Design Studio Reverberation Time Calculations
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Transcript of Design Studio Reverberation Time Calculations
NATIONAL UNIVERSITY OF
SCIENCE & TECHNOLOGY
FACULTY OF THE BUILT
ENVIRONMENT
DEPARTMENT OF ARCHITECTURE
An Environmental Design Assignment Second Year, 2012-2013, Semester 2
Environmental Design II AAR 2204 Lecturer: Mr. Nyamande
1st Year Design Studio Acoustical Calculations By Group: Blessing Mukome (N0113440P) Nothabo Ndlovu (N01110491L) Bryan Faranando (N0110286Y)
1
Introduction The purpose of the exercise is to evaluate the acoustical effects of the materials used in
the Part 1 Design Studio by calculating the reverberation time of the room and checking
whether or not the room is suitable for its current use as a design studio. Illustrations of
the space in the form of a floor plan and pictures have also been added.
Name of space:
Part 1 Design Studio
Current function/use of space:
The space is currently being used as a design studio and class room for the first year
architecture students.
Intended function/use of space:
The space was designed to serve as office space for the university.
Size of space:
Length of room: 11540mm (clear distance)
Width of room: 6700mm (clear distance)
Height of room: approx. 2900mm
Floor area = length × width
= 11.54m × 6.7m
= 77.32m2
Volume of room = floor area × room height
= 77.32m2 × 2.9m
= 224.22m3
Estimated occupancy of space:
Deducing from observation of current use of the space, it’s current average occupancy
is 25 users.
2
Vie
w o
f th
e first year
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he f
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Vie
w o
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e first year
desig
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tudio
fro
m t
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ack
3
Image showing column, glazing and the aluminum framing in the studio
Image showing ceiling and luminaire layout (5 by 3 configuration)
4
Analysis of Materials
Material Quantity Area/Unit
(m2) Total Area (m2)
αs at 125Hz
Sα at 125Hz
αs at 4KHz
Sα at 4KHz
Furniture
Drawing boards (vanished wood)
10 1.02 10.2 0.19 1.94 0.3 3.06
Stools/seats (wood) 10 0.12 1.23 0.15 0.18 0.3 2.4
Model making tables (wood)
2 2.19 4.38 0.19 0.83 0.3 1.31
Whiteboard (porcelain) 1 2.07 2.07 1.69 3.50 1.42 2.94
Storage drawers (steel) 1 2.94 2.94 0.15 0.44 0.19 0.56
Ceiling Materials
Suspended ceiling (acoustic tiles; perforated steel)
294 0.25 73.57 0.05 3.68 0.32 23.54
Luminaires (aluminum reflecting surface)
15 0.25 3.75 0.38 1.43 0.87 3.26
Floor Materials
Floor finish (ceramic tiles)
- - 77.32 0.01 0.77 0.02 1.55
Wall Materials
Wallpaper on brick wall - - 12.915 0.02 0.26 0.08 1.03
Plastered brick wall - - 20.1 0.013 0.26 0.05 1.01
Timber partition wall - - 18.6 0.25 4.65 0.1 1.86
Window frame (aluminium 50mm cavity)
- - 6.6 0.38 2.51 0.87 5.74
Column (wallpaper on concrete)
- - 5.7 0.02 0.11 0.08 0.46
Window panes (glass) 51 0.88 45.06 0.35 15.77 0.04 1.80
Door glass panels 6 0.76 4.58 0.35 1.60 0.04 0.18
People 25 - 25 0.25 6.25 0.5 12.50
TOTAL Sα 44.19 63.20
5
Perforated steel (on ceiling)
Metal is a good sound reflector, and as such, the material on the ceiling reflects sound
back into the room. However, some of the sound is absorbed due to the perforations in
the material.
Glazing
Glazed areas are both the structurally and acoustically weak areas on a building shell,
but they can be made to be good sound absorbers when treated well to provide
insulation. The type of glass used for the first year studio – laminated glass – is a good
sound absorber; and it’s fixation to the aluminum framing with the use of rubber sealing
further adds to the sound absorption quality, as well as helping in containing sound
within the room.
Aluminum Framing
Aluminum has metal properties, and thus is a sound reflector.
Wallpaper (on brick walls and column)
Wallpaper is generally a good sound absorber – but the background on which it is fixed
onto (brick and/or concrete) reflect sound.
Timber (used on the partition wall and furniture)
Timber makes for a good sound reflector – as shown by its extensive use in acoustical
spaces. Most of the furniture in the first year studio is made mostly from plywood.
Ceramic tiles (used as floor finish)
Ceramic tiles are made of hard material, which produces sounds due to vibrations;
therefore movement of objects such as furniture makes the room noisy. Also, ceramic
material is a sound reflector, which contributes to the noise as sounds made are
reflected back into the room. Sound absorption is aided by the grout (which has sound
proof properties) which is used to fix the tiles onto the floor.
6
Calculations
Reverberation Time
The reverberation time ( ) is defined as the length of time required for sound to decay
or fall in level by 60 decibels (60dB) from its initial level. Classrooms should have
reverberation times in the range of 0.4-0.6 seconds, but many existing classrooms have
reverberation times of 1 second or more. In such cases, the teacher is competing
against the lingering reflections of his or her own voice for the student's attention. The
result is a chaotic jumble of sounds.
The table above shows the optimum reverberation times for speech and music, for a
recommended minimum volume of auditoria. Given that our room has a volume of
224.22m3, the expected reverberation time for speech should be less than 0.7 seconds.
The reverberation time can be calculated by using an equation developed by Harvard
physics professor named Wallace Clement Sabine:
Sabine’s Formula
Reverberation time,
Where : V = room volume in m3
Sα = total surface absorption in m2
x is a coefficient related to the sound attenuation of air
7
Given that the value x is not provided; an empirical formula for calculating reverberation
time is used:
Reverberation time,
The total surface absorption (Sα) is obtained by adding together the separate areas of
absorbent:
From the table of materials:
Sα at 125Hz = 44.19m2
Sα at 4kHz = 63.20m2
Reverberation time at 125Hz (low frequency/pitch sound):
A RT of 0.81 seconds implies that it takes 0.81 seconds for interrupted sound to decrease by
60dB, given a sound intensity/frequency of 125Hz. This is outside the optimum 0.4 – 0.6
seconds required for a classroom environment, but sound reflective (echo) effects may not be
as significant.
Reverberation time at 4kHz (high frequency/pitch sound):
A RT of 0.56 seconds implies that it takes 0.56 seconds for interrupted sound to decrease by
60dB, given a sound intensity/frequency of 4kHz. This is within the optimum 0.4 – 0.6 seconds
required for a classroom environment, which means that speech audio will be quite audible in
this environment.
In conclusion, the space being studied is relatively suitable for its current use, than not.
8
Sources
http://www.sengpielaudio.com/calculator-RT60Coeff.htm
http://www.engineeringtoolbox.com/accoustic-sound-absorption-d_68.html
http://www2.ibp.fraunhofer.de/akustik/ra/owa/index_e.html
http://www-958.ibm.com/software/data/cognos/manyeyes/datasets/sound-
absorption-coefficients/versions/1
http://www.bembook.ibpsa.us/index.php?title=Absorption_Coefficient
http://goodinsulationmaterials.blogspot.com/2012/01/aluminium-sound-absorption-
panel.html
http://www.bentonbrotherssolutions.com/aluminum-frame.htm
11.5
40
0.78
0
0.79
0
0.76
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0.5006.700
AA
B B
Modelmakingtable
Modelmakingtable
A1paper
cabinet
Drawingboards
Dean'sOffice
GraduateStudio
1st Year Design Studio(ceramic tiles)
FLOOR PLANScale 1:50
Cove
red
Wal
kway
2900
mm
hea
droo
m h
eigh
t
11.540
Timberboard
partitionwall
Concrete slab
SECTION A-AScale 1:50
Wallpaperon brick wall
Glazingpanels onaluminium
frameGlass
panelleddoor