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Introduction to Noise Control

Introduction to Noise Control. Environmental Science Ithan B. Zimmer, Ph.D., P.E. Basic Noise Control. Environmental Noise Studies Other Studies: Industrial, Theoretical, Mechanical Environmental Impact Statements (EIS) You need to understand the language You can participate in an EIS

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Introduction to Noise Control

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  1. Introduction toNoise Control Environmental Science Ithan B. Zimmer, Ph.D., P.E.

  2. Basic Noise Control • Environmental Noise Studies • Other Studies: Industrial, Theoretical, Mechanical • Environmental Impact Statements (EIS) • You need to understand the language • You can participate in an EIS • More background means it is harder to fool you

  3. Famous Authors • Leo Beranek • Cyril Harris (handbook) • Karl Kryter (Effects) • Charles E. Wilson (NJIT)

  4. Basic Noise Control • Noise = unwanted sound • pollution is redundant • wasted energy • What defines noise is subjective • Environmental noise generally is transient

  5. Possible Effects • Hearing Loss • Annoyance – Quality of Life Issues • Physiological Disorders • Psychological Disorders

  6. Noise Measurement • Decibel scale (dB) • Logarithmic, use common log, base 10 log xy = y log x log (xy) = log x + log y log (1/x) = - log x log (x/y) = log x – log y log 1 = 0

  7. Sound Pressure Level (SPL) • SPL (dB) = 20 log (P/P0) • P = rms sound pressure • P0 = reference pressure 20 μPa • Threshold of Hearing = 0 dB • Threshold of Pain = 140 dB

  8. Combining Noise Measurements(Fig 14.4)

  9. Equation for TotalSound Pressure Level • SPLT = 10·log (10L1/10 + 10L2/10 + … + 10Ln/10) • L1, L2 … are noise measurements in dB • Examples using table or equation

  10. Loudness • An average individual perceives an increase in sound level of ~10 dB as a doubling in loudness.

  11. Frequency Weighting • There are multiple weighting systems • A-weighting is, by far, the most common • It is the best for environmental and community applications because it reflects human response. • Abbreviated dBA, see Fig 14.5 • Humans hear 20-20,000 Hz • Most sensitive from 500-10,000 Hz

  12. Metrics – Cumulative Noise Levels • LX – noise level exceeded X% of the time • L10 • L50 – median noise level • L90 – background noise level • Transit/Highway applications

  13. Equivalent Sound Level - Leq • Average over a period of time • Equations on the board • Day-Night Level: Ldn or DNL • An Leq for 24 hours with a 10 dBA penalty for night noise (10pm to 7am) • Used in community noise, especially airports • Airports must mitigate to below DNL 65 • EPA outdoor to DNL 55, indoor DNL 45

  14. Basic Noise Control Elements Source Receiver Path Environmental concern: air path, also structure Sources: surface traffic, trains, aircraft, fans, machinery Receiver: people

  15. Noise Mitigation and Control • Reduce at the Source – almost always the best method • Increase or block the Path • Protect the Receiver

  16. Noise Mitigation and Control • Source: engine design, exhaust control, friction reduction, # of vehicles • Path: noise barrier, increase the path, Land Use Management • Receiver: home treatment, hearing protection

  17. Line Source vs. Point SourceDouble Distance = ? SPL1 – SPL2 = 10 log (r2/r1) SPL1 – SPL2 = 20 log (r2/r1)

  18. Any Questions?

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