The Hammond organ is an electric organ, invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Various models have been produced, most of which use sliding drawbars to create a variety of sounds. Until 1975, Hammond organs generated sound by creating an electric current from rotating a metal tonewheel near an electromagnetic pickup, and then strengthening the signal with an amplifier so that it can drive a speaker cabinet. Around two million Hammond organs have been manufactured, and it has been described as one of the most successful organs. The organ is commonly used with, and associated with, the Leslie speaker.