Absorbing surfaces in ray-tracing programs for coupled spaces

Nowadays architects commonly use the ‘coupled space concept’; examples are mezzanines, half-open office spaces and exhibition rooms. There is a need to predict acoustical quantities for this category of spaces, since half-open spaces may be a cause of noise annoyance. The transmission of sound between coupled spaces depends on design decisions like position, shape and dimensions of the surfaces and on the reflection characteristics. This paper deals with some problems related to the application of absorbing surfaces in coupled rooms, especially when they are modelled in a ray-tracing program. Absorption coefficients from meausurements in reverberation chambers may exceed 1.0 and they do not bear any information about angle dependent behavior, so an extra conversion must be made into input values for the ray-tracing model. Therefore ray-tracing calculations have been performed in a computer model of a reverberation chamber. From a comparison study between measurements and calculations in three coupled rooms it is found that the accuracy is good, provided that the sound reflections on the walls are introduced as angle dependent. Care should be taken in choosing a diffusion factor of flat surfaces.