The use of a reference absorber for absorption measurements in a reverberation chamber

The statistical incidence absorption coefficient is measured in a reverberation room according to ISO 354. This absorption coefficient is referred to as Sabine absorption coefficient, which assumes the chambe r to be completely diffuse. It is known that the reproducibility of these results is poor and the differences in the results between laboratories are much larger than can be accepted from a jurisdictional point of view. Actions should therefore be taken to reduce the spread. The intention of this paper is to set requirements on the diffusivity of the sound field and to apply a reference absorber, which will be used for qualification of the room and correction of the results. The present research establishes the requirements for a proper design of such an absorber and its reference absorption data. The diffuse field factor was used to quantify the diffuse sound field in several reverberation rooms. Furthermore, calculations and measurements were conducted to optimise the reference absorber. A small round r obin test was performed with this reference absorber in five European laboratories . The results of this research will be used in the proposal for the new ISO 354.