Studies on the Noise Absorption of Plants (II)
Consideration of Noise Reflection and Refraction, and Tests of Belt Location
1978 Volume 39 Issue 4 Pages 511-516
Details
1978 Volume 39 Issue 4 Pages 511-516
1. Investigation for noise absorption effect of shrub
The continuous increase of the noise level in the community during the past two decades has brought forth a growing awareness of noise pollution. Then, the author studied the noise absorption using vegetation from his preceding report, and performed the calculation of shrub effect.
Then the author have calculated the standard deviation, effective significance and limiting range of the mean absorbing noise for three kinds of plants.
In conclusion, the 3′(0.91m) height from ground had large attenuation of straight noise energy and had excellent stability of noise abatement effects.
2. Interference between the direct sound wave and reflected wave
In order to interpret the systematical variation of the experimental data, an interference pattern between a source and its reflection image was constructed. The noise source was located at 3′(0.61m) height from the ground, which was a value used in most of the experiments. The relative position of the source, its image and the receiver are shown in Fig. 3.
On the result of image and this theoretical consideration, the sound pressure level (SPL) was calculated and computer program was written. The interference patten of maximum and minimum SPL lines superimposing on the inverse square distance law is clearly shown on the three dimensional graph shown in Fig. 4.
3, Belt location test
These tests were conducted to determine the effective location of the shrub barrier between the receiver and noise source (R/S ratio) for selected receiver. The R/S ratio was preset at five levels and relative attenuations were computed with respect to the selected R/S ratio. The results were similar to those obtained by noise test of large forests of the University of Nebraska. However, the lowest relative noise attenuation was observed at R/S ratio of 0.5. The curves indicated that the noise attenuation by shrub was more effective at higher R/S ratio.
