Prediction of the reverberation time in rooms with non uniform absorptions using a diffusion model

The acoustical comfort is now a comfort’s criterion which is taken into from the conception. The designers need therefore accurate tools to predict the acoustic quality of enclosures. Most of the acoustical comfort criteria are based on the reverberation time. When the room has proportionate dimensions and an uniform absorption, the statistical theory through Sabine or Eyring formulas allows good predictions of the reverberation time. Moreover, extensions of these relations by Millington or Cremer and Müller among others give quite satisfactory when the room is composed of materials with different sound absorption. In this study, the reverberation time in an enclosure is calculated via the numerical resolution of unstationary diffusion equation, model validated in coupled and industrial rooms. Firstly, an improvement of the boundary condition is proposed for highly absorbent surfaces. The diffusion model is then compared to several formulations of the statistical theory and a ray-tracing software for a cubic room with homogeneous walls’ absorption and with non homogeneous walls’ absorptions. Finally, an experimental validation is conducted for an enclosure with non uniformly distributed absorption.