Influence of impedance phase angle on sound pressures and reverberation times in a rectangular room

In most room acoustic predictions, phase shift on reflection has been overlooked. This study aims to quantify the effects of the surface impedance phase angle of the boundary surfaces on room acoustic conditions. As a preliminary attempt, a medium-sized rectangular room is simulated by a phased beam tracing model, after verifying it numerically against boundary element simulations.

First, the absorption characteristic of the boundary surfaces varies uniformly from 0.2 to 0.8, but with various impedance phase angles. Second, typical non-uniform cases having hard walls and floor, but with an absorptive ceiling are investigated. The zero phase angle, which has commonly been assumed in practice, is regarded as reference and differences in the sound pressure level and early decay time from the reference are quantified.

As expected, larger differences in the room acoustic parameters are found for larger impedance phase angles. Additionally, binaural impulse responses are compared in a listening test for the uniform absorption cases, revealing that non-zero impedance phase angle cases can be perceptually different from the reference condition in terms of reverberance perception.

For the non-uniform settings, the change in the impedance phase angle of the ceiling does not affect the acoustic conditions significantly.