Exploration of the differences between a pressure-velocity based in situ absorption measurement method and the standardized reverberant room method

Several measurement techniques are available for the determination of the sound absorbing properties of material packages. The Kundt's method and the reverberant room method are the most commonly used techniques and they are standardized. However, both methods cannot be used in situ. In the past it has been shown that the PU in situ method can be used in a broad frequency range (typically from 300 Hz up to 10 kHz), on small samples (typically 0.03 m2 to 0.38 m2 or larger), while hardly being affected by background noise and reflections. Several studies revealed that similar results can be obtained as with the Kundt's tube if the measurements are performed under certain circumstances. A thorough comparison with the reverberant room method has not been conducted yet. In this paper preliminary results are presented of a comparison of the reverberant room method, the PU in situ method, and measurements with PU probes in a reverberant room. Several factors that may cause discrepancies amongst the methods are discussed. In addition, edge effects, which are experienced with the reverberant room method due to the finite size of the sample, are visualized with 3D intensity measurements that are performed in a reverberant roo