| 摘要 |
PURPOSE:To decrease distortion of irradiated sound and also to improve the performance of assembly by bringing a cup-shape magnetic substance having a taper whose diameter is increased as being parted from a pole face into contact with the pole face with a metallic gap. CONSTITUTION:A taper face 13 where an outer diameter of a pole 1B is increased as the face is parted from an opposite part to a lower side of the opposite part 12 of a plate 3 of the center pole 1B, and further the cup-shape magnetic substance 22 having a taper whose diameter is increased as being parted from the upper face is provided to the upper face of the center pole 1B so that the bottom is in contact with the upper face of the pole 1B. An aperture outer circumferential ridge 22a of the cup-shaped magnetic substance 22 and a magnetic face 24 of the center pole 1B are set so as to keep a prescribed distance L without giving adverse effect on the distribution of magnetic flux density. Thus, the distortion of irradiated sound is decreased and a value of a force coefficient B.l is made constant within the amplitude of at least a voice coil 5. |
