1. A method for supporting source or listener directivity in a wave-based sound propagation model, the method comprising: at a sound propagation model (SPM) module comprising executable instructions executable by at least one processor: computing, prior to run-time, one or more sound fields associated with a source or listener position in a virtual environment; and modeling, at run-time and using the one or more sound fields and a wave-based sound propagation model, source or listener directivity in the virtual environment, wherein modeling, at run-time and using the one or more sound fields and the wave-based sound propagation model, source or listener directivity in the virtual environment includes: performing a spherical harmonic (SH) decomposition of the source directivity; computing one or more SH coefficients corresponding to the SH decomposition; and computing an acoustic response of the virtual environment, wherein the acoustic response is computed as a summation of the one or more sound fields evaluated at the listener position weighted by the one or more SH coefficients.