ASTM E1050-12
(Test Method)Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones and a Digital Frequency Analysis System
Standard Test Method for Impedance and Absorption of Acoustical Materials Using a Tube, Two Microphones and a Digital Frequency Analysis System
SIGNIFICANCE AND USE
This test method can be applied to measure sound absorption coefficients of absorptive materials at normal incidence, that is, 0°. It also can be used to determine specific impedance and admittance ratios. The properties measured with this test method are useful in basic research and product development of sound absorptive materials.
Normal incidence sound absorption coefficients can be quite useful in certain situations where the material is placed within a small acoustical cavity close to a sound source, for example a closely-fitted machine enclosure.
This test method allows one to compare relative values of sound absorption when it is impractical to procure large samples for accurate random-incidence measurements in a reverberation room. Estimates of the random incidence absorption coefficients can be obtained from normal impedance data for locally-reacting materials (2).
Note 2—The classification, “locally-reacting” includes fibrous materials having high internal losses. Formulas have been developed for converting sound absorption properties from normal incidence to random incidence, for both locally-reacting and bulk-reacing materials (3).
Measurements described in this test method can be made with high precision, but these measurements may be misleading. Uncertainties of greater magnitude than those from the measurements may occur from other sources. Care should be exercised to sample nonuniform materials adequately (see 11.1).
SCOPE
1.1 This test method covers the use of an impedance tube, two microphone locations, and a digital frequency analysis system for the determination of normal incidence sound absorption coefficients and normal specific acoustic impedance ratios of materials.
1.2 Laboratory Accreditation—A procedure for accrediting a laboratory for performing this test method is given in Annex A1.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the use of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E1050 − 12
Standard Test Method for
Impedance and Absorption of Acoustical Materials Using a
Tube, Two Microphones and a Digital Frequency Analysis
1
System
This standard is issued under the fixed designation E1050; 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.
4
1. Scope Impedance Tube Method
ISO 10534–2 Acoustics—Determination of Sound Absorp-
1.1 This test method covers the use of an impedance tube,
tionCoefficientandImpedanceinImpedanceTubes—Part
two microphone locations, and a digital frequency analysis
4
2: Transfer-Function Method
system for the determination of normal incidence sound
4
2.3 ANSI Standards:
absorption coefficients and normal specific acoustic impedance
ANSI/ASAS1.11 Octave-Band and Fractional-Octave-Band
ratios of materials.
Analog and Digital Filters
1.2 Laboratory Accreditation—A procedure for accrediting
3. Terminology
a laboratory for performing this test method is given in Annex
A1.
3.1 Definitions—Theacousticalterminologyusedinthistest
method is intended to be consistent with the definitions in
1.3 The values stated in SI units are to be regarded as
Terminology C634.
standard. No other units of measurement are included in this
standard.
NOTE 1—Historical literature regarding the measurement of normal
incidence absorption coefficients referred to “transfer function” measure-
1.4 This standard does not purport to address the safety
ments; however, the term arises from Laplace transform theory and is not
concerns, if any, associated with its use. It is the responsibility
strictly rigorous when the initial conditions have a non-zero value. The
of the use of this standard to consult and establish appropriate
term “frequency response function” arises from more general Fourier
5
safety and health practices and determine the applicability of
transform theory (1). This test method shall retain the use of the former
term although not technically correct. Users should be aware that modern
regulatory limitations prior to use.
FFT analyzers may employ the latter terminology.
2. Referenced Documents
3.2 Symbols: The following symbols are used in Section 8
2
2.1 ASTM Standards: (Procedure):
C384 Test Method for Impedance andAbsorption ofAcous- 3.2.1 bρc—normal specific acoustics susceptance ratio.
tical Materials by Impedance Tube Method
3.2.2 c—speed of sound, m/s.
C634 Terminology Relating to Building and Environmental
3.2.3 gρc—normal specific acoustic conductance ratio.
Acoustics
3.2.4 G ,G —auto power spectra of the acoustic pressure
E548 Guide for General Criteria Used for Evaluating Labo- 11 22
3
signal at microphone locations 1 and 2, respectively.
ratory Competence (Withdrawn 2002)
3.2.5 G —cross power spectrum of the acoustic pressure
2.2 ISO Standards:
12
ISO 10534-1 Acoustics—Determination of Sound Absorp- signals at microphones locations 1 and 2.
tion Coefficient and Impedance or Admittance—Part 1:
3.2.6 H—transfer function of the two microphone signals
corrected for microphone response mismatch.
1 ¯
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding 3.2.7 H—measured transfer function of the two microphone
and Environmental Acoustics and is the direct responsibility of Subcommittee
signals.
E33.01 on Sound Absorption.
I II
3.2.8 H,H —calibration transfer functions for the micro-
Current edition approved April 1, 2012. Published July 2012. Originally
approved in 1985. Last previous edition approved in 2010 as E1050 - 10. DOI:
phones in the standard and switched configurations, respec-
10.1520/E1050-12.
tively.
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
4
Standards volume information, refer to the standard’s Document Summary page on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
3
5
The last approved version of this historical standard is referenced on The boldface numbers in parentheses refer to the list of references at the end of
www.astm.org. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
E1050 − 12
¯
3.2.9 H —complex microphone calibration factor. microphone positions. An extended frequency range may be
c
obtained by using tubes with various diameters and micro-
3.2.10 j—equals =21 .
phones spacings.
-1
3.2.11 k—equal 2πf/c; wave number, m .
4.3 This test method is intended to provide a much faster
3
...
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:E1050–10 Designation: E1050 – 12
Standard Test Method for
Impedance and Absorption of Acoustical Materials Using a
Tube, Two Microphones and a Digital Frequency Analysis
1
System
This standard is issued under the fixed designation E1050; 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, two microphone locations, and a digital frequency analysis system
forthedeterminationofnormalincidencesoundabsorptioncoefficientsandnormalspecificacousticimpedanceratiosofmaterials.
1.2 Laboratory Accreditation—Aprocedure for accrediting a laboratory for performing this test method is given inAnnexA1.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the
use of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2
2.1 ASTM Standards:
C384 Test Method for Impedance and Absorption of Acoustical Materials by Impedance Tube Method
C634 Terminology Relating to Building and Environmental Acoustics
E548 Guide for General Criteria Used for Evaluating Laboratory Competence
2.2 ISO Standards:
ISO 10534-1 Acoustics—Determination of Sound Absorption Coefficient and Impedance or Admittance—Part 1: Impedance
3
Tube Method
ISO 10534–2 Acoustics—Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes—Part 2:
3
Transfer-Function Method
3
2.3 ANSI Standards:
ANSI/ASA S1.11 Octave-Band and Fractional-Octave-Band Analog and Digital Filters
3. Terminology
3.1 Definitions—The acoustical terminology used in this test method is intended to be consistent with the definitions in
Terminology C634.
NOTE 1—Historical literature regarding the measurement of normal incidence absorption coefficients referred to “transfer function” measurements;
however,thetermarisesfromLaplacetransformtheoryandisnotstrictlyrigorouswhentheinitialconditionshaveanon-zerovalue.Theterm“frequency
4
responsefunction”arisesfrommoregeneralFouriertransformtheory(1). Thistestmethodshallretaintheuseoftheformertermalthoughnottechnically
correct. Users should be aware that modern FFT analyzers may employ the latter terminology.
3.2 Symbols: The following symbols are used in Section 8 (Procedure):
3.2.1 brc—normal specific acoustics susceptance ratio.
3.2.2 c—speed of sound, m/s.
3.2.3 grc—normal specific acoustic conductance ratio.
3.2.4 G ,G —auto power spectra of the acoustic pressure signal at microphone locations 1 and 2, respectively.
11 22
3.2.5 G —cross power spectrum of the acoustic pressure signals at microphones locations 1 and 2.
12
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 Sept.April 1, 2010.2012. Published December 2010.July 2012. Originally approved in 1985. Last previous edition approved in 20082010 as
E1050 - 108. DOI: 10.1520/E1050-102.
2
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM 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
The boldface numbers in parentheses refer to the list of references at the end of this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
E1050 – 12
3.2.6 H—transfer function of the two microphone signals corrected for microphone response mismatch.
¯
3.2.7 H—measured transfer function of the two microphone signals.
I II
3.2.8 H,H —calibration transfer functions for the microphones in the standard and switched configurations, respectively.
¯
3.2.9 H —complex microphone calibration factor.
c
3.2.10 j—equals –1.
=
-1
3.2.11 k—equal 2pf/c; wave number, m .
3.2.11.1 Discussion—
...
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