The Leslie speaker is a specially constructed amplifier/loudspeaker used to create special audio effects using the Doppler effect. Named after its inventor, Donald Leslie, it is particularly associated with the Hammond organ, an electric organ invented by Laurens Hammond in 1934 and manufactured by the Hammond Organ Company. While the Hammond organ was originally sold to churches as a lower-cost alternative to the wind-driven pipe organ, in the 1960s and 1970s it became a standard keyboard instrument for jazz, blues, rock music, church and gospel music. The Hammond/Leslie combination has become an element in many genres of music. Both brands are currently owned by Suzuki Musical Instrument Corporation.
Unlike a high fidelity loudspeaker, the Leslie is specifically designed, via reproduction of the Doppler effect, to alter or modify sound. Although there have been many variations over the years, the classic Leslie speaker consists of two driver units – a treble unit with horns, and a bass unit, and a crossover that divided the frequencies between the horn and the woofer. The key feature is that both the horns (in reality one working horn with a dummy to counter-balance it) and a sound baffle or scoop for the bass are electrically rotated to create ‘Doppler effect based’ vibrato, tremolo and chorus effects. The rotating elements can be stopped, switched between slow (chorale) and fast (tremolo), or transitioned between the two settings.
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The Daily Omnivore 