| 摘要 |
PROBLEM TO BE SOLVED: To obtain an excitation woofer whose minimum resonance frequency can easily be changed in matching with a prescribed setting position, even after a case main body is installed to the woofer. SOLUTION: A case is formed by providing a lower cover placed and fixed to a prescribed position and an upper cover fitted to the upper part of the lower cover, an outer cylindrical circumferential collar is placed in the inside of the case, a magnet and a plate are placed in the inner center of the outer circumferential collar to form a magnetic circuit and a butterfly damper 1 which supports the magnet and the plate via the collar is provided. A ring inner circumferential part 1a is provided to this butterfly damper 1, and an outer circumferential part 1b extended as a ring to the outside is provided, plural extending and contracting parts 1c that are placed between the outer circumferential parts 1b and the inner circumferential part 1a to be extended/ contracted through engagement, and a center shaft, extended to the outside of the case, is fixed to the inner circumferential part 1a of the butterfly damper 1 so that the length of the extending and contraction parts 1c is capable of expansion and contraction by turning the center shaft from the outside of the case.
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