Reverberation-chamber measurement of angle-dependent surface impedance

Conventional impedance-tube and reverberation-chamber methods for characterizing acoustic materials provide only normal- or diffuse-incidence sound absorption data. This limitation reduces their applicability under realistic room-acoustic conditions and motivates the development of directional characterization methods. In this work, a reverberation-chamber-based framework is presented for determining the angle-dependent surface impedance of an absorbing sample. The technique reconstructs the sound pressure and normal particle velocity at the sample surface using a plane wave decomposition of the pressure field measured with a microphone array. By separating incident and reflected components in the wavenumber domain, the angular distribution of incident sound energy is obtained, enabling the simultaneous determination of absorption for all incidence angles from a single source position. Measurements conducted in two reverberation chambers examine the validity and reproducibility of the method. The approach provides detailed phase and directional information, improving the accuracy and applicability of absorption data in room-acoustic modeling and design.