Local directional source modeling in wave-based acoustic simulation

Time-domain wave-based simulation approaches such as the finite difference time domain (FDTD) method allow for a complete solution to the problem of virtual acoustics over the entire frequency range, in contrast with the methods of geometric acoustics which are valid in the limit of high frequencies. They also allow for flexible modelling of sources and receivers, due to the inherently local nature of the computation, and complete access to the computed acoustic field over an enclosure. In this paper, a method for the emulation of sources of arbitrary directivity is presented, framed directly as an inhomogeneous wave equation. The additional terms in the wave equation take the form of Dirac delta functions and their distributional derivatives, and collections of such terms may be associated directly with an expansion of source directivity in terms of spherical harmonics. The local nature of the model implies a locally-defined efficient computational approach for wave-based methods defined over a spatial grid. Numerical results are presented