Low room with mixed diffuse-specular reflection and non-uniform absorption

Description

Academic case: Low room (30m x 20m x 10m) with mixed reflection (varying scattering coefficient ) and non-uniform surface absorption, with a single source and 1 punctual receiver.

All elements of this simulation are licensed under Licence Creative Commons Attribution 4.0 International License.

What is tested?

Comparison between SPPS and the results obtained using a hybrid method (image-sources and radiosity) as described in [Korany, 2001].

[Korany, 2001] N. Korany, J. Blauert, O. Abdel Alim, Acoustic simulation of rooms with boundaries of partially specular reflectivity, Applied Acoustics, Volume 62, Issue 7, July 2001, Pages 875-887, ISSN 0003-682X, dx.doi.org/10.1016/S0003-682X(00)00075-X.

CAUTION - The following results present comparisons between numerical simulations carried out with I-Simpa and 'reference' data available in the scientific literature.

  • It is difficult to prejudge the concept of 'reference'. The deviation between the simulations and the reference data that can be observed do not necessarily call into question the corresponding simulations but can also be associated with other sources of deviation (modeling assumptions, numerical instabilities, experimental uncertainties, etc.).
  • Note also that these comparaisons can also show the limitations of some numerical codes.

Results

Reverberation time (RT30)

The SPPS code shows a similar behavior and a perfect agreement for the reverberation time (RT30), i.e. a decrease of the RT30 with an increase of the scattering coefficient from perfectly specular to perfectly diffuse, with the hybrid method. As expected, whether for Sabine or Eyring formulae, the classical theory of reverberation is not able to predict the reverberation time in such room (disproportionate with a non-uniform absorption).

Calculation parameters

Parameters Value
Time step (s) 0.002
Active calculation of Atmospheric absorption NO
Active calculation of diffusion by fitting objects NO
Active calculation of direct field only NO
Active calculation of transmission NO
Calculation method Energetic
Limit value of the particle extinction 5.0
Number of sound particles per source 5 000 000
Number of sound particles per source (display) 0
Random initialization number 0
Receiver radius 0.31
Simulation length (s) 1.500