A framework for auralization of boundary element method simulations including source and receiver directivity.

The Boundary Element Method (BEM) is a proven numerical prediction tool for computation of room acoustic transfer functions, as are required for auralization of a virtual space. In this paper, it is validated against case studies drawn from the "Ground Truth for Room Acoustical Simulation" database within a framework that includes source and receiver directivity. These aspects are often neglected but are respectively important to include for auralisation applications because source directivity is known to affect how a room is excited and because the human auditory system is sensitive to directional cues. The framework uses weighted-sums of spherical harmonic functions to represent both the source directivity to be simulated and the pressure field predicted in the vicinity of the receiver location, the coefficients of the former being fitted to measured directivity and those of the latter computed directly from the boundary data by evaluating a boundary integral. Three validation cases are presented, one of which includes a binaural receiver. The computed results match measurements closely for the two cases conducted in anechoic conditions but show some significant differences for the third room scenario; here, it is likely that uncertainty in boundary material data limited modelling accuracy.

Simulating acoustic scattering from atmospheric temperature fluctuations using a k-space method.

This paper describes a numerical method for simulating far-field scattering from small regions of inhomogeneous temperature fluctuations. Such scattering is of interest since it is the mechanism by which acoustic wind velocity profiling devices (Doppler SODAR) receive backscatter. The method may therefore be used to better understand the scattering mechanisms in operation and may eventually provide a numerical test-bed for developing improved SODAR signals and post-processing algorithms. The method combines an analytical incident sound model with a k-space model of the scattered sound close to the inhomogeneous region and a near-to-far-field transform to obtain far-field scattering patterns. Results from two test case atmospheres are presented: one with periodic temperature fluctuations with height and one with stochastic temperature fluctuations given by the Kolmogorov spectrum. Good agreement is seen with theoretically predicted far-field scattering and the implications for multi-frequency SODAR design are discussed.

A transient boundary element method model of Schroeder diffuser scattering using well mouth impedance.

Room acoustic diffusers can be used to treat critical listening environments to improve sound quality. One popular class is Schroeder diffusers, which comprise wells of varying depth separated by thin fins. This paper concerns a new approach to enable the modeling of these complex surfaces in the time domain. Mostly, diffuser scattering is predicted using steady-state single frequency methods. A popular approach is to use a frequency domain boundary element method (BEM) model of a box containing the diffuser, where the mouth of each well is replaced by a compliant surface with appropriate surface impedance. The best way of representing compliant surfaces in time domain prediction models, such as the transient BEM is, however, currently unresolved. A representation based on surface impedance yields convolution kernels which involve future sound, so is not compatible with the current generation of time-marching transient BEM solvers. Consequently, this paper proposes the use of a surface reflection kernel for modeling well behavior and this is tested in a time domain BEM implementation. The new algorithm is verified on two surfaces including a Schroeder diffuser model and accurate results are obtained. It is hoped that this representation may be extended to arbitrary compliant locally reacting materials.