Recently highway traffic noise level increases gradually day by day and it affects largely on our environment. For reducing this influence a noise barrier is currently being used, the height of barrier increases to get large noise insulation. At present noise barrier of more than 8m is constructed for more than 30km along the highway. A new noise barrier system, by which we can get more attenuation keeping the height lower, is needed. In this study, a new barrier system installing "soft" round obstacle at the barrier edge is examined and the realization of "soft" round obstacle and its problems in practical use are checked.
In 1994, the scale model of 1/10 was used to realize the soft round obstacle. The meaning of "soft" is that the sound pressure at surface of the obstacle is zero, and then an arrangement of 1/4 wave length acoustic tubes was employed. Both of measured and calculated sound pressure at the mouth of acoustic tube were very low and the arrangement of acoustic tubes realized "soft" surface at certain design frequency. The effect of installation of "soft" obstacle at the edge was sbout 7dB (A) for the real traffic noise at the point 25m apart from the barrier.
In 1995, on the base of the result in 1994 the real scale soft round obstacle was made and its effect was checked experimentally. An hole in each well was opened for water drain and thin fins were vertically set at the well mouth for keeping well clean from litter. Despite of these processing the sound pressure at the mouth was nearly zero and the soft surface was realized. This soft round obstacle was installed at the existing noise barrier of 3m high for 200m and the effect of the installation was measured. It was about 3dB (A) at points near to the barrier, but when the distance from the barrier increases it reduces. The additional study on the obstacle would be needed for practical use.