PURPOSE: To make higher the entire height of an exciting coil and to reduce a unit outer diameter by providing a yoke or a pole piece on the upper face or the lower face of a permanent magnet so that two types of height of an exciting part and an exciting coil will be approximately equal and by driving a vibrating part.

CONSTITUTION: A circular yoke 20 is provided on the upper face of a circular permanent magnet 19, and an exciting coil 21 is arranged between a center pole 17 and the permanent magnet 19 and the yoke 20. By providing the yoke 20 on the upper face in the above-mentioned manner without changing a sectional area and the entire height of the magnet 19, the entire height of the coil 21 can be made higher, an outer diameter is substantially reduced with the same number of turns and a unit outer diameter can be smaller. Thus vibrating parts are arranged on the exciting part at every certain interval, and by fixing the vibrating part, for instance, on some part of a front panel of a television set acoustic reproduction can be performed.