Characterization of low frequency reverberation room behavior using simulation

Primary metrics for assessing the performance of acoustic materials are the normal incident and random incident sound absorption. Measurement of the former is performed in an impedance tube whereas the latter is measured in a reverberation room. It is well known that the reverberation room can greatly impact the measured random incident absorption especially at low frequencies. To determine the random incident absorption coefficient, the material is positioned on the floor of a reverberation room and the decay rate is measured after a sound source is switched off. Reproducibility and repeatability are often suspect in the low frequency range where the sound field is dominated by room modes. The low sound absorption coefficients of the walls and test samples often result in long reverberation times that lead to a less than ideal diffuse field assumption. To better understand the reverberation room at low frequencies, a study correlating experimental mapping and finite element simulation was undertaken to validate a model to guide future design changes to the room. It is hoped that the model will enable the engineers to better select diffusers or low frequency sound absorbers to improve the room performance.