Reflection and absorption coefficients for use in room acoustic simulations

Two ideas to improve the boundary conditions for room acoustic simulations are presented. First, all rooms have finite boundary surfaces, thereby a reflection coefficient for finite surfaces should be
physically more suitable than that for infinitely large surfaces. Second, absorption coefficients measured by the chamber method, so-called the Sabine absorption coefficients, have certain problems to be used in geometrical acoustics simulations; one serious problem is that they often exceed unity for porous absorbers due to the finite sample size and non-uniform intensity in the test reverberation
chamber. Therefore the Sabine absorption coefficients should be converted into the random incidence absorption coefficients, which never exceed unity, thus are more proper for room acoustic simulations.