The Leslie Speaker Sound
Donald James Leslie (April 13, 1911 – September 2, 2004) created and manufactured the Leslie speaker that refined the sound of the Hammond organ and helped popularize electronic music.
Leslie experimented with devices to, in his words, improve the sound of the Hammond organ, based on experience he gathered from other jobs, including fixing radios and one at the Naval Research Laboratory in Washington, D.C., during World War II.
Donald Leslie was very impressed with the sound of a Hammond organ in a concert hall but less taken with it in a confined space—the sound had no resonance, and the pure electronic oscillators sounded "dull, shrill, and still" to Leslie's ear. To remedy this problem, in 1937 he invented a special speaker which rotates inside its cabinet, producing a Doppler effect which modulates the sound, to a certain extent imitating the resonance of the organ in a large, hall space by projecting it in 360 degrees. This device was eventually one of over 50 patents he owned.
Source: Wikipedia
