ASTM C384-04(2016)

Standard Test Method for Impedance and Absorption of Acoustical Materials by Impedance Tube Method

SIGNIFICANCE AND USE
5.1 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.  
5.2 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.  
5.3 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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.

General Information

• Status: Historical
• Publication Date: 31-Mar-2016
• ICS: 91.120.20 - Acoustics in building. Sound insulation
• Technical Committee: E33 - Building and Environmental Acoustics
• Drafting Committee: E33.01 - Sound Absorption

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 (Reapproved 2016)
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 C634. In particular, the terms “impedance ratio,” “normal
incidence sound absorption coefficient,” and “specific normal
1.1 This test method covers the use of an impedance tube,
acoustic impedance,” appearing in the title and elsewhere in
alternatively called a standing wave apparatus, for the mea-
this test method refer to the following, respectively:
surement of impedance ratios and the normal incidence sound
absorption coefficients of acoustical materials. 3.2 Definitions:
3.2.1 impedance ratio, z/ρc ≡ r/ρc + jx/ρc;
1.2 The values stated in SI units are to be regarded as
[dimensionless]—the ratio of the specific normal acoustic
standard. No other units of measurement are included in this
impedance at a surface to the characteristic impedance of the
standard.
medium. The real and imaginary components are called,
1.3 This standard does not purport to address all of the
respectively, resistance ratio and reactance ratio. C634
safety concerns, if any, associated with its use. It is the
3.2.2 normal incidence sound absorption coeffıcient, α ;
n
responsibility of the user of this standard to establish appro-
[dimensionless]—of a surface, at a specified frequency, the
priate safety and health practices and determine the applica-
fraction of the perpendicularly incident sound power absorbed
bility of regulatory limitations prior to use.
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
C423TestMethodforSoundAbsorptionandSoundAbsorp-
surface is divided by the component of the particle velocity
tion Coefficients by the Reverberation Room Method
normal to the surface. The real and imaginary components of
C634Terminology Relating to Building and Environmental
thespecificnormalacousticimpedancearecalled,respectively,
Acoustics
specific normal acoustic resistance and specific normal acous-
E548Guide for General Criteria Used for Evaluating Labo-
3
tic reactance. C634
ratory Competence (Withdrawn 2002)
2.2 ANSI Standards:
4. Summary of Test Method
S1.6Preferred Frequencies and Band Numbers forAcousti-
4
cal Measurements
4.1 A plane wave traveling in one direction down a tube is
reflectedbackbythetestspecimentoproduceastandingwave
3. Terminology
that can be explored with a microphone.The normal incidence
3.1 The acoustical terminology used in this test method is sound absorption coefficient, α , is determined from the stand-
n
intended to be consistent with the definitions in Terminology ingwaveratioatthefaceofthetestspecimen.Todeterminethe
impedance ratio, z/ρc, a measurement of the position of the
standing wave with reference to the face of the specimen is
1
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
needed.
and Environmental Acoustics and is the direct responsibility of Subcommittee
E33.01 on Sound Absorption.
4.2 The normal incidence absorption coefficient and imped-
Current edition approved April 1, 2016. Published April 2016. Originally
ance ratio are functions of frequency. Measurements are made
approved in 1956. Last previous edition approved in 2011 as C384–04 (2011).
withpuretonesatanumberoffrequencieschosen,unlessthere
DOI: 10.1520/C0384-04R16.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
arecompellingreasonstodootherwise,fromthosespecifiedin
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
ANSI S1.6.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3
The last approved version of this historical standard is referenced on 5. Significance and Use
www.astm.org.
4
5.1 The acoustical impedance properties of a sound absorp-
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. tive material are related to its physical properties, such as
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
C384 − 04 (2016)
airflowresistance,porosity,elasticity,anddensity.Assuch,the It is best to work well below these limits whether the tube is
measurements described in this te
...

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: C384 − 04 (Reapproved 2011) C384 − 04 (Reapproved 2016)
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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 standard. No other units of measurement are included in this standard.
2. Referenced Documents
2
2.1 ASTM Standards:
C423 Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
C634 Terminology Relating to Building and Environmental Acoustics
3
E548 Guide for General Criteria Used for Evaluating Laboratory Competence (Withdrawn 2002)
2.2 ANSI Standards:
4
S1.6 Preferred Frequencies and Band Numbers for Acoustical Measurements
3. Terminology
3.1 The acoustical terminology used in this test method is intended to be consistent with the definitions in Terminology C634.
In particular, the terms “impedance ratio,” “normal incidence sound absorption coefficient,” and “specific normal acoustic
impedance,” appearing in the title and elsewhere in this test method refer to the following, respectively:
3.2 Definitions:
3.2.1 impedance ratio, z/ρc ≡ r/ρc + jx/ρc; [dimensionless]—the ratio of the specific normal acoustic impedance at a surface
to the characteristic impedance of the medium. The real and imaginary components are called, respectively, resistance ratio and
reactance ratio. C634
3.2.2 normal incidence sound absorption coeffıcient, α ; [dimensionless]—of a surface, at a specified frequency, the fraction of
n
the perpendicularly incident sound power absorbed or otherwise not reflected. C634
3.2.3 specific normal acoustic impedance, z ≡ r + jx;
-2 -1
[ML T ]; mks rayl (Pa s/m)—at a surface, the complex quotient obtained when the sound pressure averaged over the surface is
divided by the component of the particle velocity normal to the surface. The real and imaginary components of the specific normal
acoustic impedance are called, respectively, specific normal acoustic resistance and specific normal acoustic reactance. C634
4. Summary of Test Method
4.1 A plane wave traveling in one direction down a tube is reflected back by the test specimen to produce a standing wave that
can be explored with a microphone. The normal incidence sound absorption coefficient, α , is determined from the standing wave
n
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 Nov. 1, 2011April 1, 2016. Published December 2011April 2016. Originally approved in 1956. Last previous edition approved in 20042011 as
C384 – 04.C384 – 04 (2011). DOI: 10.1520/C0384-04R11. 10.1520/C0384-04R16.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3
The last approved version of this historical standard is referenced on www.astm.org.
4
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
C384 − 04 (2016)
ratio at the face of the test specimen. To determine the impedance ratio, z/ρc, a measurement of the position of the standing wave
with reference to the face of the specimen is neede
...