Toward the assessment of walls acoustic impedances from the analysis of first and second order reflections based on room impulse responses

Abstract

In order to address optimal acoustic control in rooms, an accurate characterization of the room shape and wall properties is required. There are only a few approaches that model the wall impedances. Most of them rely on finite difference time domain methods, which are limited to shoebox-shaped rooms and only valid at low frequencies (non-rectangular rooms and high frequencies lead to extremely high computational complexity). In order to overcome these limits, we propose the estimation of walls’ acoustic impedances based on the analysis of the room impulse responses. In room impulse responses, the early reflections’ amplitudes are proportional to the reflection coefficient of the corresponding wall element. The location of points on the walls (origins) for the first and second order echoes can be easily determined for a known room. The values of impedances at the origins of the first order echoes are determined directly from the room impulse response. The second order echoes' represent a product of the influence of wall points that belong to its path. Values of individual impedances are extracted from these echoes by overlapping origins of first order echoes of one receiver’s position with one origin of the second order echoes of another receiver’s position.