Effects of different diffuser types on the diffusivity in reverberation chambers

Knowledge of sound absorption properties of typical building materials is essential for all tasks related to room acoustic design. The Sabine absorption coefficient is measured in a reverberation chamber according to the international standard ISO 354. It is known that inter-laboratory reproducibility of these results is poor, which leads to uncertainties in prediction and nonconformity with building contracts. It is assumed that differences in the diffuse field conditions between laboratories are the main cause of the poor reproducibility. Achieving a diffuse sound field is the most important requirement for the reverberation chamber. Diffusing elements are therefore typically installed in reverberation chambers. In this study, the effects of hanging panel diffusers and hanging spherical volume diffusers on the diffusivity of the sound field in a reverberation chamber are investigated. The sound field diffusivity is characterized based on the equivalent sound absorption area of a highly sound absorptive sample and the diffuse field factor, which is the ratio of the measured spatial standard variation of the reverberation time to the theoretical spatial standard variation under diffuse field conditions. The results indicate that the diffuse field factor, as a potential diffuse field indicator, is suitable for rough estimation of the diffuse sound field conditions but does not constitute a reliable measure of the diffusivity in a reverberation chamber.