Noise 101: Introduction to Acoustics and Aircraft Noise Terminology

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Noise 101Introduction to Acoustics and
Aircraft Noise Terminology
The Shot Heard Round the World

• Chris Bajdek
• Harris Miller Miller Hanson Inc.

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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

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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

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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

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Common A-weighted Sound Levels, in dB
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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
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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

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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

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Sound Exposure Level (SEL)
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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

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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)

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Day-Night Average Sound Level (DNL)
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Outdoor Ambient DNL at Various Locations
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DNL Compared to Annoyance

• Schultz developed accepted dose-response
  relationship in 1970s. FICON re-affirmed, 1992

Source FICON, 1992, Data USAF Armstrong
Laboratory
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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)

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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/ai
rports/aip/aip_handbook/
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FAA Guidelines for Sound Insulation Effectiveness

• Residential Structures
• Achieve interior DNL lt 45 dB
• Achieve minimum 5 dB improvement in NLR
• School Sound Insulation Programs
• Achieve interior Leq,7 lt 45 dB
• Achieve minimum 5 dB improvement in NLR

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Noise Level Reduction (NLR)

• NLR SELoutdoor - SELindoor

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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

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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"

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Questions?

• Chris Bajdek
• Harris Miller Miller Hanson Inc.
• 77 South Bedford Street
• Burlington, MA 01803
• 781.229.0707
• cbajdek_at_hmmh.com
• www.hmmh.com

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www.hmmh.com