Normal incidence sound absorption measurement of individual patches in a reverberation room

Abstract

This work presents results of sound absorption measurement of plain patches inside a reverberation room. An in situ method has been applied (ISO 13472-1). The main purpose is to support the installation of diffusers in a reverberation room for random incidence sound absorption measurements. The in situ method is based on impulse response evaluation, in which the incident and reflected front waves can be windowed to isolate them from the room reflections. Due to the small areas of the patches (around 1 square meter) and the high reverberation time, some special steps had to be performed. In order to establish an impulse response measurement with high SNR, a long sweep sine signal with low-frequency emphasis has been used as the excitation signal. Applying the subtraction technique permitted locating the microphone very close to the sample. The sound absorption coefficient of each patch allowed selecting the most uniform set of material to compose the area required by the ISO 354. The patches not used were tested in an impedance tube, showing a good agreement between the results from the two methods. Thus, the in situ method allows quick measurement of plain samples laid on the room floor while preserving the material integrity.