Abstract:
It is well known that an absorptive obstacle installed on the edge of a noise barrier can improve sound shielding efficiency without increasing its height. In the present study, efficiency of the noise barrier with a ``soft'' cylindrical edge is investigated. Soft means a surface on which the sound pressure is zero, but it is difficult for traditional materials to realize this surface. It is shown, by numerical and experimental analysis in a two-dimensional sound field, that the ``Waterwheel cylinder'' approximately realizes a soft surface. The Waterwheel consists of acoustic tubes arranged radially; thus the acoustical properties of the Waterwheel's surface (i.e., the sound pressure at the open ends of the tubes) depend on the relation between the depths of the tubes and the wavelengths. Then sound shielding efficiency of a half-plane and a barrier sitting on the ground with the Waterwheel edge has been investigated. The results show that the Waterwheel on the edge improves the noise shielding efficiency by more than 10 dB in a certain frequency range, although the Waterwheel decreases the efficiency of a barrier in another range. The effect depends strongly on the frequency, as the sound pressure on the surface of the Waterwheel does.