Experimental study of the road noise

Driver's reduced exposure to noise and vibrations implies a higher comfort, which involves a safety increase. To reach this aim, it is necessary to know and to understand the main sound sources. Road noise is the principal noise when the tourism is cruising between 50 km/h and 100 km/h. The main objective of this paper is to characterise in frequency the road noise. The specific noises that compose the road noise were found, in accordance with classical models consulted in bibliography. Other objective is to study the influence of different parameters like vehicle's speed and the asphalt type. The measurements were repeated at the same conditions, but over different asphalts: polished asphalt (like the roller bench surface), smooth asphalt and rough asphalt. Exterior noise, interior noise and vibrations were measured in order to evaluate the global behaviour of the car. As the principal frequencies that characterise the exterior road noise have been known, it has been possible to evaluate which of these frequencies are perceived inside the car. Because of that, it has been possible to estimate the interior road noise contribution in order to improve the sound quality inside the car.