Studies on the Noise Abatement Using Trees and Shrubs

Noise Absorption Test on Trees and Shrubs using the Constant Noise Source and the Playback Noise of Farm Machinery

Abstract

The noise from Farm machinery was recorded and played back as the noise source. This noise data was used in the noise absorption test for trees and shrubs.
The following matters were clarified.
1) The capacity of noise absorption due to trees and shrubs was concerned with the area of its leaf surface and with the density of its leaves. This needs higher value and that needs greater size at lower frequency ranges (63-250Hz). At higher frequencies (4-8KHz), even the smaller leaves can produce enough absorption effect. But, at medium frequencies (500Hz-2kHz), there aren't any trees or shrubs which can decrease noise level sufficiently.
2) It seems that noise propagation reaches the peak of sound pressure level at the distance of integer times of the wave length. And more effective abatement can be attained by means of trees and shrubs which can absorb the reflection and the diffraction noise at the above distance.
Although the loud-speaker used in this study is far different from the farm machinery with regard to the sound radiation and the sound power, it can be used as the noise source to study the characteristics of noise absorption due to trees and shrubs, not only to study absolute quantity of noise absorption.