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

通过现场测量和缩尺模型实验，研究了雪地声场的传播特性，并提出了改进的雪地声场寻址方法。1999年和1999年两个冬季在新泻县进行了自然地表条件下和压缩条件下雪地上声传播的现场测量。测量了雪的表面声阻抗、吸声系数、雪介质中的声传播常数等声学特性。结果表明，在中低可听频率下，随声传播而产生的声衰减很强。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，高频下的声音传播也很顺利。当声源高度在4m或6m左右时，低频和中频传播衰减减弱，声传播特性得到改善。用超声频率声源和传声器进行的缩尺模型实验清楚地证实了这一趋势。研究还发现，随着声频的增加，雪地介质中的声衰减越强。低频时传播速度较低，高频时接近空气中的声速。这些特性与典型的多孔吸波材料如玻璃棉和岩棉的特性相同。在1/50比例尺模型实验中，采用双层毛巾和黄麻贴身作为雪地声场，利用FFT分析了不同条件下雪地声场传播的传递函数，并将其应用于雪地声场的可听化。

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.