1976 年 32 巻 9 号 p. 540-547
In analysis of road traffic noise, the width of the road is usually neglected. The road span and distribution of vehicles on it, however, have a great influence on the sound fields especially in the vicinity of the road. To investigate these problems we statistically studied the noise fields emitted by acoustic point sources randomly distributed on a strip shown in Fig. 1. Mean, variance and the other cumulants of sound intensity are derived and expressed in Eqs. (2・7)〜(2・8) respectively. Attenuation characteristics of mean sound intensity with distance along various directions are shown in Fig. 2. These attenuation curves have an identical asymptotic straight line corresponding to the mean sound intensity around a random distribution of point sources on a straight line. Similar attenuation curves for standard deviation and coefficient of variation of sound intensity are also illustrated in Fig. 3 and 4 respectively. We also consider the time and space correlation of the sound intensity fields emitted by moving point sources on the strip. When the velocity of moving sources is equal and constant a simple expression for the time correlation of sound intensity is derived as in (3・6) and shown in Fig. 6. The time correlation at the fixed observation point is a monotonically decreasing function of the time difference τ and usually becomes less than 10% for τ≧3. Furthermore the correlation curves for ρ_0≧4 tend towards the limiting one labeled as ρ=∞ and expressed by Eq. (3・10) which corresponds to the equation derived from moving point sources on a straight line.