ASTM C634-00
(Terminology)Standard Terminology Relating to Environmental Acoustics
Standard Terminology Relating to Environmental Acoustics
SCOPE
1.1 This terminology covers terms and definitions related to environmental acoustics. Only definitions common to two or more standards under the jurisdiction of Committee E-33 are listed here. The purpose of this terminology is to promote uniformity of key definitions. Definitions pertinent to only one standard and exceptions to the definitions listed below are contained in the individual standards and should be used when following those standards.
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Standards Content (Sample)
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Designation: C 634 – 00 An American National Standard
Standard Terminology Relating to
Environmental Acoustics
This standard is issued under the fixed designation C 634; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
In some of the entries, those that are measures of physical quantities, the term is followed by three
items: symbol, dimensions, and unit. The symbol, in italics, stands for the magnitude of the quantity
in mathematical expressions. The dimensions of a quantity express its measure in terms of three
fundamental quantities: M for mass, L for length, and T for time. Speed, for instance, is the quotient
obtained when the distance an object moves is divided by the time involved. The dimensions are
−1
[LT ], the negative exponent indicating division. The unit is consistently in SI, Le Système
International d’Unités. Those still using the cgs (centimetre-gram-second) or the inchpound system of
units are referred for most of the conversion factors to Practice E 380. A few conversion factors are
listed in Section 4 of this terminology.
The dimensions of a quantity are the same regardless of the units in which the quantity is measured.
−1
Speed has the dimensions [LT ] whether it is measured in miles per hour, feet per second, or metres
per second. Quantities with different dimensions are not the same. Flow resistance and specific flow
resistance, for instance, are quantities of different kinds even though the names are similar. On the
other hand, quantities with the same dimensions are not necessarily of the same kind. Sound energy
−1 −2
density, for instance, has the same dimensions as sound pressure, [ML T ], but it is not a kind of
sound pressure. Nor is absorption with the dimensions [L ] a kind of area.
1. Scope (SI) (the Modernized Metric System)
E 413 Classification for Rating Sound Insulation
1.1 This terminology covers terms and definitions related to
E 492 Test Method for Laboratory Measurement of Impact
environmental acoustics. Only definitions common to two or
Sound Transmission Through Floor-Ceiling Assemblies
more standards under the jurisdiction of Committee E-33 are
Using the Tapping Machine
listed here. The purpose of this terminology is to promote
2.2 ANSI Standard:
uniformity of key definitions. Definitions pertinent to only one
ANSI S1.4 Specification for Sound Level Meters
standard and exceptions to the definitions listed below are
ANSI S1.6 Preferred Frequencies, Frequency Levels, and
contained in the individual standards and should be used when
Band Numbers for Acoustical Measurements
following those standards.
ANSI S1.11 Octave-Band and Fractional Octave-Band Ana-
2. Referenced Documents log and Digital Filters, Specifications for
2.1 ASTM Standards:
3. Terminology
C 423 Test Method for Sound Absorption and Sound Ab-
3.1 Terms and Definitions:
sorption Coefficients by the Reverberation Room Method
−4 −1
E 90 Test Method for Laboratory Measurement of Airborne
acoustic impedance, Z [ R + jX; [ML T ]; mks acoustic
Sound Transmission Loss of Building Partitions
ohm (Pa·s/m )—of a surface, for a given frequency, the
E 336 Test Method for Measurement of Airborne Sound
complex quotient obtained when the sound pressure aver-
Insulation in Buildings
aged over the surface is divided by the volume velocity
E 380 Practice for Use of the International System of Units
through the surface. The real and imaginary components are
called, respectively, acoustic resistance and acoustic reac-
tance.
acoustical material—any material considered in terms of its
This terminology is under the jurisdiction of ASTM Committee E-33 on
Environmental Acoustics and is the direct responsibility of Subcommittee E33.07 on
Definitions and Editorial.
Current edition approved February 10, 2000. Published May 2000. Originally
Annual Book of ASTM Standards, Vol 14.02.
published as C 634 – 69. Last previous edition C 634 – 99b.
Available from American National Standards Institute, 11 W. 42nd St., 13th
Annual Book of ASTM Standards, Vol 04.06.
Floor, New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
C 634
acoustical properties. Commonly and especially, a material
p 5 20 μPa, reference sound pressure.
designed to absorb sound.
background noise—noise from all sources unrelated to a
admittance ratio, yrc [ grc−jbrc; [dimensionless]—the
particular sound that is the object of interest. Background
reciprocal of the impedance ratio. The real and imaginary
noise may include airborne, structureborne, and instrument
components are called, respectively, conductance ratio and
noise.
susceptance ratio.
−2 −1
characteristic impedance of the medium, rc; [ML T ];
airborne sound—sound that arrives at the point of interest,
mks rayl (Pa·s/m)—the specific normal acoustic impedance
such as one side of a partition, by propagation through air.
−4 −1
at a point in a plane wave in a free field. It is a pure specific
airflow resistance, R; [ML T ]; mks acoustic ohm (Pa·s/
resistance since the sound pressure and the particle velocity
m )—the quotient of the air pressure difference across a
are in phase and it is equal in magnitude to the product of the
specimen divided by the volume velocity of airflow through
density of the medium, r, and the speed of sound in the
the specimen. The pressure difference and the volume
medium, c. Its value when the medium is air at 20°C and
velocity may be either steady or alternating.
−3 −1 2
101.325 kPa is 413 mks rayl (Pa·s/m).
airflow resistivity, r ; [ML T ]; mks rayl/m (Pa·s/m )—of a
o
cutoff frequency—of an anechoic wedge or set of wedges, the
homogeneous material, the quotient of its specific airflow
lowest frequency above which the normal incidence sound
resistance divided by its thickness.
absorption coefficient is at least 0.990.
ambient noise—the composite of airborne sound from many
damp—to cause a loss or dissipation of the oscillatory or
sources near and far associated with a given environment.
vibrational energy of an electrical or mechanical system.
No particular sound is singled out for interest.
−1
decay rate, d; [T ]; dB/s—for airborne sound, the rate of
arithmetic mean sound pressure level—of several related
decrease of sound pressure level after the source of sound
sound pressure levels measured at different positions or
has stopped; for vibration, the rate of decrease of vibratory
different times, or both, in a specified frequency band, the
acceleration, velocity, or displacement level after the exci-
sum of the sound pressure levels divided by the number of
tation has stopped.
levels.
decibel, dB—the term used to identify ten times the common
DISCUSSION—The arithmetic mean sound pressure level is sometimes
logarithm of the ratio of two like quantities proportional to
used to approximate the average sound pressure level. The accuracy
power or energy. (See level, sound transmission loss.)
of this approximation depends upon the range of sound pressure levels.
0.1
Thus, one decibel corresponds to a power ratio of 10 and
0.1 n
average sound pressure level—of several related sound
n decibels corresponds to a power ratio of (10 ) .
pressure levels measured at different positions or different
DISCUSSION—Since the decibel expresses the ratio of two like
times, or both, in a specified frequency band, ten times the
quantities, it has no dimensions. It is, however, common practice to
common logarithm of the arithmetic mean of the squared
treat “decibel” as a unit as, for example, in the sentence, “The average
pressure ratios from which the individual levels were de-
sound pressure level in the room is 45 decibels.”
rived.
diffraction—a change in the direction of propagation of sound
DISCUSSION—1—An average sound pressure level obtained by aver-
energy in the neighborhood of a boundary discontinuity,
aging the A-weighted sound level continuously over a specified period
such as the edge of a reflective or absorptive surface.
is called the time-average sound level.
diffuse sound field—the sound in a region where the intensity
DISCUSSION—2—Since, by definition, a squared pressure ratio, p /
i
2 L /10
i
p , is equal to 10 , average sound pressure level is calculated from is the same in all directions and at every point.
the expression:
direct sound field—the sound that arrives directly from a
n
source without reflection.
L /10
¯ i
L 5 10 log 10
S D
i (
n dummy microphone—a microphone substitute which has
i 5 1
electrical characteristics identical to a functional micro-
where:
phone, but which has essentially no sensitivity to incident
¯
L 5 average sound pressure level, dB,
p
sound pressure.
n 5 number of individual sound pressure levels,
field sound transmission class, FSTC—sound transmission
p 5 rms pressure at an individual position or time, or both,
i
class calculated in accordance with Classification E 413
Pa,
using values of field transmission loss.
p 5 20 μPa, reference sound pressure, and
field transmission loss, FTL—sound transmission loss mea-
L 5 an individual sound pressure level, dB.
i
sured in accordance with Annex A1 of Test Method E 336.
If conditions warrant, an integral expression may be used:
flanking transmission—transmission of sound from the
source to a receiving location by a path other than that under
t2
2 2
¯
L 5 10 log ~p ~t!/p ! dt
p S * 0 D
consideration.
T t1
impedance ratio, z/rc [ r/rc + jx/rc; [dimensionless]—the
where:
ratio of the specific normal acoustic impedance at a surface
¯
L 5 average sound pressure level during a specified time
p to the characteristic impedance of the medium. The real and
interval, dB,
imaginary components are called, respectively, resistance
T 5 t −t 5 a specified time interval, s, min, h, or day,
2 1
ratio and reactance ratio.
p(t) 5 instantaneous sound pressure, Pa, and
impact insulation class, IIC—a single-number rating derived
C 634
from measured values of normalized impact sound pressure values of noise reduction. It provides an estimate of the
levels in accordance with Annex A1 of Test Method E 492. sound isolation between two enclosed spaces that are acous-
It provides an estimate of the impact sound insulating tically connected by one or more paths.
performance of a floor-ceiling assembly.
noise reduction, NR—in a specified frequency band, the
impulsive sound, n—a brief, intrusive sound, such as that
difference between the average sound pressure levels mea-
associated with a tire blowout, operation of a punch press,
sured in two enclosed spaces or rooms due to one or more
the discharge of a firearm, a door slam, or a shout, usually
sound sources in one of them.
characterized by a rapid rise time in the initial pressure pulse
DISCUSSION—It is implied that in each room there is a meaningful
of less than a few milliseconds, and by a decay time of less
average level; that is, that in each room the individual observations are
than a few seconds.
randomly distributed about the average value, with no systematic
variation with position within the permissible measurement region.
DISCUSSION—No mathematical description exists to unequivoJune-
Noise reduction becomes meaningless and should not be used in
cally define the presence of impulsive sound.
situations where this condition is not met.
insertion loss, IL—of a silencer or other sound-reducing
noise reduction coefficient, NRC—a single-number rating
element, in a specified frequency band, the decrease in sound
derived from measured values of sound absorption coeffi-
power level, measured at the location of the receiver, when
cients in accordance with 11.7 of Test Method C 423. It
a sound insulator or a sound attenuator is inserted in the
provides an estimate of the sound absorptive property of an
transmission path between the source and the receiver.
acoustical material.
interference, n—any activity or event that could produce
normal incidence sound absorption coefficient, a ;
anomalous measurements.
n
[dimensionless]— of a surface, at a specified frequency, the
level, L—ten times the common logarithm of the ratio of a
fraction of the perpendicularly incident sound power ab-
quantity proportional to power or energy to a reference
sorbed or otherwise not reflected.
quantity of the same kind. (See sound power level, sound
pressure level.) The quantity so obtained is expressed in normal mode—of a room, one of the possible ways in which
decibels. the air in a room, considered as an elastic body, will vibrate
level reduction, LR—in a specified frequency band, the naturally when subjected to an acoustical disturbance. With
decrease in sound pressure level, measured at the location of each normal mode is associated a resonance frequency and,
the receiver, when a barrier or other sound-reducing element in general, a group of wave propagation directions compris-
is placed between the source and the receiver. ing a closed path.
normalized noise isolation class, NNIC—a single-number
DISCUSSION—Level reduction is a useful measure in circumstances
rating calculated in accordance with Classification E 413
when measures of transmission loss, insertion loss, or noise reduction
using measured values of normalized noise reduction. (See
are not possible.
normalized noise reduction.)
maximum sound level, L [nd], (dB) n—Ten times the
AFmax
normalized noise reduction, NNR—between two rooms, in a
common logarithm of the square of the ratio of the largest
specified frequency band, the value that the noise reduction
frequency-weighted and exponential-time-weighted (or
in a given field test would have if the reverberation time in
other wise time-averaged) sound pressure during the mea-
the receiving room were 0.5 s. NNR is calculated as follows:
surement period to the square of the reference-sound-
NNR 5 NR 1 10 log ~T/0.5!
pressure of 20 micro pascals. The subscripts designate the
frequency weighting (A or C), and time the weighting or
where:
averaging (F for fast, S for slow, I for impulse, or a number
NR 5 noise reduction, dB and
with proper units to indicate time interval).
T 5 reverberation time in receiving room, s.
DISCUSSION—The time weighting or averaging time must be speci-
DISCUSSION—The normalized noise reduction is intended to approxi-
fied. The frequency weighting should be specified; otherwise,
mate the noise reduction that would exist between two ordinarily
A-weighting will be understood.
furnished rooms.
measurement plan, n—a document formally describing the
octave band, n—a band of sound frequencies for which the
sp
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