| 摘要 |
PURPOSE:To reduce a drive current of the pulse current modulating system and to obtain a small-sized acoustic sound body applicable to a watch, by providing a magnetic circuit driving a voice coil and the 2nd magnetic circuit reducing the inductance of the magnetic circuit. CONSTITUTION:Yokes 30, 40 are located on frames 38, 39 in common use of the yokes respectively, a magnet 32 is located on the yoke 30 and a yoke 31 is provided on the magnet 32. The magnetic circuit driving the voice coil 33 is constituted with the frames 38, 39 and yokes 30, 31, 40, and the magnetic resistance for magnetic flux produced at the voice coil 33 is reduced by the magnetic circuit consisting of the frames 38, 39 and the yokes 40, 30. A part of the yoke of the magnetic circuit reducing the magnetic resistance is constituted on the back cover of a watch, and a driven current of the pulse current modulation system is reduced, to make small the size of the sounding body causing alarm sound. |
