| 摘要 |
PURPOSE:To decrease the three-dimensional high frequency distortion and to obtain a speaker unit with the low distortion by providing a voice coil with larger winding width than the width of a magnetic gap, and by setting the driving force constant in spite of the dislocation of the voice coil. CONSTITUTION:A center pole 1B of a pole yoke 1 has the height which is more than the upper limit in the up and down oscillation range of the upper end of a voice coil 5, and taper faces 13 and 13 are formed at the center pole 1B. These taper faces 13 and 13 constitute a magnetic-flux density setting means which makes the value of a force factor B.l constant within the oscillation of the voice coil 5 at least, and thus, the magnetic-flux density distribution in an opposite part 12 of the center pole 1B and the taper faces 13 and 13 becomes the step state. Thus, even if the voice coil 5 has the dislocation, the total magnetic flux which intersects with the coil 5 does not change. Therefore, the value of the force factor B.l becomes constant within the amplitude of the coil 5, and the driving force which operates the coil 5 also become constant. As a result, the driving force of a sine wave is obtained for the sine wave current. |
