Does diffusivity affect the spatial variance of reverberation time?

Davy, J 2018, 'Does diffusivity affect the spatial variance of reverberation time?', in Proceedings of the 25th International Congress on Sound and Vibration (ICSV25 2018), Hiroshima, Japan, 8-12 July 2018, pp. 1-8.


Document type: Conference Paper
Collection: Conference Papers

Title Does diffusivity affect the spatial variance of reverberation time?
Author(s) Davy, J
Year 2018
Conference name ICSV25 2018
Conference location Hiroshima, Japan
Conference dates 8-12 July 2018
Proceedings title Proceedings of the 25th International Congress on Sound and Vibration (ICSV25 2018)
Publisher The International Institute of Acoustics and Vibration
Place of publication United States
Start page 1
End page 8
Total pages 8
Abstract Annex A of the 2017 draft revision of ISO 354:2003 contains a qualification test of the diffusivity of the reverberant sound field based on the spatial variance of the reverberation time. This was initially based on experimental measurements that showed that the spatial variance of reverberation time decreased when diffusing panels were added to the reverberation room. Davy's theory shows that the spatial variance of reverberation time is proportional to the reverberation time. Adding diffusers to the reverberation room increases the sound absorption and hence reduces the reverberation time and its spatial variance, as was experimentally observed. Because of this observation Annex A now requires the ratio of the experimental to the theoretical spatial standard deviation of reverberation time averaged over the third octave bands from 250 to 3150 Hz to be less than or equal to one. When Davy was initially comparing his theory with experimental results, he found no difference in the agreement between theory and experiment for rooms with and without diffusers and with and without a highly sound absorbing material on the floor for rooms ranging in volume from 100 to 600 cubic metres. This suggests that the qualification test of Annex A is not sensitive enough to make sure that the reverberation room decaying sound field is adequately diffuse when there is a highly sound absorbing sample on the floor. Davy's original papers combined the experimental data from the eight different room configurations. This paper examines the eight individual room configuration results separately. It shows that a room without sufficient diffusers to be able to measure the correct sound absorption coefficients at high frequencies would pass the Annex A diffusivity qualification test. Based on this result, it recommends that Annex A be removed from the 2017 draft revision of ISO 354:2003.
Subjects Acoustics and Acoustical Devices; Waves
Acoustics and Noise Control (excl. Architectural Acoustics)
Architectural Science and Technology (incl. Acoustics, Lighting, Structure and Ecologically Sustainable Design)
Keyword(s) reverberation time
spatial variance
diffusivity
ISBN 9788378805526
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