Far-field extrapolation of Maximum Noise Levels produced by individual vehicles

This paper describes a combination of analytical and experimental investigations for the identification of the drivers responsible for the generation of Maximum Noise Levels (MNL) and the prediction of the extrapolated levels to the far-field positions where the receiver is situated. An on-board acquisition system composed of two microphones situated inside the engine hood and close to the right back tyre respectively provides a measurement of rolling and power-train noise. This electro-acoustic system has been shown to be able to discriminate the noisiest vehicles in different environments and for different driving behaviours. Based on this estimation of the near-field levels, we have developed a complete procedure for extrapolating the noise up to the receiver positions with a combination of analytical predictions and experimental measurements. The corrections for the extrapolated levels are due to atmospheric factors, to the spherical wave divergence term and to the absorbing conditions of the propagating surface that have been determined experimentally. For the microphone situated close to the engine we also need to characterise the acoustic properties of the engine hood. Both noise levels are extrapolated independently to the far-field position, where a comparison between prediction and measurements is performed to confirm that the methodology is reliable to estimate the remote impact of traffic noise.