摘要：

PURPOSE:To suppress unnecessary peak acoustic pressure at a high band by setting the fixed part at peripheral part of a piezo-electric vibrator to the non- circular shape, and suppressing efficiently the higher resonance. CONSTITUTION:Basically, the fixed part 15 at peripheral part of a piezo-electric vibrator 6 consisting of a metallic diaphragm 1 combining a ceramic piezo-electric body 2 is set to the non-circular shape as shown by the oblique lines. Concretely, the shape of stepped part 5 of a case 4 having a sound releasing hole 3 at the upper surface is set to an oval shape. The actual lines in the figure show an acoustic pressure frequency characteristic when the ratio of the long diameter and the short diameter of the oval is 1.05/1, and the broken lines show an acoustic pressure frequency characteristic when the ratio of the long diameter and the short diameter is 1.25/1. The smaller the ratio of the long diameter and the short diameter is, the larger the unnecessary acoustic pressure peak at the high band is. As the ratio goes to larger, the unnecessary acoustic pressure peak at the high band goes to smaller. The ripple goes to larger in the unnecessary reproducing band up to 3.4kHz. Practically, the ratio of the long diameter and the short diameter is preferable to exists in the range of 1.05/1-1.25/1.

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