 Less common types of drivers are supertweeters and rotary woofers.The mechanism most widely used in speakers to convert the electric current to sound waves is the "dynamic" or "electrodynamic" driver, invented in 1925 by Edward W. Kellogg and Chester W. Rice, which creates sound with a coil of wire called a voice coil suspended between the poles of a magnet.There are others which are far less widely used