ASTM C423-07a
(Test Method)Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
SIGNIFICANCE AND USE
Measurement of the sound absorption of a room is part of the procedure for other acoustical measurements, such as determining the sound power level of a noise source or the sound transmission loss of a partition. It is also used in certain calculations such as predicting the sound pressure level in a room when the sound power level of a noise source in the room is known.
The sound absorption coefficient of a surface is a property of the material composing the surface. It is ideally defined as the fraction of the randomly incident sound power absorbed by the surface, but in this test method it is operationally defined in 4.2. The relationship between the theoretically defined and the operationally measured coefficients is under continuing study.
Diffraction effects5 usually cause the apparent area of a specimen to be greater than its geometrical area, thereby increasing the coefficients measured according to this test method. When the test specimen is highly absorptive, these values may exceed unity.
The coefficients measured by this test method should be used with caution because not only are the areas encountered in practical usage usually larger than the test specimen, but also the sound field is rarely diffuse. In the laboratory, measurements must be made under reproducible conditions, but in practical usage the conditions that determine the effective absorption are often unpredictable. Regardless of the differences and the necessity for judgment, coefficients measured by this test method have been used successfully by architects and consultants in the acoustical design of architectural spaces.
Field Measurements—When sound absorption measurements are made in a building in which the size and shape of the room are not under the operator’control, the approximation to a diffuse sound field is not likely to be very close. This matter should be considered when assessing the accuracy of measurements made under field conditions. (See Appendix X2 for a procedure...
SCOPE
1.1 This test method covers the measurement of sound absorption in a reverberation room by measuring decay rate. Procedures for measuring the absorption of a room, the absorption of an object, such as an office screen, and the sound absorption coefficients of a specimen of sound absorptive material, such as acoustical ceiling tile, are described.
1.2 Field Measurements - Although this test method primarily covers laboratory measurements, the test method described in 4.1 can be used for making field measurements of the absorption of rooms (see also 5.5). A non-standard method to measure the absorption of rooms in the field is described in .
1.3 This test method includes information on laboratory accreditation (see Annex A1), asymmetrical screens (see ), and reverberation room qualification (see Annex A3).
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:C423–07a
Standard Test Method for
Sound Absorption and Sound Absorption Coefficients by
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the Reverberation Room Method
This standard is issued under the fixed designation C 423; 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.
This standard has been approved for use by agencies of the Department of Defense.
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1. Scope Numbers for Acoustical Measurements
S1.11 Specification for Octave-Band and Fractional-
1.1 This test method covers the measurement of sound
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Octave-Band Analog and Digital Filters
absorption in a reverberation room by measuring decay rate.
S1.26 Method for the Calculation of the Absorption of
Procedures for measuring the absorption of a room, the
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Sound by the Atmosphere
absorption of an object, such as an office screen, and the sound
2.3 ASTM Adjuncts:
absorption coefficients of a specimen of sound absorptive
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Historical Applications Note on Sound Absorber
material, such as acoustical ceiling tile, are described.
1.2 Field Measurements—Although this test method prima-
3. Terminology
rily covers laboratory measurements, the test method described
3.1 Except as noted in 3.3, the terms and symbols used in
in 4.1 can be used for making field measurements of the
this test method are defined in Terminology C 634. The
absorption of rooms (see also 5.5). A non-standard method to
following definition is not currently included in Terminology
measure the absorption of rooms in the field is described in
C 634:
Appendix X2.
3.1.1 sound absorption average, SAA—a single number
1.3 This test method includes information on laboratory
rating, the average, rounded off to the nearest 0.01, of the
accreditation (see Annex A1), asymmetrical screens (see An-
sound absorption coefficients of a material for the twelve
nexA2), and reverberation room qualification (seeAnnexA3).
one-third octave bands from 200 through 2500 Hz, inclusive,
1.4 This standard does not purport to address all of the
measured according to this test method.
safety concerns, if any, associated with its use. It is the
3.1.1.1 Discussion—The sound absorption coefficients shall
responsibility of the user of this standard to establish appro-
be rounded off to the nearest 0.01 before averaging. If the
priate safety and health practices and determine the applica-
unrounded average is an exact midpoint, round to the next
bility of regulatory limitations prior to use.
higher multiple of 0.01. For example, report 0.625 as 0.63.
2. Referenced Documents 3.2 In previous versions of this test method a single number
2 rating, called the noise reduction coefficient (NRC), was
2.1 ASTM Standards:
defined as follows:
C 634 Terminology Relating to Building and Environmen-
9Round the average of the sound absorption coefficients
tal Acoustics
for 250, 500, 1000, and 2000 Hz to the nearest multiple
E 548 Guide for General Criteria Used for Evaluating
of 0.05. If the unrounded average is an exact midpoint,
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Laboratory Competence
round to the next higher multiple of 0.05. For example,
0.625 and 0.675 would be reported as 0.65 and 0.70, respectively.9
E 795 Practices for Mounting Test Specimens During
Sound Absorption Tests
The noise reduction coefficient shall be reported in order to
2.2 ANSI Standards:
provide comparison with values reported in the past see
S1.6 Preferred Frequencies, Frequency Levels, and Band
12.1.3).
3.3 Definition of Term Specific to This Standard—The
followingtermhasthemeaningnotedforthistestmethodonly:
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ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
3.3.1 outputinterval, Dt,[T],s—ofareal-timeanalyzer,the
and Environmental Acoustics and is the direct responsibility of Subcommittee
time between successive outputs; this time is not necessarily
E33.01 on Sound Absorption.
the same as the integration time.
Current edition approved June 1, 2007. Published June 2007. Originally
approved in 1958. Last previous edition approved 2007 as C 423 – 07.
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For referenced ASTM standards, visit the ASTM website, www.astm.org, or
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contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Standards volume information, refer to the standard’s Document Summary page on 4th Floor, New York, NY 10036.
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the ASTM website. A drawing of this specimen is available at a nominal charge from ASTM
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Withdrawn. International Headquarters. Order Adjunct No. ADJC0423.
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C423–07a
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