| 摘要 |
According to the present invention, a rotation preventive portion for preventing the rotation of bead portion, such as a stepped projection, is provided on the bead portion of diaphragm, which is squeezed between a front shell and a rear shell. When the front shell and the rear shell are assembled with such a diaphragm, the rotation of the bead portion is prevented by this rotation preventive portion (stepped bead). As the result, outer lip of the bead portion of diaphragm or the rolling portion of diaphragm are not squeezed between the front shell and the rear shell, and the front shell and the rear shell can be assembled without damaging or breaking the diaphragm.
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