Comparison of sound power levels of vehicles traveling on expressways determined by the Square integration method and the Pass-by method

This paper reports on unit patterns (time-histories) of traveling automobile noise measured on expressways. In general, symmetrical patterns were the most common, but many patterns with high noise levels were also recorded for approaching vehicles and after the vehicles had passed. The A-weighted sound power level LW A,Fmax determined by the Pass-by method were compared with the LW A,RMS obtained by the Square integration method. The noise unit patterns were classified by pavement and vehicle type. In all groups, LW A, Fmax corresponded well with LW A,RMS, and the average level difference between them were 0.1 and 0.4 dB. It was found that the difference in the levels of LW A, Fmax and LW A,RMS was related to driving speed, which was thought to be influenced by the time weighting circuit (characteristic F) of the sound level meter. However, the effect is considered to be less than 0.5 dB if the vehicle had been traveling at a speed of about 100 km/h.