Vibration of the whole body is the most important sensory input that influences the assessment of ride by vehicle occupants; among other factors influencing ride assessment, noise is probably second in importance. A proportion of the overall noise inside a moving vehicle is generated by interaction between the tyres and the road surface. This report describes an investigation to determine the level and characteristics of road noise generated within passenger vehicles by a range of commonly used surfacings. Noise measurements were made in four different saloon cars travelling over eleven types of road surfacing at selected speeds between 20 and 95 km/h. Spectral analysis showed that most of the noise energy occurs at the lower audible frequencies, below 5 kHz. The surfacings examined did not exhibit significant peaks (or tones) in their spectra. Impulse-type noise was a feature on certain surfacings. The road noise component ranged up to 5 db(a), depending on surfacing type and its rate of increase with speed was found to be independent of type of surfacing. Road noise was greatest from the grooved concrete surfacing containing grooves of the largest cross-section. Of the five grooved concrete surfacings examined, that having grooves with the smallest cross-section generated the least noise at a level intermediate between that from the surface dressing (14 mm stone chippings) and from the hot rolled asphalt. Noise levels from brushed concrete and hot rolled asphalt were similar. Road noise was least from the pervious macadam surfacing; its previous character appears to increase the attenuation of noise on this surfacing. (Author/publisher)
Abstract