The influence of surface diffusivity on reverberation time prediction

Abstract

It has been reported in the literature that the reverberation time tends to be overestimated if the ray-tracing simulation does not consider surface scattering effects. However no simple, quantitative method is available to estimate the effect of surface diffusivity on reverberation time. This article provides such a model to establish the relation between reverberation time and a surface diffusivity factor. It has also been observed that the influence of scattering reflections increases when the material is less uniformly distributed. Therefore the authors studied the current prediction method with non-uniformly distributed material and observed the following: Kutruff equation based on the diffusive surface assumptions yields shorter reverberation times than Eyrings formula, while another equation containing reflective assumptions yields longer RT than Eyrings formula. It is demonstrated that the difference can reach up to 50%. Therefore the authors propose a linear combination of these two equations, with the proportion to each end determined by the surface diffusivity, assessed against Hann and Fricks method. A comparison between Boston Symphony Hall and New York Avery Fisher Hall is performed to demonstrate the significance of the surface diffusivity, and a Monte-Carlo simulation is included to support the result even under parameter uncertainties.