Energy decay analysis of non-diffuse sound fields in rectangular rooms

Rectangular rooms with irregular aspect ratio or nonuniform absorption distribution apt to have non-diffuse sound fields, where the curvature of energy decay curve occurs in the reverberation process. In general, this curvature leads to longer reverberation times than the estimates by the Sabine or Eyring formula; however, it can be suppressed to a certain extent with diffusive wall surfaces. Recently, the author has proposed a new approximate theory of reverberation in rectangular rooms with specular and diffuse reflections. In this paper, the validity of the theory is investigated by two case studies with geometrical and wave-based acoustic simulation. In the first study, energy decay in a variety of rectangular rooms with changing the aspect ratio, the absorption distribution and the scattering coefficient, is simulated with the image source method and the ray tracing method. In the second study, a two-dimensional FDTD analysis is performed to demonstrate the frequency dependence of energy decay in a variety of rectangular rooms with flat or corrugated walls. Finally, the simulated results are compared with the theoretical ones, and the validity and the limitation of the approximation are discussed.