Journal of Japanese Society of Turfgrass Science
Online ISSN : 1884-4022
Print ISSN : 0285-8800
ISSN-L : 0285-8800
Studies on Noise Reduction by Vegetation and Ground
Akira MISAWA
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1980 Volume 9 Issue 2 Pages 155-174

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Abstract
The author made some experiments on the functions of noise reduction by vegetation and ground in a reverberation room, nurseries and fields.
The qualitative results of the investigations are summarized as follows:
The noise reduction by forests are classified according to their functions in two categories; reflection and absorption. It was explained that reflection was more important than absorption for the function of noise reduction. This theory is not the traditional one. The effect of the reflection increased as the density of foliage and the size of the leaves. Therefore, the broad leaved trees were better than the conifers.
The noise was notably reduced according to the reflection by forests at high frequency bands. But by grass fields, it was remarkably reduced at a low frequency of less than 500Hz, and the reason was cosidered that the noise reduction was related to the softness of the top soil, not the species of grass. For that reason, the excess attenuations in decibels by forest become smaller at a frequency between 500 and 2000Hz. But by hedge, they become uniformly larger in proportion as the frequency increases, because the quantity of absorption by ground is too small.
As mentioned above, it was considered that the most appropriate planting design had many hedges each owning foliage until the ground was perpendicular with the couse of sound propagation and kept the top soil soft on the planting site.
On the other hand, plants assist the wind in masking some offensive noises. This masking is not effective against traffic noise, but it is very interesting in acoustical psychology and further quantitative studies are necessary for acoustical control in the exterior environment.
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