Sound Absorption Measurements: Comparison of Standard Tests in Reverberant Room with Measurements using a Synthetized Diffuse Acoustic Field

This communication mainly aims at providing a comprehensive comparison of measurements of sound absorption coefficients performed following standards in a reverberant room or using a synthetized Diffuse Acoustic Field. The sound absorption coefficient under this latter approach is reconstructed from transfer function measurements between a microphone doublet and a synthetic array of acoustic monopoles facing the material sample in a hemi-anechoic room, thereby removing the need of a reverberant room.Five different acoustic materials are tested. Melamine foam is used as a reference case, while the other four are utilized in the building industry: fiberglass batts, heavy-density fiberglass boards, polyurethane foam and ceiling tiles. The results obtained with the synthetized diffuse field are compared with those measured in the reverberant room together with theoretical predictions based on the transfer matrix approach. It is shown that the sound absorbing coefficients under a diffuse acoustic field excitation can be estimated with a satisfactory accuracy using the synthetic array approach, with a sample area significantly reduced compared to standard requirements. The effect of the source height and of the array source density on obtained results is also briefly investigated using FEM calculations. Possible improvements of the method at low frequency are finally discussed.