A trial expansion of the in-situ measurement method using the ensemble averaging technique for sound absorption characteristics of materials in lower frequency region

Recently, sound absorption characteristics of materials have become of more importance for broad range of acoustics, especially for data-driven-room-acoustics. The authors proposed a measurement method using the ensemble averaging technique for sound absorption characteristics, i.e., surface impedance and sound absorption coefficient; and we name the method EA-method, for short. Originally, the frequency range of the EA-method is targeted from 100 to 1500 Hz, and, afterword, it is extended from 100 to 3000 Hz. However, a room's acoustics in the lower frequency region, such as below 100 Hz, becomes non-negligible or of more importance, nowadays. Herein, an improvement of pu-sensor calibration is applied and results of trial measurements are presented. Since the major target of the EA-method is in-situ applications at practical building environments, a simple, light and efficient system is indispensable. Several case studies at practical measurements show the effectiveness of the improvement.