Studies on the Noise Abatement Using Trees and Shrubs (II)

On the Effects of Reducing Noise with Variation of Farm Working Noise and Many Kinds of Plants

Abstract

The noise abatement quantity due to trees and shrubs was experimented on the condition that the sound pressure level at the noise source was changed. On the other hand, the capacity of noise abatement due to a tree were measured, and compared with the above noise abatement quantity. Furthermore, we studied the capacity of noise abatement due to trees under the changing sound pressure level at the each spectrum from the play back noise source of some farm machines. The experimental results may be summarized as follows.
1) The capacities of noise abatement of the test grove of Magnolia grandiflora at every frequencies were down by same dB for the distance in spite of the differences of the sound pressure level at the noise source.
2) When the play back noises of a tractor, a forage harvester and a combine in operation were passed through a tree, we found the same abatement tendency on the spectrum distribution.
3) There were some differences in the capacity of noise abatement between the actual test vegetation and the ideal one which was planted densely. The difference of the maidenhair tree was 2.6dB(A), the Japanese ceder 3.4dB(A), the mulberry tree 10dB(A) and Irex rotunda THUNB 0.3dB(A).
The mass of Irex rotunda THUNB was the most superior in these plants on the noise abatement.
4) The variation of the sound pressure level by the tracor was largest at frequencies over 1kHz in the three tested farm machines.
The noise which had smaller variation of sound pressure level was advantageous on the noise abatement due to trees.