ASTM C634-22

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C634 − 22
Standard Terminology Relating to
Building and Environmental Acoustics
This standard is issued under the fixed designation C634; 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 (´) 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 several
items: an abbreviation or a symbol, or both, the dimensions of quantities, the measurement units, and
the part of speech. The abbreviation, where applicable, indicates the term as typically referenced. The
symbol 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
−1
by the time involved. The dimensions are [LT ], the negative exponent indicating division. The
measurement units are 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 IEEE/ ASTM SI 10. Some conversion factors are listed in Section 6 of this document for
convenient reference.
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 responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This terminology covers terms, related definitions, and
mine the applicability of regulatory limitations prior to use.
descriptions of terms used or likely to be used in building and
1.4 This international standard was developed in accor-
environmental acoustics standards. Definitions of terms are
dance with internationally recognized principles on standard-
special-purpose definitions that are consistent with the standard
ization established in the Decision on Principles for the
definitions but are written to ensure that a specific building and
Development of International Standards, Guides and Recom-
environmental acoustics standard is properly understood and
mendations issued by the World Trade Organization Technical
precisely interpreted. The primary focus of this document is
Barriers to Trade (TBT) Committee.
upon terms, definitions and descriptions found within standards
under the jurisdiction of ASTM Committee E33; however,
2. Referenced Documents
terms, definitions and descriptions that are of general interest to
2.1 ASTM Standards:
the field of acoustics are also included.
C367/C367M Test Methods for Strength Properties of Pre-
1.2 This building and environmental acoustics standard
fabricated Architectural Acoustical Tile or Lay-In Ceiling
cannot be used to provide quantitative measures.
Panels
1.3 This standard does not purport to address all of the C384 Test Method for Impedance and Absorption of Acous-
safety concerns, if any, associated with its use. It is the tical Materials by Impedance Tube Method
C423 Test Method for Sound Absorption and Sound Absorp-
tion Coefficients by the Reverberation Room Method
This terminology is under the jurisdiction of ASTM Committee E33 on
Building and Environmental Acoustics and is the direct responsibility of Subcom-
mittee E33.07 on Definitions and Editorial. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2022. Published February 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1969. Last previous edition approved in 2021 as C634 – 13 (2021). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C0634-22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C634 − 22
C522 Test Method for Airflow Resistance of Acoustical E1265 Test Method for Measuring Insertion Loss of Pneu-
Materials matic Exhaust Silencers
E1289 Specification for Reference Specimen for Sound
C635/C635M Specification for Manufacture, Performance,
Transmission Loss
and Testing of Metal Suspension Systems for Acoustical
E1332 Classification for Rating Outdoor-Indoor Sound At-
Tile and Lay-in Panel Ceilings
tenuation
C636/C636M Practice for Installation of Metal Ceiling Sus-
E1374 Guide for Office Acoustics and Applicable ASTM
pension Systems for Acoustical Tile and Lay-In Panels
Standards
E90 Test Method for Laboratory Measurement of Airborne
E1414/E1414M Test Method for Airborne Sound Attenua-
Sound Transmission Loss of Building Partitions and
tion Between Rooms Sharing a Common Ceiling Plenum
Elements
E1503 Test Method for Conducting Outdoor Sound Mea-
E336 Test Method for Measurement of Airborne Sound
surements Using a Statistical Sound Analysis System
Attenuation between Rooms in Buildings
E1573 Test Method for Measurement and Reporting of
E413 Classification for Rating Sound Insulation
Masking Sound Levels Using A-Weighted and One-Third-
E477 Test Method for Laboratory Measurements of Acous-
Octave-Band Sound Pressure Levels
tical and Airflow Performance of Duct Liner Materials and
E1574 Test Method for Measurement of Sound in Residen-
Prefabricated Silencers
tial Spaces
E492 Test Method for Laboratory Measurement of Impact
E1686 Guide for Applying Environmental Noise Measure-
Sound Transmission Through Floor-Ceiling Assemblies
ment Methods and Criteria
Using the Tapping Machine
E1704 Guide for Specifying Acoustical Performance of
E557 Guide for Architectural Design and Installation Prac-
Sound-Isolating Enclosures
tices for Sound Isolation between Spaces Separated by
E1780 Guide for Measuring Outdoor Sound Received from
Operable Partitions
a Nearby Fixed Source
E596 Test Method for Laboratory Measurement of Noise
E2179 Test Method for Laboratory Measurement of the
Reduction of Sound-Isolating Enclosures
Effectiveness of Floor Coverings in Reducing Impact
E756 Test Method for Measuring Vibration-Damping Prop-
Sound Transmission Through Concrete Floors
erties of Materials
E2202 Practice for Measurement of Equipment-Generated
E795 Practices for Mounting Test Specimens During Sound
Continuous Noise for Assessment of Health Hazards
Absorption Tests
E2235 Test Method for Determination of Decay Rates for
E966 Guide for Field Measurements of Airborne Sound Use in Sound Insulation Test Methods
Attenuation of Building Facades and Facade Elements E2249 Test Method for Laboratory Measurement of Air-
E989 Classification for Determination of Single-Number borne Transmission Loss of Building Partitions and Ele-
Metrics for Impact Noise ments Using Sound Intensity
E2459 Guide for Measurement of In-Duct Sound Pressure
E1007 Test Method for Field Measurement of Tapping
Levels from Large Industrial Gas Turbines and Fans
Machine Impact Sound Transmission Through Floor-
E2611 Test Method for Normal Incidence Determination of
Ceiling Assemblies and Associated Support Structures
Porous Material Acoustical Properties Based on the Trans-
E1014 Guide for Measurement of Outdoor A-Weighted
fer Matrix Method
Sound Levels
E2638 Test Method for Objective Measurement of the
E1042 Classification for Acoustically Absorptive Materials
Speech Privacy Provided by a Closed Room
Applied by Trowel or Spray
E2963 Test Method for Laboratory Measurement of Acous-
E1050 Test Method for Impedance and Absorption of
tical Effectiveness of Ship Noise Treatments Laboratory
Acoustical Materials Using a Tube, Two Microphones and
Measurement of Acoustical Effectiveness for Marine
a Digital Frequency Analysis System
Bulkhead and Deck Treatments
E1110 Classification for Determination of Articulation Class
E2964 Test Method for Measurement of the Normalized
E1111/E1111M Test Method for Measuring the Interzone
Insertion Loss of Doors
Attenuation of Open Office Components
E3090/E3090M Test Methods for Strength Properties of
E1123 Practices for Mounting Test Specimens for Sound
Metal Ceiling Suspension Systems
Transmission Loss Testing of Naval and Marine Ship
E3091 Specification for Systems to Measure Sound Levels
Bulkhead Treatment Materials
E3133 Test Method for Laboratory Measurement of Floor
E1124 Test Method for Field Measurement of Sound Power
Impact Sound Radiation Using the Tapping Machine
Level by the Two-Surface Method
(Withdrawn 2023)
E1130 Test Method for Objective Measurement of Speech
E3222 Classification for Determination of High-frequency
Privacy in Open Plan Spaces Using Articulation Index
Impact Sound Ratings
E1179 Specification for Sound Sources Used for Testing
IEEE/ ASTM SI 10 Standard for Use of the International
Open Office Components and Systems
E1222 Test Method for Laboratory Measurement of the
Insertion Loss of Pipe Lagging Systems 3
The last approved version of this historical standard is referenced on www.ast-
E1264 Classification for Acoustical Ceiling Products m.org.
C634 − 22
System of Units (SI): The Modern Metric System 3.2.2 A specific definition of a given term is applicable to
2.2 ASA/ANSI Standards: the standard or standards in which the term is described and
used.
ASA/ANSI S1.1-2013 Acoustical Terminology
ASA/ANSI S1.4-2014, Part 1 / NAIS IEC 61672-1 Electroa- 3.2.3 Different definitions of the same term are acceptable
provided each one is consistent with and is not in conflict with
coustics – Sound Level Meters – Part 1: Specifications
ASA/ANSI S1.6-2016 Preferred Frequencies and Filter the standard definition for the same term, that is, the general
concept the term describes.
Band Center Frequencies for Acoustical Measurements
ASA/ANSI S1.11-2014, Part 1/NAIS IEC 61260-1 Electroa- 3.2.4 If a standard under the jurisdiction of ASTM Commit-
tee E33 specially defines a term, i.e. provides a definition
coustics – Octave-Band and Fractional Octave-Band Ana-
log and Digital Filters – Part 1: Specifications different in any way from what is given in Section 4 of
Terminology C634, that standard shall list the term and its
ANSI S1.43-1997 (R2007) Specifications For Integrating-
Averaging Sound Level Meters description under the subheading, Definitions of Terms Specific
to This Standard.
ASA/ANSI S12.9-2013 Quantities And Procedures For De-
scription And Measurement Of Environmental Sound – 3.2.4.1 Discussion—The mandatory language of section
3.2.4 is consistent with the mandatory language from §E2 of
Part 1: Basic Quantities And Definitions
Form and Style for ASTM Standards (April 2020) and with the
2.3 Other Standards:
ASTM Committee E33 bylaws in place when this standard was
IEEE P260.4-2018 IEEE Standard for Letter Symbols and
published; it reflects a situation that exists, it does not prescribe
Abbreviations for Quantities Used in Acoustics
anything.
ASME B1.20.1-2013 (R2018) Pipe Threads, General
Purpose, Inch
3.3 Definitions for some terms associated with building and
2017 ASHRAE Handbook Fundamentals, Chapter 37, Mea-
environmental acoustic issues and not included in Terminology
surement and Instruments
C634 are found in ISO/TR 25417 or IEEE P260.4. When
ISO 9614-1:1993 Acoustics — Determination of Sound
discrepancies exist, the definition in Terminology C634 shall
Power Levels of Noise Sources Using Sound Intensity —
prevail.
Part 1: Measurement at Discrete Points
4. Terminology
ISO 9614-2:1996 Acoustics — Determination of Sound
Power Levels of Noise Sources Using Sound Intensity —
4.1 Terms and their standard definitions within the scope of
Part 2: Measurement by Scanning
this standard are given in Section 4 in alphabetical order.
ISO 9614-3:2002 Acoustics — Determination of Sound
Appendix X1 contains the definitions of terms from the
Power Levels of Noise Sources Using Sound Intensity —
“Definitions of Terms Specific to This Standard” sections from
Part 3: Precision Method for Measurement by Scanning
all standards under the jurisdiction of ASTM Committee E33.
ISO 15186-1:2000 Acoustics — Measurement of Sound
4.2 Discussions associated with definitions are printed di-
Insulation in Buildings and of Building Elements Using
rectly under the appropriate definition. The date following each
Sound Intensity — Part 1: Laboratory Measurements
definition or discussion indicates the year of introduction or of
ISO 16283-1:2014 Acoustics — Field measurement of
latest revision of that particular definition or discussion.
sound insulation in buildings and of building elements —
4.2.1 Discussion—If the year of introduction or last review
Part 1: Airborne sound Insulation
of the term and its definition or discussion is unknown, the year
ISO/TR 25417:2007 Acoustics — Definitions of basic quan-
stated indicates the year the definition or discussion was
tities and terms
brought into compliance with this paradigm.
IEC 61043 Ed. 1.0 b:1993 Electroacoustics — Instruments
4.3 If the exact term sought by the user cannot be found in
For The Measurement Of Sound Intensity — Measure-
4.4, it is possible that the term may exist within Section 5,
ments With Pairs Of Pressure Sensing Microphones
Compound Terms.
IEC 61094-4 (1995) Measurement Microphones Part 4:
Specifications for Working Standard Microphones
4.4 Terms and their Definitions:
−4 −1
acoustic impedance, Z[ML T ], (mks acoustic ohm or
3. Significance and Use
Pa·s/m ), n—of a surface, for a given frequency, the complex
3.1 Definitions—Terms and related definitions given in Sec- quotient obtained when the sound pressure averaged over the
tion 4 are intended for use uniformly and consistently in all surface is divided by the volume velocity through the
building and environmental acoustic test standards in which surface. The real and imaginary components are called,
they appear. respectively, acoustic resistance and acoustic reactance.
3.2 Definitions of Terms Specific to Each Standard: Z[R1jX (1)
3.2.1 As indicated in Section 4, terms and their definitions
where:
are intended to provide a precise understanding and interpre-
R = the real component of acoustic impedance, and
tation of the building and environmental acoustic test standards
X = the imaginary component of acoustic impedance.
in which they appear.
(2021)
acoustical barrier, n—contiguous objects such as solid walls,
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. buildings, or earthen berms that substantially block the direct
C634 − 22
n
path of sound between a source and receiver, and which, if
L /10
¯
i
L 5 10log 10 (3)
S D
p 10 (
they have an open edge or edges allowing diffraction around n
i51
them, are sufficiently wide and high to cause significant
where:
reduction of the sound traveling from the source to the
¯
L = average sound pressure level, dB,
p
receiver. (2021)
n = number of individual sound pressure levels,
p = rms pressure at an individual position or time, or both,
acoustical material, n—any material considered in terms of its
i
Pa,
acoustical properties. Commonly and especially, a material
p = 20 μPa, reference sound pressure, and
designed to absorb sound. (2021)
L = an individual sound pressure level, dB.
i
admittance ratio, yρc[dimensionless], n—the reciprocal of the
If conditions warrant, an integral expression may be used:
impedance ratio. The real and imaginary components are
1 t2
2 2
¯
called, respectively, conductance ratio and susceptance
L 5 10log p t /p dt (4)
* ~ ~ ! !
S D
p 10 0
T t1
ratio. (2021)
where:
ypc[gpc 2 jbpc (2)
¯
L = average sound pressure level during a specified time
p
where:
interval, dB,
gρc = the real component of admittance ratio, and
T = t − t = a specified time interval, s, min, h, or day,
2 1
bρc = the imaginary component of admittance ratio.
p(t) = instantaneous sound pressure, Pa, and
p = 20 μPa, reference sound pressure.
(2021)
(2021)
airborne sound, n—sound that arrives at the point of interest,
such as one side of a partition, by propagation through air. background noise, n—noise from all sources unrelated to a
(2021)
particular sound that is the object of interest. Background
noise may include airborne, structureborne, and instrument
−4 −1
airflow resistance, R[ML T ], (mks acoustic ohm or Pa·s/
noise. (2021)
m ), n—the quotient of the air pressure difference across a
cutoff frequency, n—of an anechoic wedge or set of wedges,
specimen divided by the volume velocity of airflow through
the lowest frequency above which the normal incidence
the specimen. The pressure difference and the volume
sound absorption coefficient is at least 0.990. (2021)
velocity may be either steady or alternating. (2021)
−3 −1 2
damp, v—to cause a loss or dissipation of the oscillatory or
airflow resistivity, r [ML T ], (mks rayl/m or Pa·s/m ),
o
vibrational energy of an electrical or mechanical system.
n—of a homogeneous material, the quotient of its specific
(2021)
airflow resistance divided by its thickness. (2021)
−1
decay rate, d[T ], (dB/s), n—for airborne sound, the rate of
ambient noise, n—the composite of airborne sound from many
decrease of sound pressure level after the source of sound
sources near and far associated with a given environment.
has stopped; for vibration, the rate of decrease of vibratory
No particular sound is singled out for interest. (2021)
acceleration, velocity, or displacement level after the exci-
arithmetic mean sound pressure level, n—of several related
tation has stopped. (2021)
sound pressure levels measured at different positions or
decibel, dB[dimensionless], n—the term used to identify ten
different times, or both, in a specified frequency band, the
times the common logarithm of the ratio of two like
sum of the sound pressure levels divided by the number of
quantities proportional to power or energy. (See level, sound
levels. (2021)
transmission loss.) Thus, one decibel corresponds to a
DISCUSSION—The arithmetic mean sound pressure level is sometimes
0.1
power ratio of 10 and n decibels corresponds to a power
used to approximate the average sound pressure level. The accuracy
0.1 n
ratio of (10 ) . (2021)
of this approximation depends upon the range of sound pressure levels.
DISCUSSION—Since the decibel expresses the ratio of two like
(2021)
quantities, it has no dimensions. It is, however, common practice to
¯
average sound pressure level, L [dimensionless], n—of sev- treat “decibel” as a unit as, for example, in the sentence, “The average
p
sound pressure level in the room is 45 decibels.” (2021)
eral related sound pressure levels measured at different posi-
tions or different times, or both, in a specified frequency band,
diffraction, n—a change in the direction of propagation of
ten times the common logarithm of the arithmetic mean of the
sound energy in the neighborhood of a boundary
squared pressure ratios from which the individual levels were
discontinuity, such as the edge of a reflective or absorptive
derived. (2021)
surface. (2021)
DISCUSSION—1—An average sound pressure level obtained by aver-
diffuse sound field, n—the sound in a region where the sound
aging the A-weighted sound level continuously over a specified period
intensity is the same in all directions and at every point.
is called the time-average sound level. (2021)
(2021)
DISCUSSION—2—Since, by definition, a squared pressure ratio, p /
i
2 L /10
i
direct sound field, n—the sound that arrives directly from a
p , is equal to 10 , average sound pressure level is calculated from
the expression: source without reflection. (2021)
C634 − 22
dummy microphone, n—a microphone substitute which has at the location of the receiver, when a barrier or other
electrical characteristics identical to a functional sound-reducing element is placed between the source and the
microphone, but which has essentially no sensitivity to receiver. (2021)
DISCUSSION—Level reduction is a useful measure in circumstances
incident sound pressure. (2021)
when measures of transmission loss, insertion loss, or noise reduction
field sound transmission class, FSTC[dimensionless],
are not possible. (2021)
n—sound transmission class calculated in accordance with
maximum sound level, L [dimensionless], (dB), n—Ten
AFmax
Classification E413 using values of field transmission loss.
times the common logarithm of the square of the ratio of the
(2021)
largest frequency-weighted and exponential-time-weighted
field transmission loss, FTL[dimensionless], n—sound trans-
(or otherwise time-averaged) sound pressure during the
mission loss measured in accordance with Annex A1 of Test
measurement period to the square of the reference-sound-
Method E336. (2021)
pressure of 20 μPa. The subscripts designate the frequency
weighting (A or C), and time the weighting or averaging (F
flanking transmission, n—transmission of sound from the
for fast, S for slow, I for impulse, or a number with proper
source to a receiving location by a path other than that under
units to indicate time interval). (2021)
consideration. (2021)
DISCUSSION—The time weighting or averaging time must be speci-
impact insulation class, IIC[dimensionless], n—a single-
fied. The frequency weighting should be specified; otherwise,
number rating derived from measured values of normalized A-weighting will be understood. (2021)
impact sound pressure levels in accordance with Annex A1
measurement plan, n—a document formally describing the
of Test Method E492. It provides an estimate of the impact
specific steps to be taken during a measurement, including
sound insulating performance of a floor-ceiling assembly.
any unique requirements. (2021)
(2021)
measurement set, n—the set of acoustical measurements and
impedance ratio, z/ρc[dimensionless], n—the ratio of the
related data obtained at a single measurement location
specific normal acoustic impedance at a surface to the
during a specified time interval. (2021)
characteristic impedance of the medium. The real and
DISCUSSION—The specified time interval may include brief docu-
imaginary components are called, respectively, resistance
mented periods during which data recording or analysis are paused for
ratio and reactance ratio. (2021)
the purpose of eliminating the effects of interference. (2021)
z⁄pc[r⁄pc1jx⁄pc (5)
metric sabin, [L ], n—the unit of measure of sound absorption
where:
in the metre-kilogram-second system of units. (2021)
r/ρc = the real component of impedance ratio, and
noise isolation class, NIC[dimensionless], n—a single-number
x/ρc = the imaginary component of impedance ratio.
rating calculated in accordance with Classification E413
(2021)
using measured values of noise reduction. It provides an
estimate of the sound isolation between two enclosed spaces
impulsive sound, n—a brief, intrusive sound, such as that
that are acoustically connected by one or more paths. (2021)
associated with a tire blowout, operation of a punch press,
the discharge of a firearm, a door slam, or a shout, usually
noise reduction, NR[dimensionless], n—the difference be-
characterized by a rapid rise time in the initial pressure pulse
tween the average sound pressure levels either at two well
of less than a few milliseconds, and by a decay time of less
defined locations based on existing conditions, or at a single
than a few seconds. (2021)
location before and after some mitigation measure is imple-
DISCUSSION—No mathematical description exists to unequivocally
mented. (2021)
define the presence of impulsive sound. (2021)
DISCUSSION—Specific standards may use a more restrictive definition
insertion loss, IL[dimensionless], n—of a silencer or other related to the difference either between two locations or before and after
a mitigation measure, and some standards may require the noise
sound-reducing element, in a specified frequency band, the
reduction to be measured in specified frequency bands. (2021)
decrease in sound power level, measured at the location of
the receiver, when a sound insulator or a sound attenuator is
noise reduction coefficient, NRC[dimensionless], n—a single-
inserted in the transmission path between the source and the
number rating, the average, rounded to the nearest 0.05, of
receiver. (2021)
the sound absorption coefficients of a material for the four
one-third octave bands at 250 Hz, 500 Hz, 1000 Hz, and
interference, n—any activity or event that could produce
2000 Hz, inclusive, measured according to the test method
anomalous measurements. (2021)
described in Test Method C423. (2021)
level, L[dimensionless], n—ten times the common logarithm of
normal incidence sound absorption coefficient,
the ratio of a quantity proportional to power or energy to a
α [dimensionless], n—of a surface, at a specified frequency,
reference quantity of the same kind. (See sound power
n
the fraction of the perpendicularly incident sound power
level, sound pressure level.) The quantity so obtained is
absorbed or otherwise not reflected. (2021)
expressed in decibels. (2021)
level reduction, LR[dimensionless], n—in a specified fre- normal mode, n—of a room, one of the possible ways in which
quency band, the decrease in sound pressure level, measured the air in a room, considered as an elastic body, will vibrate
C634 − 22
naturally when subjected to an acoustical disturbance. With percentile level, L [dimensionless], (dB), n—of a time varying
x
each normal mode is associated a resonance frequency and, level, the level exceeded x percent of the time during the
in general, a group of wave propagation directions compris- stated measurement period. (2021)
DISCUSSION—Percentile levels are affected by measurement param-
ing a closed path. (2021)
eters such as bandwidth, frequency weighting, time weighting, and
normalized noise isolation class, NNIC[dimensionless], n—a
sampling rate that must be explicitly stated. (2021)
single-number rating calculated in accordance with Classi-
pink noise, n—noise with a continuous frequency spectrum
fication E413 using measured values of normalized noise
and with equal power per constant percentage bandwidth.
reduction. (See normalized noise reduction.) (2021)
For example, equal power in any one-third octave band.
normalized noise reduction, NNR[dimensionless], (2021)
n—between two rooms, in a specified frequency band, the
receiving room, n—in architectural acoustical measurements,
value that the noise reduction in a given field test would have
the room in which the sound transmitted from the source
if the reverberation time in the receiving room were 0.5 s.
room is measured. (2021)
NNR is calculated as follows:
reverberant sound field, n—the sound in an enclosed or
NNR 5 NR110log T/0.5 (6)
~ !
partially enclosed space that has been reflected repeatedly or
where:
continuously from the boundaries. (2021)
NR = noise reduction, dB and
reverberation, n—the persistence of sound in an enclosed or
T = reverberation time in receiving room, s.
partially enclosed space after the source of sound has
(2021)
stopped; by extension, in some contexts, the sound that so
DISCUSSION—The normalized noise reduction is intended to approxi-
persists. (2021)
mate the noise reduction that would exist between two ordinarily
furnished rooms. (2021)
reverberation room, n—a room so designed that the reverber-
ant sound field closely approximates a diffuse sound field,
octave band, n—a band of sound frequencies for which the
both in the steady state when the sound source is on, and
highest frequency in the range is (within 2%) twice the
during decay after the source of sound has stopped. (2021)
lowest frequency. The position of the band is identified by
the rounded geometric mean of the highest frequency and the
reverberation time, T [T], (s), n—for airborne sound, the
lowest frequency of the band. The nominal mid-band fre-
time it takes a reverberant sound field to decay 60 dB after
quencies of “preferred” octave bands as defined in ANSI
the source is interrupted. (2021)
S1.6 fall in the series 16, 31.5, 63, 125, 250, 500, 1000 Hz
DISCUSSION—If an ambient sound field limits the ability to measure
etc. (2021) 60 dB of decay, then this time can be extrapolated from the measure of
the shorter decay. (2021)
octave band sound pressure level, OBSPL or L where f
pl/lf
sabin, [L ], n—the unit of measure of sound absorption in the
indicates the nominal center frequency of a specific band if
inch-pound system. (2021)
applicable[dimensionless], (dB), n—sound pressure level for
sound filtered using an octave-band filter meeting the re-
self-noise, n—extraneous non-acoustical signals, generated or
quirements of ANSI S1.11. (2021)
induced in a measurement system. (2021)
outdoor-indoor transmission loss, OITL[dimensionless],
sound absorption, n—(1) the process of dissipating sound
n—of a building facade, in a specified frequency band, ten
energy. (2) the property possessed by materials, objects and
times the common logarithm of the ratio of the airborne
structures such as rooms of absorbing sound energy. (3) A,
sound power incident on the exterior of the facade to the 2
[L ]; metric sabin—in a specified frequency band, the
sound power transmitted by the facade and radiated to the
measure of the magnitude of the absorptive property of a
interior. The quantity so obtained is expressed in decibels.
material, an object, or a structure such as a room. (2021)
(2021)
DISCUSSION—Sound energy passing through a wall or opening may
be regarded as being absorbed in certain calculations. (2021)
−1
particle velocity, u[LT ], (m/s), n—a fluctuating velocity
superimposed by the presence of sound on the other veloci-
sound absorption average, SAA[dimensionless], n—a single
ties the particles of the medium may have. In analogy with number rating, the average, rounded to the nearest 0.01, of
alternating voltage its magnitude can be expressed in several
the sound absorption coefficients of a material for the twelve
ways, such as instantaneous particle velocity or peak particle one-third octave bands from 200 through 2500 Hz, inclusive,
velocity, but the unqualified term means root-mean-square
measured according to the test method described in Test
particle velocity. In air, the other velocities are those due to Method C423. (2021)
thermal agitation and wind currents. (2021)
sound absorption coefficient, α[dimensionless], (metric sabin/
peak sound pressure level, L [dimensionless], (dB), n—ten m ), n—of a surface, in a specified frequency band, the
PK
times the common logarithm of the square of the ratio of the measure of the absorptive property of a material as approxi-
largest absolute value of the instantaneous sound pressure in mated by the method of Test Method C423. Ideally, the
a stated frequency band during a specified time interval to fraction of the randomly incident sound power absorbed or
the reference sound pressure of 20 μPa. (2021) otherwise not reflected. (2021)
C634 − 22
sound attenuation, n—the reduction of sound pressure as it source. In general, the rate of flow of sound energy, whether
travels from the source to a receiving location. Sound from a source, through an area, or into an absorber. (2021)
absorption is often involved as, for instance, in a lined duct.
sound power level, L [dimensionless], n—of airborne sound,
W
Spherical spreading and scattering are other attenuation
ten times the common logarithm of the ratio of the sound
mechanisms. (2021)
power under consideration to the standard reference power
2 −2
sound energy, E[ML T ], (J), n—energy added to an elastic
of 1 pW. The quantity so obtained is expressed in decibels.
medium by the presence of sound, consisting of potential
(2021)
energy in the form of deviations from static pressure and of
−1 −2
sound pressure, p[ML T ], (Pa), n—a fluctuating pressure
kinetic energy in the form of particle velocity. (2021)
superimposed on the static pressure by the presence of
sound insulation, n—the capacity of a structure to prevent
sound. In analogy with alternating voltage its magnitude can
sound from reaching a receiving location. Sound energy is
be expressed in several ways, such as instantaneous sound
not necessarily absorbed; impedance mismatch, or reflection
pressure or peak sound pressure, but the unqualified term
back toward the source, is often the principal mechanism.
means root-mean-square sound pressure. In air, the static
(2021)
pressure is barometric pressure. (2021)
DISCUSSION—Sound insulation is a matter of degree. No partition is a
sound pressure level, L [dimensionless], n—of airborne
perfect insulator of sound. (2021)
p
sound, ten times the common logarithm of the ratio of the
−3 2
sound intensity, I[MT ], (W/m ), n—the quotient obtained
square of the sound pressure under consideration to the
when the average rate of energy flow in a specified direction
square of the standard reference pressure of 20 μPa. The
and sense is divided by the area, perpendicular to that
quantity so obtained is expressed in decibels. (2021)
direction, through or toward which it flows. The intensity at
DISCUSSION—The pressures are squared because pressure squared,
a point is the limit of that quotient as the area that includes
rather than pressure, is proportional to power or energy. (2021)
the point approaches zero. (2021)
sound transmission class, STC[dimensionless], n—a single-
sound isolation, n—the degree of acoustical separation be-
number rating calculated in accordance with Classification
tween two locations, especially adjacent rooms. (2021)
E413 using values of sound transmission loss. It provides an
DISCUSSION—This qualitative term may be used in lieu of the more
estimate of the performance of a partition in certain common
quantitative term noise reduction. Sound isolation is achieved by using
sound insulation problems. (2021)
sound-insulating or sound-attenuating elements. (2021)
sound transmission coefficient, τ[dimensionless], n—of a
sound level, L [dimensionless], (dB), n—of airborne sound,
AF
partition, in a specified frequency band, the fraction of the
a sound pressure level obtained using a signal to which a
airborne sound power incident on the partition that is
standard frequency-weighting and exponential time weight-
transmitted by the partition and radiated on the other side.
ing has been applied, where the subscript A designates the
(2021)
frequency weighting and the subscript F designates fast
DISCUSSION—Unless qualified, the term denotes the value obtained
exponential time weighting (the A is replaced by C to
when the specimen is exposed to a diffuse sound field as approximated,
designate C-weighting, and the F by either S or I to designate
for example, in reverberation rooms meeting the requirements of Test
slow or impulse time weighting). (2021)
Method E90. (2021)
NOTE 1—Standard frequency-weightings designated A and C, and
sound transmission loss, TL[dimensionless], n—of a
exponential time weightings designated fast, slow, and impulses, are
partition, in a specified frequency band, ten times the
defined in ANSI S1.4, Specification for Sound Level Meters.
common logarithm of the ratio of the airborne sound power
NOTE 2—The frequency-weighting and exponential time weighting
must be specified unless made clear from the context.
incident on the partition to the sound power transmitted by
NOTE 3—The frequency-weighting modifies the amplitude of the signal
the partition and radiated on the other side. The quantity so
as a function of frequency to adjust for differences in perception of sound
obtained is expressed in decibels. (2021)
at different frequencies.
DISCUSSION—Unless qualified, the term denotes the sound transmis-
NOTE 4—In symbols, A-weighted sound level L , at running time, t, is
AF
sion loss obtained when the specimen is exposed to a diffuse sound field
1 t
as approximated, for example, in reverberation rooms meeting the
2 2~t 2 ξ!⁄T
P ~ξ!e dξ
*
A
2` requirements of Test Method E90. (2021)
T
H J
L t 5 10*log (7)
~ !
AF 10
P
o
source room, n—in architectural acoustical measurements,
where: the room that contains the noise source or sources. (2021)
T = the time constant for the time averaging, s (T = 0.125 s for
−2 −1
specific airflow resistance, r[ML T ], (mks rayl or Pa·s/m),
“Fast” time weighting),
n—the product of the airflow resistance of a specimen and its
ξ = a dummy variable of integration,
area. This is equivalent to the quotient of the air pressure
P (ξ) = the squared, instantaneous, time varying, A-weighted sound
A
pressure, Pa, and
difference across the specimen divided by the linear velocity,
P = the reference sound pressure of 20 μPa.
o measured outside the specimen, of airflow through the
specimen. (2021)
(2021)
2 −3 −2 −1
sound power, W[ML T ], (W), n—in a specified frequency specific normal acoustic impedance, z[ML T ], (mks rayl
band, the rate at which acoustic energy is radiated from a or Pa·s/m), n—at a surface, the complex quotient obtained
C634 − 22
when the sound pressure averaged over the surface is divided class, sound transmission
by the component of the particle velocity normal to the coefficient, noise reduction
surface. The real and imaginary components of the specific coefficient, normal incidence sound absorption
normal acoustic impedance are called, respectively, specific coefficient, sound absorption
normal acoustic resistance and specific normal acoustic
coefficient, sound transmission
reactance. (2021) conductance ratio—see admittance ratio
density, sound energy
z[r1jx (8)
energy, sound
where:
energy density, sound
r = the real component of the specific normal acoustic
equivalent continuous sound level, see time-average sound
impedance, and
level
x = the imaginary component of the specific normal acoustic
equivalent sound level, see time-average sound level
impedance.
exponential time weighting—see sound level
fast, sound level
(2021)
fast exponential time weighting—see sound level
thermal insulation, n—a material or assembly of materials
field, diffuse sound
used primarily to provide resistance to heat flow. (2021)
field, direct sound
field, reverberant sound
time-average sound level, TAV or L where the subscript T
AT
frequency, cutoff
is the time of the interval of measurement[dimensionless],
(dB), n—ten times the logarithm to the base ten of the ratio frequency weighted, sound level
impedance, acoustic
of mean-square instantaneous A-weighted sound pressure,
during a stated time interval T, to the square of the standard impedance, specific normal acoustic
reference sound pressure. (2021) impedance of the medium, characteristic
DISCUSSION— Time-average sound level is also termed equivalent
impulse, sound level
sound level or equivalent continuous sound level with corresponding
impulse exponential time weighting—see sound level
abbreviation LEQ and symbol L . (2021)
AeqT
insulation, sound
insulation, thermal
tonal, adj—in reference to audible sound, capable of exciting
an auditory sensation having pitch. (2021) insulation class, impact
intensity, sound
unit, n—measurement, a precisely specified quantity in terms
isolation, sound
of which the magnitudes of other quantities of the same kind
isolation, vibration
can be stated. (2021)
isolation class, noise
vibration isolation, n—a reduction, attained by the use of a level, arithmetic mean sound pressure
resilient coupling, in the capacity of a system to vibrate in level, sound
response to mechanical excitation. (2021)
level, sound power
level, sound pressure
white noise, n—noise with a continuous frequency spectrum
loss, field transmission
and with equal power per unit bandwidth. For example,
loss, insertion
equal power in any band of 100-Hz width. (2021)
loss, sound transmission
5. Compound Terms material, acoustical
mode, normal
5.1 The definitions of compound terms may be found in the
noise, ambient
alphabetical section under the word in boldface type as listed
noise, background
below.
noise, pink
A-weighted, sound level
noise, white
absorption, sound
noise isolation class, normalized
absorption coefficient, normal incidence sound
noise reduction, normalized
absorption coefficient, sound
normal acoustic admittance, specific
acoustic admittance, specific normal
normal acoustic impedance, specific
acoustic impedance, specific normal
power, sound
acoustic reactance—see acoustic impedance
power level, sound
acoustic resistance—see acoustic impedance
pressure, sound
admittance, specific normal acoustic
pressure level, arithmetic mean sound
airflow resistance, specific
attenuation, sound pressure level, average sound
pressure level, equivalent sound—see average sound
C-weighted, sound level
class, field sound transmission pressure level
pressure level, sound
class, impact insulation
class, noise isolation rate, decay
C634 − 22
TABLE 1 Conversion Factors
ratio, admittance
ratio, conductance—see admittance ratio multiply
Quantity to convert from to
by
ratio, impedance
acoustic cgs acoustic ohm mks acoustic ohm 10
ratio, reactance—see impedance ratio
impedance (Pa·s/m )
ratio, resistance—see impedance ratio
specific acoustic cgs rayl mks rayl (Pa·s/m) 10
impedance
ratio, susceptance—see admittance ratio
airflow resistivity cgs rayl/cm mks rayl/m 10
reactance, acoustic—see acoustic impedance
(Pa·s/m )
reactance ratio—see impedance ratio
absorption sabin metric sabin 0.0929
reduction, level
reduction, noise
reduction, normalized noise susceptance ratio—see admittance ratio
reduction coefficient, noise time weighting—see sound level
resistance, acoustic—see acoustic impedance transmission class, field sound
resistance, airflow transmission class, sound
resistance, specific airflow transmission coefficient, sound
resistance ratio—see impedance ratio
transmission, flanking
resistivity, airflow transmission loss, field
room, receiving
transmission loss, outdoor-indoor
room, reverberation transmission loss, sound
room, source velocity, particle
sabin, metric
6. Conversion Factors
slow, sound level
slow exponential time weighting—see sound level 6.1 Most factors for converting from measurements in other
sound, absorption average systems to the International System, SI, are listed in IEEE/
sound, airborne ASTM SI 10. A few conversion factors that are not listed
sound, structureborne explicitly are listed in Table 1.
sound absorption coefficient, normal incidence
7. Keywords
sound field, diffuse
sound field, direct 7.1 acoustic; acoustic classification; acoustic measurement;
sound field, reverberant acoustics; ASTM committee E33; building acoustics; building
sound level, equivalent—see average sound pressure level and environmental acoustics; definitions; environmental acous-
sound transmission class, field tics; standard terminology; terminology
APPENDIXES
(Nonmandatory Information)
X1. DEFINITIONS OF TERMS FROM ASTM COMMITTEE E33 STANDARDS
INTRODUCTION
Terms from the section on “Definitions of Terms Specific to This Standard” from ASTM Committee
E33 standards, their definitions, and the standard(s) to which they apply are given below in
alphabetical order.
NOTE X1.1—Given the fact that there may be time between when a new
least 40 m in a specified frequency band, the impact sound
term is added or changed within an ASTM Committee E33 standard and
pressure level (ISPL) normalized to a reference absorption of
when that addition or change can be reflected within this Terminology
10 m in the receiving room. (2021)
Standard, this section may not represent a completely comprehensive list
DISCUSSION—10 m is equivalent to 108 Sabins. (2021) E1007
of all terms and their definitions from specific ASTM Committee E33
standards.
NOTE X1.2—While this appendix is non-mandatory, the sections within absorption-normalized high-frequency impact rating,
each ASTM standard where these terms are define
...