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, and a treble and bass speaker—though specific components depend upon the model. A musician controls the Leslie speaker by either an external switch or foot pedal that alternates between a fast and slow 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 sound 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. 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. Today, Suzuki Musical Instrument Corporation owns 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 electronics. Many musicians have used the Univox Uni-Vibe, the Neo Ventilator, or Hammond-Suzuki's own simulator in a box.