抄録
It is well-known that an absorptive obstacle installed on the edge of a noise barrier improvessound shielding efficiency without increasing the height of the barrier. In the present study, the efficiency of a noise barrier with an acoustically “soft” cylindrical edge is investigated. “Soft” indicates that the sound pressure at the surface is zero. It is dimcult, however, frotraditional materials to achieve a soft surface. It is shown that a “Waterwheel cylinder” approximates a soft surface by both theoretical and experimental analysis in a twodimensionalsound field. The Waterwheel consists of acoustic tubes arranged radially; therefore, the sound pressure at the open ends of the tubes (i.e., the surface sound pressure ofthe Waterwheel) depends on the relation between the depths of the tubes and the soundwavelength. The sound shielding efficiency of a half-plane with the Waterwheel cylinderwas measured using a scale model. The results show an improvement in the noise shieldingefficiency by more than 10 dB in a certain frequency range but, unfortunately, the Waterwheeldecreases the noise shielding efficiency of a barrier in another frequency range. Thenoise shielding efficiency is strongly frequency dependent, as is the surface sound pressure ofthe Waterwheel.
