In a previous paper, a unified procedure of evaluation of noise and vibration control systems has been proposed for the case when random noise and vibration waves of arbitrary distribution type is passed through various type of linear noise and vibration control systems. The validity of this theoretical consideration was experimentally confirmed by applying to only a typically simple noise control system like a single-wall. In this paper, systematical consideration about the insulation properties of general double walls with arbitrary random incident sound waves, which are used very often in the actual engineering field of noise control and its statistical evaluation are given in detail as a typical example of a methodological study on statistical evaluation of noise and vibration control systems. That is, firstly, the impulse and step response properties of general double walls are concretely discussed by developing the theoretical results shown in the previous paper and by using the method of transfer function. Next, a probability density expression of the noise intensity, which is sometimes more important than the instantaneous sound pressure itself in the evaluation and control problems, have been theoretically shown. Experiment was carried out for a double wall composed of two identical aluminum panels which was fixed between two reverberant rooms, using a white noise generator. We can find a good agreement between theoretical and experimental results.
The graphical expression of the internal structure on the problem of elastic dynamics written in stress tensor and velocity vector, makes the consideration of the performance of elastic systems easy. This paper is concerned with the equivalent electrical circuit expressions and wave equations of the elastic systems. The spatial distributed electrical circuit corresponding to the equation of motion and the equation of equilibrium for a three dimensional isotropic elastic medium, is introduced by mobility analogy. The equivalent circuit expressions are made for longitudinal waves and transverse waves propagating through infinite medium, for those waves in plates, for those waves and torsional waves in bars, and for transverse waves in the stiff strings and in the plates on elastic medium. From these expressions the wave equations are derived. By neglecting some components of the equivalent circuit according to the condition of the medium, methods of simplifying the wave equation are shown. The equivalent circuits including loss factors are discussed. As computer simulation of the equivalent circuits can be realized by means of the finite difference method, the numerical solution of the problem of the vibration written in wave equation can easily be obtained.
In this paper, an analytical technique for calculating the amplitude of reflected sound waves from a cylindrical target of finite length is treated. Both sound source and receiving point are assumed to be located at the same position, apart far from the target. The approximate formulas for the reflectivity are derived under certain geometrical restrictions. The reflectivity is termed as the "directional sound reflectivity of the cylindrical target", which is defined as the ratio of the sound pressure of the reflected wave from a target to a certain pressure which is to be calculated based on the theory of geometrical optics. To verify the validity of the approach, some experiments were performed in air at the frequency of 39. 00 kHz. The results qualitatively agree with the calculated ones by the present method. This confirms the usefulness of the present technique to calculate the reflection of sound waves from a cylindrical target.
The effects of wind and temperature profiles on sound propagation are discussed on the base of a generalized wave equation, which is obtained from the fundamental equations of hydrodynamics. It is assumed that the sound source and receiver are both located on a absorptive ground, and that the profile shapes of wind velocity and air temperature are expressed as functions of height only. The approximate solution for the wave equation is found out by the method of smooth perturbation. By considering the contribution of the scattered waves of higher order, an approximate expression for SPL increase on the ground is obtained. The validity of our theoretical discussion is confirmed by the scale model experiments in a wind tunnel, which were carried out by authors as well as by Tachibana et al. . Finally, comparing the experimental data by Tachibana et al. with the results of V. I. Tatarski's theory for the fluctuation of sound pressure amplitude, it is found that takagi's theory explains satisfactorily the amplitude fluctuation characteristics of the sound which propagates leeward.