ESP 179- Winter 2013
Noise
February 26, 2013
Instructor: Michael Carr, INCE, CTS
Extant Acoustical Consulting LLC
mcarr@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 Fundamentals
What 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 Fundamentals
What is Sound?

Noise Fundamentals
dB 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 Fundamentals
dB or not dB

Noise Fundamentals
Human 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 Fundamentals
Human Perception – Fletcher-Munson

Noise Fundamentals
Human Perception

Noise Fundamentals
Noise 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 Fundamentals
Metrics
Ldn or DNL, CNEL, Leq24
Lmax, Lxx
Leq, Lmax, Lxx
Leq, Lmax, Lxx

Noise Fundamentals
Metrics – Ldn, CNEL
Red = +10dB
Orange = +5dB
 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)

Noise Fundamentals
Metrics – Lmax
Lmax =
85
• Lmax
• Maximum Sound Level Over a Period

Noise Fundamentals
Metrics – 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 Fundamentals
Metrics – 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 Code
Code of Federal Regulations – Titles
Agency Delegation – FAA, FHWA, EPA, NPS, Etc.
 State Government – similar
 Regional, and Local Government
General Plan Noise Element
City/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
 Activity
 Location

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

Environmental Noise Studies
 Noise 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 Methodology
 Review all pertinent documentation
 Establish baseline
 Determine appropriate laws, regulations,
standards, and develop thresholds
 Conduct measurements
 Predict and analyze noise sources resulting
from and affecting the project

Approach and Methodology
 Compare 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 Studies
 Development Projects

Case Studies
 Highway Projects

Case Studies
 Bridge Construction/Pile Driving

Questions?
Michael Carr, INCE, CTS
Extant Acoustical Consulting LLC
mcarr@extantacoustical.com