| 摘要 |
PURPOSE:To avoid the lowering in resonance frequency with depth of water, by providing a plurality of wedge projections to a reflecting plate made of hard resin member, and supporting an oscillator via an very thin closed cell sponge at the tip of the wedge projection. CONSTITUTION:In a water-proof cover made of a soft resin member, an oscillator and a reflecting plate 8 of hard resin member are provided. This reflecting plate 8 is provided with a plurality of wedge projections and the oscillator is supported at the tip of the wedge projections via a very thin closed cell sponge rubber 9. The oscillator and a boundary surface B' between the oscillator and the rubber 9 are in contact without adhering. With this constitution, sufficient anti-pressure strength under a high water pressure is provided, the contact area with the oscillator is reduced and the effect on the reflecting plate 8 due to contact is decreased. Thus, as the water depth is deeper, the resonance frequency cannot be lowered. |
