반무향실 내에서의 가속 주행 소음 예측 방법

Abstract

We investigated passby noise measurement method In a small-sized semi-anechoic chamber satisfying the American based SAE J1470 Recommended Practice to facilitate the measurements. We have tried two passby noise prediction methods. One is line array microphone method In which the free space sound field Is decomposed into its eigenfunctions in the spherical coordinates and rearranged according to the order of the spherical Hanked function. However, due to the characteristics of the spherical Hanked function, it is Impossible to distinguish the function"s characteristics according to the order In farfield. Consequently It can be applied in the transient region of the nearfield and the farfield. The other method Is nearfield acoustic holography(NAH). Although measuring hologram for the several operational engine sp을effs by conventional scanning method is time-consuming work, we can greatly reduce the measuring time by selecting the appropriate engine speed through preexperimental knoledge. To verify this method we experimented with the outdoor passby noise measurements and the passby noise prediction in the small-sized semi-anechoic chamber for the Identical passenger vehicle and obtained reasonable and acceptable results.