Investigation On Sound Insulation Mechanism By 3-D Techniques From The View Point Of System Shape

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At first, sound transmission measurements through plates with SI-technique were carried out followed by the investigations of sound fields on the both sides of the plate using a vector intensity prove. In the measurement, a steel plate was installed in the measurement system to increase the reflected acoustic energy.Since huge amount of three-dimensional data could be obtained in the measurements, they were visualized qualitatively to show the relation between the vibrating plate and sound fields around it. The results shows that, especially in the narrow band measurement below 125 Hz, natural modes of the mounting space give peak-dips in the sound transmission loss measured.Next, on the computational method to obtain the approximated value of radiation impedance, an equivalent circle was newly employed and the required CPU time could be reduced without loosing accuracy. The approximation is effective for the programing of the radiation impedance computing procedure.Then, in acoustic measurements in reverberation rooms, especially measurements in low frequency region below about 125 Hz, the diffusion of the sound field give much influence onto measured data. So, detailed investigations on the relation between room-shapes and their diffusion were carried out by using FEM-program which has been developed and the accuracy of which has been confirmed in this research project. The results which were derived from the comparisons of the standard deviations of the sound pressure distribution in rooms in 1/3 octave band measurements show that the diffusion of the sound field does not change so much according to the source location, i.e. on-corner, on-wall, in-space, in the irregular shaped reverberation room used in this research project. Another investigation on narrow band measurements revealed that almost the same diffusion can be expected if the shape of the reverberation room is irregular.