Predictions of the reverberation time in high absorbent room using a modified-diffusion model

A modification of the diffusion model’s boundary condition, based on the Eyring absorption coefficient, to account for high walls absorption is proposed. Numerical comparisons are carried out for three geometrical configurations (a proportionate room, a corridor and a flat enclosure). Comparisons with the statistical theory and a ray-tracing software show that the modified boundary condition increases the accuracy of the diffusion model in term of reverberation time in all the simulated configurations. An experimental comparison in the case of a non-uniformly absorbent room (a reverberation chamber covered with patches of glass wool) is also carried out. The modified-diffusion model results match well with the ray-tracing ones. Both models are in agreement with the experimental data for most of third octave bands (discrepancy close to or below 10%). However, some discrepancies up to 40% can also be observed in a few octave bands, probably due to experimental considerations and to the modal behaviour of the room at low frequencies