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February 26 esp 179 noise
- 1. ESP 179- Winter2013 Noise February 26, 2013 Instructor: Michael Carr, INCE, CTS Extant Acoustical Consulting LLC mcarr@extantacoustical.com
- 2. Lecture Outline NoiseFundamentals 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 isSound? 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)
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- 5. Noise Fundamentals dB ornot 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
- 6. Noise Fundamentals dB ornot dB
- 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.
- 8. Noise Fundamentals Human Perception– Fletcher-Munson
- 9.
- 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.
- 11. Noise Fundamentals Metrics Ldn or DNL, CNEL, Leq24 Lmax, Lxx Leq, Lmax, Lxx Leq, Lmax, Lxx
- 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)
- 13. Noise Fundamentals Metrics –Lmax Lmax = 85 • Lmax • Maximum Sound Level Over a Period
- 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, andStandards 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, andStandards 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, andStandards 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 Exposureof 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
- 24. Case Studies DevelopmentProjects
- 25. Case Studies HighwayProjects
- 26. Case Studies BridgeConstruction/Pile Driving
- 27. Questions? Michael Carr, INCE,CTS Extant Acoustical Consulting LLC mcarr@extantacoustical.com
Editor's Notes
- #4 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
- #5 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.
- #8 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.)
- #9 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.)
- #10 The A-weighted sound level achieves this goal. Federal and State governments have adopted the A-weighted sound level for environmental analyses.
- #18 Historical reference examples: Governor's Office of Planning and Research, General Plan Guidelines State of California Model Community Noise Control Ordinance
- #25 Gas Station Expanding to two islands, adding automated car wash, stand vacuums. Residential on three sides at varying distances.
- #26 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
- #27 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