Effectiveness of the ensemble averaging technique in measurements for sound absorption characteristics of materials

The ensemble averaging is one of the most important concepts for scientific measurements, especially for sound absorption measurements of materials. Applying a technique based on ensemble averaging to the sound field where a measurement is undertaken, the authors have proposed a novel measurement method for sound absorption characteristics, surface normal impedance and corresponding absorption coefficient, of materials. We named it EA method and we presented the method's excellent robustness and good reproducibility. Herein, a theoretical background of the method is given, briefly. Then, the outline of an EA-method measurement conducted in a reverberation room using pseudo-random incident noises is described and measured values of both ensemble averaged surface normal impedance and corresponding absorption coefficient are shown to examine the effectiveness of the averaging. In the EA-method measurement, two types of sensors are utilized: pu-sensor and two-microphone. Finally, the applicability of the EA method to in situ measurements at various field environments is exhibited and the importance of on-site calibration is confirmed.