Phased Beam Tracing Method Using the Reflection Coefficient Calculated from the Absorption Coefficient

The phased beam tracing method (PBTM) is a technique which can calculate the pressure impulse response instead of energy impulse response, by taking the phase information into account. Inclusion of the phase information can extend the application of beam tracing technique to the mid frequency range in spite of the fact that the usual assumptions of geometric acoustics still hold. In the calculation of pressure impulse response, it is essential to have the reflection characteristics of the surfaces in the enclosed space. There is a method to obtain the reflection coefficient of the surface using the measured surface impedance. However, it is not always possible to get the measured impedance data of the surface, so that a practical way of getting reflection characteristics is needed. Generally, in the architectural acoustics field, the absorption coefficients have been employed in the calculations, whereas Rindel proposed the angle dependent reflection coefficient which can be calculated from absorption coefficient under the several assumptions. In this research, the angle dependent reflection coefficients were adopted in the phased beam tracing method and the results are compared with measurement. This angle dependent/independent reflection coefficient can be a good alternative of measured data when the large, locally reacting surfaces are of interest.