Scattering from objects and surfaces in room acoustical simulations

In room acoustical simulations, scattering objects are often modelled as impenetrable boxes with high scattering coefficients assigned to the surfaces. In some cases, a cluster of objects is modelled as a virtual impenetrable box, such that no sound propagation can take place between the objects. Thus, the scattering only takes place on the boundary surfaces of the box and the acoustic volume of the room is reduced. Another challenge with representing scattering objects by reflecting surfaces is that it increases the number of surfaces, which greatly increases the calculation complexity for methods such as the image source method. In this paper a modelling method where the scattering from objects takes place in certain parts of the room volume is proposed. In this method, sound can still travel through scattering objects, but be partly scattered. This volume scattering method has at present been implemented in the simulation tool PARISM (Phased Acoustical Radiosity and Image Source Method). Scattering from objects and surfaces is likely to be strongly frequency dependent and the frequency dependence can depend on their sizes, shapes and structure. The importance of the frequency dependence is investigated and discussed through simulations.