Study on investigation of sound propagation on snow field and study on improvement method of sound information addressing

通过野外测量和缩尺模型试验，研究了雪地声传播特性，并提出了改进的雪地声寻址方法。1999年冬季和1999年冬季，在新泻县进行了自然和压缩条件下雪地声传播的现场测量。对雪的声学特性，如表面声阻抗、吸声系数、声传播常数等进行了测量。结果表明，在中低频区，声传播过程中的声衰减非常强烈。这样的频率区域是非常重要的，其中几乎包括语音的频谱。另一方面，在高频中的声音传播被平稳地执行。当声源高度较高时，在4 m或6 m左右，中低频传播衰减减弱，声传播特性得到改善。利用超声频率声源和传声器进行的缩尺模型实验再次证实了这一趋势。研究还发现，随着声音频率的增加，雪介质中的声音衰减更强。低频时传播速度较低，高频时传播速度接近空气中的声速。这些特性与玻璃棉、岩棉等典型的多孔吸附材料相同。在1/50的模型试验中，以双层毛巾和黄麻布作为雪场，利用FFT分析了不同条件下雪场声传播的传递函数和雪介质中的传递函数，并将其应用于与雪有关的声场可听化。

Field measurements and scale model experiments were carried out to investigate the sound propagation characteristics over snowfield and to obtain the improved sound addressing method over snowfields. Field measurement of sound propagation over snowfield with natura1 surface condition and compressed condition were carried out at Niigata prefecture in both winters of 1999 and 1999. Acoustical properties of snow, such as acoustic impedance of the surface, absorption coefficient, sound propagation constant in snow media also was measured. It was found that sound attenuation with sound propagating was very strong at low and middle audible frequency. Such a frequency area is very important, where spectra of speech almost are included. On the other hand, sound propagation in high frequency was smoothly performed. In case of height of sound source was high about 4m or 6m, attenuation at low and middle frequency propagation weakened and sound propagation characteristics would be improved. This tendency was clearly reconfirmed by the scaled model experiments using ultrasonic frequency sound source and microphone. It was also found that sound attenuation in snow media was stronger as frequency of sound was higher. As for propagation speed was low at low frequency and it closed to the sound speed in the air in higher frequency. Such characteristics were same as those of typical porous absorptive materials such as glass wool and rock wool. Double layered towel and jute close was match as the snowfield in 1/50 scale model experiment.Transfer functions analyzed by FFT on sound propagation over snowfield with various condition and those in the snow media were applied to auralization of the sound field concerning with snow.