It is well-known that the experimental results for transmission loss of a single wall usually show greater values than those based on only the mass law in the low frequency region. In order to explain this phenomenon, A. London introduced the resistive factor of the wall impedance in addition to the mass law. However, the value of this resistive factor R was established adaptively from the observed experimental data and was not systematically calculated from the standpoint of the internal energy dissipation mechanism of wall materials. This paper proposes a trial of systematic method for estimating the resistive factor R of the single wall based on the sequential observation of noise evaluation level L_x. The stochastic approximation method is used in order to overcome the difficulties based on both the non-Gaussian property of random fluctuation wave form and the non-linearity being latent in the environmental noise phenomena. This estimation method is applied to observed data obtained by means of the reverberation room method. The estimated results are in good agreement with the experimental results obtained by other investigators and those by authors.
By use of the S. E. A. evaluation method by Crocker and Price, a considerable discrepancy between the theoretically evaluated values and experimentally observed values can be seen specially in the low frequency region. In this paper, a new trial of improved S. E. A. method is proposed which introduces the proper nonresonant power flow II_15 into the Crocker and Price's method. A good agreement between the theoretical values and experimental data is able to be found for several different types of double-walls. Essentially, our improved method is applicable not only to a general type of parallel double-wall but also to an absorbent double-wall having sound-absorbing material around the edges of the air cavity between two panels. Furthermore, for the purpose of confirming its effectiveness and flexibility, the evaluation method is newly proposed for non-parallel double-wall which has not been previously studied from a theoretical viewpoint. An agreement between theory and experiment is satisfactorily explained for these three kinds of double-wall structure by using our improved S. E. A. method.
The paper presents the characteristics of a horizontal resonant frequency of the rectangular rigid bodies on soil surfaces. It is confirmed that the horizontal resonant frequency is more affected by the height of the center of gravity, and also it is closely related with areas and shapes of contact base of the rigid bodies. It is shown experimentally and theoretically that the horizontal resonant frequency considerably decreases with increasing the height of the center of gravity and the side length ratio, and decreasing the contact areas. Furthermore, this paper describes the theoretical investigations which agree approximately with experimental results for the characteristics of the coupled motion of the vibration pickup with the rectangular contact base.