The effects of uncertain scattering coefficients on the reverberation time

Abstract

Uncertain scattering coefficients are still a weak point in room acoustical computer simulations and predictions. The definition of the scattering coefficient s, their values as well as the simulation model are uncertain. Not only the roughness of infinite walls but also the edge effect are included in a combined diffusivity coefficient ray tracing models utilize. Most interesting in practical room acoustics is the influence on the uncertainty of the reverberation time (RT), which depends very sensitively on s. However, there is no analytical formula for the RT for only partially diffusely reflecting surfaces. In non-diffuse sound fields, the RT depend on the room shape, the distribution of absorption and especially on the scattering coefficients, too. A crucial example is a long rectangular room with totally absorbing side walls and partially scattering front walls. For this case a semi-analytical approach had been found. These and other typical cases in 2D and 3D have now been investigated numerically by the Sound Particle Simulation Method (SPSM) and the Anisotropic Reverberation Model (ARM). The aim is to find semi-analytically formulae or rules to estimate the uncertainty in the prediction of the RT by the Sabine formula. Is an “equivalent scattering area” a useful concept?