Leslie speaker

The Leslie speaker is a combined amplifier and loudspeaker that modifies the sound of an electric musical instrument by rotating a baffle chamber (drum) in front of the loudspeaker. A similar effect is provided by a rotating system of horns in front of the treble driver. It is most commonly associated with the electric Hammond organ, though it was later used for the electric guitar and other instruments. A typical Leslie speaker contains an amplifier, a treble horn and a bass speaker—though specific components depend upon the model. Some models have two speed settings, known as chorale and tremolo.

The speaker is named after its inventor, Donald Leslie, who began working in the late 1930s to get a speaker for a Hammond organ that better emulated a pipe or theatre organ, and discovered that baffles rotating along the axis of the speaker cone gave the best effect. Hammond was not interested in marketing or selling the speakers, so Leslie sold them himself as an add-on, targeting other organs as well as Hammond, beginning in 1941. The sound of the organ being played through his speaker received national radio exposure across the US, and it became a commercial and critical success, becoming popular with jazz organists. In 1965, Leslie sold his business to CBS who, in 1980, sold it to Hammond. Suzuki Musical Instrument Corporation subsequently acquired the Hammond and Leslie brands.

Because the Leslie is a sound modification device in its own right, various attempts have been made to simulate the effect using electronic effect units. These include the Uni-Vibe, the Neo Ventilator, and Hammond-Suzuki's own simulator in a box.