ASTM E1050-07
(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).4
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 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: E 1050 – 07
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 E 1050; 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.
1. Scope 3. Terminology
1.1 This test method covers the use of an impedance tube, 3.1 Definitions—The acoustical terminology used in this
two microphone locations, and a digital frequency analysis test method is intended to be consistent with the definitions in
system for the determination of normal incidence sound Terminology C 634.
absorption coefficients and normal specific acoustic impedance
NOTE 1—Historical literature regarding the measurement of normal
ratios of materials.
incidence absorption coefficients referred to “transfer function” measure-
1.2 Laboratory Accreditation—A procedure for accrediting
ments; however, the term arises from Laplace transform theory and is not
a laboratory for performing this test method is given inAnnex
strictly rigorous when the initial conditions have a non-zero value. The
term “frequency response function” arises from more general Fourier
A1.
4
transform theory (1). This test method shall retain the use of the former
1.3 This standard does not purport to address the safety
term although not technically correct. Users should be aware that modern
concerns, if any, associated with its use. It is the responsibility
FFT analyzers may employ the latter terminology.
of the use of this standard to consult and establish appropriate
3.2 Symbols: The following symbols are used in Section 8
safety and health practices and determine the applicability of
(Procedure):
regulatory limitations prior to use.
3.2.1 brc—normal specific acoustics susceptance ratio.
2. Referenced Documents
3.2.2 c—speed of sound, m/s.
3.2.3 grc—normal specific acoustic conductance ratio.
2.1 ASTM Standards:
3.2.4 G ,G —auto power spectra of the acoustic pressure
C 384 Test Method for Impedance and Absorption of 11 22
signal at microphone locations 1 and 2, respectively.
Acoustical Materials by Impedance Tube Method
3.2.5 G —cross power spectrum of the acoustic pressure
C 634 Terminology Relating to Building and Environmen-
12
signals at microphones locations 1 and 2.
tal Acoustics
3.2.6 H—transfer function of the two microphone signals
E 548 Guide for General Criteria Used for Evaluating
2
corrected for microphone response mismatch.
Laboratory Competence
¯
3.2.7 H—measured transfer function of the two micro-
2.2 ISO Standards:
phone signals.
ISO 10534-1 Acoustics—Determination of Sound Absorp-
I II
3.2.8 H,H —calibration transfer functions for the micro-
tion Coefficient and Impedance or Admittance—Part 1:
3
phones in the standard and switched configurations, respec-
Impedance Tube Method
tively.
ISO 10534–2 Acoustics—Determination of SoundAbsorp-
¯
3.2.9 H —complex microphone calibration factor.
tionCoefficientandImpedanceinImpedanceTubes—Part c
3
3.2.10 j—equals –1.
2: Transfer-Function Method =
-1
3.2.11 k—equal 2pf/c; wave number, m .
3.2.11.1 Discussion—In general the wave number is com-
1
ThistestmethodisunderthejurisdictionofASTMCommitteeE33onBuilding
plex where k = k8-jk9.k8 is the real component, 2pf/c and k9
and Environmental Acoustics and is the direct responsibility of Subcommittee
is the imaginary component of the wave number, also referred
E33.01 on Sound Absorption.
-1
to as the attenuation constant, Nepers-m .
Current edition approved Dec. 1, 2007. Published January 2008. Originally
approved in 1985. Last previous edition approved in 2006 as E 1050 - 98 (2006).
2
Withdrawn.
3 4
Available from American National Standards Institute (ANSI), 25 W. 43rd St., The boldface numbers in parentheses refer to the list of references at the end of
4th Floor, New York, NY 10036, http://www.ansi.org. this test method.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
E1050–07
3.2.12 l—distance from the test sample to the centre of the 5.2 Normal incidence sound absorption coefficients can be
nearest microphone, m. quite useful in certain situations where the material is placed
3.2.13 r/rc—normal specific acoustic resistance ratio. within a small acoustical cavity close to a sound source, for
3.2.14 R—complex acoustic reflection coefficient. example a closely-fitted machine enclosure.
3.2.15 s—centre-to-center spacing between microphones,
5.3 This test method allows one to compare relative values
m. of sound
...
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:E1050–98(Reapproved 2006) Designation: E 1050 – 07
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 E 1050; 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.
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 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
2.1 ASTM Standards:
C 384 Test Method for Impedance and Absorption of Acoustical Materials by Impedance Tube Method
C 634 Terminology Relating to Building and Environmental Acoustics
E 548 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
2
Tube Method
ISO 10534–2 Acoustics—Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes—Part 2:
2
Transfer-Function Method
3. Terminology
3.1 Definitions— The acoustical terminology used in this test method is intended to be consistent with the definitions in
Terminology C 634.
NOTE 1—Historical literature regarding the measurement of normal incidence absorption coefficients referred to “transfer function” measurements;
however,thetermarisesfromLaplacetransformtheoryandisnotstrictlyrigorouswhentheinitialconditionshaveanon-zerovalue.Theterm“frequency
3
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
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
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.Dec. 1, 2006.2007. Published September 2006.January 2008. Originally approved in 1985. Last previous edition approved in 20002006 as
E 1050 - 98 (2006).
2
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
3
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 ----------------------
E1050–07
-1
3.2.11 k—equal 2pf/c; wave number, m .
3.2.11.1 Discussion—In general the wave number is complex where k = k8-jk9.k8 is the real component, 2pf/c and k9 is the
-1
imaginary component of the wave number, also referred to as the attenuation constant, Nepers-m .
3.2.12 l—distance from the test sample to the centre of the nearest microphone, m.
3.2.13 r/rc—normal specific acoustic resistance ratio.
3.2.14 R—complex acoustic reflection coefficient.
3.2.15 s—centre-to-center spacing between microphones, m.
3.2.16 x/rc—normal spe
...
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