ASTM C384-04
(Test Method)Standard Test Method for Impedance and Absorption of Acoustical Materials by Impedance Tube Method
Standard Test Method for Impedance and Absorption of Acoustical Materials by Impedance Tube Method
SIGNIFICANCE AND USE
The acoustical impedance properties of a sound absorptive material are related to its physical properties, such as airflow resistance, porosity, elasticity, and density. As such, the measurements described in this test method are useful in basic research and product development of sound absorptive materials.
Normal incidence sound absorption coefficients are more useful than random incidence coefficients in certain situations. They are used, for example, to predict the effect of placing material in a small enclosed space, such as inside a machine.
Estimates of the random incidence or statistical absorption coefficients for materials can be obtained from normal incidence impedance data. For materials that are locally reacting, that is, without sound propagation inside the material parallel to its surface, statistical absorption coefficients can be estimated from specific normal acoustic impedance values using an expression derived by London (1).5 Locally reacting materials include those with high internal losses parallel with the surface such as porous or fibrous materials of high density or materials that are backed by partitioned cavities such as a honeycomb core. Formulas for estimating random incidence sound absorption properties for both locally and bulk-reacting materials, as well as for multilayer systems with and without air spaces have also been developed (2).
SCOPE
1.1 This test method covers the use of an impedance tube, alternatively called a standing wave apparatus, for the measurement of impedance ratios and the normal incidence sound absorption coefficients of acoustical materials.
1.2 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.
1.3 The values stated in SI units are to be regarded as the standard.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:C384–04
Standard Test Method for
Impedance and Absorption of Acoustical Materials by
1
Impedance Tube Method
This standard is issued under the fixed designation C384; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope incidence sound absorption coefficient,” and “specific normal
acoustic impedance,” appearing in the title and elsewhere in
1.1 This test method covers the use of an impedance tube,
this test method refer to the following, respectively:
alternatively called a standing wave apparatus, for the mea-
3.2 Definitions:
surement of impedance ratios and the normal incidence sound
3.2.1 impedance ratio, z/rc [ r/rc+jx/rc;
absorption coefficients of acoustical materials.
[dimensionless]—the ratio of the specific normal acoustic
1.2 This standard does not purport to address all of the
impedance at a surface to the characteristic impedance of the
safety concerns, if any, associated with its use. It is the
medium. The real and imaginary components are called,
responsibility of the user of this standard to establish appro-
respectively, resistance ratio and reactance ratio. C634
priate safety and health practices and determine the applica-
3.2.2 normal incidence sound absorption coeffıcient, a ;
bility of regulatory limitations prior to use. n
[dimensionless]—of a surface, at a specified frequency, the
1.3 The values stated in SI units are to be regarded as the
fraction of the perpendicularly incident sound power absorbed
standard.
or otherwise not reflected. C634
2. Referenced Documents 3.2.3 specific normal acoustic impedance, z [r+jx;
-2 -1
2
[ML T ]; mks rayl (Pa s/m)—at a surface, the complex
2.1 ASTM Standards:
quotient obtained when the sound pressure averaged over the
C423 Test Method for Sound Absorption and Sound Ab-
surface is divided by the component of the particle velocity
sorption Coefficients by the Reverberation Room Method
normal to the surface. The real and imaginary components of
C634 Terminology Relating to Building and Environmental
thespecificnormalacousticimpedancearecalled,respectively,
Acoustics
specific normal acoustic resistance and specific normal acous-
E548 Guide for General Criteria Used for Evaluating Labo-
3
tic reactance. C634
ratory Competence
2.2 ANSI Standards:
4. Summary of Test Method
S1.6 Preferred Frequencies and Band Numbers for Acous-
4 4.1 A plane wave traveling in one direction down a tube is
tical Measurements
reflectedbackbythetestspecimentoproduceastandingwave
3. Terminology that can be explored with a microphone.The normal incidence
sound absorption coefficient, a , is determined from the
3.1 The acoustical terminology used in this test method is n
standing wave ratio at the face of the test specimen. To
intended to be consistent with the definitions in Terminology
determine the impedance ratio, z/rc, a measurement of the
C634. In particular, the terms “impedance ratio,” “normal
position of the standing wave with reference to the face of the
specimen is needed.
1
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
4.2 The normal incidence absorption coefficient and imped-
and Environmental Acoustics and is the direct responsibility of Subcommittee
ance ratio are functions of frequency. Measurements are made
E33.01 on Sound Absorption.
withpuretonesatanumberoffrequencieschosen,unlessthere
Current edition approved April 1, 2004. Published May 2004. Originally
approved in 1956. Last previous edition approved in 2003 as C384–03. DOI:
arecompellingreasonstodootherwise,fromthosespecifiedin
10.1520/C0384-04.
ANSI S1.6.
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
5. Significance and Use
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
5.1 The acoustical impedance properties of a sound absorp-
3
Withdrawn. The last approved version of this historical standard is referenced
tive material are related to its physical properties, such as
on www.astm.org.
4
airflowresistance,porosity,elasticity,anddensity.Assuch,the
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036.
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C384–04
measurements described in this test method are useful in basic tubearenotlikelytobeplanewaves.Ifsoundwithafrequency
research and product development of sound absorptive mate- below the limiting value e
...
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