Diffusing boundaries in the digital waveguide mesh and their effect on reverberation time

The digital waveguide mesh is often used to simulate the propagation of sound waves in an acoustic system. The diffusing layer is an approach that has been shown as appropriate for simulating diffuse boundary reflections as this is a fundamental acoustic property of real surfaces. Incoming wavefronts are rotated randomly according to a chosen probability function at a layer of mesh nodes adjacent to the boundary of interest. Although this method offers a high level of control and consistency, the nature of the interaction between terminating boundary function and incident wave is altered with an associated potential impact on the resultant wave propagation behaviour for the rest of the space. This paper explores this effect based on impulse response measurements obtained from a simulated space. Results are presented demonstrating the effect diffusion modelling has on early reflections and that depending on the conditions imposed increased boundary diffusivity can lead to either an increase or decrease in reverberation time. Standard objective measures are used to demonstrate the perceptual effect of increased boundary diffusivity on the spatially encoded diffuse field for the modelled space.