In this paper, an expression for predicting L_<50> of noises from an exponentially distributed vehicles flow was derived mathematically based on a simplified new model which consists of a point source and line sources. The location of the point source was determined from a case where the road length is infinite and observation point is on the road so that the SPL from the new model may coincide with L_<50> from the exponentially distributed vehicles flow in the same situation. It was found out that the value from the expression agreed satisfactorily to the value from simulated calculations and that the expression is applicable not only to an infinite-length road but also to an arbitrary finite-length road. Some consideration was also taken on a method of correction often used for predicting L_<50> where the road length is finite.
Rotating diffuser is practically indispensable for sound power determenation of discrete-frequency sound source in a reverberation room. If the rotating diffuser has full effectiveness, even a single fixed microphone may be sufficient to measure the space-averaged mean square pressure, or else the relation between the diffuser rotating speed and the microphone traversing or switching speed shall be considered for effective averaging when the microphone traverse or array is used with the rotating diffuser. In this paper, the variances for squared pressure with frequency, microphone position, diffuser direction and those interrelation, and the correlation with diffuser direction were theoretically and experimentallay discussed on a simple plane diffuser, using the field variation coefficient and the number of independent sound fields by the diffuser rotation. Then the good agreement was obtained between theoretical and experimental results. The diffuser vary the sound field incompletely in a room, but create independent fields at every quarter wave length of displacement of the diffuser edge within the varied fields.
Some experiments concerning the propagation characteristics of stress pulses in strip plate with a discontinuous cross section were made for purpose to investigate about the propagation of sound wave in various constructions. Reflection phenomena depending on the pulse duration time and the ratio of cross section of incident and transmitted media were observed by means of semiconductor strain gauge. Reflection coefficient of pulse decreased with increasing of the duration time and the ratio of the cross section. Moreover the propagation behavior of stress pulse passing through a discontinuous cross section in strip plate were observed by dynamic photoelasticity method. The transmitted pulse passing through the discontinuous cross section propagated spherically. Maximum stress by super-position of incident pulse and reflected one was produced at the position of about 5mm in incident side from the discontinuous position. Propagation velocity of spherical stress pulse in transmitted media increased with increasing of the ratio of cross section of strip plate.
Up to now, various studies for finding the mutual relationship among several type noise evaluation indices closely connected with an equivalent continuous sound level, L_<eq>, and a widely used evaluation index, L_x. which are very important in the field of noise evaluation and regulation problems, were reported by many investigators. Almost all of these studies, however, were confined only to the practical method of applying directly the well-known linear regression analysis method to actually observed data and/or finding an approximate evaluation under the assumption of a standard Gaussian distribution form of level fluctuations. If one want to find universally and objectively the more precise relationship among the above noise evaluation indices for the non-Gaussian type actual noise level fluctuations in a daily life, one can not use the above practical method just as it is. From such an essential point of view, in this paper, a general theory for the mutual relationship among several type noise evaluatin indices connected with two typical indices, L_<eq> and L_x, which is objectively applicable for any kind of random noise data, has been first proposed in a general form including the well-known simplified relationship based on the Gaussian distribution in a special case. Finally , the validity of the proposed theory has been experimentally confirmed too by applying it to the actually observed road traffic noise