***Acoustical holography**—An inspection method using the phase interference between sound waves from an object and a reference signal to obtain an image of reflections in the test object.

***Action level**—The cumulative work-shift noise dose at which a hearing conservation program is mandated by the Occupational Safety and Health Administration (OSHA). An 8-hour time-weighted average of 85 dB measured with A-weighting and slow response or the equivalent, a dose of 50 percent. *See* hearing conservation program.

***Active control**—Reducing sound and secondary sources of excitation to cancel, or at least reduce, the response of a system to prime noise sources; also to suppress self-excitation oscillations of an unstable system.

†**Ambient noise**—All-encompassing sound at a given place, usually a composite of sounds from many sources near and far.

***Annoyance**—A person’s internal response to a noise. Annoyance is quantifiable (1) psychologically by subjective rating or (2) technically by a physical noise descriptor, for example, the equivalent continuous A-weighted sound pressure level . For a given person, the correlation coefficient between descriptor and related ratings usually does not exceed 0.5 due to the influence of other factors in determining annoyance. *See* equivalent continuous A-weighted sound pressure.

†**Background noise**—Total noise from all sources of interference in a system used for the production, detection, measurement, or recording of a signal, independent of the presence of the signal.

NOTES:

1. Ambient sound detected, measured, or recorded with the signal is part of the background noise.

2. Interference resulting from primary electric power supplies (commonly described as a *hum* when heard separately) is included in the definition of background noise.

†**Day average sound level**—Time-average sound level between 0700 and 2200 hours. Unit, decibel (dB); abbreviation, DL; symbol, *L*_{d}.

NOTE: Day average sound level in decibels is related to the corresponding day sound exposure level, *L*_{Ed}, according to

where 54,000 is the number of seconds in a 15-hour day.

†**Day-night average sound level****—**Twenty-four-hour average sound level for a given day, after addition of 10 decibels to levels from midnight to 0700 hours and from 2200 hours (10 p.m.) to midnight. Unit, decibel (dB); abbreviation, DNL; symbol, *L*_{dn}.

NOTES:

1. Day-night average sound level in decibels is related to the corresponding day-night sound exposure level, *L*_{Edn}, according to

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Appendix I
glossary of Selected Terms1
*Acoustical holography—An inspection method using the NOTES:
phase interference between sound waves from an object and
a reference signal to obtain an image of reflections in the 1. Ambient sound detected, measured, or recorded with
test object. the signal is part of the background noise.
*Action level—The cumulative work-shift noise dose at 2. Interference resulting from primary electric power
which a hearing conservation program is mandated by the supplies (commonly described as a hum when heard sepa-
Occupational Safety and Health Administration (OSHA). rately) is included in the definition of background noise.
An 8-hour time-weighted average of 85 dB measured with
†Day average sound level—Time-average sound level be-
A-weighting and slow response or the equivalent, a dose of
50 percent. See hearing conservation program. tween 0700 and 2200 hours. Unit, decibel (dB); abbreviation,
DL; symbol, Ld.
*Active control—Reducing sound and secondary sources of
excitation to cancel, or at least reduce, the response of a sys - NOTE: Day average sound level in decibels is related
tem to prime noise sources; also to suppress self-excitation to the corresponding day sound exposure level, LEd, ac-
oscillations of an unstable system. cording to
†Ambient noise—All-encompassing sound at a given place, Ld = LEd – 10 lg(54,000/1)
usually a composite of sounds from many sources near and
far. where 54,000 is the number of seconds in a 15-hour
day.
*Annoyance—A person’s internal response to a noise.
†Day-night average sound level—Twenty-four-hour aver-
Annoyance is quantifiable (1) psychologically by subjec-
tive rating or (2) technically by a physical noise descriptor, age sound level for a given day, after addition of 10 decibels
for example, the equivalent continuous A-weighted sound to levels from midnight to 0700 hours and from 2200 hours
⋅
pressure level (LAeq.T). For a given person, the correlation (10 p.m.) to midnight. Unit, decibel (dB); abbreviation,
coefficient between descriptor and related ratings usually DNL; symbol, Ldn.
does not exceed 0.5 due to the influence of other factors
in determining annoyance. See equivalent continuous A- NOTES:
weighted sound pressure. 1. Day-night average sound level in decibels is related to
the corresponding day-night sound exposure level, LEdn,
†Background noise—Total noise from all sources of in- according to
terference in a system used for the production, detection,
measurement, or recording of a signal, independent of the Ldn = LEdn – 10 lg(86,400/1)
presence of the signal.
1The asterisk (*) and the dagger (†) indicate the source of the definition,
as explained at the end of the glossary.
7

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76 TECHNOLOGY FOR A QUIETER AMERICA
where 86,400 is the number of seconds in a 24-hour 3. In principle, the sound pressure signal is not exponen-
day. tially time weighted, either before or after squaring.
*Frequency weighting—Modification of the spectrum of an
2. A frequency weighting is understood, unless another
frequency weighting is specified explicitly. acoustical signal by means of an analog or digital filter hav -
ing one of the standardized response characteristics known as
†Decibel—Unit of level when the base of the logarithm is the A, B, C, etc., defined in IEC 61672-1. The A-weighting filter
tenth root of 10 and the quantities concerned are proportional is the one most commonly used. See weighting network.
to power. Unit symbol, dB.
*Hearing conservation program—A system to identify
NOTE: Examples of quantities that qualify are power noise-exposed workers and monitor their exposure and au-
(in any form), sound pressure squared, particle veloc- diometric function.
ity squared, sound intensity, sound-energy density, and
*Hearing loss—Increase in the threshold of audibility due
voltage squared. Thus, the decibel is a unit of sound-
to disease, injury, age, or exposure to intense noise. Conduc-
pressure-squared level; in common practice, however,
tive hearing loss: Hearing loss caused either by blockage
called sound pressure level, unless an ambiguity results
from so doing. of the external ear or by disease or damage in the middle
ear, so that the signal amplitude reaching the inner ear is
†Effective perceived noise level—Level of the time integral reduced. Noise-induced hearing loss (NIHL): Cumulative
of the antilogarithm of one-tenth of tone-corrected perceived hearing loss associated with repeated exposure to noise.
Sensorineural hearing loss: Hearing loss due to a lesion or
noise level over the duration of an aircraft flyover, the refer-
ence duration being 10 seconds. Unit, decibel (dB); abbrevia- disorder of the inner ear or of the auditory nervous system.
⋅ Nonoccupational hearing loss: Hearing loss caused by
tion, EPNL; symbol, LEPN.
exposure outside of the occupational environment.
NOTE: The integral is usually approximated by summa-
*Hertz (Hz)—A unit of frequency measurement represent-
tion, over the top 10 decibels of an aircraft noise signal
of the antilogarithms of one-tenth of tone-corrected per- ing cycles per second.
ceived noise level at successive 0.5 second intervals.
†Muffler—Duct designed to reduce the level of sound. The
† Equivalent continuous sound level —Ten times the sound-reducing mechanisms may be either absorptive, reac-
logarithm to the base 10 of the ratio of time-mean-square tive, or a combination of both.
instantaneous A-weighted sound pressure, during a stated
*Newton (N)—A unit of force. The force of one Newton
time interval T, to the square of the standard reference sound
accelerates a 1 kg mass at 1 m/s2.
pressure. Unit, decibel (dB); respective abbreviations, TAV
and TEQ; respective symbols, LAT and LAeqT.
*Noise dose—(1) According to the definition given by Oc-
NOTES: cupational Safety and Health Administration (OSHA), noise
1. A frequency weighting other than the standard A- dose is the ratio, expressed as a percentage of (a) the time
weighting may be employed if specified explicitly. A integral, over a stated time or event, of the 0.6 power of the
frequency weighting that is essentially constant between measured “S” (slow) exponential time-averaged, squared A-
limits specified by a manufacturer is called “flat.” weighted sound pressure and (b) the product of the criterion
duration (8 hours) and the 0.6 power of the squared sound
2. In symbols, time-average (time-interval equivalent pressure corresponding to the criterion sound pressure level
continuous) A-weighted sound level in decibels is (90 dB). (2) According to the definition given by OSHA,
noise dose is the percentage of actual exposure relative to
the amount of allowable exposure, and for which 100 percent
(1/T ) T p2 (t )dt
∫0 A
and above represents exposures that are hazardous. The noise
= 10 lg
LAT
2
p0 dose is calculated using:
= LAeqT
D = ∑ i =1 Ci / Ti × 100%
n
where pA2 is the squared instantaneous A-weighted sound
where Ci is the total time of exposure at a specified noise
pressure signal, a function of elapsed time t; in gases
level, and Ti is the exposure time at which noise for this level
reference sound pressure p0 = 20 µPa; T is a stated time
becomes hazardous.
interval.

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77
APPENDIX I
†Noise—(a) Undesired sound, by extension is any unwar- midband frequencies from 50 to 10 kHz used in the calcula-
ranted disturbance in a useful frequency band, such as unde- tion of perceived noise level. Unit, noy; abbreviation, n.
sired electric waves in a transmission channel or device. (b)
Erratic, intermittent, or statistically random oscillation. NOTE: The prescribed function is given in Federal Avia-
tion Regulation Part 36, Noise Standards: Aircraft Type
NOTES: and Airworthiness Certification, Appendix B, and in In-
ternational Civil Aviation Organization Annex 16, Volume
1. If ambiguity exists as to the nature of the noise, a 1, Aircraft Noise, 3rd ed., July 1993.
term such as “acoustic noise” or “electric noise” should
*Permissible exposure level (PEL)—Regulatory limit
be used.
of sound exposure. The OSHA (Occupational Safety and
2. Since definitions 3.25 (a) and (b) are not mutually Health Administration) PEL is a noise dose of 1.0 based on
exclusive, it is usually necessary to depend on context an 8-hour A-weighted sound exposure level at 90 dB with
for the distinction. a 5-dB exchange rate. European PEL is generally an 8-hour
A-weighted sound exposure level at 85 dB with a 3-dB
*Noise-induced hearing loss—See hearing loss. exchange rate.
†Noise-induced permanent threshold shift—Permanent †Phon—Unit of loudness, judged or calculated.
hearing loss resulting from noise exposure. Abbreviation:
*Radiation efficiency; radiation factor—The ratio of the
NIPTS.
sound power radiated by a vibrating surface, with a given
†Noise-induced temporary threshold shift—Temporary time-mean-square velocity, to the sound power, which would
hearing loss resulting from noise exposure. Abbreviation: be emitted as a plane wave by the same vibrating surface with
NITTS. the same vibration velocity. The radiation factor is given by
the following equation:
*Octave band—A frequency band with upper and lower fre-
quency limits in the ratio of 2. See one-third octave band. PS
σ=
ρcSS υ 2
*One-third octave band—A frequency band with upper and
lower frequency limits in the ratio of 21/3.
where Ps is the airborne sound power emitted by the vibrat-
ing surface, rc is the characteristic impedance of air, Ss is
*One-third octave filter—A filter with upper and lower
the area of the vibrating surface, and υ 2 is the squared rms
passband limits in the ratio of 21/3 centered at one of the pre-
value of the vibratory velocity averaged over the area Ss.
ferred frequencies given in ISO 266. Should meet the attenu-
Unit; none; symbol, σ. See sound power.
ation characteristics of IEC 61260 and ANSI S1.11–1986.
* Single-event sound pressure level—Time-integrated
*Pascal (Pa)—unit of pressure corresponding to a force of
sound pressure level of an isolated single sound event of
1 Newton acting uniformly on an area of 1 square meter. 1
specified duration T (or specified measurement time T) nor-
Pa = 1 N/m2.
malized to T0 = 1 s. It is given by the formula:
†Perceived noise level—Frequency-weighted sound pres-
1 p 2 (t )
T
sure level obtained by a stated procedure that combines the
∫
L p,1s =10 log10 dt
sound pressure levels in the 24 one-third octave bands with 2
T0 p0
0
midband frequencies from 50 to 10 kHz. Unit, decibel (dB);
T
abbreviation, PNL; symbol, LPN. = L peq , T + 10 log dB,
T0
NOTE: Procedures for computing perceived noise level
are stated in Federal Aviation Regulation Part 36, Noise
where p(t) is the instantaneous sound pressure, p0 is the refer-
Standards: Aircraft Type and Airworthiness Certifica-
ence sound pressure, and Lpeq.T is the equivalent continuous
tion, Appendix B, and in International Civil Aviation
sound pressure level. Unit, decibel (dB); symbol: Lp,1s.
Organization Annex 16, Volume 1, Aircraft Noise, 3rd
ed., July 1993.
†Sound exposure—Time integral of squared instantaneous
frequency-weighted sound pressure over a stated time inter-
†Perceived noisiness—Prescribed function of sound pres-
val or event. Unit, pascal-squared second; symbol, E.
sure levels in the 24 one-third octave bands with nominal

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78 TECHNOLOGY FOR A QUIETER AMERICA
NOTES: normal to this direction at the point considered. Unit, watt-
per square meter (W/m2); symbol, l.
1. If frequency weighting is not specified, A-frequency
w eighting is understood. If other than A-frequency NOTES:
weighting is used, such as C-frequency weighting, an
appropriate subscript should be added to the symbol 1. Sound intensity in the specified direction is given by
(e.g., EC). the expression
2. Duration of integration is implicitly included in the T
I = (1 / T ) ∫ pdt ,
time integral and need not be reported explicitly. For the
0
sound exposure measured over a specified time interval,
where
such as 1 hour, a 15-hour day, or a 9-hour night, the du-
T = time, which should be long compared with the
ration should be indicated by the abbreviation or letter
reciprocal of the lowest frequency of interest;
symbol, for example 1-hour sound exposure (1HSE or
p = instantaneous sound pressure;
E1h) for a particular hour; day sound exposure (DSE or
= component of instantaneous particle velocity in the
Ed) from 0700 to 2200 hours; and night sound exposure
specified direction; and
(NSE or En) from 0000 to 0700 hours plus from 2200 to
t = time.
2400 hours.
2. In the case of a free plane or spherical wave having
3. Day-night sound exposure (DNSE or Edn) for a 24-
time-mean-square pressure p2, velocity of propagation c,
hour day is the sum of the day sound exposure and 10
in a medium of density p, the intensity in the direction of
times the night sound exposure.
propagation is given by
4. Unless otherwise stated, the normal unit for sound
I = p2/pc.
exposure is the pascal-squared second.
†Sound-level meter—Device used to measure sound pres-
†Sound exposure level—Ten times the logarithm to the
sure level with a standardized frequency weighting and
base 10 of the ratio of a given time integral of squared in-
indicated exponential time weighting for measurements of
stantaneous A-weighted sound pressure, over a stated time
sound level, or without time weighting for measurements of
interval or event, to the product of the squared reference
time-average sound pressure level or sound exposure level.
sound pressure of 20 micropascals and reference duration
of 1 second. The frequency weighting and reference sound
†Sound power—Sound energy radiated by a source per unit
exposure may be otherwise if stated explicitly. Unit, decibel
of time. Unit, watt (W), symbols, P or W.
(dB); abbreviation, ASEL; symbol, LAE.
†Sound power level—Ten times the logarithm to the base
NOTE: In symbols, (A-weighted) sound exposure level
10 of the ratio of a given sound power in a stated frequency
is
band, to the reference power of 1 picowatt (1 pW). Unit,
decibel (dB), abbreviation PWL; symbols, LP or LW.
T 2
∫ pA (t )dt
= 10 lg 0 2
†Sound pressure—Root-mean-square instantaneous sound
LAE
pressure at a point during a given time interval. Unit, pascal
p0 t0
(Pa).
= 10 lg( E / E0 ) NOTE: In the case of periodic sound pressures, the in-
terval is an integral number of periods or an interval that
= LAT + 10 lg(T / t0 ),
is long compared to a period. In the case of nonperiodic
sound pressures, the interval should be long enough to
2
where pA is the squared instantaneous A-weighted sound make the measured sound pressures essentially indepen-
pressure, a function of time t; for gases p0 = 20 µPa; t0 = dent of small changes in the duration of the interval.
2
1 s; E is sound exposure; E0 = p0 t0 = (20 µPa)2s is refer-
ence sound exposure. †Sound pressure level—(a) Ten times the logarithm to the
base 10 of the ratio of the time-mean-square pressure of a
†Sound intensity—Average rate of sound energy transmit- sound, in a stated frequency band, to the square of the ref-
ted in a specified direction at a point through a unit area erence sound pressure band, to the square of the reference

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7
APPENDIX I
†Time-average sound level—See description for equivalent
sound pressure in gases of 20 µPa. Unit, decibel (dB); abbre-
viation, SPL; symbol, LP . (b) For sound in media other than continuous sound level.
gases, unless otherwise specified, reference sound pressure
*Turbulence—A fluid mechanical phenomenon that causes
is one micropascal (1 µPa).
fluctuation in the local sound speed relevant to sound gen-
NOTE: A sound pressure level with reference to a pres- eration in turbo machines (pumps, compressors, fans, and
sure of 1 µPa is numerically 10 lg(202/12) = 26 decibels turbines), pumping and air-conditioning systems, or propa-
greater than the sound pressure level for the same sound gation from jets and through the atmosphere.
pressure but with reference to 20 µPa.
*Weighting network—Electronic filter in a sound-level
†Speech interference level—One-fourth of the sum of the meter that approximates, under defined conditions, the fre-
band sound pressure levels for octave bands with nominal quency response of the human ear. The A-weighting network
midband frequencies of 500, 1,000, 2,000, and 4,000 Hz. is most commonly used. See frequency weighting.
Unit, decibel; abbreviation, SIL; symbol, LSI.
*Tire/road noise—Unwanted sound generated by the inter-
action between a rolling tire and the surface on which it is
rolling. Also known as tire/paement noise.
† Reprinted from ANSI S1.1-1994 (R 2004) American National Standard
Acoustical Terminology, © 1994, with the permission of the Acousti -
cal Society of America, 35 Pinelawn Road, Suite 114E, Melville, NY
11747, USA.
* Handbook of Noise and Vibration Control. ISBN 978-0-471-39599-7,
edited by Malcolm J. Crocker. Copyright John Wiley, 2007. Reprinted
with permission of John Wiley & Sons, Inc.
Please note: No rights are granted to use content that appears in the work
with credit to another source.

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