“…Statistical-acoustic methods (Summers et al, 2004;Summers, 2012) are based on the diffuse sound field hypothesis that the acoustic energy is uniform in the field and travels in all directions with the same probability. The diffusion-equation model (Xiang et al, 2009;Luizard et al, 2014) is an extension of the statistical theory to spatially varying reverberant sound fields and is based on the analogy of the sound energy density with a density of "sound particles" travelling along straight lines. The geometric acoustics methods are adequate for high sound frequencies and most systems for geometric modelling are based on the ray tracing method (Summers et al, 2005), the beam tracing algorithm (Funkhouser et al, 2004;Laine et al, 2009), the image source method (Dance et al, 1995;Lehmann, Johansson, 2009), or the mirror source method (Mechel, 2002;Aretz et al, 2014).…”