ASTM C423-17
(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
5.1 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.
5.2 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.
5.3 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.
5.4 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.
5.5 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's 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 Te...
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 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 method to measure the absorption of rooms in the field is described in Test Method E2235.
1.3 This test method includes information on laboratory accreditation (see Annex A1), asymmetrical screens (see Annex A2), and reverberation room qualification (see Annex A3).
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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 − 17
Standard Test Method for
Sound Absorption and Sound Absorption Coefficients by
1
the Reverberation Room Method
This standard is issued under the fixed designation C423; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope E2235 Test Method for Determination of Decay Rates for
Use in Sound Insulation Test Methods
1.1 This test method covers the measurement of sound
absorption in a reverberation room by measuring decay rate. 2.2 ANSI Standards:
Procedures for measuring the absorption of a room, the
S1.6 Preferred Frequencies, Frequency Levels, and Band
3
absorption of an object, such as an office screen, and the sound
Numbers for Acoustical Measurements
absorption coefficients of a specimen of sound absorptive
S1.11 Specification for Octave-Band and Fractional-Octave-
3
material, such as acoustical ceiling tile, are described.
Band Analog and Digital Filters
S1.26 Method for the Calculation of the Absorption of
1.2 Field Measurements—Although this test method covers
3
Sound by the Atmosphere
laboratory measurements, the test method described in 4.1 can
S1.43 Specifications for Integrating-Averaging Sound Level
be used for making field measurements of the absorption of
3
Meters
rooms (see also 5.5). A method to measure the absorption of
rooms in the field is described in Test Method E2235.
2.3 IEC Standards
IEC 61672 Electroacoustics–Sound Level Meters–Part 1:
1.3 This test method includes information on laboratory
3
Specifications
accreditation (see Annex A1), asymmetrical screens (see An-
nexA2), and reverberation room qualification (see AnnexA3).
2.4 ASTM Adjuncts:
4
Historical Applications Note on Sound Absorber
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
standard. 3. Terminology
1.5 This standard does not purport to address all of the
3.1 Except as noted in 3.3, the terms and symbols used in
safety concerns, if any, associated with its use. It is the
this test method are defined in Terminology C634. The follow-
responsibility of the user of this standard to establish appro-
ing definition is not currently included in Terminology C634:
priate safety and health practices and determine the applica-
3.1.1 sound absorption average, SAA—a single number
bility of regulatory limitations prior to use.
rating, the average, rounded off to the nearest 0.01, of the
sound absorption coefficients of a material for the twelve
2. Referenced Documents
one-third octave bands from 200 through 2500 Hz, inclusive,
2
2.1 ASTM Standards:
measured according to this test method.
C634 Terminology Relating to Building and Environmental
3.1.1.1 Discussion—The sound absorption coefficients shall
Acoustics
be rounded off to the nearest 0.01 before averaging. If the
E795 Practices for Mounting Test Specimens During Sound
unrounded average is an exact midpoint, round to the next
Absorption Tests
higher multiple of 0.01. For example, report 0.625 as 0.63.
3.2 In previous versions of this test method a single number
1
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
rating, called the noise reduction coefficient (NRC), was
and Environmental Acoustics and is the direct responsibility of Subcommittee
defined as follows:
E33.01 on Sound Absorption.
Current edition approved Jan. 15, 2017. Published February 2017. Originally
approved in 1958. Last previous edition approved 2009 as C423 – 09a. DOI:
10.1520/C0423-17.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM 4th Floor, New York, NY 10036, http://www.ansi.org.
4
Standards volume information, refer to the standard’s Document Summary page on A drawing of this specimen is available at a nominal charge from ASTM
the ASTM website. International Headquarters. Order Adjunct No. ADJC0423.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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C423 − 17
5. Significance and Use
9Round the average of the sound absorption coefficients
for 250, 500, 1000, and 2000 Hz to the nearest multiple
5.1 Measurement of the sound absorption of a room is part
of 0.05. If the unrounded average is an exact midpoint,
round to the next higher multiple of 0.05. For example, of the procedure for other acoustical measurements, suc
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C423 − 09a C423 − 17
Standard Test Method for
Sound Absorption and Sound Absorption Coefficients by
1
the Reverberation Room Method
This standard is issued under the fixed designation C423; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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 Appendix X2Test Method E2235.
1.3 This test method includes information on laboratory accreditation (see Annex A1), asymmetrical screens (see Annex A2),
and reverberation room qualification (see Annex A3).
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
2. Referenced Documents
2
2.1 ASTM Standards:
C634 Terminology Relating to Building and Environmental Acoustics
E795 Practices for Mounting Test Specimens During Sound Absorption Tests
E2235 Test Method for Determination of Decay Rates for Use in Sound Insulation Test Methods
2.2 ANSI Standards:
3
S1.6 Preferred Frequencies, Frequency Levels, and Band Numbers for Acoustical Measurements
3
S1.11 Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters
3
S1.26 Method for the Calculation of the Absorption of Sound by the Atmosphere
3
S1.43 Specifications for Integrating-Averaging Sound Level Meters
2.3 IEC Standards
3
IEC 61672 Electroacoustics–Sound Level Meters–Part 1: Specifications
2.4 ASTM Adjuncts:
4
Historical Applications Note on Sound Absorber
3. Terminology
3.1 Except as noted in 3.3, the terms and symbols used in this test method are defined in Terminology C634. The following
definition is not currently included in Terminology C634:
1
This test method is under the jurisdiction of ASTM Committee E33 on Building and Environmental Acoustics and is the direct responsibility of Subcommittee E33.01
on Sound Absorption.
Current edition approved Oct. 15, 2009Jan. 15, 2017. Published October 2009February 2017. Originally approved in 1958. Last previous edition approved 2009 as
C423 – 09.C423 – 09a. DOI: 10.1520/C0423-09A.10.1520/C0423-17.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
4
A drawing of this specimen is available at a nominal charge from ASTM International Headquarters. Order Adjunct No. ADJC0423.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
C423 − 17
3.1.1 sound absorption average, SAA—a single number rating, the average, rounded off to the nearest 0.01, of the sound
absorption coefficients of a material for the twelve one-third octave bands from 200 through 2500 Hz, inclusive, measured
according to this test method.
3.1.1.1 Discussion—The sound absorption coefficients shall be rounded off to the nearest 0.01 before averaging. If the
unrounded average is an exact midpoint, round to the next higher multiple of 0.01. For example, report 0.625 as 0.63.
3.2 In previous versions of this test method a single number rating, called the noise reduction coefficient (NRC),
...
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