Experimental validation of the modelling of surface roughness effects by an effective impedance

Natural grounds can exhibit small geometry irregularities, compared to the wavelength, which are called surface roughness. Using effective impedance is a useful way to model the effects of surface roughness on outdoor sound propagation, particularly in numerical methods as it avoids the meshing of small irregularities. In this paper, firstly an effective impedance model taking into account the surface roughness spectrum of the ground is exposed. Secondly, an experimental campaign of sound pressure measurements above 1/10 scale 2D rough surfaces is presented. The same profile characterized by a gaussian roughness spectrum is designed in two polystyrene boards coated with resin. One board is felt-covered to simulate an absorbing rough surface and the other is left uncovered to simulate a reflective rough surface. Finally, the experimental results are compared to analytical calculations with the effective impedances corresponding to the two experimental rough surfaces, respectively. Those results show good agreement, thus validating the effective impedance approach and allowing more accurate SPL predictions for future impact studies in environmental acoustics.