A study on the dependence of PEMs acoustic properties on incidence angle

The objective of this paper is to study the variability of on-site acoustic measurements in non-normal conditions, as a function of the angle. A porous European mix was investigated. In order to reject the hypothesis that the cause of the variations in the acoustic properties is the surface inhomogeneity, texture properties were investigated according to the standard ISO 13473-1 and ISO/CD TS 13473-4. The acoustic absorption coefficient was measured according to ISO 13472-1. Results were compared and analysed in terms of averages and standard deviations. Result analyses may allow us to derive how absorption properties may vary as a function of the angle of incidence (under the hypothesis of homogeneous surface texture of the friction course). A tentative theoretical framework for explaining the dependence of acoustic absorption on incidence angle was formulated. The outcomes of this study are expected to benefit both practitioners and researchers.