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The Leslie speaker is a specially constructed amplifier/loudspeaker used to create special audio effects using the Doppler effect by rotating the speakers or a sound-directing duct. Named after its inventor, Donald Leslie, it is particularly associated with the Hammond organ but is used with a variety of instruments as well as vocals. The Hammond/Leslie combination has become an element in many genres of music. The Leslie Speaker and the Hammond Organ brands are currently owned by Suzuki Musical Instrument Corporation.
A chord is played on the organ while the Leslie speaker is switched from slow to fast and back to slow.
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Leslie originally bought a Hammond organ in 1937, in the hope it would be a suitable substitute for a pipe organ, but was disappointed with the sound in his home compared to the large showroom where he had originally heard it. Consequently, he attempted to design a speaker to overcome this. He initially tried making a cabinet similar to Hammond's own, but then surmised the variation in sound a pipe organ produced because of the different location of each pipe meant he should try making a moving speaker. He tried various combinations of speakers and speeds and discovered a single one running at what's now known as the "tremolo" speed worked best. Further experimentation resulted in the familiar combination of a rotating drum and horn for bass and treble frequencies respectively.
By 1940, Leslie decided his prototype was ready to market, and went to the Hammond Organ Company to demonstrate it. But Laurens Hammond in particular was not impressed with Leslie's attempt to better his own organ design. Leslie did work for the local electric company, in a contract with Hammond, to replace the old fifty-cycle rotor tone generators with the new sixty-cycle units, in customers' homes. The speaker's first name, in 1941, was the "Vibratone". The name was used later by Fender Guitar Company for a speaker system and effects unit containing a Leslie rotating speaker. Fender also used the name "Leslie" after Leslie sold his company, in 1965, to CBS, which had also acquired Fender. From 1941, when the first units were produced, the speaker went by several names, including "Brittain Speakers", "Hollywood Speakers" and "Crawford Speakers", before returning to the name "Leslie Vibratone" in 1946. Seventeen years after it had rejected him, Leslie offered to sell the company to Hammond. After thirty days he had heard no word from Hammond, Don Leslie said: "After seventeen years, the thirty day period is up. Too late".
In 1980, the Hammond Corporation finally bought Electro Music and the Leslie name from CBS. To this day it remains part of Hammond under Hammond Suzuki, USA.
Leslie never advertised his speakers. After demonstrating a prototype (a rotating baffle in a hole in a small closet with a big speaker in the closet near Leslie's home organ) with Bob Mitchell, an organist with radio station KFI in Los Angeles, a contract was made to install another prototype in the station's studios, where Mitchell would be the only organist authorized to use it. Mitchell was so impressed, that he even tried to patent the speaker, but discovered that he couldn't. Soon afterwards, Mitchell became an organist with the Mutual Broadcasting System, and played a Hammond with the Leslie on its shows. The national exposure was swift and sure. Organists, professional and amateur alike, wanted to have "that sound". Jazz organist Jimmy Smith helped to popularize "that sound" among rock-n-roll musicians in the late 1950s and early 1960s. The Leslie of that time was over sixty inches tall (about the size of a modern refrigerator), and was named the 30A. Don Leslie made a whole series based on the 30A, called "Tall Boys" (31 series). In the 1950s, Leslie introduced the 21H for use in homes, concert hall venues and smaller radio sound stages.
Today, Leslie parts are available from a number of sources. There are also websites with plans (and photographic examples) for constructing a Leslie speaker, with much improved electronics and speakers. On the web, one can see a 500 W high-performance Leslie.
The classic Leslie is still made and sold to this day, though similar effects can now be obtained via analogue electronic devices and digital emulation. Chorus and phase shifter devices can mimic the sounds produced by a Leslie speaker; in fact, early phase shifters like the Uni-Vibe were specifically marketed as low-cost Leslie substitutes for guitarists, and used a foot-operated fast/slow switch. Although the sound of a Leslie speaker heard in person is quite distinct, some digital emulations of the Leslie Doppler effect have become virtually indistinguishable from the sound of a recorded Leslie speaker.
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 stationary treble unit with spinning horns, and a stationary woofer and spinning rotor, with a crossover, that divides 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 counterbalance it) and a sound baffle or scoop for the bass are electromechanically 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.
To stop a Leslie's rotor, a special brake circuit was added to the Leslie motor controls, that incorporated a tube relay, which sent the rotors into chorale before cutting power from the rotors to bring them to a quicker stop. Solid state relays now make this possible. A three-position switch must be used to allow the rotors to "brake" on a two-speed Leslie. Some other model Leslies had no slow motor and were basically one speed, "fast" or "off."
Much of the Leslie's unique tone is due to the fact that the system is at least partially enclosed, whereby linear louvres along the sides and front of the unit can vent the sound from within the box after the sound has bounced around inside, mellowing it. The tone is also affected by the wood used. Tone differences, due to cost cutting using particle board for speaker and rotor shelves instead of the previous plywood, are evident in the Leslie's sound. The thinner ply of the top of the cabinet adds a certain resonance as well. Like an acoustic instrument, a Leslie's tone is uniquely defined by its cabinet design and construction, the amp and speakers used, and the motors—not merely by the spinning of rotors.
Unlike most popular music amplifiers and equipment, Leslie Speakers use an amphenol connector to interface directly to an organ. Older models that used tube power amps used a variety of 6-pin connectors, while later models used a 9-pin connector. In all cases, the mains power, audio and control signals were all carried on the connector, and the design of the pin layouts varied between organs and speakers. Care must be taken when attempting to service them, as an incorrectly or poorly wired cable can cause permanent damage to the organ and / or speaker, or result in electrocution.
A separate device known as the "Combo Preamp" is necessary to connect a vintage Leslie to another instrument such as a guitar. The Combo Preamp combines a separate AC input and line level input onto a single amphenol connector. Modern products such as the Trek II UC-1A  allow any instrument with a phone jack connection to use a variety of Leslie speakers.
Modern Leslie speakers have an 11-pin interface that is safer to service, as the mains power is carried separately using a standard IEC mains connector.
The smallest Leslie is the Leslie Model 16, made in 1970. It has a Fender-like speaker body and a rotating foam dispersion block. It was built for rough club touring, was portable, and had "Leslie" written on the front. It was also released later as Fender/CBS's "Vibratone". Stevie Ray Vaughan used this model on the song "Cold Shot" from the album Couldn't Stand the Weather. It can also be heard on Cream's "Badge" and Jimi Hendrix' "Little Wing".
An earlier model, essentially a single-speed 125. Like its successor, the 25 has one 12-inch speaker pointed into a single wooden baffle. These Leslies are relatively inexpensive, and in recent years have been made popular with guitarists wanting to achieve effects similar to those of Pink Floyd.
The Model 122 is the classic two speed 40 Watt tone cabinet most commonly used with Hammond console organs, such as the B3, C3 and A100 models. Some organists connect two or more of these to their organ for a louder and more widely-spaced "surround" effect. A modern reproduction is the model 122A. This is the Leslie of choice for recording studios or other sonically demanding applications due to the quiet operation of the Model 122's differential signal input design. Leslie Model 142 is identical to Model 122, except that it is housed in a 33-inch-tall cabinet, and thus slightly easier to transport than the 41-inch-tall Model 122, with a different overall sound, that being of less but tighter bass.
Model 122 RV
This unit has the same amp, speakers, motors, 6-pin Leslie cable, as the 122 with the addition of a dedicated tube reverb amp and an extra reverb speaker. The reverb amp is located next to the treble rotor in an enlarged upper cavity to compensate for the amp, which shortens the bass rotor speaker cavity slightly, keeping the RV the same overall dimensions as the 122. The reverb amp, tapping AC off the 122 amp from a stock AC outlet set aside for a reverb amp, receives an audio signal taken off the Leslie crossover. The reverberant signal then feeds a single Jensen 6x9-inch speaker situated within the bass speaker cavity with its own enclosure to seal it off from the 15 inch bass speaker.
The 6x9-inch speaker vents to smaller louvers, cut on either side of the Leslie cabinet situated just under the top rotor louvers. But only one set of smaller louvers has any signal. The other side is blocked off with a plate and for all intents looks to be there for decoration and visual balance. No one knows for certain, why Leslie did this for the 122 RV as other models like the 222 RV had dual 6x9-inch speakers. Part of the design for the 122 RV, the 6x9-inch speaker mount location incorporates two round openings, that vent into the upper rotor cavity, through the wood shelf, just under the treble rotor.
These two holes catch the 6x9-inch speakers' reverb sound coming off the special 6x9-inch enclosure as the speaker vents to both the louvers and the round holes into the rotor cavity at the same time. Perhaps this was a time align feature to mix some of the separate reverb signal into the Doppler effect of the treble rotor's physical spin, "fanning" the reverb beam with the rotor's rotation. The reverb amount can be adjusted by a control on the reverb amp itself, or remotely from the organ by a special halfmoon switch and dedicated cable that has 3 select settings, "off/medium/on" with actual reverb amount settings preset to taste at the reverb amp in the RV with a variable potentiometer.
Identical to Model 145 but with the Model 122 amplifier. Essentially a short Leslie 122
Same technical specifications as Leslie 147 but in a shorter cabinet.
The Model 147 has the same cabinet, speaker, and mechanical components as the Model 122; however, the amplifier input and motor speed control circuits are different. This is primarily because this series was designed to be "universal," which means it could be connected to other organ brands. The signal input is "single-ended," allowing a simpler connection to organs, that have a built-in speaker system, such as the Hammond A100 or a Wurlitzer. The Model 122 input is a differential "double-ended," or "balanced line," design that provides for cancellation of any spurious noise that may be present. Also, the motor speed switching uses a separate 120 volts AC signal, rather than the DC voltage control of the Model 122. In operation, the noticeable differences between the Model 122 and the Model 147 are the Model 122's lower susceptibility to induced noise, and a delay between operation of the speed control and the actual change in speed. Just like with the 122 and 142, the Leslie Model 145 is identical to Model 147, except that it is housed in a 33-inch-tall cabinet, and thus slightly easier to transport than the 41-inch-tall Model 147.
Model 330 was issued in 1975. The concept is the same as model 760 - a classic horn/rotor speaker in a portable tolex-covered cabinet. The cabinet size is 37 inches with casters, i.e. roughly the same size as the older model 145. Technically this speaker is slightly different than the 760. The amplifier is a single channel 60 watts with a passive cross-over like in the old tube Leslies. This makes the 330 a popular Leslie to convert to tube amplification. Another noticeable difference is, that the input socket is the modern 11pin type, making it necessary for the speaker to have a separate power cord (see below). The 11-pin socket allows modern Hammond clonewheels – such as the XB-2, XK-2 and XK-3 – to link to and operate the 330 with ease.
One of the favorite models for gigging Hammond owners, the Model 760 with 90 watts of power is still a popular choice for organs with 9-pin connectors, despite being a "solid-state" model. It has a black Tolex cabinet and is easy to carry, thanks to integrated handles. These features make it rather roadworthy. Model 770 is technically the same as 760, only with more sophisticated wooden cabinet. Model 760 was primarily used with spinet Hammonds, such as M100 or L100 -series. Leslie 760 has a rotating treble horn as well as a rotating bass drum.
A smaller, more portable version of the 760 is the 825. It is a solid-state cabinet like the 760, and it connects to the organ with a 9-pin connector as well. However, it only has a 70-watt amplifier and only a single rotor with a full-range 12-inch speaker.
- Vail, Mark (2002). The Hammond Organ - Beauty in The B. Backbeat Books. pp. 129–131. ISBN 0-87930-705-6.
- "Electro Music Purchased by Columbia Distribution". Billboard (Cincinnati, Ohio: Billboard Publishing) 77 (38): p. 6. September 18, 1965.
- Clifford A. Henricksen (April 1981). "UNEARTHING THE MYSTERIES OF THE LESLIE CABINET". Recording Engineer/Producer magazine.
- Harvey Olsen (2006). "Uncle Harvey's Guide to Leslie Pinouts". Retrieved 22 June 2006.
- "The Leslie Combo Preamps". Retrieved 22 June 2012.
- "UC-1A Combo Pre Amp". Retrieved 25 Jun 2012.
- Official website
- Captain Foldback's Hammond and Leslie Page - includes reviews of several Leslies
- Inside the Fender Vibratone - the history and workings of the Fender Vibratone cabinet (and similar boxes)
- Unearthing the Mysteries of the Leslie Speaker - A more in-depth analysis of the Leslie.
- A website about the Leslie Model 16
- Reference article showing several homemade Leslie designs
- Laurens Hammond and Don Leslie (adapted from first-hand conversations with organist Bob Mitchell and with Don Leslie)
- A complete list of vintage Hammond & Leslie models