A STUDY ON THE NOISE BARRIER WITH SOFT SURFACE

1993 Fiscal Year Final Research Report Summary

• Project/Area Number: 04650542
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 建築環境・環境工学
• Research Institution: KYUSHU INSTITUTE OF DESIGN
• Principal Investigator: FUJIWARA Kyoji KYUSHU INSTITUTE OF DESIGN FACULTY OF DESIGN PROFESSOR, 芸術工学部, 教授 (00038978)
• Project Period (FY): 1992 – 1993
• Keywords: ROAD TRAFFIC NOISE / NOISE BARRIER / SOFT SURFACE

Research Abstract

As the most convenient method for traffic noise control, we have a method to build noise barrier along the road sides. This method have been used for a long time until now. The surface of the noise barrier currently used is absorptive because of getting large shielding efficiency. But the efficiency is not so large, therefore the efficiency is not taken into account for barrier design. On the other hand, it is not very known that a barrier with "soft" surface reduces noise more than one with absorptive surface does. This study is aimed to make clear theoretically and experimentally how this barrier with soft surface can reduce noise.
In 1992 it was studied whether it satisfies the soft boundary condition to cover the noise barrier surface with array of one quarter wave length acoustic tubes, as the result it was found theoretically and experimentally that this structure satisfies the boundary condition approximately. When one third octave band noise was used as a signal, the same result was obtained. But following the experimental result the array of acoustic tubes did not satisfy the boundary condition perfectly, a little more study was left for the next year.
In 1993 the two dimensional sound field behind the barrier covered with acoustic tubes stood "on the reflective ground" was studied theoretically using Boundary Element Method. Following the result this surface also satisfies the soft boundary condition and it was found that this barrier can reduce the noise more than the absorptive noise barrier can. The same result was also obtained experimentally. Even in this year the perfectness of the soft surface has not been realized.
There is one peak in the frequency characteristics of the road traffic noise, and when the design frequency of the acoustic tube is tuned at the peak frequency, then the noise reduction efficiency of the soft barrier is 3 to 5 dB greater than that of the absorptive one.