientnoise which are given in Section 1 ofBuilding Bulletin 93 ‘The Acoustic Designof Schools’, produced by DfES.”

The requirements of Section 1 cameinto force on 1st July 2003, at the sametime as those contained in the newApproved Document Part E[3], insupport of the Building Regulations.

Requirement E4 from Part E ofSchedule 1 to The Building Regulations2000 (as amended) states that:

“Each room or other space in a schoolbuilding shall be designed and constructedin such a way that it has the acousticconditions and the insulation againstdisturbance by noise appropriate to itsintended use.”

The Education (School Premises)Regulations 1999, SI 1999 No.2 whichapplies to both new and existing schoolbuildings, contains a similar statement: “Each room or other space in a schoolbuilding shall have the acoustic conditionsand the insulation against disturbance bynoise appropriate to its normal use.”

Compliance with the acousticperformance standards specified inSection 1 will satisfy both regulations fornew schools.

Although Building Regulations do notapply to all alteration and refurbishmentwork, it is desirable that such work shouldconsider acoustics and incorporateupgrading of the acoustics as appropriate.(In the case of existing buildings, theBuilding Regulations apply only to‘material alterations’ as defined inRegulations 3 and 4.) Although it wouldbe uneconomic to upgrade all existingschool buildings to the same standards as

new school buildings, where there is aneed for upgrading the acousticperformance of an existing building orwhen refurbishment is happening forother reasons, then the designer shouldaim to meet the acoustic performancegiven in Section 1 of BB93 to satisfy theSchool Premises Regulations and theDisability Discrimination Act.

The exemption of Local EducationAuthority (LEA) maintained schools fromthe Building Regulations has ended. Newschool buildings, including extensions toexisting school buildings and new schoolsformed by change of use of otherbuildings, are now included in theBuilding Regulations and may be subjectto detailed design checks and on-siteinspections by Building Control Bodies.

The Building Regulations and hencethe requirements of BB93 only apply inEngland and Wales. They apply to bothLEA maintained schools and independentschools.

Temporary buildings are exempt fromthe Building Regulations. Temporarybuildings are defined in Schedule 2 to theBuilding Regulations as those which arenot intended to remain in place for longerthan 28 days. What are commonly calledtemporary buildings in schools are classedas prefabricated buildings and arenormally subject to the same BuildingRegulations requirements as other typesof building. Additional guidance is givenin Clause 0.6 of Approved DocumentE[3]. A building that is created bydismantling, transporting and re-erectingthe sub-assemblies on the same premises,or is constructed from sub-assembliesobtained from other premises or fromstock manufactured before 1st July 2003,would normally be considered to meet therequirements for schools if it satisfies therelevant provisions relating to acousticstandards set out in the 1997 edition ofBuilding Bulletin 87[2].

The extension of Part E of Schedule 1to the Building Regulations 2000 (asamended by SI 2002/2871) to schoolsapplies to teaching and learning spaces.Therefore the performance standards in

Introduction

4

Introduction

the tables in Section 1 are required forcompliance with Part E for all teachingand learning spaces. Part E of theBuilding Regulations is not intended tocover the acoustic conditions inadministration and ancillary spaces not usedfor teaching and learning except in as far asthey affect conditions in neighbouringteaching and learning spaces. Thereforeconsideration needs to be given toadjoining areas, such as corridors, whichmight have doors, ventilators, or glazingseparating them from a teaching orlearning space. The performance standardsgiven in the tables for administration andancillary spaces are for guidance only.

Rooms used for nursery andadult/community education within schoolcomplexes are also covered by Part E. PartE does not apply to nursery schools whichare not part of a school, sixth form collegeswhich have not been established as schools,and Universities or Colleges of Furtherand Higher Education2. However, manyof the acoustic specifications are desirableand can be used as a guide to the designof these buildings. The standards areparticularly appropriate for nurseryschools as figures are quoted for nurseryspaces within primary schools.

The Disability Discrimination Act

1995[1], as amended by the SpecialEducational Needs and Disability Act2001, places a duty on all schools andLEAs to plan to increase over time theaccessibility of schools for disabled pupilsand to implement their plans. Schools andLEAs are required to provide:• increased access for disabled pupils tothe school curriculum. This coversteaching and learning and the widercurriculum of the school such as after-school clubs, leisure and culturalactivities.• improved access to the physicalenvironment of schools, includingphysical aids to assist education. Thisincludes acoustic improvements and aidsfor hearing impaired pupils.

When alterations affect the acoustics ofa space then improvement of the acousticsto promote better access for children withspecial needs, including hearingimpairments, should be considered. Approved Document M: 1999 – Accessand facilities for disabled people, insupport of the Building Regulations[4]

includes requirements for access forchildren with special needs. See also BS8300: 2001 Design of buildings and theirapproaches to meet the needs of disabledpeople[5].

2. Part E of the Building Regulations quotes the definition of school given in Section 4 of the1996 Education Act. In the case of sixth form colleges Section 4 of the 1996 Act should be readin conjunction with Section 2 of the same Act, in particular subsections (2), (2A) and (4) whichdeal with the definition of secondary education.

If a sixth form college is established as a school under the 1998 School Standards andFramework Act then it will be classed as a school under Section 4 of the 1996 Education Act andPart E of the Building Regulations on acoustics will apply. Only one sixth form college has beenestablished in this way up until now.

Therefore, most sixth form colleges are institutions in the Further Education sector and notschools, and Part E of the Building Regulations will not apply.

In the case of a new sixth form college it will be necessary to contact the LEA to enquire if thesixth form college has been established as a school or as an Institute of Further Education.

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Introduction

Section 1: Specification of AcousticPerformance consists of three parts.

Section 1.1 gives the performancestandards for new school buildings tocomply with the Building Regulations. These provide a good minimum standardfor school design. However, on occasionhigher standards will be necessary.

Section 1.2 sets out the preferredmeans of demonstrating compliance tothe Building Control Body.

Section 1.3 gives the testsrecommended to be conducted as part ofthe building contract.

Section 2: Noise Control describes howto conduct a site survey and to plan theschool to control noise. It also includesrecommendations on maximum externalnoise levels applying to playing fields,recreational areas and areas used forformal and informal outdoor teaching.External levels are not covered byBuilding Regulations but are taken intoconsideration in planning decisions bylocal authorities[6].

Section 3: Sound Insulation gives detailedguidance on constructions to meet theperformance standards for soundinsulation specified in Section 1.1.

Section 4: The Design of Rooms forSpeech and Section 5: The Design ofRooms for Music give guidance onvarious aspects of acoustic design relevantto schools.

Section 6: Acoustic Design andEquipment for Pupils with SpecialHearing Requirements discusses designappropriate for pupils with hearingimpairments and special hearingrequirements. It discusses the necessaryacoustic performance of spaces anddescribes the range of aids available tohelp these pupils.

Section 7 contains 10 case studiesillustrating some of the most importantaspects of acoustic design of schools.

Appendix 1 defines the basic concepts andtechnical terms used in the Bulletin.

Appendices 2 and 3 describe the basicprinciples of room acoustics and soundinsulation.

Appendices 4 to 7 give examples ofcalculations of sound insulation,reverberation time and absorption.

Appendix 8 gives equipment specificationsfor sound field systems to guide thosewho need to specify this type of equipment.

Appendix 9 gives an overview of theNoise at Work Regulations as they relateto teachers.

Appendix 10 gives an example of asubmission for approval by a BuildingControl Body.

The DfES acoustics websitewww.teachernet.gov.uk/acoustics containsfurther reference material which expandson the source material for acousticiansand designers. For example, it links to aspreadsheet which can be used to calculatethe sound insulation of the buildingenvelope and the reverberation time ofinternal rooms. The website will beregularly updated with new information,discussion papers and case studies. Thewebsite also contains complete downloadsof BB93.

Overview of contents of Building Bulletin 93

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References[1] Disability Discrimination Act (1995) Part IVwww.hmso.gov.uk[2] Building Bulletin 87, Guidelines forEnvironmental Design in Schools (Revision of Design Note 17), The Stationery Office, 1997. ISBN 011 271013 1. (Now superseded by2003 version of BB87, which excludesacoustics, and is available onwww.teachernet.gov.uk/energy)[3] Approved Document E – Resistance to thepassage of sound. Stationery Office, 2003. ISBN 0 11 753 642 3. www.odpm.gov.uk[4] Approved Document M:1999 Access andfacilities for disabled people, in support of theBuilding Regulations, Stationery Office, 1999 ISBN 0 11 753469. To be replaced shortly byApproved Document M, Access to and use ofbuildings.www.odpm.gov.uk [5] BS 8300: 2001 Design of buildings andtheir approaches to meet the needs of disabledpeople, Code of Practice. [6] PPG 24, Planning Policy Guidance: Planningand Noise, Department of the Environment, TheStationery Office, September 1994. To bereplaced by revised Planning Policy documents.

Introduction

The normal way of satisfyingRequirement E4 of The BuildingRegulations is to demonstrate that all theperformance standards in Section 1.1, asappropriate, have been met.

Section 1.2 sets out the preferredmeans for demonstrating compliance ofthe design to the Building Control Body.

Section 1.3 describes acoustic tests thatcan be used to demonstrate compliancewith the performance standards in Section1.1. It is strongly recommended that theclient require acoustic testing to becarried out as part of the buildingcontract, because testing of the completed

construction is the best practical means ofensuring that it achieves the design intent.

In all but the simplest of projects it isadvisable to appoint a suitably qualifiedacoustic consultant1 at an early stage ofthe project, before the outline design hasbeen decided. This will prevent simplemistakes which can be costly to design outat a later stage. An acoustic consultant willnormally be needed to check the designdetails and on-site construction, and tocarry out acoustic tests to confirm thatthe building achieves the requiredacoustic performance.

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Contents1.1 Performance standards 9

1.1.1 Indoor ambient noise levels in unoccupied spaces 91.1.2 Airborne sound insulation between spaces 121.1.3 Airborne sound insulation between circulation spaces and

other spaces used by students 121.1.4 Impact sound insulation of floors 131.1.5 Reverberation in teaching and study spaces 141.1.6 Sound absorption in corridors, entrance halls and stairwells 151.1.7 Speech intelligibility in open-plan spaces 16

1.2 Demonstrating compliance to the Building Control Body 171.2.1 Alternative performance standards 17

1.3 Demonstrating compliance to the client 181.3.1 Timetabling of acoustic testing 181.3.2 Remedial treatments 181.3.3 Indoor ambient noise levels in unoccupied spaces 181.3.4 Airborne sound insulation between spaces 181.3.5 Airborne sound insulation between circulation spaces and

other spaces used by students 181.3.6 Impact sound insulation 181.3.7 Reverberation in teaching and study spaces 181.3.8 Sound absorption in corridors, entrance halls and stairwells 191.3.9 Speech intelligibility in open-plan spaces 19References 19

Specification of acoustic performance 1Section 1 of Building Bulletin 93 sets the performance standards for theacoustics of new buildings, and describes the normal means of demonstrating

compliance with The Building Regulations.

1 The primary professionalbody for acoustics in theUK is the Institute ofAcoustics. An experiencedprofessional acousticianwho is competent to beresponsible for theacoustic design of schoolbuildings would normally bea corporate member of theInstitute of Acoustics.

SE

CT

ION

1.1 Performance standardsThe overall objective of the performancestandards in Section 1.1 is to provideacoustic conditions in schools that (a)facilitate clear communication of speechbetween teacher and student, andbetween students, and (b) do notinterfere with study activities.

Performance standards on thefollowing topics are specified in thissection to achieve this objective:• indoor ambient noise levels • airborne sound insulation betweenspaces• airborne sound insulation betweencorridors or stairwells and other spaces• impact sound insulation of floors• reverberation in teaching and studyspaces• sound absorption in corridors, entrancehalls and stairwells• speech intelligibility in open-planspaces.

All spaces should meet theperformance standards defined in Tables1.1, 1.2, 1.3, 1.4 and 1.5 for indoorambient noise level, airborne and impactsound insulation, and reverberation time.Open-plan spaces should additionallymeet the performance standard for speechintelligibility in Table 1.6.

The notes accompanying Tables 1.1,1.2, 1.3 and 1.5 contain additionalguidance that should be considered whendesigning the spaces to meet theperformance standards in these tables.Although good practice, this guidancewill not be enforced under the BuildingRegulations.

1.1.1. Indoor ambient noise levels inunoccupied spacesThe objective is to provide suitableindoor ambient noise levels (a) for clearcommunication of speech betweenteacher and student, and betweenstudents and (b) for study activities.

The indoor ambient noise levelincludes noise contributions from:• external sources outside the schoolpremises (including, but not limited to,noise from road, rail and air traffic,industrial and commercial premises) • building services (eg ventilation system,

plant, etc). If a room is naturallyventilated, the ventilators or windowsshould be assumed to be open as requiredto provide adequate ventilation. If a roomis mechanically ventilated, the plantshould be assumed to be running at itsmaximum operating duty.

The indoor ambient noise levelexcludes noise contributions from: • teaching activities within the schoolpremises, including noise from staff,students and equipment within thebuilding or in the playground. Noisetransmitted from adjacent spaces isaddressed by the airborne and impactsound insulation requirements.• equipment used in the space (egmachine tools, CNC machines, dust andfume extract equipment, compressors,computers, overhead projectors, fumecupboards). However, these noise sourcesshould be considered in the designprocess. • rain noise. However, it is essential that

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NOTES ON TABLE 1.11 Research indicates that teaching can bedisrupted by individual noisy events such asaircraft flyovers, even where the noise level isbelow the limits in Table 1.1. For roomsidentified in Table 1.1 having limits of 35 dB orless the noise level should not regularly exceed55 dB LA1,30min.2 Acoustic considerations of open-plan areasare complex and are discussed in Section1.1.7 and Section 4. 3 Studios require specialised acousticenvironments and the noise limits for these willvary with the size, intended use and type ofroom. In some cases noise limits below 30 dB LAeq may be required, and separatelimits for different types of noise may beappropriate; specialist advice should be sought.4 Halls are often multi-functional spaces(especially in primary schools) used foractivities such as dining, PE, drama, music,assembly, and performing plays and concerts.In such multi-functional spaces the designershould design to the lowest indoor ambientnoise level for which the space is likely to beused. For large halls used for formal drama andmusic performance lower noise levels thanthose in Table 1.1 are preferable, and levels of25 dB LAeq,30min may be appropriate. In thesecases specialist advice should be sought.

Specification of acoustic performance1

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Table 1.1: Performance standardsfor indoor ambient noise levels - upperlimits for the indoor ambient noiselevel, LAeq,30min

Type of room

Nursery school playroomsNursery school quiet roomsPrimary school: classrooms, class bases, generalteaching areas, small group roomsSecondary school: classrooms, general teaching areas,seminar rooms, tutorial rooms, language laboratoriesOpen-plan2

Teaching areasResource areasMusicMusic classroomSmall practice/group roomEnsemble room Performance/recital roomRecording studio3

Control room for recordingLecture rooms Small (fewer than 50 people)Large (more than 50 people)Classrooms designed specifically for use by hearingimpaired students (including speech therapy rooms)Study room (individual study, withdrawal, remedialwork, teacher preparation)LibrariesQuiet study areasResource areasScience laboratoriesDrama studiosDesign and Technology• Resistant materials, CADCAM areas• Electronics/control, textiles, food,

graphics, design/resource areasArt roomsAssembly halls4, multi-purpose halls4 (drama, PE,audio/visual presentations, assembly, occasional music) Audio-visual, video conference roomsAtria, circulation spaces used by studentsIndoor sports hallDance studioGymnasiumSwimming poolInterviewing/counselling rooms, medical rooms Dining roomsAncillary spaces Kitchens*

Offices*, staff rooms*Corridors*, stairwells*Coats and changing areas*Toilets*

Room classification for the purpose ofairborne sound insulation in Table 1.2

Activity noise(Source room)HighLow

Average

Average

AverageAverage

Very highVery highVery highVery highVery highHigh

AverageAverage

Average

Low

LowAverageAverageHigh

High

AverageAverage

HighAverageAverageHighHighHighHighLowHighHighAverageAverage - HighHighAverage

Noise tolerance(Receiving room)LowLow

Low

Low

MediumMedium

LowLowVery lowVery lowVery lowLow

LowVery low

Very low

Low

LowMediumMediumVery low

High

MediumMedium

LowLowMediumMediumMediumMediumHighLowHighHighMediumHighHighHigh

Upper limit for theindoor ambientnoise levelLAeq,30min (dB)

351

351

351

351

401

401

351

351

301

301

301

351

351

301

301

351

351

4040301

40

4040

351

351

4540404050351

455040454550

1Specification of acoustic performance

* Part E of Schedule 1 to the Building Regulations 2000 (as amended by SI 2002/2871) applies to teaching and learning spaces and is not intended to coveradministration and ancillary spaces (see under Scope in the Introduction). For theseareas the performance standards are for guidance only.

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this noise is considered in the design oflightweight roofs and roof lights as it cansignificantly increase the indoor ambientnoise level (see the design guidance inSection 3.1.1). It is intended that aperformance standard for rain noise willbe introduced in a future edition ofBB93. To satisfy this edition of BB93 itshould be demonstrated to the BuildingControl Body that the roof has beendesigned to minimise rain noise (seeSection 1.2).

Table 1.1 contains the required upperlimits for the indoor ambient noise levelsfor each type of unoccupied space. Thenoise levels in Table 1.1 are specified interms of LAeq,30min. This is an averagenoise level over 30 minutes, as explainedin Appendix 1. The specified levels referto the highest equivalent continuous A-weighted sound pressure level,

LAeq,30min, likely to occur during normalteaching hours. The levels due to externalsources will depend on weatherconditions (eg wind direction) and localactivities. High noise levels due toexceptional events may be disregarded.

The indoor ambient noise levels inTable 1.1 apply to finished butunoccupied and unfurnished spaces.

Tonal and intermittent noises aregenerally more disruptive than othertypes of noise at the same level. Noisefrom plant, machinery and equipment innoise–sensitive rooms should therefore beconstant in nature and should not containany significant tonal or intermittentcharacteristics. Noise from buildingservices which is discontinuous, tonal, orimpulsive (ie noise which can bedistracting) should be reduced to a level atleast 5 dB below the specified maximum.

Minimum DnT (Tmf,max),w (dB) Activity noise in source room (see Table 1.1)

Low Average High Very high

High 30 35 45 55

Medium 35 40 50 55

Low 40 45 55 55

Very low 45 50 55 60

Noi

se t

oler

ance

in

rec

eivi

ng r

oom

(see

Tab

le 1

.1)

Table 1.2: Performancestandards for airbornesound insulation betweenspaces - minimum weightedBB93 standardized leveldifference, DnT (Tmf,max),w

NOTES ON TABLE 1.21 Each value in the table is the minimum required to comply with the Building Regulations. A valueof 55 dB DnT (Tmf,max),w between two music practice rooms will not mean that the music will beinaudible between the rooms; in many cases, particularly if brass or percussion instruments areplayed, a higher value is desirable. 2 Where values greater than 55 dB DnT (Tmf,max),w are required it is advisable to separate the roomsusing acoustically less sensitive areas such as corridors and storerooms. Where this is not possible,high performance constructions are likely to be required and specialist advice should be sought.3 It is recommended that music rooms should not be placed adjacent to design and technologyspaces or art rooms.4 These values of DnT (Tmf,max),w include the effect of glazing, doors and other weaknesses inthe partition. In general, normal (non-acoustic) doors provide much less sound insulation than thesurrounding walls and reduce the overall DnT (Tmf,max),w of the wall considerably, particularly forvalues above 35 dB DnT (Tmf,max),w. Therefore, doors should not generally be installed inpartitions between rooms requiring values above 35 dB DnT (Tmf,max),w unless acoustic doors,door lobbies, or double doors with an airspace are used. This is not normally a problem as roomsare usually accessed via corridors or circulation spaces so that there are at least two doorsbetween noise-sensitive rooms. For more guidance see Section 3.


11

In rooms with very low noise tolerance,including music rooms, studios androoms used for formal music and dramaperformance, any audible intermittentnoise source of this type is likely to causeproblems and specialist advice should besought.

1.1.2. Airborne sound insulationbetween spaces The objective is to attenuate airbornesound transmitted between spacesthrough walls and floors.

Table 1.2 contains the requiredminimum airborne sound insulationvalues between rooms. These values aredefined by the activity noise in the sourceroom and the noise tolerance in thereceiving room. The activity noise andnoise tolerance for each type of room aregiven in Table 1.1. The airborne soundinsulation is quoted in terms of theweighted BB93 standardized leveldifference, DnT (Tmf,max),w, between tworooms.

The BB93 standardized leveldifference, DnT (Tmf,max), is the leveldifference, in decibels, corresponding to aBB93 reference value of the reverberationtime in the receiving room:

DnT(Tmf,max) = D+10 lg dB

whereD is the level difference (dB)

T is the reverberation time in thereceiving room (s)Tmf,max is the reference reverberationtime equal to the upper limit of thereverberation time, Tmf, given in Table1.5 for the type of receiving room. Thisreference reverberation time shall be usedfor all frequency bands.

The BB93 standardized leveldifference, DnT (Tmf,max),w, is measuredin accordance with BS EN ISO 140-4:1998[1] in octave or one-third octavebands, the results are weighted andexpressed as a single-number quantity,DnT (Tmf,max),w, in accordance with BSEN ISO 717-1:1997[2].

The prediction and measurement ofDnT (Tmf,max),w between two roomsmust be carried out in both directions asits value depends upon the volume of thereceiving room, see the example below.

1.1.3 Airborne sound insulationbetween circulation spaces and otherspaces used by studentsThe objective is to attenuate airbornesound transmitted between circulationspaces (eg corridors, stairwells) and otherspaces used by students.

Table 1.3 contains the requiredminimum airborne sound insulation forthe separating wall construction, anydoorset in the wall and any ventilators inthe wall. The airborne sound insulationfor walls and doorsets is quoted in terms

Example to determine the performance standards for airborne sound insulation between a music classroom and asecondary school general teaching area.

From the music classroom (source room) to the general teaching area (receiving room): Table 1.1 shows that music classrooms have ‘very high’ activity levels and that general teaching areas have ‘low’tolerance. Table 1.2 shows that at least 55 dB DnT (0.8s),w is required.

From the general teaching area (source room) to the music classroom (receiving room): Table 1.1 shows that general teaching areas have ‘average’ activity levels and that music classrooms have ‘low’ tolerance.Table 1.2 shows that at least 45 dB DnT (1.0s),w is required.

In this example the requirement to control noise from the music classroom to the general teaching area is more stringent.

The construction should be designed to achieve at least 55 dB DnT (0.8s),w from the music classroom (source room) tothe general teaching area (receiving room), and at least 45 dB DnT (1.0s),w from the general teaching area (source room)to the music classroom (receiving room).


TTmf,max

of the weighted sound reduction index,Rw, which is measured in the laboratory.The airborne sound insulation forventilators is quoted in terms of theweighted element-normalized leveldifference, Dn,e,w. The performancestandard for ventilators is quoted in termsof Dn,e,w –10lgN where N is the numberof ventilators with airborne soundinsulation Dn,e,w.

The weighted sound reduction index ismeasured in accordance with BS EN ISO140-3:1995[3] and rated in accordancewith BS EN ISO 717-1:1997[2].

The weighted element-normalized leveldifference is measured in accordance withBS EN 20140-10:1992[4] and rated inaccordance with BS EN ISO 717-1:1997[2].

Table 1.3 excludes:• service corridors adjacent to spaces thatare not used by students• lobby corridors leading only to spacesused by students that have a hightolerance to noise as defined in Table 1.1.

The performance standard is set using

12

Type of space used by students Minimum Rw (dB) MinimumDn,e,w –10lgN

Wall including Doorset1 (dB)any glazing

All spaces except music rooms 40 30 39

Music rooms2 45 35 453

Table 1.3: Performancestandards for airbornesound insulation betweencirculation spaces andother spaces used bystudents - minimum soundreduction index, Rw andminimum Dn,e,w –10lgN(laboratory measurements}

a laboratory measurement because of thedifficulty in accurately measuring theairborne sound insulation between roomsand corridors, or rooms and stairwells inthe field. Therefore it is crucial that theairborne sound insulation of the walland/or doorset is not compromised byflanking sound transmission, eg soundtransmission across the junction betweenthe ceiling and the corridor wall (seeguidance in Section 3.10.3).

1.1.4. Impact sound insulation offloorsThe objective is to attenuate impactsound (eg footsteps) transmitted intospaces via the floor.

Table 1.4 contains the recommendedmaximum weighted BB93 standardizedimpact sound pressure level, L′nT (Tmf,max),w, for receiving rooms ofdifferent types and uses.

The BB93 standardized impact soundpressure level, L′nT (Tmf,max), is theimpact sound pressure level in decibelscorresponding to a BB93 reference valueof the reverberation time in the receivingroom:

L′nT(Tmf,max) = Li – 10 lg dB

whereL i is the impact sound pressure level (dB)T is the reverberation time in thereceiving room (s)Tmf,max is the reference reverberationtime equal to the upper limit of thereverberation time, Tmf , given in Table1.5 for the type of receiving room. Thisreference reverberation time shall be usedfor all frequency bands.

The BB93 standardized impact soundpressure level, L′nT (Tmf,max), is measured

NOTES ON TABLE 1.31 The Rw ratings are for the doorset alone.Manufacturers sometimes provide doorsetsound insulation data as a combined rating forthe wall and doorset where the Rw refers to theperformance of an ≈10 m2 high-performancewall containing the doorset. This is notappropriate as it gives higher figures than theRw of the doorset itself. However, withknowledge of the wall and doorset areas theRw of the doorset can be calculated from thesetest results. 2 Special design advice is recommended.3 Wherever possible, ventilators should not beinstalled between music rooms and circulationspaces.


TTmf,max

13

Type of room(receiving room)

Nursery school playroomsNursery school quiet roomsPrimary school: classrooms, class bases, general teaching areas, small group roomsSecondary school: classrooms, general teachingareas, seminar rooms, tutorial rooms, language laboratoriesOpen-planTeaching areasResource areasMusicMusic classroomSmall practice/group roomEnsemble room Performance/recital roomRecording studioControl room for recordingLecture roomsSmall (fewer than 50 people)Large (more than 50 people)Classrooms designed specifically for use by hearingimpaired students (including speech therapy rooms)Study room (individual study,withdrawal, remedial work,teacher preparation)LibrariesScience laboratoriesDrama studiosDesign and Technology• Resistant materials, CADCAM areas• Electronics/control, textiles, food,

graphics, design/resource areasArt roomsAssembly halls, multi-purpose halls (drama, PE, audio/visual presentations, assembly,occasional music) Audio-visual, video conference roomsAtria, circulation spaces used by studentsIndoor sports hallGymnasiumDance studioSwimming poolInterviewing/counselling rooms, medical rooms Dining roomsAncillary spaces Kitchens*

Offices*, staff rooms*Corridors*, stairwells*Coats and changing areas*Toilets*

Maximum weightedBB93 standardizedimpact soundpressure level L′nT (Tmf,max),w (dB)

6560

60

60

6060

555555555555

6055

55

60606555

65

6060

6060656565606560656565656565

Table 1.4: Performance standards for impact sound insulation of floors -maximum weighted BB93 standardized impact sound pressure level L′nT (Tmf,max),w

in accordance with BS EN ISO 140-7:1998[5] in octave or one-third octavebands, the results are weighted andexpressed as a single-number quantity,L′nT (Tmf,max),w, in accordance with BS EN ISO 717-2:1997[6].

Impact sound insulation should bedesigned and measured for floors withouta soft covering (eg carpet, foam backedvinyl) except in the case of concretestructural floor bases where the softcovering is an integral part of the floor.

1.1.5. Reverberation in teaching andstudy spaces The objective is to provide suitablereverberation times for (a) clearcommunication of speech betweenteacher and student, and betweenstudents, in teaching and study spaces and(b) music teaching and performance.

Table 1.5 contains the required mid-frequency reverberation times for roomswhich are finished but unoccupied andunfurnished. The reverberation time isquoted in terms of the mid-frequencyreverberation time, Tmf , the arithmeticaverage of the reverberation times in the500 Hz, 1 kHz and 2 kHz octave bands.

Sound absorption from pinboards andnoticeboards can change when they arecovered up or painted. Absorptioncoefficients for pinboards and noticeboardsused in design calculations should be forfully covered or painted boards, asappropriate. If these data are not availablethen the absorption coefficient for theboard area used in the design calculationshould be the absorption coefficient ofthe wall to which the board is attached.

* Part E of Schedule 1 to the BuildingRegulations 2000 (as amended by SI 2002/2871) applies to teaching andlearning spaces and is not intended to coveradministration and ancillary spaces (see underScope in the Introduction). For these areas theperformance standards are for guidance only.


14

1.1.6. Sound absorption in corridors,entrance halls and stairwellsThe objective is to absorb sound incorridors, entrance halls and stairwells sothat it does not interfere with teachingand study activities in adjacent rooms.

The requirement is to provideadditional sound absorption in corridors,entrance halls and stairwells. The amountof additional absorption should becalculated according to ApprovedDocument E[7], Section 7. This describestwo calculation methods, A and B, forcontrolling reverberation in the commoninternal parts of domestic buildings. Oneof these methods should be used todetermine the amount of absorptionrequired in corridors, entrance halls andstairwells in schools. (See samplecalculations using calculation methods Aand B in Appendix 7.)

Sound absorption from pinboards andnoticeboards can change when they arecovered up or painted. Absorptioncoefficients for pinboards andnoticeboards used in design calculationsshould be for fully covered or paintedboards, as appropriate. If these data arenot available then the absorption

Type of roomNursery school playroomsNursery school quiet roomsPrimary school: classrooms, class bases, generalteaching areas, small group roomsSecondary school: classrooms, general teachingareas, seminar rooms, tutorial rooms, language laboratoriesOpen-planTeaching areasResource areasMusicMusic classroomSmall practice/group roomEnsemble room Performance/recital room3

Recording studioControl room for recordingLecture rooms3

Small (fewer than 50 people)Large (more than 50 people)Classrooms designed specifically for use by hearingimpaired students (including speech therapy rooms)Study room (individual study,withdrawal, remedial work, teacher preparation)LibrariesScience laboratoriesDrama studiosDesign and Technology• Resistant materials, CADCAM areas• Electronics/control, textiles, food,

graphics, design/resource areasArt roomsAssembly halls, multi-purpose halls (drama, PE,audio/visual presentations, assembly, occasional music)2,3

Audio-visual, video conference roomsAtria, circulation spaces used by studentsIndoor sports hallGymnasiumDance studioSwimming poolInterviewing/counselling rooms, medical rooms Dining roomsAncillary spacesKitchens*Offices*, staff rooms*Corridors, stairwellsCoats and changing areas*Toilets*

Tmf1 (seconds)

<0.6<0.6

<0.6

<0.8

<0.8<1.0

<1.0<0.80.6 - 1.21.0 - 1.50.6 - 1.2<0.5

<0.8<1.0

<0.4

<0.8<1.0<0.8<1.0

<0.8

<0.8<0.8

0.8 - 1.2<0.8<1.5<1.5<1.5<1.2<2.0<0.8<1.0

<1.5<1.0See Section 1.1.6<1.5<1.5

Table 1.5: Performancestandards for reverberationin teaching and studyspaces – mid-frequencyreverberation time, Tmf, infinished but unoccupiedand unfurnished rooms

NOTES ON TABLE 1.5 1 Common materials often absorb most soundat high frequencies. Therefore reverberationtimes will tend to be longer at low frequenciesthan at high frequencies. In rooms usedprimarily for speech, the reverberation times inthe 125 Hz and 250 Hz octave bands maygradually increase with decreasing frequency tovalues not more than 30% above Tmf.2 For very large halls and auditoria, and forhalls designed primarily for unamplified musicrather than speech, designing solely in termsof reverberation time may not be appropriateand specialist advice should be sought. In largerooms used primarily for music, it may beappropriate for the reverberation times in the125 Hz and 250 Hz octave bands to graduallyincrease with decreasing frequency to valuesup to 50% above Tmf. For more guidance seeSection 5.3 Assembly halls, multi-purpose halls, lecturerooms and music performance/recital roomsmay be considered as unfurnished when theycontain permanent fixed seating. Whereretractable (bleacher) seating is fitted, theperformance standards apply to the space withthe seating retracted.


* Part E of Schedule 1 to the BuildingRegulations 2000 (as amended by SI2002/2871) applies to teaching and learningspaces and is not intended to coveradministration and ancillary spaces (see underScope in the Introduction). For these areas theperformance standards are for guidance only.

15

coefficient for the board area used in thedesign calculation should be theabsorption coefficient of the wall to whichthe board is attached.

1.1.7 Speech intelligibility in open-plan spaces The objective is to provide clearcommunication of speech between teacherand student, and between students, inopen-plan teaching and study spaces.

For enclosed teaching and study spacesit is possible to achieve good speechintelligibility through specification of theindoor ambient noise level, soundinsulation and reverberation time. Open-plan spaces require extra specification asthey are significantly more complexacoustic spaces. The main issue is that thenoise from different groups of peoplefunctioning independently in the spacesignificantly increases the backgroundnoise level, thus decreasing speechintelligibility.

Open-plan spaces are generallydesigned for high flexibility in terms ofthe layout of teaching and study spaces.In addition, the layout is rarely finalisedbefore the school is operational. Thisincreases the complexity of assessingspeech intelligibility in the open-planspace. Therefore, at an early stage in thedesign, the designer should establish theexpected open-plan layout and activityplan with the client. The open-plan layout should include:• the positions at which the teacher willgive oral presentations to groups ofstudents• the seating plan for the students andteachers in each learning base• the learning base areas.The activity plan should include:• the number of teachers giving oralpresentations to groups of students at anyone time• the number of students engaged indiscussion at any one time• the number of people walking throughthe open-plan space (eg along corridorsand walkways) during teaching and studyperiods• any machinery (eg engraving machines,CNC machines, dust and fume extract

equipment, computers, printers, AVA)operating in the open-plan space.

The expected open-plan layout andactivity plan should be agreed as the basison which compliance with BB93 can bedemonstrated to the Building ControlBody.

The activity plan should be used toestablish the overall noise level due to thecombination of the indoor ambient noiselevel, all activities in the open-plan space(including teaching and study), andtransmitted noise from adjacent spaces. Acomputer prediction model should beused to calculate the Speech TransmissionIndex (STI)[8] in the open-plan space,using the overall noise level as thebackground noise level. Other methods ofestimating STI may also be applicable.

The performance standard for speechintelligibility in open-plan spaces isdescribed in terms of the SpeechTransmission Index in Table 1.6. Thecalculated value of STI should be between0.60 and 1.00, which gives an STI ratingof either ‘good’ or ‘excellent’. Thisperformance standard applies to speechtransmitted from teacher to student,student to teacher and student to student.

The performance standard in Table 1.6is intended to ensure that open-planspaces in schools are only built whensuited to the activity plan and layout.With some activity plans, room layoutsand open-plan designs it will not bepossible to achieve this performancestandard. At this point in the designprocess the decision to introduce anopen-plan space into the school should bethoroughly re-assessed. If, after re-assessment, there is still a need for theopen-plan space, then the inclusion ofoperable walls between learning basesshould be considered. These operablewalls will form classrooms and be subjectto the airborne sound insulationrequirements in Table 1.2. It is notappropriate to simply adjust the activity

Room type

Open-plan teaching and study spaces

Speech Transmission Index (STI)

>0.60

Table 1.6: Performancestandard for speechintelligibility in open-planspaces – SpeechTransmission Index (STI)


16

plan until the performance standard forspeech intelligibility is met.

Computer prediction software capableof simulating an impulse response shouldbe used to create a three-dimensionalgeometric model of the space, comprisingsurfaces with scattering coefficients andindividually assigned absorptioncoefficients for each frequency band. Themodel should allow for the location andorientation of single and multiple sourceswith user-defined sound power levels anddirectivity. (See guidance on computerprediction models on the DfES acousticswebsite www.teachernet.gov.uk/acoustics.)

Assumptions to be made in theassessment of speech intelligibility are:• for students, when seated, the headheight (for listening or speaking) is 0.8 mfor nursery schools, 1.0 m for primaryschools and 1.2 m for secondary schools• for students, when standing, the headheight (for listening or speaking) is 1.0 mfor nursery schools, 1.2 m for primaryschools and 1.65 m for secondary schools• for teachers, when seated, the headheight (for listening or speaking) is 1.2 m• for teachers, when standing, the headheight (for listening or speaking) is 1.65 m• the background noise level is the overallnoise level due to all activities (includingteaching and study) in the open-plan space.

1.2 Demonstrating compliance tothe Building Control BodyThe preferred means of demonstratingcompliance to the Building Control Bodyis to submit a set of plans, constructiondetails, material specifications, andcalculations, as appropriate for each areaof the school which is covered byRequirement E4 of the BuildingRegulations.The plans should identify:• the highest estimate for the indoorambient noise level, LAeq,30min, in eachspace and the appropriate upper limitfrom Table 1.1• the estimated weighted BB93standardized level difference, DnT (Tmf,max),w, between spaces and theappropriate minimum value from Table 1.2• the proposed values of Rw for partitionwalls and for doors, Dn,e,w –10lgN for

ventilators between circulation spaces andother spaces used by students, and theappropriate minimum values from Table 1.3• the estimated weighted BB93standardized impact sound pressure level,L′nT (Tmf,max),w, of floors above spacesand the appropriate maximum valuesfrom Table 1.4 • the estimated value of mid frequencyreverberation time Tmf in each space andthe appropriate range of values fromTable 1.5 • the proposed absorption treatments incorridors, entrance halls and stairwells• for open plan spaces, the estimatedrange of STI values for speechcommunication from teacher to student,student to teacher and student to student.

The supporting information shouldinclude:• construction details and materialspecifications for the external buildingenvelope• construction details and materialspecifications for all wall and floorconstructions, including all flankingdetails• calculations of the sound insulationDnT (Tmf,max),w and L′nT (Tmf,max),w• calculations of reverberation times inteaching and study spaces• calculations of the absorption area tobe applied in corridors, entrance halls andstairwells• measurements and/or calculationsdemonstrating how rain noise has beencontrolled• sound insulation test reports(laboratory and/or field) • sound absorption test reports(laboratory)• activity plan and layout for open-planspaces.

An example of a submission to aBuilding Control Body, with explanatorynotes, is contained in Appendix 10.

1.2.1 Alternative performancestandardsIn some circumstances alternativeperformance standards may beappropriate for specific areas withinindividual schools for particular


educational, environmental or health andsafety reasons. In these cases, thefollowing information should be providedto the Building Control Body:• a written report by a specialist acousticconsultant, clearly identifying (a) all areasof non-compliance with BB93performance standards (b) the proposedalternative performance standards and (c)the technical basis upon which thesealternative performance standards havebeen chosen• written confirmation from theeducational provider (eg school or LocalEducation Authority) of areas of non-compliance, together with the justificationfor the need and suitability of thealternative performance standards in eachspace.

1.3 Demonstrating compliance tothe clientTo ensure that the performance standardsare met, it is recommended that the clientshould include a requirement for acoustictesting in the building contract.

The design calculations submitted tothe Building Control Body demonstrateonly that the construction has thepotential to meet the performancestandards in Section 1.1. In practice, theperformance of the construction isstrongly influenced by workmanship onsite. If the design calculations anddetailing are correct, the most likelycauses of failure to meet the performancestandards will be poor workmanship,product substitution and design changeson site. Therefore, acoustic testing isrecommended.

The DfES acoustics website(www.teachernet.gov.uk/acoustics) will beused to encourage manufacturers andothers to disseminate acoustic test resultsalongside construction details forconstructions that consistently satisfy theperformance standards.

1.3.1 Timetabling of acoustic testingTimetabling of acoustic testing isimportant because any test that results ina failure to satisfy the performancestandards will require remedial work torectify the failure and potential design

changes to other parts of the building.For this reason it is desirable, wherepossible, to complete a sample set ofrooms in the school for advance testing.

1.3.2 Remedial treatmentsWhere the cause of failure is attributed tothe construction, other rooms that havenot been tested may also fail to meet theperformance standards. Therefore,remedial treatment may be needed inrooms other than those in which the testswere conducted. The efficacy of anyremedial treatment should be assessedthrough additional testing.

1.3.3 Indoor ambient noise levels inunoccupied spaces To demonstrate compliance with thevalues in Table 1.1, measurements ofindoor ambient noise levels should betaken in at least one in four roomsintended for teaching and/or studypurposes, and should include rooms onthe noisiest façade. These rooms shouldbe finished and unoccupied but may beeither furnished or unfurnished.Measurements should be made whenexternal noise levels are representative ofconditions during normal schooloperation.

During measurements, the followingshould apply:• Building services (eg ventilation system,plant) should be in use during themeasurement period.• For mechanically ventilated rooms, theplant should be running at its maximumdesign duty.• For naturally ventilated rooms, theventilators or windows should be open asrequired to provide adequate ventilation.• There should be no more than oneperson present in the room. (The valuesin Table 1.1 allow for one person to bepresent in the room during the test)• There should be dry weatherconditions outside.

Measurements of LAeq,T should bemade at least 1 m from any surface of theroom and at 1.2 m above floor level in atleast three positions that are normallyoccupied during teaching or studyperiods. A sound level meter complying

17


with BS EN 60804:2001 (IEC60804:2001)[9] should be used. Furtherinformation on noise measurementtechniques is available in the Associationof Noise Consultants Guidelines on NoiseMeasurement in Buildings[10].

Where there is negligible change innoise level over a teaching period,measurements of LAeq,T over a timeperiod much shorter than 30 minutes (egLAeq,5min) can give a good indication ofwhether the performance standard interms of LAeq,30min is likely to be met.However, if there are significant variationsin noise level, for example due tointermittent noise events such as aircraftor railways, measurements should betaken over a typical 30 minute period inthe school day.

1.3.4 Airborne sound insulationbetween spaces To demonstrate compliance with thevalues in Table 1.2, measurements ofairborne sound insulation should be takenbetween vertically and horizontallyadjacent rooms where the receiving roomis intended for teaching and/or studypurposes. At least one in four roomsintended for teaching and study purposesshould be tested. Measurements shouldbe taken in the direction with the morestringent airborne sound insulationrequirement.

During measurements, the ventilatorsor windows should be open as required toprovide adequate ventilation in both thesource room and the receiving room.

Measurements should be made inaccordance with BS EN ISO 140-4:1998[1] and the additional guidance inApproved Document E[7] Annex B,paragraphs B2.3 – B2.8. Performanceshould be rated in accordance with BSEN ISO 717-1:1997[2].

1.3.5 Airborne sound insulationbetween circulation spaces and otherspaces used by studentsIt is not intended that field measurementsshould be taken between circulationspaces and other spaces used by students.Laboratory data for the wall, doorsets (ifany) and ventilators (if any) should be

presented as evidence of compliance withthe values in Table 1.3.

1.3.6 Impact sound insulation To demonstrate compliance with thevalues in Table 1.4, measurements ofimpact sound insulation should be takenbetween vertically adjacent rooms, wherethe receiving room is intended forteaching and study purposes. At least onein four teaching/study rooms below aseparating floor should be tested.

Measurements should be made inaccordance with BS EN ISO 140-7:1998[5]. Performance should be ratedin accordance with BS EN ISO 717-2:1997[6].

Impact sound insulation should bemeasured on floors without a softcovering (eg carpet, foam backed vinyl),except in the case of concrete structuralfloor bases where the soft covering is anintegral part of the floor.

1.3.7 Reverberation in teaching andstudy spacesTo demonstrate compliance with thevalues in Table 1.5, measurements ofreverberation time should be taken in atleast one in four rooms intended forteaching and study purposes.

One person may be present in theroom during the measurement.

Depending upon the completionsequence for spaces within the school, itmay be possible to reduce themeasurement effort by utilisingmeasurements of reverberation time thatare required as part of airborne or impactsound insulation measurements. For thisreason, two measurement methods,described below, are proposed for themeasurement of reverberation time. Forthe purpose of demonstrating compliance,either method can be used to assesswhether the performance standards havebeen met. If one method demonstratescompliance with the performancestandard and the other demonstratesfailure, then the performance standardshould be considered to have been met.Measurement method 1: Measurementsshould be made in accordance with eitherlow coverage or normal coverage

18


measurements described in BS EN ISO3382:2000[11].Measurement method 2: Reverberationtime measurements should be made inaccordance with BS EN ISO 140-4:1998[1] (airborne sound insulation) orBS EN ISO 140-7:1998[5] (impact soundinsulation) in octave bands.

1.3.8 Sound absorption in corridors,entrance halls and stairwellsIt is not intended that field measurementsof reverberation time should be taken incorridors, entrance halls and stairwells.

1.3.9 Speech intelligibility in open-plan spacesTo demonstrate compliance with thevalues in Table 1.6, measurements of theSpeech Transmission Index (STI) shouldbe taken in at least one in ten studentpositions in the open-plan spaces.

Measurements should be made inaccordance with BS EN 60268-16:1998[8].

Measurements should be made usingthe following heights for listening orspeaking:• to represent seated students, a headheight of 0.8 m for nursery schools, 1.0 mfor primary schools and 1.2 m forsecondary schools• to represent standing students, a headheight of 1.0 m for nursery schools, 1.2 mfor primary schools and 1.65 m forsecondary schools• to represent seated teachers, a headheight of 1.2 m• to represent standing teachers, a headheight of 1.65 m.

Simulation of the estimated occupancynoise should be carried out in the STImeasurement. This noise level will havebeen established at the design stage (seeSection 1.1.7) and is defined as the noiselevel due to the combination of theindoor ambient noise level, all activities inthe open-plan space (including teachingand study), and transmitted noise fromadjacent spaces.

References[1] BS EN ISO 140-4:1998 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 4. Fieldmeasurements of airborne sound insulationbetween rooms.[2] BS EN ISO 717-1:1997 Acoustics – Ratingof sound insulation in buildings and of buildingelements. Part 1. Airborne sound insulation.[3] BS EN ISO 140-3:1995 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 3. Laboratorymeasurement of airborne sound insulation ofbuilding elements.[4] BS EN 20140-10:1992 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 10. Laboratorymeasurement of airborne sound insulation ofsmall building elements.[5] BS EN ISO 140-7:1998 Acoustics –Measurement of sound insulation in buildingsand of building elements. Part 7. Fieldmeasurements of impact sound insulation offloors.[6] BS EN ISO 717-2:1997 Acoustics – Ratingof sound insulation in buildings and of buildingelements. Part 2. Impact sound insulation.[7] Approved Document E – Resistance to thepassage of sound. Stationery Office 2003. ISBN 0 11 753 642 3.www.odpm.gov.uk[8] BS EN 60268-16:1998 Sound systemequipment – Part 16: Objective rating ofspeech intelligibility by speech transmissionindex.[9] BS EN 60804:2001 (IEC 60804:2001)Integrating-averaging sound level meters.[10] Guidelines on Noise Measurement inBuildings, Part 1: Noise from Building Servicesand Part 2: Noise from External Sources.Association of Noise Consultants.[11] BS EN ISO 3382:2000 Acoustics –Measurement of the reverberation time ofrooms with reference to other acousticalparameters.

19


21

2.1 Choosing a siteThe acoustic design of a school starts withthe selection of the site, a noise survey ofthe site and planning the layout of theschool buildings.

Economic sites for new schools witheasy access to transport often suffer fromtraffic noise and pollution. In the past,schools have sometimes been built onsites which would not normally have beenconsidered suitable for housing. This hasbeen in part because schools have notalways been recognised as requiringparticularly high environmental standards,and in part because there has been lessformal control or regulation of noiselevels in schools than for housing.

Where school sites are adjacent to busyroads they will require the use ofintelligent design, zoning, noise screeningand, if necessary, sound insulatingbuilding envelopes together withmechanical ventilation or acousticallydesigned passive ventilation.

Many of the acoustic problems inexisting schools derive directly from theschool’s location in a noisy area. Forexisting schools, noise from road traffic isa common problem, but in some areasnoise from railways and aircraft isintrusive[1]. Noise from industrial andleisure sources is a less frequent problemand can normally be dealt with at sourceby the Local Authority using their powersunder the Environmental Pollution Act.

2.2 Recommendations for externalnoise levels outside school buildingsAlthough Requirement E4 does not applyto external noise, the followingrecommendations are considered goodpractice for providing good acoustic

conditions outside school buildings.For new schools, 60 dB LAeq,30min

should be regarded as an upper limit forexternal noise at the boundary of externalpremises used for formal and informaloutdoor teaching, and recreational areas.

Under some circumstances it is possibleto meet the specified indoor ambientnoise levels on sites where external noiselevels are as high as 70 dB LAeq,30min butthis will require considerable buildingenvelope sound insulation, screening orbarriers.

Noise levels in unoccupiedplaygrounds, playing fields and otheroutdoor areas should not exceed 55 dBLAeq,30min and there should be at leastone area suitable for outdoor teachingactivities where noise levels are below 50 dB LAeq,30min. If this is not possibledue to a lack of suitably quiet sites,acoustic screening should be used toreduce noise levels in these areas as muchas practicable, and an assessment ofpredicted noise levels and of options forreducing these should be carried out.

Playgrounds, outdoor recreation areasand playing fields are generally consideredto be of relatively low sensitivity to noise,and indeed playing fields may be used asbuffer zones to separate school buildingsfrom busy roads where necessary.However, where used for teaching, forexample sports lessons, outdoor ambientnoise levels have a significant impact oncommunication in an environment whichis already acoustically less favourable thanmost classrooms. Ideally, noise levels onunoccupied playing fields used forteaching sport should not exceed 50 dBLAeq,30min. If this is not possible at alllocations, there should be at least one area

Noise control 2Section 2 gives recommendations and guidance concerning noise control,starting with the choice of a site and the control of external noise. Local

government planning policy will be influenced by the recommendations onmaximum external noise levels in playing fields and other external areas usedby the school. Section 2 also includes discussion of the means of controlling

indoor ambient noise.

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at which noise levels are below 50 dBLAeq,30min so that some outdoorteaching is possible.

Acoustic screening from fences, wallsor buildings may be used to protectplaygrounds from noise. At positions nearthe screen, traffic noise can be reduced byup to 10 dB(A).

All external noise levels in this sectionapply to measurements made atapproximately head height and at least 3 mfrom any reflecting surface other than theground.

2.3 Noise surveyFigure 2.1 shows typical external andinternal sources of noise which can affectnoise levels inside a school.

In order to satisfy the limits for theindoor ambient noise levels in Table 1.1,it is necessary to know the external noiselevel so that the building envelope can bedesigned with the appropriate soundinsulation.

The external noise level should beestablished by carrying out a noisemeasurement survey. (Note that a briefsurvey is advisable even if the site appearsto be quiet, in case there are noisy eventsat certain times of the day.) Themeasurements should be taken duringFigure 2.1: Typical

sources of noise

PLANTROOM NOISEAND VIBRATION

NOISYCORRIDORS

NOISE VIA OPEN WINDOWS

WEATHER& RAIN NOISE

BREAK-OUT/BREAK-INOF DUCTBORNE

NOISE

DUCTBORNE NOISE

PLUMBING NOISE

DUCTBORNE NOISE FAN

TRAFFIC NOISEAND VIBRATION

PLAYGROUNDNOISE

NOISE THROUGHDOORS & WALLS

AIRCRAFT NOISE

typical school hours and include noisyevents (eg road traffic at peak hours,worst case runway usage in the case ofairports, etc). The measurements mustalso take account of the weatherconditions. For long-distance propagationof noise, the measured level is affected bywind gradients, temperature gradients andturbulence. With wind, the noise level isgenerally increased downwind or reducedupwind. (Note that temperatureinversions can radically change noisepropagation, but tend to occur only atnight-time, outside school hours.)

A noise measurement survey mustinclude octave or one-third octavefrequency band levels. This is because theattenuation of sound, for example by asound insulating wall or noise barrier,depends upon the frequency of sound. Ingeneral materials and barriers are lesseffective at controlling low frequencynoise than mid and high frequency noise.Although overall noise levels andperformance standards can be quoted asoverall A-weighted levels, calculationsmust be carried out in octave or one-thirdoctave bands (see Appendix 1) and theresults converted into overall A-weightedlevels.

In addition to the noise measurement

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Barrier

Soundsource Receiver

Ground

ab

c

Path difference = a + b – c

Figure 2.2: Attenuationby a noise barrier as afunction of path difference

2000 Hz

1000 Hz500 Hz

250 Hz

125 Hz

30

25

20

15

10

5

0 0.5 1.0 1.5 2.0

Path difference, m

Atte

nuat

ion,

dB

survey, consideration should be given topredicting the potential increases in noiselevels due to future developments (egincreases in traffic flows, new transportschemes, changes in flight paths). Thelocal highway authority should be able toadvise on whether significant changes inroad traffic noise are expected in thefuture. This is likely to be relevant fordevelopments near new or recentlyimproved roads. Where road traffic noiselevels are likely to increase, it is reasonableto base the sound insulation requirementson the best estimate of noise levels in 15years time. Similar information is likely tobe available from railway operators, andairports. The prediction[2,3] of futureexternal noise levels should be carried outby an acoustic consultant.

If the noise measurement survey showsthat the ambient external noise levels onthe site are below 45 dB LAeq,30min, andprediction work shows that they willremain below 45 dB LAeq,30min in thefuture, no special measures are likely to benecessary to protect the buildings orplaying fields from external noise.

2.4 Road and rail noiseSources of road and rail noise requireindividual assessment because of theircharacteristics.

Road traffic noise is a function of trafficflow, percentage of heavy goods vehicles,traffic speed gradient (rate of acceleration),road surface and propagation path of thenoise.

Rail noise is a function of train type, number, speed, rail type and propagationpath of the noise.

In general it is advisable to locate aschool at least 100 m away from busyroads and railways, but in towns and citiesthis is often not possible. However, theuse of distance alone is a relativelyineffective way to reduce noise. Simplerules of thumb are that the noise levelfrom a busy road increases by 3 dB(A) fora doubling of the traffic flow anddecreases by 3 dB(A) for a doubling ofdistance from the road (over hardground).

2.5 Aircraft noiseWhere a school is to be located in an areaaffected by aircraft noise, special measuresare necessary and an acoustic consultantshould be appointed.

2.6 VibrationRailways, plant and heavy vehicles close toa school can lead to vibration within theschool buildings. This vibration can re-radiate as audible noise, even when thevibration itself is not perceptible asshaking in the building. The propagationof vibration depends on groundconditions but in general when planning anew school building it is advisable for thenoise survey to include vibrationmeasurements when there is a railwaywithin 30 m of a building, or a road withsignificant HGV traffic within 20 m. Inthese cases airborne noise is also likely tobe a problem.

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2.7 Noise barriersNoise barriers are much more effectivethan distance in reducing noise from roador rail traffic. In its simplest form a noisebarrier can be a continuous close-boardedwooden fence, with a mass of not lessthan 12 kg/m2. There is relatively littlepoint in increasing the weight of thebarrier beyond this because a significantproportion of the noise passes over thetop (or round the ends) of the barrier.

The attenuation of a barrier is afunction of the path difference, that is theextra distance that the sound has to travelto pass over the top of the barrier, seeFigure 2.2. Barriers are less effective atreducing low frequency noise than midand high frequency noise. Hence, tocalculate the effectiveness of a noisebarrier it is necessary to know the sourcenoise levels in octave or one-third octavebands (see Appendix 1).

Hedges or single trees (or rows oftrees) do not in themselves make effectivenoise barriers. A common and effectivesolution is a wooden fence to act as anoise barrier, located within a band oftrees to create an acceptable visual effect.

Barriers can also be formed by otherbuildings or by landscaping using earthbunds, see Figure 2.3. The pathdifference, and hence the attenuation, will

be affected by whether the road or railwayis in a cutting or on an embankment.

2.8 Noise from schools tosurrounding areasNoise from schools to the surroundingarea can also be a problem, andconsideration should be given to nearbyresidential and other noise-sensitivedevelopments which could be disturbedby noise from playgrounds, playing fields,music rooms and halls used for eventssuch as after school concerts and discos.The local planning authority will normallyconsider this in assessing any planningapplication for new schools or extensionsto existing premises.

The effect of playground noise onchildren inside parts of the school nearthe playground should also be consideredas part of the design.

2.9 Planning and layoutAmong the most common problemsfound in schools is noise transfer betweenrooms. To a large extent this can bedesigned out without resort to very highperformance sound insulating walls orfloors, but by good planning and zoningof the building at the earliest stages ofdesign. At this stage it is possible toidentify noise-sensitive areas and to

POORNo acoustical shieldingfrom landscaping

BETTERShielding from embankment would beimproved by a fence within the trees

BESTEarth bund acts as acoustic barrier, plantingacts as visual barrier

Figure 2.3: Traffic noisebarriers

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Otherclassroom

Store Store

Store

Store

StoreGroupRoom

GroupRoom

GroupRoom

GroupRoom

GroupRoom

GroupRoom

Musicclassroom

Musicclassroom

StaffBase

GroupRoom

Instrumentstore

EnsembleRoom

Recording/ControlRoom

To otherdepartments

Corridorcreatesacoustic

separation

Easyaccess tosupportspaces

Storesprovide

acousticbuffer

Acoustic separationfor ensemble room and

group rooms

Store

Store

GroupRoom

Fig 2.4: Planning acoustic‘buffer zones’

separate these from noisy areas usingbuffer zones such as storerooms,corridors or less sensitive rooms, or bylocating buildings a suitable distanceapart. See Figure 2.4 for an example ofroom layout in a music department usingbuffer zones.

When considering external noise suchas that from roads, it is sensible to locatenoise-sensitive rooms, such as classrooms,away from the source.

Tables 1.1 and 1.2 give the requiredmaximum indoor ambient noise levels andthe minimum sound insulation levelsbetween rooms. The performancestandards in these tables should be usedin the early planning stages of a project todetermine (a) the layout of the school (b) the constructions needed to providesound insulation and (c) the compatibilityof school activities in adjacent rooms.

2.10 Limiting indoor ambient noiselevelsThe total indoor ambient noise level isdetermined by combining the noise levelsfrom all the known sources. The indoorambient noise level due to externalsources such as traffic must be added tothe noise from mechanical ventilation,heating systems, lighting and otherbuilding services. Unless care is taken,these individual sources can be loudenough to cause disturbance, particularlyin spaces where low indoor ambient noiselevels are required.

It should be noted that noise levels indB or dB(A) cannot be simply addedtogether. For example, two noise levels of40 dB(A) when combined will produce alevel of 43 dB(A). The addition of noiselevels is explained in Appendix 1.

2.11 Impact noise Impact noise within a space from footfallson balconies, stairs and circulation routes,or from movement of furniture or otherclass activities, can be a significantdistraction to teaching and learning.

Carpets and other soft yet resilientfloor finishes such as resilient backed vinylor rubber type flooring materials can beuseful in limiting this impact noise withina space. However, carpets may be difficult

to clean and are sometimes not usedbecause of their effect on indoor airquality and resultant health implications.

Resilient feet can also be fitted tofurniture to reduce impact noise within aspace.

2.12 Corridors, entrance halls andstairwellsNoise in corridors, entrance halls andstairwells can cause disturbance toneighbouring classrooms and otherteaching spaces. It is therefore importantthat reverberation in corridors, entrancehalls and stairwells is kept as low as

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possible in order to minimise noise levelsin these areas. The requirement is toprovide sound absorption in accordancewith Section 1.1.6. To satisfy thisrequirement, corridors outside classroomstypically need acoustically absorbentceilings and/or wall finishes. Carpets andother soft floor finishes can also help toreduce reverberation and the noise fromfootfalls. However, as discussed in Section2.11, the use of carpets may not beappropriate in all schools.

2.13 Masking noiseThe audibility and intrusiveness of noisefrom other areas (break-in noise) is afunction of both the level of the break-innoise and the noise level in the roomunder consideration (the receiving room).If the ambient noise level in the receivingroom is unnecessarily low, break-in noisewill be more audible. Hence where roomsare mechanically ventilated, the noisefrom the ventilation system can be usedto mask the noise from activities inneighbouring rooms. In these casesventilation noise should not be more than5 dB below the maximum ambient noiselevels listed in Table 1.1. For this type ofmasking to work it is important to ensurethat the ventilation noise follows a specificmasking noise curve and has no tonal orintermittent characteristics. Specialistacoustic advice is required before usingbuilding services noise for masking.

Other possible sources of maskingnoise are fan convectors, electric lightingcircuits, and constant levels of road trafficnoise, for example from distant arterialroads. However it should be noted thatthe noise from some sources (eg fans andother mechanical equipment) may causeannoyance to individuals, particularlyhearing impaired people, in somecircumstances. Also, some buildingservices systems may only operate atcertain times of the year.

2.14 Low frequency noise andhearing impaired pupilsMany hearing impaired pupils make useof low frequencies below 500 Hz toobtain information from speech.Therefore, for hearing impaired pupils tobe included in classes with pupils havingnormal hearing, special care should betaken to minimise low frequency indoorambient noise levels. Given the prevalenceof infections leading to temporary hearingloss, it is advisable to minimise lowfrequency indoor ambient noise levels inall classrooms, especially those used byyounger pupils.

The indoor ambient noise levels inTable 1.1 are given in terms ofLAeq,30min which is an A-weighted noiselevel. This is a convenient and widely-used parameter but is not a goodindicator of low frequency noise. Toassess indoor noise there are other ratingsystems in use which address lowfrequency noise but these are beyond thescope of this document. In cases wherelow frequency noise is likely to be aproblem, specialist advice from anacoustics consultant should be sought.Such cases include schools exposed tohigh levels of external noise (in excess of60 dB LAeq,30min, see Section 2.2),where sound insulation may reduce highfrequency noise while leavingcomparatively high levels of lowfrequency noise.

More information is given in CIBSEGuide B5 Noise and Vibration Controlfor HVAC.[4]

References [1] B Shield, J Dockrell, R Jeffery and I Tachmatzidis. The effects of noise on theattainments and cognitive performance ofprimary school children. Department of Health,2002.[2] Calculation of road traffic noise (CRTN),Department of Transport, The StationeryOffice, 1988.[3] Calculation of railway noise (CRN),(Supplement 1), Department of Transport, The Stationery Office, 1995.[4] CIBSE Guide B5, Noise and vibrationcontrol for HVAC, CIBSE, 2002ISBN 1 903287 2 51.

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General principles of sound insulation and typical constructions are discussed inthis section. Space does not allow all details for each type of construction to be

shown. Many such details are illustrated and discussed in greater detail inApproved Document E[1]. Further guidance and illustrations are also available in

Sound Control for Homes[2] and in manufacturers’ literature for proprietarymaterials and systems.

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3.1 RoofsThe sound insulation of a pitched roofdepends upon the mass of the ceiling andthe roof layers and the presence of asound absorbing material in the roofspace. Mineral wool, used as thermalinsulation in the ceiling void, will alsoprovide some acoustic absorption, whichwill have a small effect on the overallsound insulation of a roof. A denserspecification of mineral wool, ascommonly used for acoustic insulation,would have a greater effect on the overallsound insulation of the roof.

Where it is necessary to ventilate theroof space, it is advisable to make anynecessary improvements to the soundinsulation by increasing the mass of theceiling layer, which should be airtight.Recessed light fittings can make thisdifficult and sometimes it is better toplace the sound insulating material belowthe roof covering and to extend partitionwalls up to the roof layer (providingadequate ventilation can be maintained).

3.1.1 Rain noiseThe impact noise from rain on the roofcan significantly increase the indoor noiselevel; in some cases the noise level inside aschool due to rain can be as high as 70 dB(A).

Although rain noise is excluded fromthe definition of indoor ambient noise in

Section 1.1, it is a potentially importantnoise source which must be considered atan early point in the roof design tominimise disturbance inside the school.

Excessive noise from rain on the roofcan occur in spaces (eg sports halls,assembly halls) where the roof is madefrom profiled metal cladding and there isno sealed roof space below the roof toattenuate the noise before it radiates intothe space below. With profiled metalcladding, the two main treatments thatshould be used in combination to providesufficient resistance to impact sound fromrain on the roof are: • damping of the profiled metal cladding(eg using commercial damping materials) • independent ceilings (eg two sheets of10 kg/m2 board material such asplasterboard, each supported on its ownframe and isolated from the profiled metalcladding, with absorptive material such asmineral fibre included in the cavity.)

Profiled metal cladding used without adamping material and without anindependent ceiling is unlikely to providesufficient resistance to impact sound fromrain on the roof. A suitable system thatcould be used in schools is shown inFigure 3.1. The performance of such asystem was measured by McLoughlin etal[3].

Prediction models are available topredict the noise radiated from a singlesheet of material; however, a single sheetwill not provide sufficient attenuation ofimpact noise from rain. Suitablelightweight roof constructions that doprovide sufficient attenuation will consistof many layers. For these multi-layer roofconstructions, laboratory measured datafor the entire roof construction is needed.At the time of writing, a new laboratory

Figure 3.1: Profiled metalclad roof incorporatingacoustic damping

Damped aluminium tiles

Plasticised steel top sheet

50 – 100 mm mineral fibreTwo sheets of Fermacell board

Steel liner panel50 – 100 mm mineral fibre

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measurement standard for impact soundfrom rain on the roof, ISO 140-18[4], isunder development. In the future this willallow comparison of the insulationprovided by different roof, window andglazing elements and calculation of thesound pressure level in the space belowthe roof.

When designing against noise from rainon the roof, consideration should also begiven to any glazing (eg roof lights) inthe roof. Due to the variety of differentroof constructions, advice should besought from an acoustic consultant whocan calculate the sound pressure level inthe space due to typical rainfall on thespecific roof.

3.2 External WallsFor masonry walls, such as a 225 mmsolid brick wall, a brick/block cavity wallor a brick-clad timber frame wall, thesound insulation performance willnormally be such that the windows,ventilators and, in some cases, the roofwill dictate the overall sound insulation ofthe building envelope.

Timber frame walls with lightweightcladding and other lightweight systems ofconstruction normally provide a lowerstandard of sound insulation at lowfrequencies, where road traffic and aircraftoften produce high levels of noise. Thiscan result in low airborne soundinsulation against these noise sourcesunless the cladding system has sufficientlow frequency sound insulation. Theairborne sound insulation can be assessedfrom laboratory measurements carried outaccording to BS EN ISO 140-3:1995[5].

3.3 VentilationThe method of ventilation as well as thetype and location of ventilation openingswill affect the overall sound insulation ofthe building envelope. When externalnoise levels are higher than 60 dBLAeq,30min, simple natural ventilationsolutions may not be appropriate as theventilation openings also let in noise.However, it is possible to use acousticallyattenuated natural ventilation rather thanfull mechanical ventilation when externalnoise levels are high but do not exceed

70 dB LAeq,30min.The School Premises Regulations[6]

require that: “All occupied areas in a school building

shall have controllable ventilation at aminimum rate of 3 litres of fresh air persecond for each of the maximum number ofpersons the area will accommodate.

All teaching accommodation, medicalexamination or treatment rooms, sickrooms, sleeping and living accommodationshall also be capable of being ventilated at aminimum rate of 8 litres of fresh air persecond for each of the usual number ofpeople in those areas when such areas areoccupied.”

In densely occupied spaces such asclassrooms, 8 litres per second per personis the minimum amount of fresh air thatshould be provided by a natural ormechanical ventilation system undernormal working conditions, in order tomaintain good indoor air quality.

In order to satisfy the limits for theindoor ambient noise levels in Table 1.1,it is necessary to consider the soundattenuation of the ventilation openings sothat the building envelope can bedesigned with the appropriate overallsound insulation. In calculations of overallsound insulation the attenuation assumedfor the ventilation system should be fornormal operating conditions.

The main choices for the naturalventilation of typical classrooms areshown in Figure 3.2. Case Studies 7.8and 7.9 describe the recent application oftwo of these design solutions in newsecondary school buildings.

Additional ventilation such as openablewindows or vents may be required toprevent summertime overheating.

3.3.1 VentilatorsPassive ventilators normally penetrate thewalls, but in some cases they penetrate thewindow frames (eg trickle ventilators) orthe windows themselves. Often windowsare not used as intended as they causeuncomfortable draughts. For this reason,increased use is being made of purposedesigned ventilation systems with orwithout acoustic attenuation.

Many proprietary products are

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Figure 3.2: Possibletypes of natural ventilation

Secondary glazing withstaggered openingsAcoustically treated high capacity air inlet

Secondary glazing with staggered openings

Absorbent duct liningAcoustic louvres on outsideplus secondary glazing with staggered openings andacoustically treated high capacity air inlet

CLASSROOMCORRIDOR 2.7 m

2.7 m

2.7 m

2.7 m

CROSS-VENTILATION

SINGLE-SIDED VENTILATION

STACK VENTILATION

WIND TOWER/TOP DOWNVENTILATION

Absorbent duct liningAcoustic louvres on outsideSecondary glazing with staggered openingsAttenuator plenum boxElectronic noise

POSSIBLE SOUNDINSULATION MEASURES

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designed for the domestic sector and insome cases they do not have large enoughopenings for classrooms and other largerooms found in schools. The acousticperformance of any ventilator can beassessed with laboratory sound insulationtest data measured according to BS EN20140-10:1992[7]. Because of thecomplexity of the assessment of theacoustic performance of a ventilator,advice may be needed from a specialistacoustic consultant. To maintain adequateventilation, it is essential that the effectivearea of the ventilator is considered as itmay be smaller than the free area (see prEN 13141-1[8]).

It is important, particularly in the caseof sound-attenuated products, that a goodseal is achieved between the penetrationthrough the wall or window and theventilator unit. Where through-the-wallproducts are used, the aperture should becut accurately and the gap around theperimeter of the penetrating duct shouldbe packed with sound insulating materialprior to application of a continuous,flexible, airtight seal on both sides.

In some schools bespoke ventilatordesigns, such as that shown in Figure 3.3,are needed. For more examples ofventilator solutions see Case Studies 7.8and 7.9.

3.4 External WindowsThe airborne sound insulation ofwindows can be assessed from laboratorymeasurements of the sound reductionindex according to BS EN ISO 140-3:1995[5]. When choosing suitablewindows using measured data, care mustbe taken to differentiate betweenmeasured data for glazing and measureddata for windows. The reason is that theoverall sound insulation performance of awindow is affected by the window frameand the sealing as well as the glazing.

To achieve the required soundinsulation with thin glass it is oftennecessary to use two panes separated byan air (or other gas) filled cavity. Intheory, the wider the gap between thepanes, the greater the sound insulation.In practice, the width of the cavity indouble glazing makes relatively little

difference for cavity widths between 6 mmand 16 mm. Wider cavity widths performsignificantly better.

In existing buildings, secondary glazingmay be installed as an alternative toreplacing existing single glazing withdouble glazing. The effectiveness ofsecondary glazing will be determined bythe thickness of the glass and the width ofthe air gap between the panes. Anotheralternative may be to fit a completely newdouble-glazed window on the inside ofthe existing window opening, leaving theoriginal window intact. The use of soundabsorbing reveal linings improves theperformance of double-glazed windows,but the improvement is mainly in themiddle to high frequency region, where ithas little effect on road traffic and aircraftnoise spectra.

To achieve their optimumperformance, it is essential that theglazing in windows makes an airtight sealwith its surround, and that opening lightshave effective seals around the perimeterof each frame. Neoprene compressionseals will provide a more airtight seal thanbrush seals. The framing of the windowshould also be assembled to achieve anairtight construction.

It is equally important that an airtightseal is achieved between the perimeter ofthe window frame and the opening intowhich it is to be fixed. The openingshould be accurately made to receive thewindow, and the perimeter packed withsound insulating material prior toapplication of a continuous seal on bothsides.

For partially open single-glazedwindows or double-glazed windows withopposite opening panes, the laboratorymeasured airborne sound insulation isapproximately 10-15 dB Rw . Thisincreases to 20-25 dB Rw in the openposition for a secondary glazing systemwith partially open ventilation openings,with the openings staggered on plan orelevation, and with absorbent lining ofthe window reveals (see Figure 3.3). Insitu, the degree of attenuation providedby an open window also depends on thespectrum of the noise and the geometryof the situation.

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The spreadsheet of sound reductionindices on the DfES acoustic websitegives values of Rw for various types ofwindow, glazing thickness, and air gap.Indications are also given of the soundreduction indices of open windows.

3.5 External DoorsFor external doors the airborne soundinsulation is determined by the door set,which is the combination of door andframe. The quality of the seal achievedaround the perimeter of the door iscrucial in achieving the potentialperformance of the door itself. Effectiveseals should be provided at the threshold,jambs and head of the door frame. Aswith windows, neoprene compressionseals are more effective than brush seals,but their effectiveness will be stronglyinfluenced by workmanship on site. Brush

seals can however be effective and tend tobe more hard wearing than compressionseals.

It is also important that an airtight sealis achieved between the perimeter of thedoor frame and the opening into which itis to be fixed. The opening should beaccurately made to receive the door frameand any gaps around the perimeter packedwith insulating material prior toapplication of a continuous, airtight sealon both sides.

A high level of airborne soundinsulation is difficult to provide using asingle door; however, it can be achievedby using a lobby with two sets of doors,as often provided for energy efficiency, ora specialist acoustic doorset.

Softwood framing toextend reveals

Sound absorbing reveallinings to head and sides

Second casement openablefor cleaning only

Bottom hung casement,openable for ventilation,fitted with secure adjustable stay

Supporting framing below cill

Existing inward opening light,movement to be restricted

Existing brickwork wall

200 mm nominal

300 mm nominal

Figure 3.3: Secondaryglazing producing astaggered air flow path

Retrofit secondary glazing producinga staggered air flow path. Designedto limit aircraft noise intrusion toscience laboratories at a secondaryschool near an airport.

A sound reduction of approximately 20-25 dB Rw was achieved using thisdesign.

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SOUND INSULATION OF THEBUILDING ENVELOPE

There are two methods by which it ispossible to calculate the indoor ambientnoise levels due to external noise.

The first method is to calculate theindoor ambient noise level according tothe principles of BS EN 12354-3:2000[9].An Excel spreadsheet to calculate thesound insulation of building envelopes,based on BS EN 12354-3:2000 isavailable via the DfES acoustics website.The principles of this calculationspreadsheet are given in Appendix 5.

The second method is to calculate theindoor ambient noise level using themeasured façade sound insulation datafrom an identical construction at anothersite.

3.6 Subjective characteristics ofnoiseThe indoor ambient noise levels in Table1.1 provide a reasonable basis forassessment, but some noises have tonal orintermittent characteristics which makethem particularly noticeable or disturbing,even below the specified levels. This ismost common with industrial noise. At aminority of sites, achieving the levels inTable 1.1 will not prevent disturbancefrom external industrial sources, andadditional noise mitigation may berequired. In these cases advice from anacoustic consultant should be sought.

The potentially beneficial maskingeffect of some types of continuousbroadband external noise (such as roadtraffic noise) must also be borne in mind,see Section 2.12. This noise may partiallymask other sounds, such as fromneighbouring classrooms, which may bemore disturbing than the external noise.There are acoustic benefits, as well as costbenefits, in ensuring that the level ofinsulation provided is not over-specifiedbut is commensurate with the externalnoise.

3.7 Variation of noise incident ondifferent facadesIt may be convenient to determine theexternal noise level at the most exposedwindow (or part of the roof) of a

building, and to assume this exposure forother elements too. This may be suitableat the early design stage for large schools.However, where external noise levels varysignificantly, this approach can lead toover-specification and unnecessary cost.

3.8 CalculationsA calculation of the internal noise levelaccording to BS EN 12354-3:2000 canbe used to estimate whether, for the levelsof external noise at any particular site, aproposed construction will achieve thelevels in Table 1.1. By estimating theinternal levels for various differentconstructions, designers can determinethe most suitable construction in anygiven situation. BS EN 12354-3:2000allows the effects of both direct andflanking transmission to be calculated, butin many cases it is appropriate to consideronly direct transmission.

3.9 Test methodField testing of an existing buildingenvelope should be conducted accordingto BS EN ISO 140-5:1998[10], withreference to the clarifications given in thissection.

BS EN ISO 140-5:1998 sets outvarious test methods. The three ‘global’tests using the prevailing external noisesource(s) (road traffic, railway traffic, airtraffic) are preferable. At most sites roadtraffic is likely to be the dominant sourceof noise, and the correspondingstandardised level difference is denotedDtr,2m,nT . Where aircraft noise is themajor concern measurements should bemade accordingly, and the standardisedlevel difference denoted Dat,2m,nT .Similarly the standardised level differenceusing railway noise as the source isdenoted Drt,2m,nT .

The global loudspeaker test method(which generates Dls,2m,nT values) maybe used only if the prevailing externalnoise sources are insufficient to generatean adequate internal level.

It is reasonable, under certainconditions as specified below, to use thetest results to indicate the likelyperformance of building envelopes of asimilar construction, exposed to similar

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sources. If the conditions are not metthen it is not reasonable to infer theperformance from existing soundinsulation test results and the calculationprocedure should be used.

3.9.1 Conditions for similarconstructionsThe following features of any untestedconstruction should be similar to those ofthe tested construction:• type and number of ventilators • glazing specification, frame

construction and area of windows• type and number of doors• external wall construction and area• roof construction and area.

3.9.2 Conditions for similar sourcesOnly test results in terms of Dtr,2m,nT ,Dat,2m,nT , Drt,2m,nT and Dls,2m,nTvalues are applicable, and these shouldnot be used interchangeably. Thefollowing features concerning theprevailing sources of noise should besimilar to those of the previously testedconstruction:• relative contributions of road traffic,

railway and aircraft noise• orientation of the building relative to

the main noise source(s)• ground height of the building relative

to the main noise source(s).

SOUND INSULATION BETWEENROOMS

This section describes constructionscapable of achieving the different levels ofsound insulation specified in Tables 1.2and 1.4.

Appendix 3 describes how soundinsulation between adjacent rooms ismeasured and calculated.

In addition to the transmission ofdirect sound through the wall or floor,additional sound is transmitted into thereceiving room via indirect, or 'flanking'paths, see Figure 3.4.

3.10 Specification of the airbornesound insulation between rooms using RwTable 1.2 describes the minimumweighted sound level difference between

Figure 3.4: Soundtransmission pathsbetween adjacent rooms:direct sound paths throughthe wall and floor andflanking paths through thesurrounding ceiling, walland floor junctions

airborne sound

impact sound

rooms in terms of DnT (Tmf,max),w.However, manufacturers provideinformation for individual buildingelements based on laboratory airbornesound insulation data measured accordingto BS EN ISO 140-3:1995[5], in terms ofthe sound reduction index, Rw. Figure3.5 shows the values of Rw for sometypical building elements.

This section provides some basicguidance for the designer on how to uselaboratory Rw values to choose a suitableseparating wall or floor for the initialdesign. However, specialist advice shouldalways be sought from an acousticconsultant early on in the design stage toassess whether the combination of theseparating and flanking walls is likely toachieve the performance standard in Table1.2. An acoustic consultant can useadvanced methods of calculation topredict the sound insulation (eg StatisticalEnergy Analysis or BS EN 12354-1:2000[11]). The correct specification offlanking walls and floors is of highimportance because incorrect specificationof flanking details can lead to reductions inthe expected performance of up to 30 dB.

Sound insulation3

34

The following procedure can be usedto choose an appropriate type ofseparating wall or floor before seekingspecialist advice on appropriate flankingdetails.

1. From Table 1.2 determine therequired minimum weighted BB93standardized sound level differencebetween rooms, DnT(Tmf,max),w .

2. Estimate the required weighted soundreduction index for the separating wall orfloor, as follows:

a. Use the following formula to providean initial estimate of the measured sound reduction index (Rw,est) thatshould be achieved by the separating wallor floor in the laboratory.

Rw,est =

DnT(Tmf,max),w +10 lg ( ) +8 dB

where DnT(Tmf,max),w is the minimumweighted BB93 standardized leveldifference between rooms from Table 1.2S is the surface area of the separating

element (m2)Tmf,max is the maximum value of thereverberation time Tmf for the receivingroom from Table 1.5 (s)V is the volume of the receiving room(m3).

b. Estimate the likely reduction, X dB, inthe airborne sound insulation that wouldoccur in the field, to account for lessfavourable mounting conditions andworkmanship than in the laboratory test.X can be estimated to be 5 dB assumingthat flanking walls and floors are specifiedwith the correct junction details.However, if flanking walls and floors arenot carefully designed then poor detailingcan cause the airborne sound insulation tobe reduced by up to 30 dB. To allow thedesigner to choose a suitable separatingwall for the initial design it isrecommended that X of 5 dB is assumedand an acoustic consultant is used tocheck the choice of separating elementand ensure that the correct flankingdetails are specified.

c. Calculate the final estimate for the

STmf,maxV

Figure 3.5: Typical soundreduction indices forconstruction elements

60

55

50

45

40

35

30

25

20

15

10

5

01 10 20 50 100 200 400

Mass per unit area, kg/m2

Sou

nd re

duct

ion

inde

x, d

B

6 mmglass200 mmspace

6 mmglass10 mmspace

12 mmglass

25 mmwall board

6 mmglass

3 mmglass

Hollow corepanel door

Solid coretimber door

12 mmplasterboardwith50 x 100 studs

100 mm breezeunplastered

100 mm breezeplasteredone side 115 mm

brickworkplastered

115 mmconcrete slabwith 50 mmscreed

100 mm slabwith resilienthangers

100 mm slabwith rigidhangers

225 mmbrickworkplastered

150 mmstaggered studwith 12 mmplasterboard

100 mm breezeplasteredboth sides

3Sound insulation

35

weighted sound reduction index Rw thatshould be used to select the separatingwall or floor from laboratory test data:

Rw = Rw,est + X dB

3.10.1 Flanking detailsA simplified diagram indicating the mainflanking transmission paths is shown inFigure 3.6. General guidance on flankingdetails for both masonry and framedconstructions can be found in ApprovedDocument E[1]. Specific guidance onflanking details for products can alsosometimes be found from manufacturers'data sheets, or by contactingmanufacturers’ technical advisers.

3.10.2 Examples of problematicflanking detailsIn some buildings it is considereddesirable to lay a floating screed (eg asand-cement screed laid upon a resilientmaterial) across an entire concrete floorand build lightweight partitions off thescreed to form the rooms, see Figure3.7(a). This allows the flexibility tochange the room spaces. However, acontinuous floating screed can transmit asignificant quantity of structure-borneflanking sound from one room toanother.

For example, if a lightweight partitionwith 54 dB Rw was built off a continuousfloating screed the actual sound insulationcould be as low as 40 dBDnT(Tmf,max),w. In fact, even if a moreexpensive partition with a higherperformance of 64 dB Rw was built, theactual sound insulation would still be 40 dB DnT(Tmf,max),w, because themajority of sound is being transmitted viathe screed, which is the dominant flankingpath. This demonstrates the importanceof detailing the junction between thescreed and the lightweight partition. Toreduce the flanking transmission, thefloating screed should stop at thelightweight partition, see Figure 3.7(b).

Another flanking detail that can causeproblems is where a lightweight profiledmetal roof deck runs across the top of aseparating partition wall. With profilessuch as trapezoidal sections, it is verydifficult for builders to ensure that they

do not leave air paths between the top ofthe partition wall and the roof.

3.10.3 Junctions between ceilings andinternal wallsCeilings should be designed in relation tointernal walls to achieve the requiredcombined performance in respect ofsound insulation, fire compartmentationand support.

In the case of suspended ceiling systemsthe preferred construction is one in which

Through the junctionwith the external walls

Through the junctionwith the internal walls

Through the junctionwith the ceiling andfloor slab above

Through the junctionwith the floor slab below

Figure 3.6: The mainflanking transmission paths

Figure 3.7: Flankingtransmission via floatingscreed (a) Incorrect detail(b) Correct detail

(a) (b)

partitions or walls pass through thesuspended ceiling membrane, do notrequire support from the ceiling system,and combine with the structural soffitabove to provide fire resistingcompartmentation and sound insulation.

The alternative construction in whichpartitions or walls terminate at, or justabove the soffit of a suspended ceiling, isnot recommended as it demands a ceilingperformance in respect of fire resistanceand sound insulation which is difficult toachieve and maintain in practice in schoolbuildings. This is because the number offittings required at ceiling level isincompatible with testing of fire resistanceto BS 476[12], which is based on a testspecimen area of ceilings without fittings.Furthermore, the scale and frequency ofaccess to engineering services in theceiling void through the membrane (inrespect of fire) and through insulationbacking the membrane (in respect ofsound) is incompatible with maintenanceof these aspects of performance.

3.10.4 Flanking transmission throughwindowsFlanking transmission can occur betweenadjacent rooms via open windows in theexternal walls. Side opening casementwindows near the separating wall shouldhave their hinges on the separating wallside to minimise airborne soundtransmitted from one room to another.Where possible, windows in external wallsshould be located away from the junctionbetween the external walls and theseparating wall or floor. In particular,windows in the external walls of noisesensitive rooms and in the external wallsof rooms adjacent to them should be asfar as possible from the separating wall orfloor.

3.11 Specification of the impactsound insulation between rooms using Ln,wTable 1.4 describes the minimum impactsound insulation between rooms in termsof L′nT(Tmf,max),w. However,manufacturers usually provide informationfor floors based on laboratory impactsound insulation data measured according

to BS EN ISO 140-6:1998[13], in termsof Ln,w.

This section provides some basicguidance for the designer on how to uselaboratory Ln,w values to design a suitableseparating floor. However, specialistadvice should always be sought from anacoustic consultant early on in the designprocess to assess whether the combinationof the separating floor and flanking wallsis likely to achieve the performancestandard in Table 1.4. An acousticconsultant can use advanced methods ofcalculation to predict the sound insulation(eg Statistical Energy Analysis or BS EN12354-2:2000[14]).

The following procedure can be usedto choose an appropriate type ofseparating floor before seeking specialistadvice on flanking details from anacoustic consultant.

1. Determine the maximum weightedBB93 standardized impact sound pressurelevel, L′nT(Tmf,max),w from Table 1.4.

2. Estimate the required weightednormalized impact sound pressure levelfor the separating floor, as follows:

a. Use the following formula to providean initial estimate of the weightednormalized impact sound pressure level(Ln,w,est) that should be achieved by theseparating floor in the laboratory:

Ln,w,est =

L′nT(Tmf,max),w + 10 lg –18 dB

where L′nT(Tmf,max),w is the maximumweighted BB93 standardized impactsound pressure level from Table 1.4 V is the volume of the receiving room(m3)Tmf,max is the maximum value of thereverberation time Tmf for the receivingroom from Table 1.5 (s).

b. Estimate the likely increase, X dB, inthe impact sound pressure level thatwould occur in the field to account forless favourable mounting conditions andgood workmanship than in the laboratorytest.

X can be 5 dB assuming that flankingwalls are specified with the correct

36

Sound insulation3

VTmf,max

junction details. However, if flankingwalls are not carefully designed the impactsound pressure level can increase by up to10 dB. To allow the designer to choose asuitable separating floor for the initialdesign it is suggested that X of 5 dB isassumed and an acoustic consultant isused to check the choice of separatingfloor and ensure that the correct flankingdetails are specified.

c. Calculate the final estimate for theweighted normalised impact soundpressure level Ln,w that should be used toselect the separating wall or floor fromlaboratory test data.

Ln,w = Ln,w,est – X dB

3.12 Internal walls and partitions

3.12.1 General principlesFigure 3.5 shows typical values of thesound reduction index (Rw) for differentwall constructions. For comparison theperformance of other constructionsincluding doors, glazing and floors isincluded.

The solid line shows the theoreticalvalue based purely on the mass law. Forsingle leaf elements (eg walls, singleglazing, doors, etc) the mass law statesthat doubling the mass of the elementwill give an increase of 5 to 6 dB in Rw .When constructions provide less soundinsulation than predicted by the mass lawit is usually because they are not airtight.

In general, lightweight double-leafconstructions such as double glazing,cavity masonry or double-leafplasterboard partitions provide bettersound insulation than the mass law wouldindicate. At medium and highfrequencies, double-leaf constructionsbenefit from the separation of the twoleaves, with performance increasing withthe width of the air gap between theleaves and the physical separation of theleaves. (Note that for double-leafplasterboard constructions, timberstudwork is rarely used to achieve highstandards of sound insulation becauselightweight metal studs provide bettermechanical isolation between the leaves.)

37

3Sound insulation

Figure 3.8: Chart toestimate Rw for acomposite wall consistingof two elements withdifferent transmissionlosses

15.0

14.0

13.0

12.0

11.0

10.0

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.02 6 10 14 18 22 26 30

Corr

ectio

n, d

B

Transmission loss difference, dB

5%

10%

20%

30%

40%

50%

60%

Area

The percentage of the total area of the wall occupiedby the element with the lower transmission loss, eg adoor, and the difference between the higher Rw andthe lower Rw, are used to calculate the correction indB which is added to the lower Rw to give the Rw ofthe whole wall.

For example: Assume a classroom to corridor wallhas an Rw of 45 dB and a door in the wall has an Rwof 30 dB. If the area of the door is 0.85 m x 2.1 m =1.785 m2 and the area of the wall is 7 m x 2.7 m =18.9 m2, then the percentage of the wall occupied bythe door is 1.785/18.9 x 100 = 9.4%

The difference in Rw = 15 dB.

Therefore reading from the chart gives a correction ofabout 9 dB to be added to the lower Rw, giving acomposite Rw of 39 dB.

If a higher performance door of say 35 dB had beenused, the composite Rw would be 35 + 7 = 42 dB.

At low frequencies the performance ofplasterboard partitions is limited by themass and stiffness of the partition.Masonry walls can provide better lowfrequency sound insulation simplybecause of their mass. This is not obviousfrom the Rw figures, as the Rw ratingsystem lends more importance toinsulation at medium and highfrequencies rather than low frequencies.This is not normally a problem in generalclassroom applications where soundinsulation is mainly required at speechfrequencies. However, it can be importantin music rooms and in other cases wherelow frequency sound insulation isimportant.

A combination of masonry and dry-lining can be very effective in providingreasonable low frequency performancewith good sound insulation at higherfrequencies. This combination is oftenuseful when increasing the soundinsulation of existing masonry walls.

While partition walls may be providedas a means of achieving sound reduction,it should be remembered that soundinsulation is no better than that providedby the weakest element.

Figure 3.8 can be used to assess theoverall effect of a composite constructionsuch as a partition with a window, door,hole or gap in it. The sound insulation ofthe composite structure is obtained byrelating the areas and sound insulationvalues of the component parts using thegraph.

Partitions should be well sealed, assmall gaps, holes, etc. significantly reducesound insulation. (Note that this appliesto porous materials, eg porous blockwork,which can transmit a significant amountof sound energy through the pores.)

3.12.2 Sound insulation of commonconstructionsFigure 3.9 shows the approximateweighted sound reduction index Rw formasonry and plasterboard constructions.

Using the procedures given in Section3.10, it is possible to determine whichconstructions are capable of meeting therequirements between different types ofrooms.

The values in Figure 3.9 are necessarilyapproximate and will depend on theprecise constructions and materials used.Many blockwork and plasterboardmanufacturers provide data for specificconstructions.

More sound reduction indices, bothsingle value and octave band data, andfurther references to specificmanufacturers’ data are in the soundreduction indices spreadsheet included onthe DfES acoustics website.

3.12.3 Flanking transmission In general, a weighted sound leveldifference of up to 50 dB DnT(Tmf,max),wcan be achieved between adjacent roomsby a single partition wall using one of theconstructions described above, providedthat there are no doors, windows or otherweaknesses in that partition wall, and thatflanking walls/floors with their junctiondetails are carefully designed. Flankingtransmission is critical in determining theactual performance and specialist adviceshould be sought from an acousticconsultant.

3.12.4 High performanceconstructions – flanking transmissionHigh-performance plasterboard partitionsor masonry walls with independent liningscan provide airborne sound insulation ashigh as 70 dB Rw in the laboratory.However, to achieve high performance inpractice (ie above 50 dB DnT(Tmf,max),w),flanking walls/floors with their junctiondetails must be carefully designed.Airborne sound insulation as high as 65 dBDnT(Tmf,max),w can be achieved on siteusing high performance plasterboardpartitions, or masonry walls withindependent linings with lightweightisolated floors and independent ceilings tocontrol flanking transmission. This willrequire specialist advice from an acousticconsultant.

For rooms which would otherwiseneed high-performance partitions it maybe possible to use circulation spaces,stores and other less noise-sensitive roomsto act as buffer zones between roomssuch that partitions with lower levels ofsound insulation can be used. Case Study

38

Sound insulation3

39

3Sound insulation

Performance Rw (dB) Walls - typical forms of construction

35–40 1x12.5 mm plasterboard each side of a metal stud (total width 75 mm)

100 mm block (low density 52 kg/m2)plastered/rendered 12 mm one side

40–45 1x12.5 mm plasterboard each side of a 48 mm metal stud with glass fibre/mineral wool in cavity (total width 75 mm)

100 mm block (medium density 140 kg/m2)plastered/rendered 12 mm one side

45–50 2x12.5 mm plasterboard each side of a 70 mm metal stud (total width 122 mm)

115 mm brickwork plastered/rendered 12 mm both sides

100 mm block (medium density 140 kg/m2)plastered/rendered 12 mm both sides

50–55 2x12.5 mm plasterboard each side of a 150 mm metal stud with glass fibre/mineral wool in cavity (total width 198 mm)

225 mm brickwork plastered/rendered 12 mm both sides

215 mm block (high density 430 kg/m2)plastered/rendered 12 mm both sides

55–60 2x12.5 mm plasterboard each side of a staggered 60 mm metal stud with glass fibre/mineral wool in cavity (total width 178 mm)

100 mm block (high density 200 kg/m2) with 12 mm plaster on one side and 1x12.5 mm plasterboard on metal frame with a50 mm cavity filled with glass fibre/mineral wool on other side

Figure 3.9: Walls -airborne sound insulationfor some typical wallconstructions

40

Sound insulation3

Performance Rw (dB) Glazing - typical forms of construction

25 4 mm single float (sealed)


4/12/4: 4 mm glass/12 mm air gap/4 mm glass

30 6/12/6: 6 mm glass/12 mm air gap/6 mm glass

10 mm single float (sealed)



35 10 mm laminated single float (sealed)



12 mm laminated single float (sealed)

40 10/12/6 lam: 10 mm glass/12 mm air gap/6 mm laminated glass

19 mm laminated single float (sealed)



12 lam/12/10: 12 mm laminated glass/12 mm air gap/10 mm glass

45 6 lam/200/10: 6 mm laminated glass/200 mm air gap/10 mm + absorptive reveals

17 lam/12/10: 17 mm laminated glass/12 mm air gap/10 mm glass

Figure 3.10: Glazing - airborne sound insulation for some typical glazing constructions

7.5 (see also Figure 2.4) describes apurpose built music suite which usesbuffer zones effectively. In some cases,such as the refurbishment of musicfacilities in existing buildings, roomlayout may not allow this, and in thesecases high levels of sound insulationbetween adjacent rooms will be required.

3.12.5 Corridor walls and doorsThe Rw values in Table 1.3 should beused to specify wall (including any glazing)and door constructions between corridorsor stairwells and other spaces. To ensurethat the door achieves its potential interms of its airborne sound insulation, itmust have good perimeter sealing,including the threshold where practical.

Note that a lightweight fire door willusually give lower sound insulation than aheavier, sealed acoustic door.

Greatly improved sound insulation willbe obtained by having a lobby doorarrangement between corridors orstairwells and other spaces. However, thisis not often practicable between classroomsand corridors. Some noise transmissionfrom corridors into classrooms isinevitable, but this may not be importantif all lesson changes occur simultaneously.

For some types of room, such as musicrooms, studios and halls for music anddrama performance, lobby doors shouldgenerally be used.

3.13 Internal doors, glazing, windowsand folding partitions Internal doors, glazing and windows arenormally the weakest part of anyseparating wall. Figures 3.10 and 3.11show the performance of a number ofdifferent types of window and door. Ingeneral, rooms which require at least 35dB DnT(Tmf,max),w should not havedoors or single glazing in the separatingwall or partition.

3.13.1 DoorsThe choice of appropriate doors withgood door seals is critical to maintainingeffective sound reduction, and controllingthe transfer of sound between spaces.

Internal doors are often of lightweighthollow core construction, providing only

around 15 dB Rw which is about 30 dBless than for a typical masonry wall (seeFigure 3.5). The sound insulation of anexisting door can be improved byincreasing its mass (eg by adding twolayers of 9 mm plywood or steel facings)as long as the frame and hinges cansupport the additional weight. However,it is often simpler to fit a new door.

The mass of a door is not the onlyvariable that ensures good soundinsulation. Good sealing around the frameis crucial. Air gaps should be minimisedby providing continuous grounds to theframe which are fully sealed to themasonry opening. There should be agenerous frame rebate and a proper edgeseal all around the door leaf. Acousticseals can eliminate gaps between the doorand the door frame to ensure that thedoor achieves its potential in terms of itsairborne sound insulation.

As a rule of thumb, even a goodquality acoustically sealed door in a 55 dBRw wall between two classrooms willreduce the Rw of the wall so that theDnT(Tmf,max),w is only 30-35 dB. Twosuch doors, separated by a door lobby, arenecessary to maintain the soundinsulation of the wall. Figure 3.12 showsthe effect of different doors on the overallsound insulation of different types of wall.In a conventional layout with access toclassrooms from a corridor, the corridoracts as a lobby between the two classroomdoors.

3.13.2 LobbiesThe greater the distance between thelobby doors, the better the soundinsulation, particularly at low frequencies.Maximum benefit from a lobby isassociated with offset door openings asshown in Figure 3.13(a) and acousticallyabsorbent wall and/or ceiling finishes.

A lobby is useful between aperformance space and a busy entrancehall. Where limitations of space preclude alobby, a double door in a single wall willbe more effective than a single door; thisconfiguration is illustrated in Figure3.13(b).

Inter-connecting doors between twomusic spaces should be avoided and a

41

3Sound insulation

Sound insulation3

42

Acoustic performance Typical construction

30 dB Rw This acoustic performance can be achieved by a well fitted solid core doorset where the door is sealed effectively around its perimeter in a substantial frame with an effective stop. A 30 minute fire doorset (FD30) can be suitable.

Timber FD30 doors often have particle cores or laminated softwood cores with a mass per unit area ≈ 27 kg/m2 and a thickness of ≈ 44 mm.

Frames for FD30 doors often have a 90 mm x 40 mmsection with a stop of at least 15 mm.

Compression or wipe seals should be used around the door’s perimeter along with a threshold seal beneath. A drop-down or wipe type threshold seal is suitable.

Doors incorporating 900 mm x 175 mm vision panels comprising 7 mm fire resistant glass can meet this acoustic performance.

35 dB Rw This acoustic performance can be achieved by specialist doorsets although it can also be achieved by a well fitted FD60 fire doorset where the door is sealed effectively around its perimeter in a substantial frame with an effective stop.

Timber FD60 doors often have particle core or laminated softwood cores with a mass per unit area ≈ 29 kg/m2 and a thickness of ≈ 54 mm. Using a core material with greater density than particle or laminated softwood can result in a door thickness of ≈ 44 mm.

Frames for FD60 doors can have a 90 mm x 40 mm section with stops of at least 15 mm.

Compression or wipe seals should be used around the door’s perimeter along with a threshold seal beneath. A drop-down or wipe type threshold seal is suitable.

Doors incorporating 900 mm x 175 mm vision panels comprising 7 mm fire resistant glass can meet this performance.

Figure 3.11: Doors -airborne sound insulationfor some typical doorconstructions

44 mm

54 mm

44 mm thick timber door, half hour fire rated

54 mm thick timber door, one hour fire rated

NOTES ON FIGURE 3.11 1 Care should be taken to ensure that the force required to open doors used in schools is notexcessive for children. To minimise opening forces, doors should be fitted correctly and goodquality hinges and latches used. Door closers should be selected with care.2 The opening force at the handles of doors used by children aged 5–12 should not exceed 45 N.3 Manufacturers should be asked to provide test data to enable the specification of doorsets.4 Gaps between door frames and the walls in which they are fixed should be ≤ 10 mm.5 Gaps between door frames and the walls in which they are fixed should be filled to the full depthof the wall with ram-packed mineral wool and sealed on both sides of the wall with a non-hardening sealant.6 Seals on doors should be regularly inspected and replaced when worn.

3Sound insulation

43

lobby used to provide the necessaryairborne sound insulation.

3.13.3 Folding walls and operablepartitions Folding walls and operable partitions aresometimes used to provide flexibility inteaching spaces or to divide open planareas. A standard folding partition withno acoustic seals or detailing may providea value as low as 25 dB Rw . However,folding partitions are available that canprovide up to 55 dB Rw . The soundinsulation depends on effective acousticsealing and deteriorates if seals or tracksare worn or damaged.

It is important that the specification offolding partitions takes into account theirweight, ease of opening and maintenance.Regular inspection and servicing willextend the life of a partition and ensurethat it achieves the required soundinsulation.

Folding partitions are useful in manyapplications but they should only be usedwhen necessary and not as a response to anon-specific desire for flexibility in layoutof teaching areas.

3.13.4 Roller shuttersRoller shutters are sometimes used toseparate kitchens from multi-purposespaces used for dining. Because rollershutters typically only provide soundinsulation of around 20 dB Rw it iscommon for noise from the kitchen todisturb the teaching activities. One

(a)

(b)

Figure 3.13: Use oflobbies and double doors(a) Lobbied doorway(b) Double door

Figure 3.12: Reductionof sound insulation of awall incorporating differenttypes of door

20

50

40

30

30 40 50

Double doors, ie one door either sideof a lobby (the diagonal straight line illustrates how the insulation value ofthe original partition can only bemaintained at 100% by incorporating aset of double doors with a lobby)

Heavy door with edge seal

Light door with edge seal

Any door (gaps round edges)

Sound insulation of wallwithout door (dB)

Sound insulation of wallwith door (dB)

'very good'

'good'

'poor'

eg 100 mm: stud work with plasterboardand skin both sides (no insulation)

eg 300 kg/m 150 mm 'high' densityblockwork, plastered at least one side

eg 225 mm common brick plasteredboth sides

2

Sound insulation3

44

Figure 3.14: Existing timber floors - airborne and impact sound insulation for some typical floor/ceiling constructions

1

2

3

4

5

6

7

Basic timber floor consisting of 15 mm floorboardson 150-200 mm wooden joists, plaster orplasterboard ceiling fixed to joists

As 1, ceiling consisting of one layer of 15 mmplasterboard and one layer of 12.5 mm denseplasterboard fixed to proprietary resilient bars onunderside of joists

As 1, ceiling retained, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedon a proprietary metal ceiling system to give 240 mm cavity containing 80-100 mm mineralwool (>10 kg/m3)

As 1, ceiling removed, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedon a proprietary metal ceiling system to give 275 mm cavity containing 80-100 mm mineralwool (>10 kg/m3)

As 1, ceiling removed, with suspended ceilingconsisting of 2 layers of 15 mm wallboard or 2layers of 12.5 mm dense plasterboard, suspendedspecial resilient hangers to give 275 mm cavitycontaining 80-100 mm mineral wool (>10 kg/m3)

As 1 with proprietary lightweight floating floor usingresilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board supported on 45 mm softwood battens laid on 25 mm thickopen-cell foam pads). 80-100 mm mineral wool(>10 kg/m3) laid on top of existing floorboards

As 1, floorboards removed and replaced with 15 mm tongue-and-groove floorboards on a 15 mmplywood, chipboard or fibre-bond board supportedon 12 mm softwood battens laid on 25 mm thickopen-cell foam pads bonded to the joists, 80-100 mm mineral wool (>10 kg/m3) laid on topof existing ceiling

35–40 80–85 180–230

50–55 65–70 220–270

55–60 60–65 450–500

55–60 60–65 450–500

60–65 55–60 450–500

50–55 60–65 270–320

55–60 55–60 240– 290

Option Construction - timber floors Rw Ln,w Depth(dB) (dB) (mm)

3Sound insulation

45

buildings. Both airborne noise and impactnoise can be problematic with woodenfloors, and both problems need to beconsidered when dealing with verticallyadjacent spaces. Adding carpets or othersoft coverings to wooden floors reducesimpact noise but has very little effect onairborne noise transmission.

Impact noise can also be a problemwith concrete floors (although airbornenoise may not be a problem); this cansometimes be solved by adding a carpet.

Where the use of carpet is proposed

solution is to provide doors in front ofthe shutters to improve the soundinsulation.

3.14 Floors and ceilingsBoth airborne and impact noise can betransmitted between vertically adjacentrooms through the separating floor andits associated flanking constructions.

Vertical noise transmission betweenclassrooms can be a problem in oldermulti-storey buildings with woodenfloors, such as traditional Victorian school

8

9

10

11

As 7 but mineral wool replaced by 100 mmpugging (80 kg/m2) on lining laid on top of ceiling

As 8 but with 75 mm pugging laid on top of boardfixed to sides of joists

As 1 with proprietary lightweight floating floorusing a continuous layer (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 6-12 mm thickcontinuous open-cell foam mat)

As 10, ceiling removed and replaced withsuspended ceiling consisting of 2 layers of 15 mmwallboard or 2 layers of 12.5 mm denseplasterboard, suspended on a proprietary metalceiling system to give 275 mm cavity containing80-100 mm mineral wool (>10 kg/m3)

55–60 50–55 240– 290

50–55 55–60 240– 290

50–55 55–60 220– 270

60–65 50–55 360– 410

NOTES ON FIGURE 3.141 Where resilient floor materials are used, the material must be selected to provide the necessarysound insulation under the full range of loadings likely to be encountered in that room and mustnot become over-compressed, break down or suffer from long-term ‘creep’ under the higher loadslikely to be encountered. Where large ranges of loading are encountered, or where there are highpoint loads such as pianos, heavy furniture or operable partitions, the pad stiffness may have tobe varied across the floor to take account of these.2 All figures are approximate guidelines and will vary between different products andconstructions. Manufacturers' data should be obtained for all proprietary systems andconstructions. These must be installed in accordance with good practice and manufacturers'recommendations and all gaps sealed.

Figure 3.14 Continued

Option Construction - timber floors Rw Ln,w Depth(dB) (dB) (mm)

Sound insulation3

46

Figure 3.15: Lightweightconcrete floors - airborneand impact soundinsulation of some typicalconstructions

1

2

3

4

5

6

7

Lightweight floor consisting of concrete planks(solid or hollow) or beam and blocks, with 30-50mm screed, overall weight approximately 100 kg/m2, no ceiling or floor covering

As 1 with soft floor covering >5 mm thick

As 1 with suspended ceiling consisting of 2 layersof 15 mm wallboard or 2 layers of 12.5 mmdense plasterboard, suspended on a proprietarymetal ceiling system to give 240 mm cavitycontaining 80-100 mm lightweight mineral wool(>10 kg/m3)


As 1 with proprietary lightweight floating floorusing resilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 25 mm thickopen-cell foam pads)


As 1 with heavyweight proprietary suspendedsound insulating ceiling tile system

35–40 90–95 100–150

35–40 75–85 105–155

60–65 55–60 370–420

60–65 50–55 375–425

50–60 50–60 155–205

50–55 55–60 150–200

45–55 60–70 250– 500

Option Construction - lightweight concrete floors Rw Ln,w Depth(dB) (dB) (mm)

issues of cleaning, maintenance andeffects on air quality may need to beconsidered.

3.14.1 Impact sound insulationImpact noise on floors may arise from:• foot traffic, particularly in corridors atbreak times/lesson changeover• percussion rooms

• areas for dance or movement• loading/unloading areas (eg in kitchens and workshops) • machinery.

Where possible, impact noise should bereduced at source through use of softfloor coverings or floating floors. Carpetsare not an option in practical spaces butother soft floor coverings, such as acoustic

3Sound insulation

47

Figure 3.16: Heavyweightconcrete floors - airborneand impact sound insulationof some typicalconstructions

1

2

3

4

5

Solid concrete floor consisting of reinforcedconcrete with or without shuttering, concretebeams with infill blocks and screed, hollow orsolid concrete planks with screed, of thicknessand density to give a total mass of at least 365kg/m2, with soft floor covering >5 mm thick

As 1 with proprietary lightweight floating floorusing resilient pads or strips (eg 15 mm tongue-and-groove floorboards on a 15 mm plywood,chipboard or fibre-bond board on 25 mm thickopen-cell foam pads)


As 1 with suspended ceiling consisting of 2 layersof 15 mm wallboard or 2 layers of 12.5 mmdense plasterboard, suspended on a proprietarymetal ceiling system to give 240 mm cavitycontaining 80-100 mm mineral wool (>10 kg/m3)


50–55 60–65 150–200

55–60 50–55 200–250

55–60 50–60 175–230

60–70 55–60 420–470

60–70 50–55 425–475

NOTES ON FIGURES 3.15 AND 3.161 Where soft floor covering is referred to this should be a resilient material or a material with aresilient base, with an overall uncompressed thickness of at least 4.5 mm ; or any floor coveringwith a weighted reduction in impact sound pressure level of not less than 17 dB when measuredin accordance with BS EN ISO 140-8:1998[15] and calculated in accordance with BS EN ISO 717-2:1997[16].2 Where resilient floor materials are used, the material must be selected to provide thenecessary sound insulation under the full range of loadings likely to be encountered in that roomand must not become over-compressed, break down or suffer from long-term ‘creep’ under thehigher loads likely to be encountered. Where large ranges of loading are encountered, or wherethere are high point loads such as pianos, heavy furniture or operable partitions, the pad stiffnessmay have to be varied across the floor to take account of these.3 All figures are approximate guidelines and will vary between different products andconstructions. Manufacturers' data should be obtained for all proprietary systems andconstructions. These must be installed in accordance with good practice and manufacturers'recommendations and all gaps sealed.

Option Construction - heavyweight concrete floors Rw Ln,w Depth(dB) (dB) (mm)

Sound insulation3

48

vinyl floor or vinyl flooring laid on anacoustic mat, may be suitable.

Planning and room layout can be usedto avoid impact noise sources on floorsabove noise-sensitive rooms. Soft floorcoverings and floating floor constructionsand independent ceilings are the mosteffective means of isolation, and resilientfloor finishes are also appropriate forsome sources.

Typical airborne and impact noiseperformance are listed for a number ofconstructions in Figures 3.14, 3.15 and3.16. Note that, unlike airborne soundinsulation, impact sound insulation ismeasured in terms of an absolute soundlevel, so that a lower figure indicates abetter standard of insulation.

3.14.2 Voids above suspendedceilingsWhere partitions run up to the undersideof lightweight suspended ceilings, theairborne sound insulation will be limitedby flanking transmission across the ceilingvoid, which will often prevent theminimum values for airborne soundinsulation in Table 1.2 being achieved.Therefore, partitions should either becontinued through the ceiling up to thesoffit, or a plenum barrier should be used.

3.14.3 Upgrading existing woodenfloors using suspended plasterboardceilingsFigure 3.14 shows the airborne andimpact noise performance of a standardwooden floor with various forms ofsuspended plasterboard ceiling.

Option 2 is possibly the most widelyused system of increasing both impactand airborne sound insulation, with orwithout the original plaster ceiling. Insmall rooms good results can be achievedusing timber studs fixed only to the walls,but large timber sections are needed tospan wider rooms.

In wider span rooms it is generally moreconvenient to suspend the plasterboardfrom the floor joists above, fixing throughthe existing ceiling if this is retained,using a proprietary suspension and gridsystem (option 4). The grid can be hungfrom simple metal strips or, for higher

performance, special flexible ceiling hangers.The major manufacturers of dry-lining

systems all provide their own systems forthese options, and provide soundinsulation data and specifications for avariety of configurations. The performancefor both airborne and impact soundimproves with the depth of the ceilingvoid, with the mass of the ceiling andwith the deflection of the ceiling hangersunder the mass of the ceiling. Adding alayer of lightweight acoustically absorbentglass wool or mineral wool in the ceilingvoid increases the sound insulation,typically by 2-3 dB, but there is no pointin adding more than specified.

Performance on site is stronglydependent on good workmanship toavoid air gaps, so careful attention shouldbe given to ensuring that joints are close-butted, taped and filled and that all gapsare properly sealed. At the perimeter asmall gap should be left between theplasterboard and the walls, and thisshould be sealed using non-setting masticto allow a small amount of movementwithout cracking.

Penetrations through the ceiling needto be properly detailed to maintain anairtight seal while allowing movement,and services should not be allowed toprovide a rigid link between the ceilingand the floor above. This can be aparticular problem with sprinkler pipes. Aproblem with these constructions is thatrecessed light fittings, grilles and diffuserssignificantly reduce the sound insulation soany services should be surface-mounted.

A plasterboard finish is acousticallyreflective whereas in some rooms anacoustically absorbent ceiling is required,to meet the specifications for roomacoustics and reverberation times. Onesolution to this, if there is sufficientheight, is to suspend a separatelightweight sound absorbing ceiling underthe sound insulating plasterboard ceiling.This can be a standard lightweightcomposite or perforated metal tile system.These lightweight, acoustically absorbent,ceilings add very little to the soundinsulation but do provide acousticabsorption. Lights and services can berecessed in the absorbent ceiling.

3Sound insulation

49

The term ‘acoustic ceiling’ generallyrefers to lightweight acousticallyabsorbent ceiling tile systems, designed toprovide acoustic absorption. Note thatthese systems do not always increase thesound insulation as well.

There are, however, some systemswhich use relatively heavy ceiling tileswhich are designed to fit into ceiling gridsto provide a reasonably airtight fit. Thesemay consist of dense plasterboard ormineral fibre products, or perforatedmetal tiles with metal or plasterboardbacking plates. If properly installed andmaintained these can provide a usefulincrease in sound insulation as well asacoustic absorption. Manufacturers ofthese systems can provide both airborneand impact sound insulation figures, aswell as acoustic absorption coefficients. Ifno measured sound insulation data areprovided, it is better to err on the side ofcaution and assume that the tile will notprovide a significant increase in soundinsulation.

The sound insulation performancefigures quoted in Figure 3.14 all assumethat the floorboards are in goodcondition and reasonably airtight, withthin carpet laid on top. If retaining theoriginal floorboards it is good practice tofill in any gaps with glued wooden strips,caulking or mastic, or to lay hardboard ontop, to provide an airtight seal. If notretaining the original boards, 18 mmtongue-and-grooved chipboard can beused to achieve the same effect, with alljoints and gaps properly sealed, especiallyat the perimeters.

3.14.4 Upgrading existing woodenfloors using platform and ribbed floorsThe systems discussed in Section 3.14.3all maintain the original wooden floormounted directly on joists. This has theadvantage of maintaining the originalfloor level at the expense of loss of ceilingheight below. An alternative approach isto provide a floating floor system eitheron top of the existing floorboards (aplatform floor) or to remove the existingfloorboards and build a new floor onresilient material placed on top of thefloor joists (a ribbed floor). In both cases

the increase in both airborne and soundinsulation relies on the mechanicalisolation of the floor from the joists usingresilient material.

Figure 3.14 shows a number of typicallightweight floating floor constructionsand indicative sound insulation figures.There are many proprietary systems usinga wide range of isolating materials andmanufacturers should supply test data inaccordance with ISO 140 measurements.

The isolating layer will typically consistof rubber, neoprene, open-cell or closed-cell foams, mineral fibre or compositematerials. The isolating layer can be in theform of individual pads, strips or acontinuous layer of material.

The sound insulation increases with thedeflection of the resilient layer (up to thelimit of elasticity for the material), withthe mass of the floating layer and with thedepth of the cavity. Adding a layer oflightweight acoustically absorbent glasswool or mineral wool in the ceiling voidincreases the sound insulation, typically by2-3 dB, but there is no point in addingmore than specified. In each case thedeflection of the material under thepermanent ‘dead’ load of the floatinglayer and the varying ‘live’ loads ofoccupants and furniture must beconsidered. If the material is too resilientand the floating layer is insufficientlyheavy or rigid, the floor will deflect underthe varying loads as people move aboutthe room. For this reason it isadvantageous for the floating layer to beas heavy and as stiff as practicable, insome cases using ply or fibre-bond board(for mass) laid on top of the resilientlayer, with tongue-and-grooved chipboardon top of this.

If there are likely to be very heavy localloads in the room (eg pianos) it may benecessary to increase the stiffness of theresilient material, or, in the case of pads,to space the pads more closely together tosupport these loads.

Junctions with walls and at doors needto be designed to maintain an effectivelyairtight seal while allowing movement ofthe floating layer. Manufacturers generallyprovide their own proprietary solutionsfor this, with or without skirtings.

50

Sound insulation3

Lightweight floating floors are quitespecialist constructions, and achieving thecorrect deflection under varying live loadswithout overloading the resilient materialcan be difficult. Most materials sufferfrom long term loss of elasticity or ‘creep’under permanent loads and this should betaken into account in the design andselection of materials. The systemmanufacturer should normally be providedwith all of the relevant information andrequired to specify a system to meet all ofthe acoustic and structural requirementsover the expected lifetime of the floor. Indifficult cases the advice of an acousticsconsultant and/or structural engineershould be sought.

3.14.5 Concrete floorsIn general, concrete floors provide muchgreater low frequency airborne soundinsulation than wooden floors by virtue oftheir greater mass. There are, however,considerable variations in performancebetween dense poured concrete floors andcomparatively lightweight precast concreteplank floors. Impact sound transmissioncan be a problem even in heavy concretefloors because of the lack of damping inconcrete, and a soft or resilient floorcovering is generally required. This maysimply be carpet on suitable underlay.

Figures 3.15 and 3.16 show airborne

sound insulation and impact soundtransmission data for a number of typicalconcrete floor constructions, with andwithout suspended ceilings and floatingfloors.

3.15 Design and detailing ofbuilding elementsImportant points to remember whendesigning constructions to achieveadequate sound insulation are: • Weak elements (eg doors and glazing,service penetrations, etc) will reduce theeffectiveness of the walls in which they arelocated.• Impact sound will travel with littlereduction through a continuous membersuch as a steel beam or servicing pipe.• Partitions between sensitive spacesshould normally continue beyond theceiling up to the structural soffit or rooflayer, to prevent noise passing over thetop of the partition above the ceiling orthrough a loft space.• Openings in walls caused by essentialservices passing through should beacoustically sealed. Pipework passingbetween noise sensitive spaces should beappropriately boxed-in (see ApprovedDocument E[1]).

Figure 3.17 shows how possibletransmission paths through the structureof a building can be prevented.

allconnectionsfor plant andmachineryshould be flexible

walls must be ofadequate weightand all gaps sealed

airborne sound transmited through ceiling,light fittings, and lightweight partitions and gaps

can be dealt with by sealing gaps and increasing mass

sound can be transmitted along the structure

all gaps forducts and pipes

in walls and floorshould be well sealed

airborne sound transmittedthrough ductwork

ceiling below plant may needto be isolated from floorabove and from ductwork assuspended ceiling can bea good amplifier forstructure-borne noisecreated by badly isolatedplant

plantroomshould haveflexiblemountings,adequatefloor massand elasticity,or floatingfloor

partitions should extendup to the soffitFigure 3.17: Possible

sound transmission pathsand their prevention

51

3Sound insulation

References[1] Approved Document E - Resistance to thepassage of sound. The Stationery Office,2003, ISBN 01 753 642 3www.safety.odpm.gov.uk[2] Sound Control for Homes (BRE report 238,CIRIA report 127), 1993. Available from CRCLtd. 1993, BRE ISBN 0 85125 559 0, CIRIAISBN 0 86017 362 3, CIRIA ISBN 0305 408 X.[3] J McLoughlin, D J Saunders and R D Ford.Noise generated by simulated rainfall onprofiled steel roof structures. Applied Acoustics42 239-255, 1994[4] ISO 140-18 Acoustics - Measurement ofsound insulation in buildings and of buildingelements - Part 18: Laboratory measurementof sound generated by rainfall on buildingelements (in preparation).[5] BS EN ISO 140-3: 1995 Measurement ofsound insulation in buildings and of building elements. Part 3. Laboratory measurement ofairborne sound insulation of building elements.[6] The Education (School Premises)Regulations 1999. (Statutory Instrument 1999No 2, Education, England & Wales). TheStationery Offiice, 1999. ISBN 0 11 080331 0www.hmso.gov.uk[7] BS EN 20140-10: 1992 Acoustics -Measurement of sound insulation in buildingsand of building elements. Part 10. Laboratorymeasurement of airborne sound insulation ofsmall building elements. [8] BS 98/704582 DC. Ventilation for buildings.Performance testing of components/productsfor residential ventilation. Part 1. Externally andinternally mounted air transfer devices. Draftfor public comment (prEN 13141-1 CurrentEuronorm under approval).

[9] BS EN 12354-3:2000 Building Acoustics -Estimation of acoustic performance in buildingsfrom the performance of elements. Part 3.Airborne sound insulation against outdoorsound.[10] BS EN ISO 140-5: 1998 Measurement ofsound insulation in buildings and of building elements. Part 5. Field measurements ofairborne sound insulation of façade elementsand facades. [11] BS EN 12354–1: 2000 BuildingAcoustics. Estimation of acoustic performancein building from the performance of elements.Part 1. Airborne sound insulation betweenrooms.[12] BS 476 Fire tests on building materialsand structures.[13] BS EN ISO 140-6: 1998, Acoustics -Measurement of sound insulation in buildingsand of building elements. Part 6. Laboratorymeasurement of impact sound insulation offloors.[14] BS EN 12354-2: 2000 Building Acoustics.Estimation of acoustic performance in buildingfrom the performance of elements. Part 2.Impact sound insulation between rooms.[15] BS EN ISO 140-8: 1998 Acoustics.Measurements of sound insulation in buildingsand of building elements. Part 8. Laboratorymeasurements of the reduction of transmittedimpact noise by floor coverings on aheavyweight standard floor.[16] BS EN ISO 717-2: 1997 Acoustics - Ratingof sound insulation in buildings and of buildingelements. Part 2. Impact sound insulation.

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4.1 Approach to acoustic designThe vast majority of rooms in schools aredesigned for speech. A structuredapproach to the acoustic design of theserooms would consider the followingsubjects in the order given:1 Indoor ambient noise levels

(Table 1.1)2 Room size - floor area, shape and

volume and hence, required reverberation time (Table 1.5)

3 Amount of acoustic absorption required for reverberation time

4 Type, location, and distribution of that acoustic absorption

5 Special considerations for non-standard rooms (eg reflectors and diffusers)

6 Use of electronic sound reinforcementsystems.

4.2 Internal ambient noise levelsand speech clarityThe internal ambient noise level is veryimportant in teaching spaces as theteacher’s voice needs to be clearly heardabove the background noise. The soundpower output of conversational speech istypically 10 microwatts which results in asound pressure level of about 60 dB at 1 min front of the speaker. This output powercan be raised to around 100 microwattswhen the speaker talks as loudly aspossible without straining the voice,which increases the sound pressure level at1m to about 70 dB. By shouting, theoutput power can be further raised toaround 1000 microwatts with aconsequent further increase in soundpressure level to about 80 dB. Insubjective terms, this means that a speakercan approximately double the loudness ofthe voice by speaking very loudly, andthen double it again by shouting, seeFigure 4.1.

It is also desirable to preserve thecharacter, or nuances and intonations, ofspeech. This is particularly relevant tolanguage teaching and to the performanceof drama. The frequencies of sound inspeech range from bass to treble, that isfrom below 125 Hz to above 8 kHz.Vowels have a sustained, tonal soundwhich contains characteristics of thespeaker’s voice. Men’s voices have thelowest characteristic pitch (120 Hz),women an intermediate pitch (225 Hz),and children the highest pitch (265 Hz).Vowels contain most of the sound energyin speech but recognition of theconsonants, whose energy is generallyconcentrated towards the higherfrequency end of the speech spectrum, isthe key factor for high intelligibility.

The intelligibility of speech dependsupon its audibility as well as its clarity.Audibility is affected by the loudness ofthe speech relative to the background

Normal voice

Raised voice

Shouting

60 dB at 1 m

80 dB at 1 m

70 dB at 1 m

Figure 4.1: Soundpressure levels of speechat 1 m

The design of rooms for speech 4

SE

CT

ION

The design of rooms for speech is a critical aspect of the acoustic design of aschool. Rooms must be designed to facilitate clear communication of speech

between teachers and students, and between students.

54

noise level. An increase in the backgroundnoise will cause greater masking of speechand hence will decrease intelligibility. It ispossible to speak louder but this effect islimited and can also lead to voice strain.The indoor ambient noise levels fordifferent rooms specified in Table 1.1have been chosen to ensure that anadequate signal to noise ratio can beachieved without undue strain on theteacher’s voice, and to minimise theeffects of distraction from other sources.

4.3 Reverberation timesA classroom with a long reverberationtime of several seconds will cause syllablesto be prolonged so that they overlap andhence degrade speech intelligibility. Longreverberation times occur in large roomswith hard wall and ceiling surfaces.Adding acoustic absorption and reducingthe ceiling height will reduce thereverberation time and will improvespeech intelligibility. Table 1.5 specifiesthe reverberation times required forvarious teaching spaces ranging fromteaching classrooms to assembly halls.

Appendix 2 describes the theory andterminology of reverberation time,acoustic absorption and enclosed volume.The methodology for calculation ofreverberation time in rooms other thancorridors, entrance halls and stairwells isdescribed in Appendix 6, together withsome worked examples. There is a link toa façade sound insulation and reverberationtime computer spreadsheet for schools,from the DfES acoustics website.

Long reverberation times also increasereverberant noise levels within a room,which further decrease speechintelligibility. To compensate for this, inreverberant rooms people tend to increasetheir voice levels to make themselvesheard over the reverberant noise, whichfurther exacerbates the situation. This is acommon feature of many school diningrooms and sports halls.

4.4 Amount of acoustic absorptionrequiredThe method described in Appendix 6allows the amount and type of acousticabsorption to be calculated.

In general, in rooms for musicperformance, the reverberation timecalculations will show that relatively littleabsorption is required in addition to thatprovided by the audience.

In classrooms and other rooms forspeech, however, larger amounts of fixedacoustic absorption are often required,particularly where rooms have highceilings as often occurs in older buildings.

When calculating reverberation timesto comply with the specified values inTable 1.5 in rooms for speech, theabsorption due to furnishings such aschairs, school desks and benches, may beignored. Accurate absorption data forsuch items can be difficult to identify andif the furnishings have any effect it islikely to result in shorter, rather thanlonger, reverberation times.

4.5 Distribution of absorbentmaterialsThe location of acoustic absorption withina room is important. The traditionalcalculation of reverberation time assumesthat the absorbent surfaces in a room arereasonably evenly distributed. If this is notso, the reverberation time equation is notvalid and undesirable local variations inthe acoustics can occur, particularly inlarge rooms or halls. Large areas ofacoustically reflective material can alsolead to echoes, focusing and standingwaves.

4.6 Room geometryTo achieve adequate loudness for alllisteners in a room, it is necessary that thedirect sound from speaker to listener has aclear unobstructed path. The loudness ofthe direct sound can be enhanced bystrong, short delay reflections from roomsurfaces. These short delay reflectionsshould arrive at the listener within onetwentieth of a second (50 milliseconds) ofthe direct sound, which is approximatelythe time required for the ear to integratesuch reflections with the direct sound.Strong reflections after 50 millisecondstend to be detrimental to speechintelligibility, and ultimately, if the delay islong enough, they will be perceived asdistinct echoes.

The design of rooms for speech4

55

4.7 ClassroomsFor classrooms and other rooms forspeech, there are two approaches tolocating the acoustic absorption:

1. To make the ceiling predominantlyabsorbent. In most cases a standardacoustically absorbent suspended ceilingwill provide all of the necessaryabsorption. In the case of rooms withexposed concrete soffits (providingthermal mass to limit overheating insummertime) acoustically absorbentsuspended baffles may be used. The idealcase is often to have the central part ofthe ceiling reflective with absorption atthe edges, see Figure 4.2(a)

2. To leave the ceiling acousticallyreflective (plaster, plasterboard, concrete,etc) and to add acoustic absorption to thewalls. In these cases it is advisable tolocate most of the absorption at high leveland some on the back wall facing theteacher to prevent "slap echo" off theback wall. This is particularly important ifthe rear wall is concave or the distancefrom the speaker to the rear wall isgreater than 8.5 m. see Figure 4.2(b).

In large rooms, reflections from therear wall can be disturbing for a speaker ifthey arrive later than 50 milliseconds afterthe speech has been voiced. This canoccur if the speaker to rear wall distance isgreater than 8.5 m. To avoid this problem,the rear wall should be made acousticallyabsorbent, or acoustically diffusing.

There are instances where provision ofsound field amplification can improvespeech intelligibility, see Section 6.

4.8 Assembly halls, auditoria andlecture theatresMost school halls are used primarily forspeech functions such as assemblies,meetings and drama, and use for music isless frequent. The most common problemin school halls is excessive reverberationresulting in high noise levels and poorspeech intelligibility.

4.8.1 Room geometryThe direct sound from speaker to listenermust be as strong as possible at allpositions. Because this sound weakensrapidly with distance according to theinverse square law (the intensity isreduced by a factor of four and the soundlevel falls by 6 dB when the speaker toreceiver distance is doubled), the averagedistance between speaker and listenershould be kept as small as possible.Furthermore, there should be noobstructions along the direct sound path.

140°

speaker

audience

Figure 4.3: Ideal seatingplan

4The design of rooms for speech

b

d da

c

(b) Surface finishes in classroom or lecture theatre:a. Rear wall - sound absorbing or diffusingb. Ceiling - sound reflective (eg plasterboard)c. Floor - sound absorbing (eg carpet)d. Walls - sound reflectivee. Top of walls - sound absorbing or diffusing

d da

c

b

(a) Surface finishes in classroom or lecture theatre:a. Rear wall - sound absorbing or diffusingb. Ceiling - sound reflective (eg plasterboard)c. Floor - sound absorbing (eg carpet)d. Walls - sound reflectivee. Ceiling - sound absorbing

e e

Figure 4.2: Surfacefinishes in classroom orlecture theatre

For large rooms such as school halls,additional factors need to be consideredin relation to the direct sound. First, theseating plan should be arranged to fallwithin an angle of about 140° subtendedat the position of the speaker, see Figure4.3. This is because speech is directional,and the power of the higher frequencieson which intelligibility largely dependsfalls off fairly rapidly outside this angle.Secondly, sound is weakened as it passesover seated people at grazing incidence.Therefore, if possible, listeners should beseated on a rake where a clearance ofaround 100 mm is provided between thesightline from one row and the sightlinefrom the next, see Figures 4.4(a) and4.4(b). It is known that if people can not

see the speaker well, they will not hearwell either. It is frequently necessary inschools to have a flat floor in a schoolhall. In these cases, speakers should beraised on a platform which is sufficientlyhigh to ensure that minimum clearance isobtained at the rear rows of the hall, seeFigure 4.4(c).

The direct sound from speaker tolistener can be enhanced by strong earlyreflections that arrive within 50milliseconds, see Figure 4.4(d). Theseearly reflections increase the loudness ofthe direct sound and therefore increasespeech intelligibility. They are particularlyuseful at the furthest seats where theloudness of the direct sound has beenreduced by distance. To provide

56

b ca

(a) Adequate loudness is essential, direct sound musthave a clear unobstructed path.

(b) Loudness of direct sound towards rear isincreased with raked seating.

(c) Loudness of direct sound can be increased byputting the speaker on a platform.

(d) Reflected sound enhances direct sound if timedelay is less than 50 milliseconds.

(e) For useful sound reflections, additional pathtravelled by reflected sound must be less than 17 m:b+c – a<17 m.

(f) Rear wall can cause a disturbing echo for speakersif over 8.5 m away. Rear wall should be absorbingor diffusing.

4

Figure 4.4: Effects ofroom geometry on speech.

The design of rooms for speech

57

(c) Curved rear wall can cause focusing

(a) Barrel vault can cause focusingand flutter echoes

(b) Shallow hipped roof can causefocusing and flutter echoes

section

section

plan

Figure 4.5: Room shapeswhich can cause focusingand echoes

4reflections within 50 milliseconds of thedirect sound, hard surfaces must belocated within a certain distance of thespeaker and listener. In most rooms, thecentre part of the ceiling is the mostimportant reflecting surface and shouldbe of hard, sound-reflecting material.Other useful surfaces providing earlyreflections are side walls near the speaker,overhead reflecting panels and angledceiling panels.

The additional path travelled by thereflected sound should be no greater than17 m more than the direct sound pathbetween speaker and the seating areawhere the reflection arrives, see Figure4.4(e).

Any reflection that arrives at a listener,or back at the speaker, more than 50milliseconds after the direct sound is likelyto be disturbing, see Figure 4.4(f). Theseare most probable in school halls wherelate reflections can occur from the rearwall or a control room window at therear. Rear walls can be rendered soundabsorbing or sound diffusing to avoidthis. In the case of control roomwindows, these can be tilted to direct thereflection away from speakers andlisteners.

Focusing of sound by domes or barrelvaults illustrated in Figure 4.5(a), can be aserious fault which can cause strong latereflections or echoes. If the dome orbarrel vault is above a flat, hard floor as ina school hall, flutter echoes can occurwhich can be disturbing for speaker andlistener alike. This effect can also occurwith shallow pitched reflective roofsabove a flat floor, see Figure 4.5(b) andthe assembly hall in Case Study 7.1. Thesame effect can also occur on plan wherea room has a curved or segmented rearwall opposite a flat front wall, see Figure4.5(c).

4.8.2 Sound reinforcementWith an acoustically well designed roomit is possible for strong speakers to achievegood speech intelligibility for largeaudiences. Quieter and untrainedspeakers, however, will not be able to dothis and a speech reinforcement system islikely to be required for some functions.

The key aim of such a system is toincrease the loudness of the direct sound,particularly for more distant listeners,whilst keeping the sound as natural aspossible.

The distribution of loudspeakers andtheir directional characteristics is a keyissue in achieving high speechintelligibility. For large teaching roomsand lecture theatres, loudspeakers can bedistributed in the ceiling or on the wallsat high level. In school halls, columnloudspeakers can be located on sidewalls,or in a central cluster as shown in Figure 4.6.

The design of sound reinforcementsystems is a specialist field and specialistadvice should be sought.


4.9 Open-plan teaching andlearning areas In open-plan areas it is essential toprovide good speech intelligibility and tosecure freedom from aural distraction bymore distant sound sources and bybackground noise. Section 1 containsperformance standards for speechintelligibility in open-plan spaces. Somedegree of acoustic privacy is also desirable.This can be difficult to achieve in practiceand there have been many instances ofdistraction and disturbance between classgroups in open plan areas. Case Studies7.2, 7.3 and 7.10 describe surveys of theacoustics of open-plan teaching areas inprimary and secondary schools.

In open-plan areas, a carpeted floor isrecommended together with a soundabsorbing ceiling. In addition, soundabsorbing screens should be interposedbetween class groups. Screens should beat least 1.7 m high and ideally shouldreach to within 0.5 m of the ceiling, seeFigure 4.7.

A major improvement in the acousticprivacy between spaces in open-plan areascan be realised by installing full heightmoveable walls which, if fitted with seals,can provide a moderate degree of soundinsulation between the divided spaces. Ingeneral however it is found that suchscreens are rarely used because of the time

and effort required to open and closethem. While in theory it is possible toachieve adequate sound insulationbetween classrooms using high-performance moveable walls, there areissues of cost, weight, complexity ofinstallation and maintenance to consider.Specialist advice from an independentconsultant should always be sought ifusing such partitions to comply with thesound insulation requirements set out inSection 1 of this document.

Research has shown that in many largeopen-plan ‘flexible’ areas certain activitiesare severely restricted or have to bedropped because of noise interference.Indeed, it must be recognised that thereare but a small number of activities thatcan share a degree of acoustic linkage andeven then the timetable has to bedesigned to allow this.

Those plans which provide a generousrange of spaces in a variety of sizes can beseen to give far more opportunities inteaching than those with large openspaces and moveable screens, because inthe former it is possible to achieve goodsound insulation standards betweenspaces.

When designing open-plan areas it isimportant to provide plenty of acousticallyabsorbent surfaces and to use screens toblock direct sound paths.

58

amplifier

central cluster

microphone

Figure 4.6: Anarrangement ofloudspeakers in a schoolhall

4 The design of rooms for speech

59

Figure 4.7: Positioningof indoor screens

Screens should be as high as possibleand the ceiling must be absorbent

SECTIONIf a screen is not high enough, direct sound paths or paths with onlysmall angular changes are possible. If the angle is small, more lowand mid frequency sound will diffract over the top of the screen.If the ceiling is not absorbent, sound can be reflected over the screen.

Surrounding surfaces must be absorbent

PLANScreens near windows have littleeffect because of flanking reflectionsoff the windows.

44.10 Practical spaces Spaces for teaching practical subjects haveparticular requirements which needcareful design in order to comply with theacoustic requirements for teaching andlearning. This section addresses the needsof Design and Technology spaces and Artrooms. Music rooms are consideredseparately in Section 5. Although Scienceinvolves a significant amount of practicalactivity, the general approach describedfor classrooms (Section 4.7) can beapplied to spaces for the teaching ofScience. For further information onDesign and Technology spaces seeBuilding Bulletin 81[1] and the DfESacoustics website.

4.10.1 Design and Technology spacesDesign and Technology departments insecondary schools contain timetabledspaces for a variety of practical activities,eg graphics, resistant materials (wood,metal and plastics), electronics/control,food and textiles. They also include non-timetabled learning spaces, typicallyshared design/ ICT resource areas.

The equipment and the activities inthese spaces can vary widely dependingon the type and size of department.Activity noise and noise toleranceclassifications for different spaces aregiven in Table 1.1. It is important toestablish what activities will take place inany one space and what equipment willbe used before calculating required levelsof sound insulation to minimise thebackground noise in nearby spaces.

Resistant materials areas containingwood or metal working machinery canproduce high noise levels. Machinesextracting dust particles, CADCAM andother noisy equipment will increase theactivity noise level of a space. It isimportant to consider the effects of suchequipment on teaching activities bothwithin the space containing theequipment and in adjoining rooms.Where possible, it is advisable to locatenoisy equipment in spaces away fromrooms housing quieter activities.CADCAM equipment is sometimeshoused in a separate room or withinpurpose designed enclosures which can

reduce the noise level. The effect of noise from machines

within the space is not required to beincluded in the indoor ambient noise levelcalculations submitted for approval byBuilding Control Bodies, except in thecase of open plan arrangements. Oftenmachines can be switched off whenquieter learning activities such as grouppresentations are taking place, but thismay not always be possible. The locationand use of noisy equipment needs to bediscussed and agreed with the user.

Partially glazed partitions havecommonly been used between design andtechnology spaces, particularly between


timetabled and non-timetabled spaces.This is both for ease of supervision and toemphasise the link between related designactivities. However, these considerationsmust be balanced against the acousticrequirements. Large areas of glazing willboth increase the reverberation timewithin a space and reduce the soundinsulation of a partition. Both of thesefactors will have a detrimental effect uponthe speech intelligibility within the spaceand other nearby spaces.

Similarly, if interconnecting doors areused between neighbouring rooms thedoorsets must be chosen to provideadequate sound insulation.

Central resource areas are often locatedadjoining the circulation spaces of designand technology departments. A commonarrangement uses the central resourcearea predominantly for individual andsmall group work but such areas are notgenerally suitable for whole class teaching.Usually, there are areas of glazing anddoors between the central resource areaand adjacent practical spaces. The centralarea should be suitable for mostdesign/resource activities as long as thecirculation is restricted to the departmentand does not include access to other partsof the school.

Where spaces are open plan or dividedby moveable or extensively glazedpartitions, it may be appropriate to adoptalternative acoustic performance standardsin accordance with Section 1.2.1. Thiswill need to be based on an activity planfor the area which has been agreed withthe user.

The speech intelligibility in open planspaces will need to be assessed usingcomputer prediction models, as describedin Section 1.1.7. This may apply to ashared design/ICT resource area wheregroup presentation could take place at thesame time as other activities.

4.10.2 Art roomsArt classes in secondary schools involveindependent and group activities whichare in general quieter than those in otherpractical areas. Noise levels in secondaryschool art spaces are likely to be similar tothose in a general classroom. However,

art departments tend to have a moreinformal environment reflecting thenature of the activity, and are often ofopen-plan design. There may be moreglazing in partitions in art departmentsthan in other parts of the school, toemphasise the importance of the visualenvironment.

4.10 3 Floor finishes in practicalspacesCarpets are not appropriate for mostpractical areas and so cannot be used as away of increasing sound absorption orreducing the impact sound transmissionthrough floors in science, art and designand technology spaces. They may howeverbe suitable in some design/resource areas.

Acoustic vinyl flooring or a vinyl floorlaid on top of an acoustic mat may besuitable for practical spaces whereimproved impact sound insulation isrequired. Resistance to indentation willneed to be considered and a change offlooring may be necessary underneathfixed heavy machinery such as floormounted machine tools.

4.11 Drama roomsThere are three types of drama room incommon use:1 Rooms for small scale drama teaching

and practical work2 Drama studios – for rehearsal, teaching

and small-scale performance3 Theatres and flexible spaces primarily

for performance.Rooms for small scale drama teaching

and practical work are usually little morethan classrooms, which may be fitted withcurtains both for blackout and to reducereverberation time. They may also beprovided with a basic set of lights anddimmable main lighting.

Drama studios tend to be larger spacesdedicated to drama, with specialequipment such as moveable staging,seating rostra, lighting and sound systems.They do not normally have fixed stages orplatforms and the acoustics will tend tochange with the layout, seating andaudience. They may be fitted with heavycurtains on some or all walls, to allowsome control of reverberation time, for

60

4 The design of rooms for speech

61

Proscenium opening with afore stage projecting in frontof it

Proscenium opening at thefront of the stage, making aframe between audience andactors

Three-sided arrangement

In the round arrangement

Figure 4.8: Typicalperformance spaces fordrama

4blackout, and to allow some flexibility inthe room’s appearance. In this case thewall finishes will generally be hard(masonry or plasterboard). Studiosgenerally have wooden floors andacoustically absorbent ceilings, althoughlarge amounts of permanent lighting andrigging also provide useful diffusion.

Theatres and spaces primarily forperformance vary considerably in formand size from the conventional assemblyhall to adaptable theatres. They can betraditional theatres with fixed prosceniumand stage, open stages, thrust stages or inthe round, see Figure 4.8. Adaptabletheatres can be converted from onearrangement to another depending on thetype of performance.

Each type has different acousticcharacteristics. The basic acousticrequirements for auditoria are discussedin Section 4.8, however spaces designedspecifically for public performance arespecialised rooms and the advice both ofan acoustician and a theatre consultantshould normally be sought.

For successful drama it is necessary forthe audience to see and hear considerablybetter than in most school halls, becauseof the close relationship between actorsand their audience. In principle, toachieve close communication betweenactor and the audience it is necessary torestrict the size of the auditorium so thatthe maximum distance from any memberof the audience to the stage does notexceed 20 m. In small theatres this is notgenerally a problem, but for largeraudiences it may require the use ofbalconies and galleries, giving rise to thetraditional fan-shaped theatre (which is,however, very bad acoustically for music).Deep balconies are to be avoided as thespace under these can be acoustically‘dead’ and considerable care is required toensure that reflections from the ceilingsand walls compensate for the lack ofdirect sound in such areas.

It is common for theatres in schools tobe used not only for drama, but also forlectures, films, meetings and music, whichall have different acoustic requirements.The acoustics of multi-purpose halls arediscussed in the following section.

4.12 Multi-purpose halls In large schools the multi-purpose space,intended to act as assembly hall, theatre,concert hall and gymnasium, is passingout of favour as it is difficult for a singlehall to fulfil all of these functions well.None the less, in some cases a singleflexible hall is required for a variety ofuses and this gives rise to specific acousticproblems.

The different uses of multi-purposehalls often have conflicting acousticrequirements, making it difficult toprovide a space with optimum acousticsfor all uses. The main conflict is thatbetween speech and unamplified music.


62

4

Table 4.1 shows the general acousticrequirements for speech and music. (Seealso Section 5.7.)

Where regular performances of musicare expected, reverberation time issometimes changed using moveable areasof absorption (typically curtains) withoutchanging the volume of the space.Although this can successfully change thereverberation time at medium and highfrequencies, it often has little effect at lowfrequencies, resulting in an acoustic whichis less than ideal for either speech ormusic.

(Note that the ‘dry’ acoustic requiredfor speech is also generally suitable foramplified music.)

Further information regarding thedesign of multi-purpose auditoria is givenin Section 5.

4.13 Other large spacesSports halls, gymnasia and especiallyswimming pools have long reverberationtimes through the nature of theirconstruction and surfaces necessary totheir function. This results in high noiselevels and poor speech intelligibility.

A variety of relatively rigid, robust andhygienic, acoustically absorbent materialsare available and can be used. In general,these materials are installed on ceilingsand at high level on walls or as hangingbaffles. If there are large areas ofacoustically hard parallel surfaces, flutter


echoes can occur, significantly increasingthe reverberation time and reducingspeech intelligibility. A reasonabledistribution of acoustic absorption ordiffusion (such as provided by wallbarsagainst gymnasium walls) will eliminatethis effect.

4.14 Dining areas Dining areas suffer from excessive activitynoise. The high activity noise interfereswith conversation leading to increasingnoise levels. Therefore, sound absorptionis required in these areas to reduce thereverberant noise level. The most practicalplace to position sound absorption is onthe ceiling and the walls. Shapes insection or on plan that produce focusing,such as barrel vaulted roofs and circularwalls, should be avoided unless treatedwith sound absorbent material.

References[1] Building Bulletin 81, Design and TechnologyAccommodation in Secondary schools, to bepublished January 2004 (replacing 1986edition).

Speech

"Dry" acoustic

Short reverberation time

Good clarity, loudness and intelligibility ofspeech

Sound must appear to come from stage withsome contribution from room reflections butno perceptible reverberation

Small volume

Music

"Live" or "warm" acoustic

Long reverberation time

Even decay of sound

Good "envelopment" - audience should feelsurrounded by the sound, and musiciansshould be able to hear themselves and eachother easily

Large volume

Table 4.1: Generalacoustic requirements forspeech and music

63

5.1 Aspects of acoustic designBuilding Bulletin 86 MusicAccommodation in Secondary Schools[1]

gives detailed design advice on the rangeof types of music spaces found in schools.The performance standards of the mostcommon music room types are listed inthe tables in Section 1.

Some non-specialist classrooms may beused for teaching music theory to largegroups, with only occasional live orrecorded music. In these rooms themajority of activity depends on goodspeech intelligibility rather than anenhanced acoustic for music and in thesecases classrooms with the same acousticcriteria as normal classrooms may be used.

A brief, outlining the client's acousticrequirements, should be obtained beforestarting the design of any specialist musicfacility. The main problems are noisetransfer between spaces, unsuitablereverberation times, flutter echoes,standing waves, and high noise levels.

5.2 Ambient noise The requirements for indoor ambientnoise levels in music rooms are set out inTable 1.1. To control noise frommechanical ventilation, it is important toselect quiet fans or air handling unitswhich are connected to appropriatelysized silencers (attenuators). Typicalprimary attenuator lengths will be in therange 2.4 - 3.0 m. Air velocities in theduct system should be kept low andshould not generally exceed 5 m/s inmain ducts, 4.5 m/s in branch ducts and2.5 m/s at runouts. Terminal units(grilles etc) should be selected for lownoise output.

Noise from hot water radiator systemsshould be minimised by good design.Equipment, particularly the valves andpumps, should be designed and selectedfor quiet operation, with vibrationisolation where appropriate.

In noise-sensitive spaces, such as musicperformance spaces and recording spaces,hot water pipes should not come intorigid contact with the buildingconstruction. Resilient pipe brackets andflexible penetration details should beadopted to prevent clicking noisesresulting from expansion and contraction.

Lighting can cause disturbing buzzingand occasionally sharp cracks fromexpansion or contraction of metal fittings.In music rooms, 50 Hz fluorescent lightsshould not be used because they areinherently prone to buzzing and mainshum which is audible to some people.These effects do not occur with highfrequency (HF) fittings, which should ingeneral be specified on energy efficiencyand cost saving grounds. HF fittings areacceptable for most general music spaces.Where the quietest conditions arerequired, lighting should be restricted totungsten or similar lamps. In certainspaces such as a recording/control room,the sound caused by transformers usedwith low voltage spotlights can bedistracting.

5.3 Sound insulationStandards for sound insulation betweendifferent types of room are set out inTable 1.2. To avoid excessive noisetransfer between music rooms Table 1.2specifies a minimum of 55 dBDnT(Tmf,max),w between most music

The design of rooms for music

Music rooms require special attention in the acoustic design of a school. It is important to establish the user’s expectations of the acoustic performanceof the spaces. Musical activities range from playing, listening and composing ingroup rooms to orchestral performances in school halls, and a music room can

be anything from a small practice room to a large room for rehearsing andperforming music.

5

SE

CT

ION

64

rooms. These are minimum requirementsand will not always prevent interferencebetween adjacent rooms. It is beneficialto increase these figures, especially whenthe indoor ambient noise level issignificantly below the level in Table 1.1.This can occur in naturally ventilatedrooms on quiet sites where the indoorambient noise level is too low to provideuseful masking of distracting noise fromadjacent rooms.

The level of sound and possibledisturbance between music spaces willvary depending on the instruments beingplayed. Clearly, as the loudness of theinstruments varies from group to group,so the room-to-room sound insulationrequirement will also vary. An importantquestion is that of cost versus flexibility.High flexibility is desirable so that anyinstrument can occupy any room. Howeverit is expensive to provide sound insulationto satisfy the most stringent requirementat all locations throughout the building.Alternatively, designating groups of rooms to groups of instruments severelylimits flexibility but concentratesinvestment in sound insulation where it ismost required.

Rooms for percussion and brass willgenerate high noise levels and great careis needed in choosing their location.Rooms for percussion should, if possible,be located at ground level to minimisethe transmission of impact vibration intothe building structure. Otherwise floatingfloor constructions may be required.

Figures 2.4 and 7.5.1 illustrate theprinciples of good planning, usingcorridors and storage areas as ‘bufferzones’ between music rooms wherepossible. This allows the sound insulationrequirements to be met without resortingto very high performance constructions.However, in some cases such asrefurbishments of existing buildings theprovision of special sound insulatingconstructions, as discussed in Section 3, isthe only option.

Background noise must be controlledin circulation areas. However, limitedbreak-out of musical sounds intocirculation routes is acceptable since itallows teachers to monitor, from a

distance, unsupervised small groupmusical activities.

5.3.1 Sound insulation betweenmusic roomsThe sound insulation required betweenthe different types of music room can bedetermined from Tables 1.1 and 1.2.

Other criteria such as those of Miller[2],which take account of both soundinsulation and indoor ambient noise level,are sometimes used in the specification ofsound insulation between music rooms;however, the normal way of satisfyingRequirement E4 of The BuildingRegulations is to meet the performancestandards in Table 1.2 for airborne soundinsulation between rooms.

Case Study 7.5 gives an example of theacoustic design of a purpose built musicsuite in a secondary school.

5.4 Room acoustics

5.4.1 Reverberation time, loudnessand room volumeIn general, rooms for the performance ofnon-amplified music require longerreverberation times than rooms forspeech. Figure 5.1 shows optimum midfrequency reverberation times for speechand music as a function of room volume.

The volume of a room has a directeffect on the reverberation time (RT) andearly decay time; in general, the larger thevolume, the longer the RT. Thereverberation times should be in theranges given in Table 1.5 and should beconstant over the mid to high frequencyrange. An increase of up to 50% ispermissible, and indeed is preferred, atlow frequencies as indicated in Figure 5.2.

To achieve this it is generally necessaryfor the volume of music rooms to begreater than for normal classrooms andthis generally requires higher ceilings.These also help with the distribution ofroom modes as described in the sectionon room geometry below.

If the volume of a room is too small,even with the correct reverberation timethe sound will be very loud. This is acommon problem in small practice roomswith insufficient acoustic absorption, and

The design of rooms for music5

65

can give rise to sound levels which could,in the long term, lead to hearing damage.Many professional orchestral musicianshave noise-induced hearing loss due toextended exposure to high noise levelsboth from their own instruments and, toa lesser extent, from other instrumentsnearby. Under the Noise at WorkRegulations 1989 (see Appendix 9) thereis a general requirement to minimisenoise exposure of employees in the schoolcontext, who for this purpose include full-time, part-time and freelance peripateticmusic teachers. It is therefore importantto ensure that practice, rehearsal andteaching rooms are neither excessivelyreverberant nor excessively small for agiven occupancy.

Setting the floor area and ceilingheight is normally the first step indesigning a music room. The floor area isusually determined by the number ofoccupants and guidelines are given inBuilding Bulletin 86[1], as are methods ofcurriculum analysis to determine theneeds of a secondary school musicdepartment. A typical suite of musicrooms in a secondary school mightconsist of:

Ceiling heights and consequentlyvolumes for halls and recital rooms aregenerally equivalent to two storeys,around 6 m. For group rooms andpractice rooms, a full storey height (atleast 3 m) is normally required.

5.4.2 Distribution of acousticabsorptionThe acoustically absorbent materialrequired to achieve the correct RTshould be distributed reasonably evenlyabout the room. Where absorptionoccurs only on the floor and ceiling – forexample in a simple solution employingacoustic ceiling tiles and carpeted floor –users may experience an over-emphasis onsound reflections in a horizontal plane.This often leads to ‘flutter echoes’between walls, which result in the actual

RT being considerably longer than thecalculated RT. A better solution,especially in large rooms, is to distributesome of the absorptive material about thewalls.

Although the RT requirements in Table1.5 are for unoccupied rooms, it isimportant to remember that theoccupants will present a significantamount of absorption which will be in thelower half of the room. To give areasonably even distribution of absorptivematerial therefore, acoustic absorption is

Large performance/teaching room 85 m2

Second teaching room 65 m2

Ensemble room 20 m2

Practice/group rooms 8 m2

Control room for recording 10 m2

2.0

1.5

1.0

0.5

020 30 50 100 500 1000 2000

Reve

rber

atio

n tim

e, s

Room volume, m3

music

speech

250 500 1000 2000 4000125

160150140130120110100

Frequency, Hz

Percentageof valueat 500 Hz

Figure 5.1: Optimum mid-frequency reverberationtimes for speech andmusic, for unoccupiedspaces

Figure 5.2:Recommended percentageincrease in reverberationtimes at lower frequenciesfor rooms specifically formusic

5The design of rooms for music

66

often located at high level on the walls.Because of the absorption of the

audience, there can be large variations inRT depending on the presence or absenceof an audience. To reduce this effect,acoustically absorbent seats withupholstered backs can be used and inlarge halls the acoustic absorption of theseats has to be determined and specifiedquite carefully. An acceptable alternativein smaller halls can be the use ofretractable curtains to reduce the RTduring rehearsals when no audience ispresent.

In auditoria and music rooms, surfacesaround and above the stage orperforming area are normally reflective toprovide feedback to the performers.

Floors on stage should be reflectivealthough carpet in an auditorium may bepermissible.

5.4.3 Room geometryIt is important to consider both roomshape and proportion. In large roomssuch as halls and recital rooms, thegeometry of the room surfaces willdetermine the sequence of soundreflections arriving at the listener from agiven sound source. Early reflections, thatis those arriving within approximately 80milliseconds of the direct sound, will beintegrated by the listener’s hearing systemand will generally enhance the originalsound for music (50 milliseconds is thecorresponding figure for speech, seeSection 4).

Prominent reflections with a longerdelay (late reflections) may be perceivedas disturbing echoes. This is oftenencountered where the rear wall in a hallhas a large flat area of glass or masonry.Strong individual reflections can also lead

to ‘image shifting’ where early reflectionscan be so strong that the ear perceives thesound as coming from the reflectingsurface and not the sound source.

This problem can be exacerbated if latereflections are particularly strong. Thiscan occur when sound is focused fromlarge concave surfaces such as curved rearwalls, barrel vaults, domes, etc.Furthermore, focusing results in anuneven distribution of sound throughoutthe room. Consequently, large concavesurfaces are not generally recommendedin music spaces.

In small rooms, such as group roomsand music practice rooms, geometryaffects the distribution of standing wavesor room modes throughout the soundspectrum, particularly at low frequencies.Where the distance between two parallelwalls coincides with or is a multiple of aparticular wavelength of sound, astanding wave can be set up and thebalance of sound will be affected, seeFigure 5.3. Certain notes will beamplified more than the rest leading to anunbalanced tonal sound, sometimes calledcolouration. Bathrooms with tiled wallsare a good example of rooms withprominent room modes and, althoughthey can enhance certain notes of asinger’s voice, they will not produce abalanced sound and will tend to soundboomy. The effect is exaggerated ifdistances are the same in more than onedimension. Thus rooms which are square,hexagonal or octagonal in plan should beavoided. The same effect occurs if theroom width is the same as the roomheight, or is a simple multiple of it.

Ideally, the distribution and strength ofroom modes should be reasonablyuniform. Perhaps the best way to control

1.00.8

0.60.4

0.20

1.00.8

0.60.4

0.2

1.00.8

0.60.4

0.20

0

0

1.00.80.60.40.2

1.00.80.60.40.2

0 0

Figure 5.3: Standingwaves in different modes0 – No sound pressure1.0 – Maximum soundpressure


67

these low frequency modes is to selectroom dimensions that are not in simpleratios. It should not be possible to expressany of the room dimensional ratios aswhole numbers, for example, a proposedspace 7 m wide, 10.5 m long and 3.5 mhigh (2:3:1) would not be considered anadvisable shape from an acoustic point ofview. Mathematically, an ideal ratio is1.25 : 1 : 1.6; this is sometimes referredto as the ‘golden ratio’ but many otherratios work equally well.

Both flutter echoes and room modescan also be controlled by using non-parallel facing walls, but this is oftenimpractical for architectural reasons; theuse of absorption or diffusion is equallyeffective.

5.4.4 DiffusionIn addition to the correct RT, the roomshould be free from echoes, flutterechoes, and standing waves and the soundshould be uniformly distributedthroughout the room, both in theperformance and listening areas. Toachieve this without introducing toomuch absorption, it may be necessary tointroduce diffusing hard surfaces todiffuse, or scatter, the sound. These arenormally angled or convex curvedsurfaces but bookshelves, balcony frontsor other shapes can also provide diffusion,see Figure 5.4. Acoustic diffusion is acomplex subject, and if calculation ofdiffusion is likely to be required aspecialist should be consulted.

5.5 Types of room

5.5.1 Music classroomsFigure 5.5 shows a 65 m2 music classroomfor a range of class-based activitiesinvolving a number of differentinstruments. The room proportion avoidsan exact square. The height is assumed tobe between 2.7 m and 3.5 m, creating areasonable volume for the activities (seeSection 5.4.3). The main points to noteabout the acoustic treatment of the spaceare described below.

To minimise the possibility of flutterechoes or standing waves occurringbetween opposing parallel walls, surfaces

are modelled to promote sound diffusion.On the side wall this takes the form ofshelving to store percussion instruments,etc. On the back wall, framed pinboards(with non-absorptive covering) are set atan angle, breaking up an otherwise plainsurface.

Full length heavy drapes along the backwall can be drawn across to vary theacoustics of the space.

The observation window into theadjacent control room is detailed toensure a high level of sound insulationbetween the two spaces (see Figure 5.6and the discussion of control roomsbelow).

The door into the room is of solid coreconstruction with a small vision panel.The door and frame details, Figures 5.7

Figure 5.4: Surfaceswhich provide specular anddiffuse reflections

PLANE SURFACE - specular reflection

SIMPLE ANGLED PANELS - diffuse reflection

CURVED PANELS - diffuse reflection

50 mm to 500 mm (larger depth extendsdiffusion to lower frequencies)


68

and 5.8, are designed to maximise thesound insulation properties of the wall asa whole.

The floor is fitted with a thin pilecarpet providing an absorbent surfacewhile the ceiling has a hard reflectivesurface. The type of carpet can have asignificant effect on the overall RT in aroom. It is worthwhile checking theprecise absorption coefficient of anysurface finish. (A spreadsheet of indicativeabsorption coefficients for commonmaterials is on the DfES acousticswebsite.)

5.5.2 Music classroom/recital roomFigure 5.9 shows a larger, 85 m2,classroom. The proportions of the roomare in a ratio of fractional numbers (2.6 :3.8 : 1) with the height between 2.7 mand 3.5 m as for the 65 m2 musicclassroom. The acoustic treatment issimilar to that for the 65 m2 room but asthis space is larger, and bigger groups arelikely to rehearse and perform here,drapes are provided on two adjacentwalls.

Figure 5.5: Acoustictreatment to musicclassroom


window to control roomdetailed to provide goodlevel of sound insulation

solid core door with smallvision panel

door frame detailimportant

shelving provides surfacemodelling to help diffusesound

full length drapes used tovary acoustic response

framed pinboards set atan angle provide surfacemodelling to promotesound diffusion

room not anexact square

thin pilecarpet on

floor

69

Head & jamb with singleor double seals

Generous rebateto frame, withheavy duty hinges

Continuous grounds andfill to frame and opening

Threshold seal (may beretractable type)

Handlebut nokeyhole

1.00

m

2.00

m

Viewingpanel

914 mm widestructural opening

Solid core timber doorassemblyElevation showing how theperformance of a door assemblydepends on a number of featuresof the construction, not just on themass of the door leaf

Figure 5.7: Desirablefeatures of an acousticdoor installation

150 mm (min) dense blockwork

Solid concrete lintel

Mineral wool or equivalentTwin 75x44 mm hardwood frames

Maximum possible spacing between panes of glassPerforated metal lining

13x44 mm architrave

12 mm and 6 mm glass in neoprenechannels to hardwood beads

Softwood opening lining150x38 mm

Figure 5.6: Sectionthrough control roomwindow


70

5.5.3 Practice rooms / grouproomsFigure 5.10 shows a typical 8 m2 grouproom which will accommodate bothinstrumental lessons and compositiongroups and which can be used forindividual practice. Points to note are asfollows.• One wall is at an angle of 7° to avoid flutter echoes (a particular issue insmall rooms) and prominent standingwaves. Window and door reveals provide

useful diffusion to other walls.• A full length drape can be pulled across the window to increase surface absorption and reduce loudness. • The window is fairly small andpositioned in the centre of the wall tocontrol the amount of external noisereaching the space and avoid soundtravelling between adjacent group rooms.• Floor and ceiling finishes are as for the larger rooms.

VERTICAL SECTION

PLAN

Figure 5.8: Vertical andhorizontal sections througha door installation. Takenfrom BBC EngineeringGuide to Acoustic Practice,2nd Edition 1990. Thesedrawings are reproducedhere with the kindpermission and co-operation of the BBC


71

Figure 5.9: Acoustictreatment to musicclassroom/recital room

Figure 5.10: Acoustictreatment to 8 m2 grouproom


solid core door withsmall vision panel

door frame detailimportant

store providessound insulationbetweenclassrooms

window to control roomdetailed to provide goodlevel of sound insulation

shelving providessurface modellingto help diffusesound

framed pinboards set at an angleprovide surface modelling to promotesound diffusion

full length drapeson two sides used

to vary acousticresponse

thick pile carpeton the floor

dimensional rationot whole numbers

wall at an angle to avoidflutter echoes and standingwaves

drapes can be used to varyacoustic response

small window tominimise disturbance

from external noise

thin pile carpet onthe floor

72

5.5.4 Ensemble roomsFigure 5.11 shows a plan of a 25 m2

ensemble room. In terms of shape, thesame rules apply as for larger musicspaces. Ceilings should be high, of theorder of 3 m or more. Surface finishesmay comprise carpet on the floor, asuspended plasterboard ceiling to providethe necessary bass absorption, and amixture of hard and soft wall finishes toprovide the required RT. An acousticdrape along one wall can provide a degreeof acoustic variability.

5.5.5 Control rooms for recordingControl rooms for recording haveassumed a much greater significance dueto the need to prepare tapes ofcompositions for GCSE assessment.Figure 5.12 shows an 11 m2 controlroom for recording. A teacher or pupilcan record a music performance takingplace in an adjacent space after which therecording may be heard on headphonesor loudspeakers. The RT specified inTable 1.5 is < 0.5 s.

Notable aspects of the acoustictreatment are as follows:• Sound absorbing panels on the walls behind the monitor loudspeakers are used to control strong early soundreflections which could distortloudspeaker sound.• Shelving units on the window wall provide surface diffusion.• Drapes are fitted on all threeobservation windows. If a curtain is pulled across one window, problems of flutter echoes and prominent resonances associated with two facing hard parallel surfaces are reduced. Ideally, the effect can be avoided by installing glazing in one of each pair of windows at 5° off parallel. Drapes also provide additional privacy.• The external window is small to minimise disturbance from external noise.A venetian blind can be used to controlsunlight, or a blackout blind may beprovided if required. • The floor is carpeted.• Figure 5.6 shows a detail of a typical

Figure 5.11: Acoustictreatment to 25 m2

ensemble room

Full length drape to vary acoustic response


ENSEMBLE ROOM25 m2

73

control room window. Two panes of heavy plate glass (of different thicknessesto avoid the same resonances) areseparated by an air gap of about 100-200 mm. Such a large gap may notalways be possible but 50 mm should beconsidered a minimum. Each pane ofglass is mounted into a separate frame toavoid a direct sound path. The glass ismounted in a neoprene gasket to isolate itfrom the wooden frame. Acousticallyabsorbent material, such as mineral woolor melamine foam, is incorporated intothe reveal to absorb any energy thatenters the air gap.

5.5.6 Recording studiosA recording studio as such rarely exists ina school. The control room for recordingmay have an observation window onto anordinary ensemble room orprofessional/recital room. A professionaltype recording studio would require alower indoor ambient noise level thanthat given in Table 1.1, and specialistadvice should be sought.

5.5.7 Audio equipmentThe design and selection of recordingequipment and audio systems is a fast-evolving subject and guidance on specifictechnologies would be rapidly out ofdate. Although members of staff within aschool will have their own preferences forspecific items of equipment, these may be

based on experience of only a few systemsand alternatives should at least beconsidered. Advice from an independentdesigner or consultant familiar with thefull range of available equipment shouldbe sought.

5.6 Acoustic design of large hallsfor music performanceLarge halls designed primarily for musicare rare in schools, where the main use ofany large hall is likely to be for assembliesand other speech-related uses. Assemblyhalls, theatres and multi-purpose halls arediscussed in Section 4. If a purpose-builtconcert hall is required a specialistacoustics designer should always beconsulted early in the project, but thissection sets out some general principleswhich can be considered at the conceptstage.

5.6.1 Shape and sizeKey acoustic requirements are sufficientvolume to provide adequate reverberationand a shape that will provide a uniformsound field with strong reflections off theside walls. A rule of thumb is that thevolume of a concert hall should be at least8 m3 per member of audience, which istypically twice that for a theatre orcinema. In most cases this will lead to arectangular floor plan with a relativelyhigh ceiling. Other shapes, such as theelongated hexagon or asymmetrical

Figure 5.12: Acoustictreatment torecording/control room


half length drapes canbe pulled acrosswindow to increaseabsorbency

sound absorbing panelsbehind speakers

small window tominimise

disturbance fromexternal noise

solid core door withsmall vision panel door frame detail

important

floor carpeted

all observation windows detailedfor good acoustic insulation

74

shapes, can work well but require veryadvanced acoustic design. Fan-shapedhalls generally do not provide the lateralreflections beneficial to listening to music.

Balconies and side-wall boxes orgalleries may be used although they tendto reduce the volume of the hall for agiven audience size. Any overhangs mustbe kept small to allow reasonable soundto seats under the balcony. Figure 5.13indicates the recommended proportionsof an overhang so that good acousticconditions are maintained beneath theoverhang. Balcony, gallery and box frontscan be used to break up large areas of flatwall and provide essential diffusion,especially on parallel side walls whereflutter echoes may otherwise occur.

Ceilings can be flat with some surfacemodelling, or can be more complexshapes to direct sound towards theaudience. A steeply pitched ceiling(around 45° assuming the ridge runsalong the length of the auditorium) canalso be good. Shallow pitches can cause‘flutter’ echoes between a flat floor andthe ceiling, see Case Study 7.1.

Shapes with concave surfaces, such asdomes and barrel vaults, cause focusing ofsound which can result in problematicacoustics and these are best avoided.Where concave surfaces are unavoidableand cause a focus near the audience theyshould be treated with absorbent ordiffusing finishes.

If seating is on a rake, this should notbe too steep as musicians find it difficultperforming into a highly absorbentaudience block - in effect, they receivevery little feedback. Generally, rakes

which provide adequate sightlines willgive satisfactory acoustic conditions. Thisrake will generally be less than in atheatre or cinema.

The size and shape of the concertplatform is of great importance. A full 90-piece symphony orchestra requires a stageat least 12 x 10 m, with allowance forchoir risers behind. The front of theplatform will not generally be as high as atheatre stage and may be only 400 mmabove stalls floor level, but orchestralplayers will require risers or rostra so thatplayers at the rear of the platform can seethe conductor. Surfaces around the stageshould be acoustically reflective andshould be designed to provide somereflected sound back to the players, sothat they can hear themselves and eachother, as well as directing some soundtowards the audience. This designrequires computer or physical scalemodelling by a specialist acoustician.

5.6.2 Surface FinishesUnlike in theatres and assembly halls, thesurface finishes in a concert hall with thecorrect volume will generally beacoustically reflective, for exampleplastered or fair-faced brick or blockwork.Large areas of flat lightweight panelling,such as wood or plasterboard, tend to beabsorbent at low frequencies, whichresults in inadequate reverberation atthese frequencies. The result tends to be alack of ‘warmth’ or ‘bass response’ and isa common problem in many halls. Woodpanelling, if used, must be very heavy orstiff. Curved wooden panels are oftenused as acoustic reflectors because theircurvature gives added stiffness, reducestheir inherent panel absorption andprovides acoustic diffusion.

In most performance venues theseating and the audience provide themajority of the absorption and, therefore,constitute a controlling factor in theroom acoustic conditions. The selectionof seats and, particularly, the relativeabsorption of occupied and unoccupiedseats is of great importance. In general, itis helpful if the room acoustics arerelatively unaffected by the number ofoccupants. This, however, tends to mean

H

D

Figure 5.13:Recommended balconyoverhang proportionswhere the depth D shouldnot exeed the height H.


75

that seating must be very absorptive andprobably not a preferred type for schooluse. A seat which is moderatelyupholstered on the seat and back is likelyto be a good compromise. Where tip-upseats are provided they should beupholstered underneath as well as on theseat; otherwise acoustic conditions will bevery different during rehearsal andperformance. Most auditorium seatingmanufacturers supply acoustic test data.Where there is no fixed seating, largeareas of acoustic drapes or other operableacoustic absorption can be used to reducereverberation in rehearsal conditions whenthe seats are removed.

5.7 Design of large auditoria formusic and speechTable 5.1 lists the general acousticcharacteristics that are required for amulti-purpose auditorium.

There are four commonly consideredapproaches to designing these spaces:

1. To design a concert hall with a largevolume (≈10 m3 per seat), and to reducethe volume of the auditorium whenneeded for speech. This approach isrecommended when the overwhelmingrequirement is for a good musicalacoustic, with a relatively small proportion

of theatre or other speech use. Unless thevolume can be reduced substantially, thisapproach requires large amounts ofabsorbent material to be deployed, whichin turn can reduce loudness to the extentat which a speech reinforcement system isneeded. Nearly all auditoria adopting thisapproach depend on high-quality speechreinforcement systems, which are difficultto design in a reverberant hall.

2. To design a small volume (not morethan 6 m3 per seat) with acoustics suitablefor a theatre, with additional reverberantvolumes accessed by openable flaps ormoveable ceilings. As the volume needs tobe increased by up to 80%, withreasonably even distribution of absorption,this is often impracticable. In the few caseswhere this approach has been tried, theresults have been poor because it isdifficult to provide openings large enoughto be transparent to the long wavelengthsof low frequency sound.

3. To design to a compromise volume andRT, often with curtains or other moveableacoustic material to provide some variationin RT. The result tends to be anauditorium which is acceptable for a rangeof uses, but not particularly good for anyof them - especially music. Very large areas

Low ambient noise levels

Even distribution of sound

Lack of acoustic defects

Loudness or acoustic efficiency

Good direct sound

Good early reflections

Feedback to performers

Low noise levels from plant, ventilation, lighting and stage machinery arerequired. Noise from outside the auditorium should ideally be imperceptible.

The acoustic should not change significantly from one seat to another.

There should be no echoes or focusing effects.

The sound level reaching the listener should be as high as possible withoutcompromising other requirements.

The sightlines to the source should not be impeded and distances should beas short as possible.

Reflecting surfaces around and close to the stage, and reflections off theside walls and off the ceiling are required.

Some sound from the stage should be reflected back to the source. Thisgives confidence to the performers and helps with musical ensemble.

Table 5.1: Acousticcharacteristics for a multi-purpose auditorium


of curtain are required to have anysignificant effect in a large hall, and thesewill have relatively little effect at lowfrequencies, resulting in a room that iseither ‘boomy’ for speech or ‘dead’ formusic.

4. To design a small volume (≈6 m3 perseat) with acoustics suitable for a theatre,with an electro-acoustic enhancementsystem to introduce more reflected sound.These systems were originally designed toenhance the acoustics of naturally poorauditoria, but their success has recentlyled to their being built in to newauditoria where a wide range of acousticconditions is required. The best systemsprovide good acoustics over a wider rangeof uses than would otherwise be possible,without the audience (or musicians) beingaware that the sound that they hear is notdue to the ‘real’ acoustic of theauditorium. These systems are seen asacoustically very advanced and are notcommonly used in schools, but present aviable option where a large hall is to beused for both speech and music on aregular basis. These systems requireloudspeakers in the auditorium side wallsand ceilings, and should not be confusedwith the sound reinforcement system forspeech (in this case a central cluster ofloudspeakers over the forestage),although some electro-acousticenhancement systems can also be used forspeech reinforcement.

References[1] Building Bulletin 86, Music Accommodationin Secondary Schools. DfEE, 1977. ISBN 0 11 271002 6. [2] J Miller, Design standards for the soundinsulation of music practice rooms. AcousticsBulletin 18(6), Institute of Acoustics, 1993.

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Acoustic design and equipment for pupils withspecial hearing requirements

77

6.1 Children with listeningdifficultiesA recent survey by the British Associationof Teachers of the Deaf (BATOD)[1]

showed that about 75% of deaf childrenwere being educated within mainstreamschools. With the continuing trendtowards inclusive education there is noreason to suppose that this proportionshould do anything but increase.

In addition to the children withpermanent hearing impairments there arelarge numbers of children withinmainstream schools who have listeningdifficulties placing them in need offavourable acoustic conditions. Theseinclude children:• with speech and language difficulties • whose first language is not English • with visual impairments • with fluctuating conductive deafness • with attention deficit hyperactivity disorders (ADHD) • with central auditory processing difficulties.

Effort given to addressing the acousticneeds of the hearing impaired populationalso favours other groups whose needs forgood acoustic conditions are not dealt withelsewhere in this document. Put together,the number of children falling into one ormore of these categories couldconceivably be a significant proportionwithin every mainstream classroom.

6.2 Children with hearingimpairments and the acousticenvironmentThe majority of children with hearingimpairments use speech and hearing astheir main form of communication. TheBATOD survey[1] indicated that 67% ofchildren with hearing impairments wereusing an auditory-oral approach and a

further 26% used an approach whichcombined sign with auditory-oralcomponents. For these groups a pooracoustic environment can be a significantbarrier to inclusion.

A hearing loss is typically describedwith reference to the audiogram. This is agraphical representation of an individual’sthreshold of hearing for a number of puretones (typically measured at 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz and 8 kHz) and presented to each ear usingheadphones. At face value, it suggests thatthe hearing impairment can be consideredas a simple auditory filter and as suchshould predict a child’s understanding ofspeech using traditional acoustic models.Although reliable, it says little about anindividual’s hearing for speech or the keyskill of listening to speech withbackground noise. The audiogram is not agood predictor of educational outcome[2]

and only a poor predictor of maximumspeech recognition score[3]. Consequently,great care should be taken whenconsidering the audiogram of a child as apredictor of the difficulties the childmight have in a school environment.

At present there is little empirical datathat specifically addresses the acousticcriteria required for the hearing impairedschool population (see for example thereview of the literature by Picard andBradley[4]). What is currently available,however, suggests that the individualhearing needs of the hearing impairedchild are likely to be more demandingthan those of children with normalhearing. It would be helpful for theprofessional specifying classroom acousticsfor a particular child to have availablemeasures of the child’s aided hearing andconsequent acoustic requirements interms of, for example, acceptable levels of

When considering classroom acoustics, children with a permanent hearingimpairment have traditionally been treated as a special group, separate fromthe mainstream school population. This is a situation that is not supported bythe surveys of the school population carried out by the British Association of

Teachers of the Deaf.

6

SE

CT

ION

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6.3 Hearing impairment andhearing aidsModern hearing aids are designed to makespeech audible to the listener without beinguncomfortably loud[7]. They deal largelywith the issue of audibility and are less ableto address the issues of distortion thattypically accompany a sensorineural hearingimpairment.

One of the major challenges in thedesign of hearing aids is dealing with noise.Recent developments include the use ofalgorithms that attempt to enhance speechwhilst reducing background noise, andbetter implementation of directionalmicrophones. However, noise will continueto remain a significant obstacle to effectivelistening. Noise not only masks theamplified speech signal but also leaves achild tired from the effort required to listen.It is therefore essential that attention begiven to creating a quiet classroom.

Sound insulation must be of a highstandard, with the lowest background noiselevels possible to ensure that a good signalto noise level is achieved. Typically a signalto noise level of +20 dB is considereddesirable[5]. Short reverberation times arealso critical in ensuring that sound does notbuild up when the class are working ingroups. Care must also be taken to ensurethat the level of low frequency noise is keptto a minimum. For many people withimpaired hearing, low frequency noise canhave a devastating impact on speechrecognition, masking many importantspeech sounds in a manner that cannot beappreciated by those with normal hearing.

6.4 The speech signal and hearing aidsSpeech, as a signal, is a critical factor inclassroom listening and an importantspeech source is the teacher. Evidence hasshown that teachers’ voices are not alwayssufficiently powerful to deliver thenecessary levels of speech required toensure the best listening opportunities[8].A growing body of evidence suggests thatteachers are at above average risk fromvoice damage[9]. Few teachers have voicetraining and the vocal demands ofteaching are probably underestimated.

Hearing aids are usually set up toamplify a ‘typical’ speech signal based onvarious measures of the long-term averagespeech spectrum recorded either at theear of the speaker or at a distance of 1 mdirectly in front of the average speaker, asif in conversation. If the actual speechsignal is weaker than average, perhaps

Acoustic Parameter

Unoccupied noise level

Reverberation time(unoccupied)

Signal to noise level

British Association ofTeachers of the Deaf[5]

35 dB(A)

0.4 s across frequency range125 Hz to 4 kHz

+20 dB across frequencyrange 125 Hz to 750 Hz+15 dB across frequencyrange 750 Hz to 4 kHz

American Speech LanguageHearing Association[6]

30 – 35 dB(A)

0.4 s

≥ +15 dB

Acoustic design and equipment for pupils with special hearing requirements

Table 6.1:Recommendations ofBATOD and ASHA for theacoustics of classrooms

noise, desirable reverberation times andrequired signal to noise levels. However,such hearing measures are not routinelyobtained.

Because it is not possible at present toprovide definitive acoustic requirementsfor hearing impaired individuals, it isappropriate for acousticians and architectsto be aware of the requirements publishedby specialist professional organisations.These include the British Association ofTeachers of the Deaf[5] and the AmericanSpeech Language Hearing Association[6]

(see Table 6.1). Account has been takenof these recommendations in the settingof performance criteria in Section 1.

6

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because of distance, or is masked bybabble or steady state background noisesuch as that from a classroom computerfan, then the hearing impaired listenerwill have increased difficulty. Listening tospeech will become particularly effortfuland challenging[10].

Children are not only required to listento the teacher but also to other children.Children typically have less powerfulspeaking voices[8] and listening to theirpeers is frequently identified by childrenwith hearing impairments as beingdifficult. One study suggests that 38% ofa child’s time in the classroom might bespent working in groups and 31% of theremaining time spent in mat work[11],both situations where listening to otherchildren is important. There are nowholly satisfactory solutions to this.Technology and careful class managementhave a role to play but considerableattention needs to be paid to establishinglow reverberation times and maintaininglow ambient noise levels in order toreduce the auditory difficulties.

To minimise the challenges to hearing,use is often made of small acousticallytreated rooms attached to mainstreamclassrooms in the primary school. Theserooms are typically large enough for agroup of four to eight children to workin. To allow supervision by the classteacher they will have a large window toallow a clear view into the classroom. Theroom will need to have a sufficient degreeof sound insulation from the classroom toallow the children to talk to each otherwithout being disturbed or disturbing therest of the class. The favourable acousticconditions and short distances betweenchildren and teacher, if present, ensurethat communication is as easy as possible.

6.5 Listening demands within theclassroomMuch of educational activity withinclassrooms revolves around speech. Someexperts claim that 80% of all classroomactivities require listening and speaking. Itis important that within any room theacoustic characteristics allow for effectivespoken language communication. TheUK version of the Listening Inventories

for Education[12] identifies the followinglistening demands within the classroom:• listening to the teacher when s/he isfacing away from the listener• listening when the class is engaged in activities• listening to the teacher while s/he is moving around the classroom• listening when other children are answering questions• listening when other adults are talking within the same room• listening to peers when working in groups• listening in situations with competing background noise from multimedia equipment.

A teacher should manage teaching insuch a way as to ameliorate the challengesfaced by a student with hearingdifficulties. However, the better theacoustic conditions, the less challengingwill be the situations described above.

6.6 Strategies developed to assistchildren with hearing and listeningdifficultiesEffective classroom management by theteacher is critical in ensuring that thechildren can have access to all that isspoken and there are many guidelinesavailable for teachers (see for examplepublications by the Royal NationalInstitute for the Deaf[13], the NationalDeaf Children’s Society[14] andDfES[15]). Classroom management alone,however, cannot ensure that speechcommunication is sufficiently audible andintelligible if the classroom acoustics arenot adequate, or if a child has a hearing orlistening difficulty.

In order to ensure that children areable to hear the teacher and, to a lesserextent, their peers, a number oftechnological solutions have beendeveloped, see Table 6.2. These solutionsthat work in tandem with the child’s ownhearing aids (if used) can be classified aseither individual technology or whole classtechnology. In both these cases it isimportant to understand the underlyingprinciples when specifying classroomacoustics.

6Acoustic design and equipment for pupils with special hearing requirements

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6.7 Individual technologyThere are two main types of aid that canbe used to assist children’s hearing on anindividual basis: radio aids that can becoupled to a child’s hearing aids, andauditory trainers that are used withheadphones.

6.7.1 Radio Aids Radio aids (also known as radio hearingaids or personal FM systems) are widelyused by children with hearing impairmentsin schools. They help overcome causes ofdifficulty in a classroom situation by:• providing a good signal to noise ratio

• reducing the impact of unhelpful reverberation• effectively maintaining a constantdistance between the speaker and thelistener.

All radio aids have two maincomponents: a transmitter and a receiver.The person who is speaking (usually theteacher) wears the transmitter. Amicrophone picks up their voice. Typicallythe microphone is omnidirectional and isattached to the lapel of the speaker,however there are head wornmicrophones available that help ensure aconsistent transmitted signal to the child.

6 Acoustic design and equipment for pupils with special hearing requirements

Technology

Personal radio aids

Classroom soundfieldsystems

Personal soundfieldamplification

Auditory trainers and hard-wired systems

Induction loop systems

Advantages

Reduce the effect of the distance betweenspeaker and listenerPortable and convenientParticularly useful in situations where there isa poor signal to noise ratio at the position ofthe listener

Reduce the effect of the distance betweenthe speaker and listenerInclusive technologyBenefit to the teacher and the classCan ensure good signal to noise levels aremaintained throughout the classroom

PortableAddresses the issue of speaker to listenerdistanceCan ensure favourable signal to noise levelsfor a particular listener or small group oflisteners

Provide excellent signal to noise levelsProvide a high level of sound insulationCan be arranged to allow group work

Discreet and cheapMost hearing aids have a telecoil facility

Disadvantages

Do not address the needs of group workdirectlyCan require a high level of sophistication togain maximum benefitBenefits can be lost if the child’s personalhearing aid microphones are used in noisyenvironments

Do not address the needs of group workdirectlyPoor classroom acoustics (eg highreverberation times or poor sound separationbetween neighbouring teaching areas) canlimit the benefit of this technology

Can be cumbersome to transport andmanageDoes not address the needs of group workdirectly

Users are restricted in movement when usingthe deviceCan be heavy and uncomfortable to useNot an inclusive technology

Unpredictable acoustic response for thehearing aid userSpill over of signal into other roomsDo not deal with the needs of group workSusceptible to electromagnetic interferenceUser normally isolated from environmentalsounds

Table 6.2: Advantagesand disadvantages ofdifferent technologies foraiding hearing and listeningin the classroom

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The sounds are transmitted by an FMradio signal to the receiver, which is wornby the child. The receiver converts thesignal to a sound that the child can hear.

Radio aids are usually used inconjunction with the child's hearing aids.Most children use ‘direct input’ (alsoknown as ‘direct connection’ or ‘audioinput’) to the hearing aids using a lead.Direct input is a facility available on manybehind-the-ear (post-aural) hearing aidsand a smaller number of in-the-earhearing aids.

Alternatively, the child can use aninductive neck loop - a small wire loopthat can be worn over or under clothes.The loop is connected to a radio aidreceiver usually worn around the waist orattached to a belt.

Direct input is generally recommendedas preferable to the use of a neck loop forchildren in school. This is because thelevel of sound that a child hears using aneck loop can be variable and there is arisk of electromagnetic interference fromnearby electrical equipment.

Radio aids are also beneficial forchildren who have cochlear implants.The radio aid receiver is connected to thechild's implant processor using adedicated lead.

Traditionally, radio aid receivers havebeen worn in a chest harness or on a belt.Recent developments include miniatureradio aid receivers that connect directly toa hearing aid and are worn entirelybehind-the-ear. Behind-the-ear hearingaids that include built-in radio aidreceivers are also being manufactured.

Most radio aids can be set up so thatthe child will not only hear the voice ofthe speaker using the transmitter, but alsoenvironmental sounds such as their ownvoice and the voices of other childrennear to them. Radio aids can do this in anumber of different ways and it is oftennecessary to strike a balance betweenallowing the child to hear the voices he orshe needs to listen to and the impact ofhearing unwanted background noise.

For the best listening condition thehearing aid user will normally be requiredto mute his or her microphone on thehearing aid and listen exclusively to the

transmitted voice of the speaker. This isgood for formal teaching situations butrequires considerable skill on the part ofthe teacher to include the hearingimpaired child in classroom discussion.This solution is less helpful for childrenengaged in group activity, where the childwill need to work with a small group ofpeers.

Most radio aids are able to operate on arange of carrier frequencies. For example,each school class might have its ownfrequency so that there is no interferencewith a neighbouring class. In the UK,radio aid channels lie in the range173.350 MHz to 177.150 MHz. Thosechannels in the range 173.350 MHz to173.640 MHz are dedicated exclusively touse by radio aids. A licence is required touse radio aids operating on frequenciesbetween 175.100 MHz and 177.150MHz.

The sounds heard by a child using aradio aid will depend on the quality andcorrect use of their own hearing aids. Thelevel of amplification is determined by thesettings of the hearing aids, not the radioaid. Accepted procedures exist for settingup a radio aid to work with hearing aids(a process sometimes known as‘balancing’).

A general principle is that if a child usesa hearing aid, then the child is also likelyto find a radio aid helpful in manyclassroom situations.

Radio aids have often been seen as thesolution to poor acoustics in theclassroom. However, it must be notedthat they only partially solve the problem;the solution must lie in addressing theissue from three directions:• the class teacher and classroom management style• technology that assists listening • careful attention to classroom acoustics.

Current information about radio aids isavailable from a number of sourcesincluding the National Deaf Children’sSociety[16].

6.7.2 Auditory trainers and hard-wired systems An auditory trainer is a powerful amplifierused with high-quality headphones. As a


82

large, stand-alone piece of equipment, anauditory trainer can be designed withoutthe restrictions of size that exist withtypical behind-the-ear hearing aids, and agood quality high level sound output withextended low and high frequency rangecan be achieved.

Within the mainstream educationalenvironment, auditory trainers are mostlikely to be used for short periods ofindividual work and speech therapysessions. However, it is also possible tolink several auditory trainers together forgroup work. In some schools for deafchildren this equipment is permanentlyinstalled within a classroom. The teacher’svoice is picked up by a microphone andthe output is available at every desk. Eachchild wears headphones that are configuredto meet their individual amplificationrequirements. The children may also wearmicrophones to enable everyone in theclass to participate in discussions.

6.8 Whole class technology The use of a personal system is sometimesessential for a hearing aid user to be ableto succeed in a particular environment.

There is, however, a trend to use theinclusive technology termed ‘sound fieldamplification’ to ensure that the signallevel of the speech is delivered to all partsof the classroom at an appropriate levelabove the background noise. Thistechnology is of benefit for all withlistening difficulties in the classroom, notjust the hearing aid user, and has particularbenefits for classroom management andthe voice of the class teacher.

It is important to note that whole classtechnology is not a substitute forremedying poor classroom acoustics.However, it can be particularly valuable inmaintaining good signal to noise levelsand improving classroom management.Soundfield amplification systems are alsoused in conjunction with personal radioaids. In situations where a deaf child ispart of a mainstream class, advice shouldbe sought from members of a relevantprofessional group (educationalaudiologist, clinical audiologist or teacherof the deaf) as to the most appropriatetechnology.

6.8.1 Whole classroom soundfieldsystemsSoundfield systems provide distributedsound throughout a classroom. They usea wireless link between the microphoneand amplifier which will operate on VHF,UHF radio or infra red frequencies.Soundfield systems have been shown tobe beneficial for hearing children andchildren with a mild or temporary hearingloss. They will not by themselves usuallyprovide sufficient improvement in signal-to-noise ratio for a child with a significanthearing loss, when a personal radio aid isalso usually necessary.

A soundfield system is perhaps morewidely known as a sound reinforcementsystem; the term ‘soundfield’ systemoriginated from the field of Audiologyand continues to be associated withclassroom sound reinforcement systems.The technology has matured since it wasfirst introduced into classrooms in the late1970s in the USA, and has evolved totake into account new technologies andteaching management styles. Its benefitshave been variously described as:

Figure 6.1: A simpleschematic drawing of asoundfield system in atypical classroom

Teacher radio microphonesystem

Optionalstudent (shared) system

Headwornmicrophone

Radiomicrophonetransmitter Handheld radio microphone

Optionalpersonal FM receiver(s)

Antenna 1 Antenna 2 Optional secondreceiver

Personal FMtransmitter

MIXER/AMPLIFIEROptional

Musicor

AV playerLoudspeakersconnectedas required

Radio microphonereceiver

Radio microphonereceiver

Notes:1. Main system shown in blue.2. Optional handheld transmitter can share receiver with teacher transmitter. Transmitters must be switched on and off as required.3. Alternative second receiver allows simultaneous use of teacherand student transmitters.4. Personal FM transmitter(s) for use by pupils with serious hearingimpairment can be connected to output of system.5. CD, cassette and/or video player can optionally play throughthe system.


• academic improvements for all class members• more on task behaviour• greater attentiveness• improved understanding of instructions• less repetition required from the teacher• improved measures of speech recognition• reduced voice strain and vocal fatigue for the teacher.

6.8.2 System overviewFigure 6.1 shows a simplified blockdiagram of a typical soundfield system.Each element shown can be a separateunit, or some of these can be combinedinto an integrated unit. The current trendis for manufacturers to create moreintegrated products, designed especiallyfor classroom soundfield use. Typicalarrangements of loudspeakers are shownin Figure 6.2.

Table 6.3 describes the various

components of a soundfield system. Apossible detailed specification is includedin Appendix 9.

Where a soundfield system has notbeen designed specifically for theclassroom it should be used for a trialperiod before being selected from therange available. The manufacturers andresellers should all provide installationinformation including commissioning ofinstallations, operating instructions andongoing support. Large rooms or roomsthat are unusually shaped will usuallyneed specialist advice. Teachers mustreceive adequate training in using thesystems.

6.8.3 Personal soundfield systems A child who cannot physically wear aconventional hearing aid, who has aunilateral hearing loss, or has CentralAuditory Processing Disorder or

83


1

2

3

4

Figure 6.2: A plan of aclassroom showing fouralternative speaker layouts.The speakers are drawnhorn-shaped to show thedirectionality of the speakeroutput, although manymodern speakers are flat

1 Speakers mounted one quarter of wall length fromcorners, mounted flush with wall, at 2 m height, directedto point on floor at angle of about 60°.2 Speakers mounted at centre of room, 600 mm apart insquare orientation, directed to the room corners.3 Speakers mounted flush with ceiling, facing directly atfloor, in centres of 4 quadrants of the ceiling.4 Speakers mounted in room corners, directed to centreof room.

The four speaker layouts were investigated using acomputer model to predict the interference effects due tophase changes of the speaker outputs.

Layout 1 causes some peaks in the room, but is likely towork reasonably well.

Layout 2 produces large interference effects and istherefore not recommended.

Layout 3 produces the most even coverage at allfrequencies and the least loudspeaker interaction. It istherefore recommended for all rooms where a suspendedceiling exists. Loudspeakers should be selected to providea wide and even coverage that is constant with frequency.

Layout 4 provides relatively even coverage of the roomwith interference effects which, although complex, appearrelatively benign. Location of loudspeakers in room cornerstends to produce a rise in the bass response of systems,which will usually require equalisation using system controlsto produce optimum speech clarity and naturalness.

Layouts 1 and 4 using wall mounted loudspeakers arerecommended where ceiling mounted units are notpractical. For layout 1 speakers should be mounted atleast 1 m from the side wall. Location of wall mountedspeakers at least 2 m above the floor, and at least 600mm below the ceiling is recommended. Brackets shouldkeep the loudspeakers very close to the wall to minimiseself-interference effects.

Attention Deficit Disorder, might use aportable soundfield system. Personalsoundfield systems comprise a radiotransmitter and microphone worn by theteacher and a small, portable unit for thechild. The portable unit includes an FMreceiver, amplifier and loudspeaker and isdesigned to be carried around school bythe child and placed on the desk next to

them. The sound of the teacher's voice isamplified and played through theloudspeaker.

6.8.4 Infra red technologyInfra red technology has been availablefor many years with little market presence.However, this technology has recentlyundergone considerable development and

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Component

LoudspeakerWall mounted, ceilingmounted and flat panelspeakers are used inschools.

Microphone andtransmitterUsing Infra red, UHF orVHF carrier frequenciesand high qualityheadworn or lapelmicrophones. Radiosystem information isavailable atwww.radio.gov.uk

ReceiverMatched to theTransmitter

Amplifier

Requirements

The purpose should be to provide high qualitydistributed sound reinforcement throughout thewhole classroom and over the whole speechfrequency range. Selection of appropriatespeakers should therefore address thisrequirement.

This should be a high quality system whichretains both the frequency and dynamicproperties of speech. It is important thatteaching styles can be accommodated so achoice of microphones should be available. It is important that the transmitter can operatewithout interference from other systems orfrom public services.

Will provide a complementary system to thetransmitter, avoiding interference or frequencydropout.

The amplifier should be correctly matched tothe loudspeaker system. It should offer a wideflat frequency response which can be adjustedif necessary. It should allow for additionalinputs from multimedia within the classroom,such as the TV, computer and radio andoutputs to radio systems.

Comments

Often the location of loudspeakers isdetermined by the necessity to fit in with thecurrent use of the classroom, when notinstalled as part of the original building work.

In order to retain good dynamic range acompander system is typically required (seeFigure 6.3). A head worn microphone canimprove the consistency of the transmittedsignal and help to prevent feedback that ispresent in systems that do not have feedbackcontrol technology. However teachers oftenlike a choice of microphone and will useheadworn, lapel or wrap around microphonesdepending on activity and personalpreference. Battery life of at least one schoolday is essential for a transmitter if it is to beacceptable for school use.

A compander technology and diversity systemis particularly suitable for classroom use,ensuring good dynamic range and avoidingfrequency dropout respectively. Some teaching situations require twin channelinputs, so that a pass around radiomicrophone can be used.Where infra red systems are being usedseparate additional receivers might benecessary to avoid ‘blind spots’.

Some schools might require an additionaloutput facility for use by deaf children withpersonal FM systems.The amplifier is usually combined with thereceiver unit.

Table 6.3: Componentsof a soundfield system


85


Technology

Infra redFrequency range2.3–2.5 MHz

Radio VHF narrowband173.35–177.15 MHz

Radio UHF wideband790–865 MHz

Advantages

Physically limited to enclosed room Allows equipment to be shared between roomsWideband transmissionCan be used with personal hearing aids using a neckloop (an induction loop worn round the neck)

Reserved frequency bands for use in schoolsMany frequency bands availableEquipment compatible across manufacturers

Can allow a higher quality signal than narrow bandequipmentMany frequency bands available, although a site licencemight be required

Disadvantages

Occasionally needs extra IR receivers ina room

Poor signal quality when compared towideband

Not available for personal FM equipment

Table 6.4: Advantagesand disadvantages of infrared and radio technologies

CompressorMicrophonepre-amplifier FM transmitter

Radiolink FM receiver

ExpanderPower

amplifierA B

C D

Overload point of microphone & pre-amplifier

Electronic noise floor

Receiver noise floor

Signal/noiseratio @ A

Signal/noise @

Signal/noise@ DB C

Compressor action Expander action

Maximum transmittermodulation

Overload point of receiver output

SignalAmplitude

&

Radio MicrophoneTransmitter Unit

Radio MicrophoneReceiver Unit

Figure 6.3: FM RadioMicrophone System

is available to be used with many of thetechnologies identified within this section.

One of the major developments is theuse of the 2.3 MHz and 2.5 MHzfrequencies, allowing greater resistance tointerference from fluorescent lighting andsunlight.

Table 6.4 compares the advantages anddisadvantages of infra red and radiotechnologies.

6.8.5 Induction loop systems Induction loop systems take advantage ofthe telecoil facility available with mosthearing aids and cochlear implants. Atelecoil is a small receiver capable ofpicking up audio frequency,electromagnetic signals. It is usuallyactivated by setting a switch on thehearing aid to the "T" position. Aninduction loop system comprises a soundinput (usually a microphone), an amplifierand a loop of cable which is run aroundthe area in which the system is to be used.The loop generates an electromagneticfield which is picked up by the telecoil inthe hearing aid. The hearing aid user willhear the sound while they are within thelooped area.

Induction loop systems have manyapplications, from large-scale installationsin theatres and cinemas to small, domesticproducts used to listen to the television.In the UK they are now rarely used in aclassroom setting. Alternatives such asradio aids offer improved and moreconsistent sound quality and are lesssusceptible to interference. Inductionloop systems can also be difficult to use inmultiple applications, as the signal fromone area can overspill into another.

In schools, induction loop or infra redhearing aid systems should be consideredin large assembly rooms or halls. This isprimarily for visitors to the school ratherthan for deaf pupils themselves, whowould normally have their own assistivelistening equipment. They should also beconsidered in performance spaces,meeting rooms and at reception areadesks. In such situations the output froman existing PA system is often connecteddirectly to the loop amplifier.

Pay phones in schools should have

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EXPLANATION OF TECHNICAL TERMS

Matching Loudspeakers and AmplifierAudio power amplifiers for sound reinforcement are made with two main typesof outputs described as ‘low impedance’ and ‘100 V’ or ‘high impedance’.Similarly loudspeakers come in 4 or 8 ohms (low impedance) or 70 V or 100 V(high impedance).

Low impedance amplifiers and loudspeakersIf an amplifier is rated for 2, 4, 8 or 16 ohms, then it is a low impedance type.Care must be taken to ensure that the loudspeakers add up to a total load thatis both within the amplifier's power rating (W or watts), and between itsmaximum and minimum load impedance range. Low impedance speakers,usually rated at 8 ohms for smaller types, have to be connected in a way thatcreates a total load within the range the amplifier is designed for. Highimpedance, 100 V or 70 V loudspeakers cannot be used satisfactorily. Theadvantage of low impedance systems is optimum audio performance, especiallyat low frequencies. Hi-fi loudspeakers are usually low impedance.

4-16 Ohm outputpower amplifier

R8 Ohms, 5 W

R8 Ohms, 5 W

R8 Ohms, 5 W

R8 Ohms, 5 W

Two loudspeakerswired in series= 16 Ohms, 10 W

+

+

+

+

+

–

–

–

–

–

Two loudspeakerswired in series= 16 Ohms, 10 W

Pairs @ 16 Ohmswired in parallel= 8 Ohms againand 20 W

4 Ohms to 16 Ohmsload range,20 watts @ 16 Ohms40 watts @ 4 Ohms

Calculating the load impedance

For loudspeakers wired in series – add up the individual impedances R = R + R +.......+ R

– add up the individual power P = P + P +.......+ P

For loudspeakers wired in parallel – add up reciprocals of the individual impedance

– add up the individual power P = P + P +.......+ P

In above example R + R = 8 + 8 = 16 for each series pair = R , R

Wiring the pairs in parallel gives

1 2

total 1 2 N

1Rtotal

1R1

1R2

1R N

= + +.......+

total 1 2 N

+ = ===+

1+2 3+4

1R +R 1

116

116

216

18

1R total

Therefore R = 8total

total 1 2 N

1

2

3

4

2 3 4

1R +R

R100 V, 5 W

R100 V, 5 W

R100 V, 5 W

R100 V, 5 W

All loudspeakers wired in parallel100 V, 20 W

+

+

+

+

+

–

–

–

–

–

Calculating the load impedance

Impedance is taken care of automatically by the 100 V transformer in the system.

Total power is the sum of all devices connected.

100 V outputpower amplifier

1

2

3

4

High impedance, 70 V or 100 V amplifiers and loudspeakers

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6Design of acoustic criteria for pupils with hearing impairments andspecial hearing requirements

inductive couplers (a form of inductionloop).

Induction loop systems should beinstalled in accordance with BritishStandard BS7594. Their advantages anddisadvantages are listed in Table 6.2.

6.8.6 Audio-visual equipmentWherever possible, classroom equipmentshould be integrated with the assistivelistening devices used by deaf children.For example, the audio output from audiovisual equipment, televisions and cassetterecorders, can be connected to radio aidor soundfield transmitters. ‘Direct input’leads are available to enable the audiooutput of computers or languagelaboratory equipment to be connecteddirectly to a child’s hearing aid.

6.8.7 Other assistive devicesThere is a wide range of other devicesthat can be used by deaf children inschool, besides those that primarily assistlistening. These include subtitled andsigned video, speech recognition softwareand text telecommunication devices, egtelephones.

For further details of these devicescontact the professional or voluntaryorganisations listed at the end of thissection. Furthermore, it is recommendedto seek advice to ensure that all publicspaces meet the needs of deaf and hard ofhearing people.

6.9 Special teaching accommodationIt is not the intention within thisdocument to address the needs of specialschools for deaf children. Specialist adviceshould always be sought from aneducational audiologist or acousticianwhen designing or modifyingaccommodation for this particularpurpose.

Many hearing impaired children attendmainstream schools with resourcefacilities, sometimes called ‘units’. Thesecontain specialised rooms that exceed theacoustic specifications for regularclassrooms. Within these rooms, childrenare able to learn the language skills thatmight not be possible in a busymainstream classroom. They are also

EXPLANATION OF TECHNICAL TERMS CONTINUED

High impedance, 70 V or 100 V amplifiers and loudspeakersIf an amplifier is rated for 70 V or 100 V, then it is a high impedanceamplifier. It will also have a power rating. High impedance loudspeakers,rated at 70 V or 100 V must be used. All loudspeakers should be either 70V or 100 V. In this case the loudspeakers are simply wired in parallel andtheir individual power requirements are added up. Thus four 100 Vloudspeakers rated at 5 W would be wired in parallel and will provide a 20W load to the amplifier. External transformers can be added to lowimpedance loudspeakers to convert them for high impedance use. Theadvantage of this method is simple wiring. PA, paging and SFSloudspeakers are usually 100 V types in the UK.

Radio Microphone System

Compander system (See Figure 6.3)FM (frequency modulated) radio links provide a signal to noise ratio that isdetermined by the modulation bandwidth of the transmitter. Widerbandwidths allow fewer channels in a band of available frequencies, soregulations limit the bandwidth to two system types described as widebandFM and narrowband FM. Even wideband provides a limited signal to noiseratio of about 65 dB from real products. This is adequate if everything isperfectly adjusted so that a user's voice hits just below the maximumpermitted signal level. However real users vary their voices, different usersshare systems AND they are often not correctly adjusted anyway. Acompander system combines a compressor on the transmitter of thesystem, and an expander on the receiver. The two are matched in theiraction so that the result on the receiver output is very close to the originalinput signal. What happens is that a larger signal range of say 90 dB iscompressed by 50% to fit into 45 dB. This allows for an improved safetymargin in the transmitter so that it does not overload, and allows a wideworking range that will tolerate user variations. At the receiver the 45 dBrange is expanded back to 90 dB. This pushes the system noise down andthe signal up. The result is a signal free from distortion due to overload andwith a much reduced background noise when a soft talker is turned up atthe receiver.

Diversity receiverA FM radio microphone system emits a signal that has a fairly longwavelength. The waves can reflect from room surfaces and arrive at thereceiver antenna in a way that causes the waves to cancel. The result is a‘dropout’ which will be heard as a disappearance of the audio from thesystem. If the dropout is maintained, for example if the user is standing stillin a location that produces a cancellation, the receiver can even hunt andlocate an alternative signal to lock onto - though this is uncommon. Adiversity receiver provides two independent radio and audio paths, includingtwo spaced antennae. The spacing minimises the risk that both antennaewill receive a cancelled signal simultaneously. The unit will automatically andinstantaneously select the stronger of the two signals to the audio output.While audio dropouts may be only slightly disturbing to a person with normalhearing, the hearing impaired child, especially one reliant upon a personalFM receiver, will get nothing and could therefore frequently lose the wholemeaning or context of a piece of verbal information. Therefore, wherepossible, diversity receivers should be used.

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British Association of Audiological Scientists

British Association of Educational Audiologists

British Association of Teachers of the Deaf

British Society of Audiology

National Deaf Children’s Society

Royal National Institute of the Deaf

Organisations

Term

Natural-oral approach

Residual hearing

Hearing aid

Cochlear implant

Central auditory processing difficulty

Radio aid

Glossary

http://www.baas.org.uk

http://www.edaud.org.uk

http://www.batod.org.uk

http://www.b-s-a.demon.co.uk

http://www.ndcs.org.uk

http://www.rnid.org.uk

Explanation

An approach to the education of children with hearing impairments thatseeks to promote the acquisition of spoken language using residualhearing.

A term used to describe the hearing abilities that remain in the case of ahearing impairment.

A battery powered device worn by an individual, either behind the ear or inthe ear. A hearing aid will be selected and programmed to provide themaximum audibility of the speech signal consistent with an individual’sresidual hearing.

A special kind of hearing aid where the inner ear is directly stimulatedelectrically via an implanted electrode.

A broad term used to describe listening difficulties, which are not due tothe outer, middle or inner ear.

An assistive listening device, designed to provide an FM radio link betweena transmitter (usually on the speaker) and the listener (coupled directly tothe hearing aids).

places where children can interact withina favourable acoustic environment.

It is not uncommon for these rooms tobe used for ‘reverse integration’, where asmall group of children from themainstream work with the hearingimpaired children. Occasionally thisprovision may be directly attached to amainstream class in the form of a ‘quietroom’ leading from the classroom. Inother situations the accommodationmight be a separate room or evenbuilding. Teachers and supportprofessionals might also use the areas fora range of activities involved in the

audiological management of the hearingimpaired child. Case Study 7.6 describes ajunior school with a hearing impairedunit, now renamed as the RPD (ResourceProvision for the Deaf). Thecharacteristics of rooms in an RPD are:• excellent sound insulation• very short reverberation times• very low ambient noise levels• flexible space for individual and small group work• good lighting• storage facilities for audiological equipment.

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References[1] M Eatough, Deaf Children and Teachers ofthe Deaf England, BATOD magazine, 2000.[2] S Powers, S Gregory and E D Thoutenhoofd, The EducationalAchievements of Deaf Children, DfES, 1998.[3] J M Bamford, et al., Pure tone audiogramsfrom hearing-impaired children. II. Predictingspeech-hearing from the audiogram. Br JAudiol, 15(1), 3-10, 1981.[4] M Picard and J S Bradley. Revisitingspeech interference in classrooms. Audiology, 40(5), 221-44, 2001.[5] BATOD, Classroom Acoustics -Recommended standards. 2001.[6] ASHA, Position Statement and guidelinesfor acoustics in educational settings. ASHA, 37(14), 15-19, 1995.[7] S Gatehouse and K Robinson. Speechtests as a measure of auditory processing, in Speech Audiometry, Second Edition, M Martin, (Editor) Whurr: London, 1997.[8] A Markides, Speech levels and speech-to-noise ratios. Br J Audiol, 20(2), 115-20, 1986.[9] J A Mattiske, J M Oates and K M Greenwood. Vocal problems among teachers: a review of prevalence, causes,prevention, and treatment. J Voice, 12(4), 489-99, 1998.[10] T Finitzo-Hieber and T W Tillman. Roomacoustics effects on monosyllabic word discrimination ability for normal andhearing-impaired children. J Speech Hear Res, 21(3), 440-58, 1978.[11] O Wilson et al., Classroom Acoustics,Oticon Foundation in New Zealand: Wellington,2002.[12] D Canning. Listening Inventories ForEducation U.K., in LIFE UK, City University,London, 1999.[13] RNID, Guidelines for mainstream teacherswith deaf pupils in their class. Education guidelines project, RNID, 2001.[14] National Deaf Children’s Society, DeafFriendly Schools – a Guide for Teachers andGovernors, NDCS, 2001.[15] DfES, Special Education Needs Code ofPractice, DfES/581/2001.[16] B Homer, R Vaughan and K Higgins, RadioAids, NDCS, 2001.[17] National Deaf Children’s Society, QualityStandards in Education - England, NDCS, 1999.

6Design of acoustic criteria for pupils with hearing impairments andspecial hearing requirements

6.10 Beyond the classroom As far as possible children with hearingimpairments should be included in allschool activities. Improving listeningconditions through better acoustics is avery important part of this, but not theonly relevant factor. There are manyothers such as teaching style and context,staff training, deaf awareness issues, and awhole school approach to specialeducational needs.

Classrooms are not the only placeswhere hearing impaired children interact.It is often overlooked in school design,but critical learning and interaction takesplace outside the classroom, and ifhearing impaired children are to be fullyincluded, attention should be given to allareas of the school where the childrenmight be expected to interact with others.These areas include rooms where aspectsof the curriculum are delivered: libraries,assembly areas, sports halls, music rooms,ICT suites and gymnasia. In these areasthe need for good speech communicationis essential although constrained by theactivities taking place.

Inclusion in most music activitiesrequires good acoustic conditions, goodplanning and structuring of lessons, andthe appropriate use of assistive listeningdevices.

Perhaps the most difficult areas forinclusion are large spaces such as assemblyhalls and sports halls. These areas requirecareful design and forethought.

In other areas, not used for deliveringthe curriculum, children still need to beable to interact verbally. These include thecorridors, cloakrooms, medical rooms,school office, dining room, play areas andtoilets. In these communal placesimportant social interaction often takesplace and if inclusion is to be effective,these areas need to be designed with theacoustic needs of the hearing impairedchild and the child with listeningdifficulties in mind.

Building Bulletin 93, Acoustic design of schools

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Transcript of Building Bulletin 93, Acoustic design of schools