Bell telephone. Historical artwork of a Bell telephone. The telephone is seen in longitudinal section at top. In this original telephone system, the speaker and receiver were identical, with a bar magnet (grainy rectangle) at upper right. In the speaker, sound waves caused vibrations in a diaphragm in the magnetic field around the magnet. These vibrations were converted into an oscillating electric current in the two copper wires touching the magnet. The current ran down the wires and on to a receiver which converted the signal back into sound waves. This telephone was invented by Alexander Graham Bell (1847-1922) who filed the patent in 1876.