Statistical energy analysis is used to predict the noise reduction and the sound radiation efficiency of the rectangular enclosure, when the enclosure are excited by the shaker. Under conditions that the various loss fact0r (especially coupling loss factor) for the enclosure are known, and the enclosure and its wall are excited with the multimodal reverberant vibration, the above equations for the noise reduction and the radiation efficiency can be obtained theoretically. It is shown that by our assumption of the reciving room being the free space or the anechoic room, the external sound pressure near the panel can be obtained from the sum of the resonant sound radiation power and the non-resonant sound transmission power of the panel. The ratio of the non-resonant sound transmission power from the test panel to the sound radiation power from the same area of the infinite rigid panel(such as the piston)having the same velocity with the test panel is obtained. Thus the sum of the second radiation efficiency and the above ratio, that is, the apparent sound radiation efficy is introduced. For the noise reduction and the apparent radiation efficiency including the non-resonant transmission power, experimental results are compared with theoretical predictions with generally good agreement.
This paper describes an experimental method for determining back-scattering in weakly inhomogeneous dispersive system, on which unified theoretical analysis has been reported previously. The requirement for the measurement system is examined generally, and the measurement cell and the electronic system are newly developed to meet those requirements in determining the differential back-scattering cross section of blood at 5MHz. Overall performance of the experimental system is proved to be quite satisfactory. The particle concentration dependency of the differentical back-scattering cross section is studied on blood cell suspension. Experimental results well agree with the theoretical prediction based on previously reported theory. Those results give an experimental support for previously reported form of the spatial correlation function describing the phase geometry of the dispersive system, and also comprises fundamental data for the design of ultrasonic Doppler flowmeter.
This paper describes on numerical calculation and its experimental result of sound field in the stepped tube having finite length with discontinuous reduction or expansion along the radial axis which has been widely used in the acoustic devices. In general, the one dimensional model analogy is easier to investigate a sound pressure distribution along the axis in a tube, however it came out a phase shift between predicted plane wave and experimental one when the node of sound pressure is located at the junction. So, investigation based on the rigorous wave theory is made by including higher order mode in addition to the plane wave in the tube. The sound pressure distributions along the axis and the radial direction in the tube are investigated. In the above mentioned case, it is shown than the effects of higher order mode can not be neglected even in the frequency range lower that first cut off frequency of radial modes.
This paper presents the experimental results on the stationary vibration radiated from the circular plate. First, the approximate expressions for transfer function between the vibration source and surface wave are introduced. These expressions are compared with the experimental results, and it is showed that these expressions are applicable for the range over 2.5 wavelength away from the source, and the dimensionless frequency less than 2. Next, the experimental method and the test results are presented. The experiments are conducted using the half-space model made of the silicone rubber which has internal dissipation. The measured compliance under the plate coincides with the Bycroft's theoretical solution for dimensionless frequency less than 2. The characteristics of the amplitude reduction with distance of radiated wave are largely affected by the dimensionless frequency. For small value of the dimensionless frequency, the amplitude reduction with distance of the wave shows nearly equal to the one of the body wave inside 0.3 wavelength from the source, and also to the one of the Rayleigh wave over the range 2.5 wavelength away from the source.