Practical aspects related to the measurement of the diffuse field absorption coefficient in scaled reverberation rooms

The scaled reverberation room has proven to be an excellent tool for acoustic consultants and professionals alike to carry out comparison tests between acoustic materials and 3D systems or structures. The suitability of a scaled reverberation room is currently under investigation for the evaluation of the frequency-dependent sound absorption. At present, no standard is available on the methods that could be used to derive acoustic absorption coefficients from scaled measurements. In this work practical aspects of ISO 354 have been investigated within a 1:5 scaled reverberation room: a balance has been sought between reducing sample size, to reduce the manufacturing costs of materials, and finding the appropriate sample area, thickness, orientation and edges treatment, to obtain reliable values at mid and high frequencies. Four different materials have been tested. The paper discusses some of the findings of the measurements conducted on the same materials in a full-scale reverberation room according to ISO 354, in a 1:5 scaled reverberation room and in an impedance tube according to ISO 10534-2. The absorption coefficients data collected have been effective in proving that small reverberation room tests can provide compatible results compared to standard ones in 400-5000 Hz frequency range.