NF EN ISO 10534-2, S31-079-2 (11/2023)

This test method covers the use of an impedance tube, two microphone locations and a frequency analysis system for the determination of the sound absorption coefficient of acoustically absorbing materials under incidence normal acoustics. It can also be used to determine the surface acoustic impedance or surface admittance of acoustic absorbing materials. By extension, it can also be used to evaluate the intrinsic properties of homogeneous acoustic materials such as characteristic impedance, characteristic wave number, dynamic density and dynamic compressibility modulus. The test method is identical to the test method 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 method is different. In this test method, plane waves are generated in a tube by a sound source, and the decomposition of the interference field is carried out by measuring the sound pressures at two fixed locations using microphones mounted on walls or a transverse microphone to the tube, then by calculating the complex acoustic transfer function and the quantities reported in the previous paragraph. The test method is intended to provide an alternative and faster measurement method to that described in ISO 10534-1. The normal incidence absorption coefficients from impedance tube measurements are not comparable to the random incidence absorption coefficients measured in a reverberant room in accordance with ISO 354. The reverberant room method will determine (under conditions ideal) the sound absorption coefficient under diffuse acoustic incidence. However, the reverberation room method requires relatively large specimens. The impedance tube method is limited to studies under normal and plane incidence and requires samples of the object under test, of a size equivalent to the section of the impedance tube. For materials with localized reaction only, the diffuse field sound absorption coefficients can be estimated from the measurement results obtained by the impedance tube method (see Annex E).
(Automatic translation from French)