植物枝葉に対する騒音の減音作用の部分的見掛け上の増幅的振る舞いについて考察

Abstract

It was begun in about 1972 year for people to investigate and to research how much degree the plant belts would effect the propagation of noise. At initial time, the investigation of very huge object, such as jungles, forests and forest lands, had been done mainly. Soon later, trends of the researching rapidly directed to micro-objects, and many papers, which were to regardto the effect of resonance, absorbing and scattering by leaves and trunks of trees, and plants, had been published. As a result, it has become clear and been proved that the plantings had intrinsically good effect for diminishing the noise figure. These could be regarded to as an action of filtering (that is, when the frequency is above 2kHz, it behaves as a low-pass filter of the cutt-off frequency fc=1～2kHz, and enlarges the attenuation of noise, propagation to the frequency-increasing. And furthermore, the existence of appearently looks-like bands of amplifing action, neighboring 1kHz, has been clearly recognized). In this paper, we would research the phenomena of the amplifing action and would describe to investigate and to consider the noise action, excited in a propagation of sound-wave, which would be appeared within a complicated vibration of object.