| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem wherein limit exists for sufficient and effective restraining of temperature rise of a voice coil. SOLUTION: A vibrating portion 12 includes the voice coil 6, a tubular voice coil bobbin 7, and a diaphragm 8. A magnetic circuit 4 includes an annular top plate 1, an annular magnet 2 bonded to a lower surface of the top plate 1 and magnetized in its vertical direction, and a yoke 30 to form an outer magnet type. The yoke 30 includes a bottom plate 30a and a center pole 30b which forms a magnetic gap G for generation of magnetic force, to drive the diaphragm 8 cooperating with the voice coil 6. The yoke 30 has a space B inside the magnetic circuit 4, surrounded by the lower surface of the top plate 1, an inner peripheral surface of the magnet 2, an outer peripheral surface of the center pole 30b, and an upper surface of the bottom plate 30a, and has a ventilating duct 31 to ventilate with an outside atmosphere of the magnetic circuit 4. COPYRIGHT: (C)2006,JPO&NCIPI
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