Stationary Motor‐Vehicle Noise Assessment in Semireverberant Spaces

An earlier paper [J. Acoust. Soc. Amer. 51, 152(A) (1972)] discussed some early work done by acoustical engineering on no‐load, semireverberant testing. The present paper describes the findings of the feasibility study completed on this type of testing and describes the equipment and facilities in operation in British Columbia to screen approximately 2000 vehicles per day. Semireverberant testing was found to be highly accurate. A control vehicle was measured on several different occasions, and the observed variation (standard deviation from mean =0.7 dBA) gives a realistic indication of the error. Contour plots of the SPL around a typical vehicle show that the measurements are relatively insensitive to microphone placement. Little correlation was found between the results of no‐load tests and the S.A.E. drive‐by test. When the characteristics of the vehicles used in the study were evaluated, several reasons for the poor correlation become apparent. These included narrow‐band muffler characteristics, sour...