Performance optimisation of small reverberant room with hanging diffusers

Small reverberant room can be an efficient and economic tool to provide fast sound absorption measurements in diffuse field of homogeneous sound absorber or more complex structure and useful for development, testing or evaluating specification requirements in many industrial fields. A 5.7 m3 reverberant room with a Schroeder frequency around 1275 Hz can have some diffusivity issues in lower and middle frequencies leading to an unsuitable level of consistency, reliability, and repeatability. This paper presents the results of a study to improve the measurement performance of this small reverberant room by adding hanging diffusers. Using Ray-Tracing method, a numerical parametric study was done to estimate sound absorption of various material by varying the number, the position, and the orientation of these diffusers based on ASTM C423 and E795 standard. Moreover, extra simulation has been performed to evaluate the effect of sample size on sound absorption consistency in function of frequency. Following these prescriptions, an experimental study was done to confirm these improvements on frequency dependent sound absorption and single rating numbers such as NRC (Noise Reduction Coefficient) and SAA (Sound Absorption Average).