The effect of mean free path on reverberation room measurement of absorption and absorption coefficients

Abstract

As diffusers are added to a reverberation chamber, the measured absorption of a sample increases. Often, absorption coefficients greater than one are measured, which is theoretically impossible. Edge diffraction is often offered as an explanation for these results. When diffusers are added, the mean free path (MFP) becomes shorter and therefore the sound waves hit the surfaces more often. This might be partially responsible for the increase in measured absorption as diffusers are added. Modern room-acoustics modeling software allows the calculation of MFP for any room configuration using ray tracing techniques. If the Sabine absorption equation were rearranged to leave in the MFP term, more accurate measurements of absorption might result.