THE LOUD SPEAKER

Hawke's Bay Tribune, Volume XX, Issue 78, 19 March 1930, Page 10

THE LOUD SPEAKER

In its simplest form, the telephone receiver or loud-speaker consists of a thin, soft-iron diaphragm, mounted close to, but not touching, one pole of a bar magnet. A fine wire is coilled round one of the ends of this magnet, and the ends of this coil (which together with bar magnet, form an electromagnet) are connected directly in the circuit where the instrument is to be used. The diaphragm is rigidly supported at its outer edge, but the centre portion will be increased, and the diaphragm will be drawn closer to the pole. If, however, a current is sent through the coil in such a direction as to set up lines of force opposing those of 'the magnet, the strength of the magnet will be diminished, and the diaphragm will spring farther from the pole. If a current that varies in value, but is always in the same direction, is sent throgh the coil, tho lines of force induced in the magnet will increase while the cur rent is increasing, and decrease while the current is decreasing. Thus, a varying pull on the diaphragm will cause vibrations that will be in harmony with the changes of current, whether the lines inrlrr-r] by the coil arc in the same direction as those of the magnet or not. If the current is an alternating one. i.e., one that is first in one direction and then in another, tho lines of force set rip in the magnet will change their direction everv time the current changes its dilection. They will

thus, while in one direction, aid to the strength of the magnet, and while m the other direction diminish it, propducing a varying pull on the diaphragm.