音源の移動による周波数・振幅変調が放射音特性に及ぼす影響

抄録

The variation of the noise metrics of a group of sound sources due to its movement at a constant velocity along a straight track is discussed in the paper. When sound sources move, frequency and amplitude modulation is observed in the radiated sound field. The frequency and amplitude increase when sound sources are approaching and decrease when going away. We found that when frequency and amplitude modulation were considered, the calculated noise levels L_Amax, L_ASmax, L_Aeq,T became larger than the calculated levels without their consideration. The difference of the calculated levels between the cases increased with respect to the sound source velocity. This difference was independent of distance between the track and the receiving point. Approximating discrete sound sources in line by a finite line source would underestimate the noise level. The level of this underestimation would increase by decreasing source division. The underestimated level was calculated for sources with reference noise spectrum for rolling stocks with a constant sound power level as we focused on the influence of frequency and amplitude modulation on the radiated sound field. The underestimated level was large for L_Amax and L_ASmax compared with L_Aeq,T. The difference of the calculated levels between the cases decreased monotonically with respect to the source frequency.