Leslie speakers

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A Leslie loudspeaker in a clear plastic case

A Leslie speaker ( Leslie speaker; as rotary speaker, Leslie sound cabinet, Leslie box or shortly Leslie known) is an effect unit in a rig a triggered by rotation for electro-acoustic sound change musical tone signals in which by using Doppler effect beats are produced.

The Leslie is named after its inventor Donald Leslie (1911-2004).


Don Leslie initially offered his invention to Laurens Hammond for his Hammond organ in 1940 , but he categorically refused it. Leslie then founded the company Electro Music in Pasadena and built his systems for the organs. It was not until 1980, after the formation of the Hammond Suzuki / USA company, through the takeover of the CBS company , to which Electro Music now belonged, that there was direct cooperation with Leslie.

Irrespective of these marketing problems, resourceful musicians and technicians have combined both systems since the 1960s and have played a decisive role in shaping the sound of the Hammond organ ever since.

The original name of the Leslie loudspeaker was "Vibratone", but it was also called "Brittain loudspeaker": In 1941, Leslie began a partnership with a Lou Brittain; this was dissolved again after the war. Leslies were also known as "Hollywood Speakers" (they were built in California near Hollywood ) and "Crawford Speakers" (organist Jesse Crawford was the first Leslie salesman in the New York area). In 1946 the name was changed back to "Leslie-Vibratone" to put an end to the mess. Most people simply called her "Leslie" and in 1949 Leslie dropped the name "Vibratone".

It was not until the 1980s that Hammond officially endorsed Leslie's products . Today the successor company Hammond Suzuki USA builds its own rotor loudspeakers with the brand name Leslie.


Cross-section of a typical Leslie loudspeaker

The outstanding feature of a Leslie are the rotating sound emitters that sit in front of the speakers . The purpose of the rotation is to generate a vibrato , that is, to modulate the pitch by using the Doppler effect and the resulting beat . Through reflection on solid walls, several slightly shifted Doppler frequencies are radiated and superimposed, so that a beat effect is created in addition to vibrato.

As the rotating speaker moves away from the listener, the sound becomes deeper. At the same time, however, he approaches the opposite wall, which is therefore exposed to a higher tone, which it also reflects in the direction of the listener. This happens at any point in time in all directions of the room. The listener experiences a very complex sound that goes far beyond a simple pitch vibrato and enriches the Hammond sound.

In connection with the Hammond organ, the Leslie fulfills the same function as a " tremulant in the main wind tunnel" in a pipe organ.


The classic Leslie is designed as a two-way system with separate speakers for the high and bass ranges. The crossover frequency between the tweeter and woofer is around 800 Hz in Leslie makes. Mechanical imitations are placed after 1500 Hz for cost reasons, which of course changes the sound.

Simple models had permanently installed mid-range / tweeters and only the bass drum rotated. There is now also a one-way system.

In the better models , the high frequency range is reproduced by a horn that is designed as a double horn. The sound is only passed through one of the two horns, the other horn serves as a counterweight. The tweeter rotor accelerates and decelerates faster than the bass rotor because the bass rotor has a greater moment of inertia due to its higher mass . The rotation is controlled in two stages via a switch on the organ or via a preamp pedal (combo preamp). Slowly turning the rotors (“chorale”) creates a chorus-like effect. Turning it quickly ("tremolo") creates an effect that is similar to a tremolo . With some models, the rotation can also be turned off. Acoustically particularly attractive are the effects that occur during acceleration and deceleration. The motors for fast and slow rotation in older Leslie models are made up of two individual mechanically coupled motors, while newer models usually only use a single motor, which is provided with a corresponding electronic control.

So-called Rotosonic drums , which function as a bass rotor instead of the sound deflector drum, sound particularly powerful . These drums actually have a 6x9 "loudspeaker in a drum and the sound signal is routed through a specially developed mercury contact. The modulation effect in the bass range is more intense with these models than with the original Leslie. These drums are a lot heavier than that Deflection drums and accelerate or decelerate accordingly more slowly. Leslies with Rotosonic bass rotors have an additional bass loudspeaker which transmits frequencies that are too low for the 6x9 "loudspeaker in the drum.

Other components of the Leslie are the built-in amplifier and, on some models, a reverb unit that is built up with a spring reverb . In addition, a loudspeaker crossover (passive or active) is integrated, which filters out the appropriate frequency ranges for the various loudspeakers. Some Leslie models also have fixed speakers that are used to reproduce non-organ sounds (e.g. string ensemble, piano, bass) or a reverb signal.

The additional designation “cabinet” already indicates a system-related disadvantage of the Leslie: The Leslie unit is large and heavy and therefore difficult to transport. The Leslie cabinet is still only used to generate sound : it does not output the audio signals fed in after processing, as is the case with other effects devices , as it does not have any microphones itself . The microphone pickup of the Leslie enables further influence on the generated sound and plays a special role in music production. At least two microphones have to be used to record the spatiality of the Leslie sound. The arrangement of the microphones and the playback room are critical factors. Mechanical and propeller-like noises can occur, particularly at high rotation speeds.

Despite the aversion of the organ builder Laurens Hammond to the "Leslie effect", the T and N organ models he manufactured were available with built-in rotating loudspeakers, which were also known as Leslie. These were housed in the substructure of the organ and were somewhat smaller than the typical cabinet loudspeakers.


Various manufacturers have tried again and again to recreate the sound character of a Leslie electronically. However, since the typical "floating, whirring" sound is a combination of vibrato, tremolo and phase shift, which also runs differently for high and low tone components, it was only with the availability of faster and cheaper computer power that the effect in the computer succeeded digitally to simulate. With live performances, however, an original Leslie cabinet can easily be distinguished from the electronic simulation for experienced ears. The use of a simulated Leslie is frowned upon among most musicians. A quote from keyboardist Bobby Sparks is: “There's nothing like the real thing, man!” (Nothing is like the real thing, man!) However, the price, weight and bulkiness of a real Leslie cabinet usually make the difference, but one to use digital simulation. An exception is the manufacturer Reussenzehn, who is building a rotary cabinet with a real rotary loudspeaker based on tubes .

Audio samples

The following examples were recorded with an XB-1, a portable, fully digital organ from Hammond.

The first example uses a simple chord to make it possible to hear how the Leslie first runs at low speed (you have to listen carefully to hear the slow rotations of the speakers). Then the Leslie is switched to high speed, and you can clearly hear that the tweeter rotor reaches its top speed much earlier than the bass rotor. Then it is switched back to low speed, whereby the tweeter rotor again drops in speed much faster than the bass rotor.

Hammond organ, Leslie effect slow-fast-slow :

The second example consists of a short chord progression with the Leslie accelerated in three places.

Hammond organ, different sequences with Leslie effects:


  • Thomas Görne: Sound engineering . 1st edition. Carl Hanser Verlag, Leipzig 2006, ISBN 3-446-40198-9 .

Individual evidence

  1. http://www.musiker-board.de/threads/%C3%9Cbersicht-%C3%BCber-die-g%C3%A4ngsten-leslies.615176/
  2. Mercotac products Structure and application of the mercury contacts used in Leslies (English).
  3. https://www.youtube.com/watch?v=Sv2DC5vx_V8
  4. ^ Hammond organ # Effects
  5. http://www.hammond.at/geschichte-musik.html 1967
  6. http://reussenzehn.de

Web links

Commons : Leslie Speakers  - Collection of Pictures, Videos and Audio Files