Rotating speaker

The Leslie speaker is a combined amplifier and two-way loudspeaker that projects the signal from an electric or electronic instrument, while modifying the sound by rotating the loudspeakers. It is most commonly associated with the Hammond organ, though it was later used for the 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. A musician controls the Leslie speaker by either an external switch or pedal that alternates between a slow and fast speed setting, known as "chorale" and "tremolo".

The speaker is named after its inventor, Donald Leslie. Leslie began working in the late 1930s to get a speaker for a Hammond organ that had a closer emulation of a pipe or theatre organ, and discovered that rotating the speaker gave the best sound 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. Leslie made the first speaker in 1941. The sound of the organ being played through his speakers received national radio exposure across the US, and it became a commercial and critical success. It soon became an essential tool for most 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 emulate the effect using electronic effect units. Musicians have used the Uni-Vibe, the Neo Ventilator, or Hammond-Suzuki's own simulator in a box.

Leslie worked as a radio service engineer at Barker Brothers Department Store in Los Angeles, which sold and repaired Hammond organs. He bought one in 1937, hoping it would be a suitable substitute for a pipe organ. He was disappointed, however, with the sound in his home compared to the large showroom where he originally heard it. Consequently, he attempted to design a speaker to overcome this. He initially tried making a cabinet similar to Hammond's, but soon concluded that pipe organs produced a spacially varied sound because of the different location of each pipe. He set out to emulate this by making a moving speaker. He tried various combinations of speakers and speeds, and discovered that a single one running at what's now known as the "tremolo" speed worked best. After further experimentation, he decided that splitting the signal into a rotating drum and horn helped accentuate bass and treble frequencies.

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