Sound field in long rooms with diffusely reflecting boundaries

A diffusion equation is used to predict the sound propagation in long rooms with diffusely reflecting boundaries. The model is defined by two paramete rs, the coefficient of diffusion depending on the mean free path, and an ex change coefficient expressing wall absorption. The diffusion equation is so lved for time-varying sources and in stationary state. Analytical expressio ns of sound attenuation and reverberation in infinite, semi-infinite and fi nite long rooms are quite in accordance with numerical simulations of diffu se sound field. It is also shown that the diffusion model allows to predict experimental observations: the decay curves are not linear, the reverberat ion time increases with the source-receiver distance, and sound attenuation is linear along corridors. The dependence of the coefficient of diffusion with the degree of wall diffusion is also discussed. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.