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

首先，通过板与SI技术的声透射测量进行了随后的调查，在板的两侧使用矢量强度证明的声场。在测量系统中安装了一块钢板以增加反射声能，由于测量过程中可以获得大量的三维数据，因此定性地可视化了振动板与其周围声场的关系，结果表明，特别是在125 Hz以下的窄带测量中，安装空间的固有模态在测量的声音传输损失中产生峰谷。其次，在计算辐射阻抗的近似值的方法上，新采用了等效圆，在不损失精度的情况下减少了所需的CPU时间。这种近似方法对于编制辐射阻抗计算程序是有效的。在混响室声学测量中，特别是在125 Hz以下的低频区域，声场的扩散对测量结果有很大的影响。因此，详细的调查房间形状和它们的扩散之间的关系进行了使用有限元程序，已经开发和准确性已在本研究项目中得到证实。通过对室内1/3倍频程声压分布标准差的比较，发现在本研究所用的不规则形状混响室中，声源位置对声场扩散的影响不大。对窄带测量的另一项研究表明，如果混响室的形状不规则，则可以预期几乎相同的扩散。

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.