Absorption measurements—A never ending story?!

A brief historical review on measurement techniques of sound absorption or the acoustic surface impedance will be presented, starting from procedures in the 1930s. Many in situ and laboratory methods have been described over the years. Most of these methods are based on the assumption of plane wave propagation or diffuse sound field. Measurement examples will be shown for some of the methods presented and compared to each other. A commonly used measurement procedure of so-called diffuse sound absorption coefficients is described in the international standard ISO 354. The present revision of the standard only focuses on the conditioning of the sound field and further applying Sabine equation. A diffuse sound field is atheoretical approach. Geometrical acoustics as the basis of sound field simulation has been applied to measurements in a virtual reverberation chamber on absorber baffle set-ups [see Probst (2015)] and showed good agreement between measured and calculated values. This approach is used to investigate the effect of sample size and sample position. Correspondingly, non-standard measurements are compared with simulation results.