Time domain simulation of sound diffusers using finite-difference schemes

Since the invention of sound diffusers three decades ago a substantial effort has been made to predict the acoustic behaviour of these structures, for auralisation and prediction purposes as well as in response to the large costs inherent in anechoic measurements. Volumetric methods such as Finite Element Methods (FEM) or the Finite Difference Time Domain method (FDTD) are not often used, due to their large computational cost. However Near Field to Far Field Transformations (NFFFT) can overcome that problem. The main advantages of the FDTD method are that a single calculation is sufficient to study a wide frequency band, and that the time domain behaviour of the reflected sound can be directly inspected. In this paper we present a comparison between the prediction techniques commented above in the context of sound diffusers, paying special attention to the FDTD method. Having demonstrated that the FDTD method can generate results comparable to more established techniques, early results concerning the modelled performance of diffusers in the time domain (‘time spreading’) are reported, opening a new field of research.