| 摘要 |
An electroacoustic calling device comprising a piezoelectric transducer contained in a housing with an aperture therein through which sound is emitted. A closure member for controlling the size of the aperture, and hence the volume of emitted sound, is located in a recess in an arm pivotally mounted on the housing and is urged against the exterior surface of the housing by a projection at the bottom of the recess. The resulting essentially point contact between the closure member and the recess allows the surface of the closure member to align accurately with the surface of the housing, thereby minimizing leakage of sound between such surfaces.
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