In accordance with the international trend towards more stringent vehicle noise regulations, it becomes increasingly important to predict the exterior noise level of the vehicle at the early stage of development. In this study, the pass-by noise of the accelerating vehicle is estimated by using the sound wave propagation theory above a ground surface of pass-by test site, in which the acoustic characteristics of noise sources measured in semi-anechoic chamber equipped with chassis dynamometer. The principal noise sources of the vehicle are classified into engine, tire-road interaction and exhaust discharge noises. Near field acoustic pattern of these noise sources are measured at several engine speeds within the range of problem engine speed detected from pass-by tests. Characteristic impedance of asphalt surfaces is employed in the wave propagation theory above a ground surface and it is measured indirectly in the actual field. Individual acoustic characteristics of noise sources are synthesized at the microphone position, that one can get the simulated overall pass-by noise distribution as a function of distance or one can rank the contributing noise sources in the problem rpm range. As a result, it is showed that the predicted pass-by noise level is overestimated but within 3 dB, however the overall trend is very similar to the measured one. In this manner, the noise control engineer can plan the countermeasure plans very efficiently from the information of the major contributor, and the refined overall sound level can be predicted. If further studies on the source characteristics including more precise directivity of the sources are pursued, the accuracy of the pass-by noise prediction would be improved considerably.
