Acoustical assessment of road surfaces at urban and peri-urban speeds by simultaneous Coast-By and Close-ProXimity measurements
Résumé
The paper deals with the acoustical assessment of road surfaces over a wide range of vehicle speed, including urban and peri-urban velocities. An experimental campaign was performed with a passenger car fitted with four identical patterned tyres rolling on a set of 15 road surfaces located on a reference test track in France. Coast-By (CB) and Close-ProXimity (CPX) noise levels were simultaneously measured for each passage at a vehicle speed ranging between 30 km/h and 110 km/h. Special care was taken towards immunity of CPX measurement with respect to wind noise. Fixing the threshold of signal to noise ratio to 6 dBA between CPX and wind noise spectra, a very good correlation between CPX and CB noise levels was obtained in the spectral domain, over the whole speed range and for each road surface. At 50 km/h, it has also been possible to extend the validity of CPX measurements at low frequencies for most of the road surfaces. Based on overall CB noise levels, it was found that the acoustical classification of road surfaces is few influenced by the vehicle speed. Finally, a categorisation of road surfaces is proposed and discussed, based on characteristic spectral shapes: quasi-smooth surfaces, intermediate dense surfaces, rough surfaces and porous surfaces.