1. ESP 179- Winter 2013
Noise
February 26, 2013
Instructor: Michael Carr, INCE, CTS
Extant Acoustical Consulting LLC
mcarr@extantacoustical.com
2. 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
3. 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)
5. 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
7. 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.
10. 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.
12. 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)
14. 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”
15. 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
16. 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
17. 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
18. Laws, Regulations, and Standards
Note:
Noise/sound is a Subjective element, that
often requires Objective evaluation.
19. 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
20. 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?
21. 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
22. Approach and Methodology
Compare project noise levels and
exposures to applicable thresholds and
criteria
Determine level of impact
…and if necessary…
23. 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
Barometric pressure changes in the weather are much too slow for the human ear to detect Pressure pulse from car door slam – detected, but not “sound” Pressure changes that occur about 20 times a second or faster can be heard and are called sound
This slide depicts how sound is created from the energy of motion to variations in air pressure and then how it travels away from the source to a receiver. The tuning fork vibrates, and that energy of motion creates rapidly-fluctuating variations in air pressure around it. These pressure variations then travel as compression waves away from the tuning fork. In the middle graphic the wave is shown with regions where the air pressure is high and low. These regions fluctuate as rapidly as the tuning fork vibrates, and travel away from the source at the speed of sound. When this fluctuating air pressure reaches our eardrums, the energy is transferred to our eardrum, which vibrates at the same rate or speed as the tuning fork.
Human ear is not equally sensitive at all frequencies Most sensitive between (2 and 5 kHz) Most sensitive in the range of speech The difference in sensitivity to different frequencies is more pronounced at low sound levels than at high sound levels Ear is less sensitive perceiving the loudness of sounds of short durations (Impulse sound < 1 sec.)
Human ear is not equally sensitive at all frequencies Most sensitive between (2 and 5 kHz) Most sensitive in the range of speech The difference in sensitivity to different frequencies is more pronounced at low sound levels than at high sound levels Ear is less sensitive perceiving the loudness of sounds of short durations (Impulse sound < 1 sec.)
The A-weighted sound level achieves this goal. Federal and State governments have adopted the A-weighted sound level for environmental analyses.
Historical reference examples: Governor's Office of Planning and Research, General Plan Guidelines State of California Model Community Noise Control Ordinance
Gas Station Expanding to two islands, adding automated car wash, stand vacuums. Residential on three sides at varying distances.
Highway Improvement Project Existing interchange Upgrading off ramps, and on ramps for future capacity Removal and replacement of one on-ramp Addition of a new access road Interspersed transient residential, commercial, retail, and limited rural residential
Seismic Upgrades and Retrofits Noise sources include construction equipment, haul trucks, and pile driving Includes both airborne and underwater noise Effects humans, marine mammals, and fish
