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February 26 esp 179 noise

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February 26 esp 179 noise

  1. 1. ESP 179- Winter 2013 Noise February 26, 2013 Instructor: Michael Carr, INCE, CTS Extant Acoustical Consulting LLC mcarr@extantacoustical.com
  2. 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. 3. 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)
  4. 4. Noise FundamentalsWhat is Sound?
  5. 5. 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
  6. 6. Noise FundamentalsdB or not dB
  7. 7. 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.
  8. 8. Noise FundamentalsHuman Perception – Fletcher-Munson
  9. 9. Noise FundamentalsHuman Perception
  10. 10. 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.
  11. 11. Noise FundamentalsMetrics Ldn or DNL, CNEL, Leq24 Lmax, Lxx Leq, Lmax, Lxx Leq, Lmax, Lxx
  12. 12. Noise FundamentalsMetrics – 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. 13. Noise FundamentalsMetrics – Lmax Lmax = 85 • Lmax • Maximum Sound Level Over a Period
  14. 14. 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”
  15. 15. 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
  16. 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. 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. 18. Laws, Regulations, and StandardsNote:Noise/sound is a Subjective element, thatoften requires Objective evaluation.
  19. 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. 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. 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. 22. Approach and Methodology Compare project noise levels and exposures to applicable thresholds and criteria Determine level of impact…and if necessary…
  23. 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. 24. Case Studies Development Projects
  25. 25. Case Studies Highway Projects
  26. 26. Case Studies Bridge Construction/Pile Driving
  27. 27. Questions?Michael Carr, INCE, CTSExtant Acoustical Consulting LLC mcarr@extantacoustical.com

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