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:

noise mitigation programs in general, and
 sound insulation programs in particular
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
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
 The A-weighted sound
level achieves this goal
 The EPA has adopted
the A-weighted sound
level for environmental
analyses
A-weighting Correction Levels
Common A-weighted Sound Levels, in dB
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
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
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
Sound Exposure Level (SEL)
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
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)
Day-Night Average Sound Level (DNL)
Outdoor “Ambient” DNL at Various Locations
DNL Compared to Annoyance
 Schultz developed accepted “dose-response”
relationship in 1970s. FICON re-affirmed, 1992
Source: FICON, 1992, Data: USAF Armstrong Laboratory
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)

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/
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
Noise Level Reduction (NLR)
NLR = SELoutdoor - SELindoor
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
“By the rude bridge that arched the flood
Their flag to April's breeze unfurled
Here once the embattled farmers stood
and fired the shot heard round the world.”
Ralph Waldo Emerson, "Concord Hymn"
Questions?
Chris Bajdek
Harris Miller Miller & Hanson Inc.
77 South Bedford Street
Burlington, MA 01803
781.229.0707
[email protected]
www.hmmh.com
www.hmmh.com