Conference_programme: 18.6 - Acoustics of reverberation chambers

Lecture: Effect of altering the test object configuration in measurements of the absorption area according to ISO 354

Author(s): Glebe Dag , Larsson Krister

Summary:
The sound fields of properly designed reverberation chambers are supposed to closely approximate a diffuse field. This assumption is supposed to hold also in presence of test objects with absorbing surfaces. But, it is also well known that the sound field in a room is affected by the sound-absorbing characteristics of its boundary surfaces. Furthermore, it has been shown that the number and positioning of diffusers in a reverberation chamber have a great impact on the measurement result of the absorption coefficient. Many new absorptive screen models have been developed in Sweden in the past few years. Although they serve a dual purpose, to screen and to absorb sound (and thus also reducing reflections), in Sweden often only their sound absorbing performances are evaluated. However, when used in regular rooms, the sound fields and thus the reverberation times are not only affected by their absorption characteristics but also by their screening properties and configuration. Therefore, it can be expected that the positions and the number of test objects will, at least to some extent, influence the sound field also when sound-absorbing characteristics of absorptive screens are measured in a reverberation chamber. The object of this study was to investigate how the resulting equivalent sound absorption area pertaining to a specific absorptive screen model, measured according to the ISO 354 test description for discrete sound absorbers, would change due to various alterations of the test object configuration. A number of configurations were evaluated in an accredited lab with the regular test equipment, and the resulting sound-absorbing characteristics were calculated and compiled. The results showed that the equivalent sound absorption area was influenced by the choice of test set-up in several cases, and that the results showed considerable variations, particularly in the low frequency range but also in higher frequency bands.

Corresponding author

Name: Dr Dag Glebe

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Country: Sweden