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BS EN ISO 10534-2:2001:2002 Edition

BS EN ISO 10534-2:2001:2002 Edition

$142.49

Acoustics. Determination of sound absorption coefficient and impedance in impedance tubes – Transfer-function method

Published By Publication Date Number of Pages
BSI 2002 32
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This test method covers the use of an impedance tube, two microphone locations and a digital frequency analysis system for the determination of the sound absorption coefficient of sound absorbers for normal sound incidence. It can also be applied for the determination of the acoustical surface impedance or surface admittance of sound absorbing materials. Since the impedance ratios of a sound absorptive material are related to its physical properties, such as airflow resistance, porosity, elasticity and density, measurements described in this test method are useful in basic research and product development.

The test method is similar to the test method specified in ISO 10534-1 in that it uses an impedance tube with a sound source connected to one end and the test sample mounted in the tube at the other end. However, the measurement technique is different. In this test method, plane waves are generated in a tube by a noise source, and the decomposition of the interference field is achieved by the measurement of acoustic pressures at two fixed locations using wall-mounted microphones or an in-tube traversing microphone, and subsequent calculation of the complex acoustic transfer function, the normal incidence absorption and the impedance ratios of the acoustic material. The test method is intended to provide an alternative, and generally much faster, measurement technique than that of ISO 10534-1.

Compared with the measurement of the sound absorption in a reverberation room according to the method specified in ISO 354, there are some characteristic differences. The reverberation room method will (under ideal conditions) determine the sound absorption coefficient for diffuse sound incidence, and the method can be used for testing of materials with pronounced structures in the lateral and normal directions. However, the reverberation room method requires test specimens which are rather large, so it is not convenient for research and development work, where only small samples of the absorber are available. The impedance tube method is limited to parametric studies at normal incidence but requires samples of the test object which are of the same size as the cross-section of the impedance tube. For materials that are locally reacting, diffuse incidence sound absorption coefficients can be estimated from measurement results obtained by the impedance tube method. For transformation of the test results from the impedance tube method (normal incidence) to diffuse sound incidence, see Annex F.

PDF Catalog

PDF Pages PDF Title
1 BRITISH STANDARD
2 National foreword
4 EN foreword
9 1 Scope
2 Definitions and symbols
2.1 sound absorption coefficient at normal incidence
2.2 sound pressure reflection factor at normal incidence
2.3 reference plane
2.4 normal surface impedance
10 2.5 normal surface admittance
2.6 wave number
2.7 complex sound pressure
2.8 cross spectrum
2.9 auto spectrum
2.10 transfer function
2.11 calibration factor
11 3 Principle
4 Test equipment
4.1 Construction of the impedance tube
12 4.2 Working frequency range
4.3 Length of the impedance tube
4.4 Microphones
13 4.5 Positions of the microphones
4.6 Acoustic centre of the microphone
Figure 1 Examples of typical microphone mounting
Figure 2 Microphone positions and distances
14 4.7 Test sample holder
4.8 Signal processing equipment
4.9 Loudspeaker
4.10 Signal generator
15 4.11 Loudspeaker termination
4.12 Thermometer and barometer
5 Preliminary test and measurements
Figure 3 Example of layout for test equipment
16 6 Test specimen mounting
7 Test procedure
7.1 Specification of the reference plane
7.2 Determination of the sound velocity, wavelength and characteristic impedance
17 7.3 Selection of the signal amplitude
7.4 Selection of the number of averages
7.5 Correction for microphone mismatch
18 Figure 4 Standard configuration (configuration I)
Figure 5 Configuration with microphones interchanged (configuration II)
20 7.6 Determination of the transfer function between the two locations
7.7 Determination of the reflection factor
7.8 Determination of the sound absorption coefficient
7.9 Determination of the specific acoustic impedance ratio
21 7.10 Determination of the specific acoustic admittance ratio
8 Precision
9 Test report
22 Annex A (normative)
Preliminary measurements
A.1 Prior to or following each test
A.2 Periodic calibration
25 Figure A.1 Tube attenuation correction
26 Figure A.2 Determination of the acoustic centre of a probe microphone
27 Annex B (normative)
Procedure for the one-microphone technique
Annex C (normative)
Pressure-release termination of test sample
28 Annex D (informative)
Theoretical background
29 Annex E (informative)
Error sources
E.1 Bias errors
30 E.2 Random error
E.3 Accuracy of the transfer function
31 Annex F (informative)
Determination of diffuse sound absorption coefficient
Annex G (informative)
Bibliography

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BS EN ISO 10534-2:2001
$142.49