COMPARISON OF THE MIRROR-IMAGE SOURCE METHOD AND THE SOUND PARTICLE SIMULATION METHOD

Both the Mirror Image Soruce Method and the Sound Particle Simulation Method are well known numerical methods of sound field simulation, based on the typical assumptions of geometrical room acoustics. More interesting than physical considerations here are the structures of the algorithms. By a thorough analysis of their typical cases and of the probabilities that the typical calculation steps following them become necessary, total calculation times are predicted. It is shown that if many reflections are to be traced-in many practical cases more than two-the Sound Particle Simulation Method, with the same accuracy, represents a considerably more efficient and hence faster algorithm. The inefficiency of the classical Mirror Image Source Method is mainly caused by the fact that the construction of a large number of mirror image sources which, with considerable effort, have to be checked afterwards, but are not 'visible' in most cases, i.e. do not exist due to the finiteness of the mirroring surfaces, is unavoidable. The Sound Particle Simulation Method is also more flexible, i.e. it allows the free selection of the best compromise between accuracy, length of the echogram, spatial resolution and calculation time. Furthermore, its calculation time does not necessarily increase with the number of sources. Looking at the possibilities of introducing the simulation of physical effects that have not previously been implemented, the Sound Particle Simulation Method, unlike the Mirror Image Source Method, can be extended to scattering and diffraction effects. By the Mirror Image Source Method only the screening effect can be computed-and this only in special cases. An extension of the Sound Particle Simulation Method to simulate diffraction effects in general appears to be difficult, but not impossible. © 1990.