Donald James Leslie (April 13, 1911 – September 2, 2004) created and manufactured the

Leslie speaker The Leslie speaker is a combined amplifier and loudspeaker that projects the signal from an electric or electronic instrument and modifies the sound by rotating a baffle chamber ("drum") in front of the loudspeakers. A similar effect is provided ...

that refined the sound of the

Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Multiple models have been produced, most of which use sliding drawbars to vary sounds. Until 1975, Hammond organs generated s ...

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 repairing

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...

s and one at the

Naval Research Laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...

Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...

, during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. Donald Leslie was impressed with the sound of a Hammond organ in a concert hall but less enthused with it in a confined space. There, 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 speaker which rotates inside its cabinet, producing a

Doppler effect The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

which modulates the sound. To some extent this imitates the resonance of the organ in a large auditorium by projecting it 360 degrees. This device was eventually one of over 50 patents he owned. When Leslie presented

Laurens Hammond Laurens Hammond (January 11, 1895 – July 1, 1973), was an American engineer and inventor. His inventions include the Hammond organ, the Hammond clock, and the world's first polyphonic musical synthesizer, the Novachord. Youth Laurens ...

with his handmade organ speaker, the company rejected it. Leslie then chose to manufacture his Leslie speaker himself. He founded Electro Music to produce the speakers. Wanting to keep control of their organ's sound, Hammond went to great lengths to defeat Leslie's invention: changing connectors on newer models, and forbidding Hammond organ merchants to sell Leslie speakers. In 1965 his company was acquired by CBS. Leslie remained as a consultant long enough to see Hammond's death in 1973, at which point Hammond's company warmed to the invention, officially honoring it in 1978. Leslie retired in 1980. It was predominantly used for liturgical and gospel church organs creating a Theatre Organ Tremulant effect. It was used with the Hammond Tone Wheel Organ as well as others in the 1940s through 1950s as well as today. The final version of the Leslie speaker is the Rotosonic drum wherein a loudspeaker is physically mounted in the spinning rotor with a narrow aperture (opening) to produce an authentic Theatre Organ tremulant sound. It was also used in

psychedelic Psychedelics are a subclass of hallucinogenic drugs whose primary effect is to trigger non-ordinary states of consciousness (known as psychedelic experiences or "trips").Pollan, Michael (2018). ''How to Change Your Mind: What the New Science of ...

and

rock music Rock music is a broad genre of popular music that originated as " rock and roll" in the United States in the late 1940s and early 1950s, developing into a range of different styles in the mid-1960s and later, particularly in the United States an ...

of the 1960s and 1970s. It has since been used in many genres of music, including pop music and jazz. It wasn't until the 1980s that Hammond bought Leslie's product to include with their organs. Leslie was inducted into the American Music Conference Hall of Fame in 2003.https://articles.latimes.com/2004/sep/07/local/me-leslie7 Los Angeles Times, Donald Leslie, Obituary, 7 Sept. 7, 2004

References

External links

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NAMM Oral History Interview
May 13, 2001 {{DEFAULTSORT:Leslie, Donald 1911 births 2004 deaths American audio engineers 20th-century American engineers 20th-century American inventors