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Noise 101: Introduction to Acoustics and Aircraft Noise Terminology

Noise 101: Introduction to Acoustics and Aircraft Noise Terminology. “The Shot Heard Round the World”. Chris Bajdek Harris Miller Miller & Hanson Inc. Goals. To introduce: Aircraft noise terminology Aircraft noise and land use compatibility Application of acoustics to:

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Noise 101: Introduction to Acoustics and Aircraft Noise Terminology

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  1. Noise 101:Introduction to Acoustics and Aircraft Noise Terminology “The Shot Heard Round the World” Chris Bajdek Harris Miller Miller & Hanson Inc.

  2. Goals To introduce: • Aircraft noise terminology • Aircraft noise and land use compatibility • Application of acoustics to: • noise mitigation programs in general, and • sound insulation programs in particular

  3. Topics • A-Weighted Decibel, dB(A) • Maximum A-Weighted Sound Level, Lmax • Equivalent Sound Level, Leq • Sound Exposure Level, SEL • Day-Night Average Sound Level, DNL • Land Use Compatibility with Yearly DNL • Noise Level Reduction, NLR

  4. A-weighted Sound Pressure Level • The human auditory system 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 A-weighting Correction Levels • The A-weighted sound level achieves this goal • The EPA has adopted the A-weighted sound level for environmental analyses

  5. Common A-weighted Sound Levels, in dB

  6. Maximum Sound Level (Lmax) • Because of the variation in level of a sound event, it is often convenient to describe the event with its maximum sound level, abbreviated as Lmax • Accounts only for sound amplitude (A-weighted level) • Two events may have the same maximum level, but much different exposures Lmax = 85

  7. Equivalent Sound Level (Leq) • A constant sound level “equivalent” on an energy basis of a time varying sound level over the same time period • Leq is time-averaged • Accounts for sound amplitude and time

  8. Sound Exposure Level (SEL) • A way to describe the “noisiness” of a complete noise event • Accounts for sound amplitude (A-weighted level) • Accounts for noise event duration

  9. Sound Exposure Level (SEL)

  10. Day-Night Average Sound Level (DNL) • A way to describe the noise dose for a 24-hour period • Accounts for noise event “noisiness” (SEL) • Accounts for number of noise events • Provides an additional weighting factor for nighttime operations • CNEL includes another weighting factor for evening operations

  11. Day-Night Average Sound Level (DNL) where Ldn = Day/Night Average Sound Level (denoted DNL in contour plots) Log10 = base 10 logarithm 86,400 = number of seconds in a day SEL,j = individual Sound Exposure Level readings during the day N = number of Sound Exposure Level readings during the day Wj = time of day weighting for the jth aircraft passby (10 dB for night) (For CNEL Wj is 4.7 dB for evening)

  12. Day-Night Average Sound Level (DNL)

  13. Outdoor “Ambient” DNL at Various Locations

  14. DNL Compared to Annoyance • Schultz developed accepted “dose-response” relationship in 1970s. FICON re-affirmed, 1992 Source: FICON, 1992, Data: USAF Armstrong Laboratory

  15. Land Use Compatibility • DNL is most widely accepted metric, worldwide • Part 150 provides FAA “guidelines” • All land uses compatible below DNL 65 dB • FICON reconfirmed in 1992 • Local responsibility for determining acceptability • US Dept. of HUD publishes “standards” for federal funding of residential construction • Acceptable ≤ DNL 65 dB • Normally unacceptable DNL 65 to 75 dB (additional sound attenuation required) • Unacceptable above DNL 75 dB (case-by-case conditional approval)

  16. FAA Guidelines In the U.S., sound insulation program guidelines are covered under: “Airport Improvement Program (AIP) Handbook” FAA Order 5100.38C Source: http://www.faa.gov/airports_airtraffic/airports/aip/aip_handbook/

  17. FAA Guidelines for Sound Insulation Effectiveness Residential Structures: • Achieve interior DNL <45 dB • Achieve minimum 5 dB improvement in NLR School Sound Insulation Programs: • Achieve interior Leq,7<45 dB • Achieve minimum 5 dB improvement in NLR

  18. Noise Level Reduction (NLR) NLR = SELoutdoor - SELindoor

  19. Goals To introduce: • Aircraft noise terminology dBA, Lmax, SEL, Leq, and DNL • Land use compatibility with aircraft noise exposure For residential land use: DNL 65 dB (exterior) • Application to noise mitigation programs in general, and sound insulation programs in particular Residential: DNL 45 dB (interior) and 5 dB improvement Schools: Leq 45 dB (interior) and 5 dB improvement

  20. “By the rude bridge that arched the floodTheir flag to April's breeze unfurledHere once the embattled farmers stoodand fired the shot heard round the world.” Ralph Waldo Emerson, "Concord Hymn"

  21. Questions? Chris Bajdek Harris Miller Miller & Hanson Inc. 77 South Bedford Street Burlington, MA 01803 781.229.0707 cbajdek@hmmh.com www.hmmh.com

  22. www.hmmh.com

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