ESP 179- Winter 2013

NoiseFebruary 26, 2013

Instructor: Michael Carr, INCE, CTS

Extant Acoustical Consulting LLCmcarr@extantacoustical.com

Lecture Outline Noise Fundamentals Recap

dB or Not dB Human Perception Noise Level Descriptors

Laws, Regulations, and Standards Subjective/Objective Noise Elements Noise Ordinances

Environmental Noise Studies CEQA Approach & Methodologies Thresholds & Impacts Mitigation & Minimization Case Studies

Noise FundamentalsWhat is Sound?

Characteristics of Sound Speed – the speed at which sound travels Frequency – rate of pressure fluctuations Wavelength – directly related to frequency Loudness – amplitude or magnitude of pressure

fluctuations

Anything we can hear. Caused by variations in pressure detected by the ear. We can detect pressure variations over a HUGE range:

0.000,000,003 to 0.03 psi or more. Normal range of hearing for a healthy young person is

20 Hz to 20,000 Hz (or 20 kHz)

Noise FundamentalsWhat is Sound?

Noise FundamentalsdB or not dB Why Decibels instead of sound pressure?

We can hear sound pressures over a HUGE range:0.000,000,003 to 0.03 psi

The decibel compresses this to a smaller range:0 to 140 dB (threshold of hearing to threshold of pain)

Match with our ear/brain system:Decibels relate better to how we hear

Sound “levels” are always expressed in decibels Decibel scale is logarithmic, like the Richter scale

used for earthquakes Increases in the same sound:

1dB is barely detectable 10dB sounds twice as loud

Noise FundamentalsdB or not dB

Noise FundamentalsHuman Perception The human auditory system perceives sound

differently depending several factors including: Frequency content Source level amplitudes Duration is not equally sensitive to all frequencies.

To be a useful environmental analysis tool we need a way to measure sound the same way the ear hears it.

The A-weighted sound level achieves this goal. Federal and State governments have adopted the

A-weighted sound level for environmental analyses.

Noise FundamentalsHuman Perception – Fletcher-Munson

Noise FundamentalsHuman Perception

Noise FundamentalsNoise Descriptors/Metrics Maximum sound level (Lmax)

Typically measured with “Fast” time-averaging

Equivalent sound levels (Leq) Energy average sound level Typically averaged over one hour

Peak-hour Leq used for assessing noise impact Day-night sound levels (Ldn or DNL, and CNEL)

Energy average sound level over 24 hour period Sound levels occurring between 10PM and 7AM are weighted

+10 decibels; and + 4.77 dB between 7 PM and 10 PM for CNEL.

Sound Exposure Levels (SEL) Statistical sound levels (L90, L50, L10, Lxx)

Sound level that is exceeded xx % of the time.

Noise FundamentalsMetrics

Ldn or DNL, CNEL, Leq24Lmax, Lxx

Leq, Lmax, Lxx

Leq, Lmax, Lxx

Noise FundamentalsMetrics – Ldn, CNEL

DNL - Day-Night Average Sound Level - The average of all SELs or Leqs over 24 hours

Adds a 10 dB penalty to nighttime events (10 times) 10pm to 7am(6:59:59am) (Red on Graph)

CNEL - Community Noise Equivalent Level Same as DNL, with an evening penalty also

Adds approx. 5 dB penalty to evening events (3 times) 7pm to 10pm(9:59:59pm) (Red & Orange on Graph)

Red = +10dB

Orange = +5dB

Noise FundamentalsMetrics – Lmax

Lmax = 85

• Lmax

• Maximum Sound Level Over a Period

Noise FundamentalsMetrics – Leq

Leq (or Leq) Equivalent Continuous Sound Level

The steady sound level with the same energy content as the fluctuating sound being described

Sometimes called the “energy-average sound level”

Noise FundamentalsMetrics – SEL

SEL Sound Exposure Level

constant level for one second which has the same sound energy as the original sound

Often used to describe the noise energy of a single event vehicle pass-by aircraft fly-over

Laws, Regulations, and Standards Legislative or Regulatory Federal Government

US CodeCode of Federal Regulations – TitlesAgency Delegation – FAA, FHWA, EPA, NPS, Etc.

State Government – similar Regional, and Local Government

General Plan Noise ElementCity/County Code, Noise Ordinance

Laws, Regulations, and Standards Subjective – easier to enforce, flexible

Qualitative Judgment based Excessive, unreasonable, unnecessary, etc.

Objective – more easily upheld Quantitative Uses measurements and numbers Can be based on:

Source General operation Specific test procedure

ActivityLocation

Laws, Regulations, and Standards

Note:Noise/sound is a Subjective element, that often requires Objective evaluation.

Environmental Noise StudiesNoise Studies can take different forms,

requiring different levels of analysis: Technical Studies and Stand-alone analysis EA, FONSI IS, MND, Cat.Ex. EIS EIR Federal or State mandated noise studies

CEQA: Noise Exposure of persons to or generation of noise

levels in excess of standards established in the local general plan or noise ordinance, or in other applicable local, state, or federal standards?

Exposure of persons to or generation of excessive groundborne vibration or groundborne noise levels?

A substantial permanent increase in ambient noise levels in the project vicinity above levels existing without the project?

A substantial temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the project?

Near a public or private airstrip?

Approach and MethodologyReview all pertinent documentationEstablish baseline Determine appropriate laws, regulations,

standards, and develop thresholdsConduct measurementsPredict and analyze noise sources

resulting from and affecting the project

Approach and MethodologyCompare project noise levels and

exposures to applicable thresholds and criteria

Determine level of impact

…and if necessary…

Mitigation & Minimization Increase setback distances from noise source. Create, use or incorporate an intervening

/shielding element (barrier, berm, building, etc) Site/project design Building design Sound insulation Absorptive materials Vegetation Active Acoustics

Case StudiesDevelopment Projects

Case StudiesHighway Projects

Case StudiesBridge Construction/Pile Driving

Questions?

Michael Carr, INCE, CTS

Extant Acoustical Consulting LLCmcarr@extantacoustical.com