Validation of the numerical simulation of the scattered sound field with a geometrical pyramid tracing approach

The paper describes the details and some validation results about a new implementation of sound scattering modelling inside a Pyramid Tracing computer program, for the simulation of the sound propagation in large rooms and outdoors. The approach makes it possible to take into account both scattering mechanisms (surface and edge), along with the frequency dependence of both effects. The surface scattering is described by means of the scattering coefficient (a physical quantity actually being standardised by an ISO WG) in each octave band; the edge scattering, instead, is computed empirically with reference to an hypothetical flat and smooth surface, and this effect is added to the surface scattering. A clever implementation made it possible to maintain an unique geometrical tracing for all the frequency bands, and thus the computation time is not increased over the previous version of the same program, which did not include explicitly the scattering effect. The comparison with experimental measurements and theoretical solutions has shown that the new algorithm greatly reduces the computational error in presence of strong reflections from scattering objects, provided that the correct value of the scattering coefficient is employed as input.