Leslie model guide
The captain's 
model guide
About this guide
This is a quick guide to Leslie speaker models suited for Hammond organs. This document is meant as a reference for when you are browsing the classifieds or eBay and is not meant to list every little detail about the speakers. Some models are covered elsewhere on this website, often in detail and with pictures.
About the background
The background is Leslie finish 'Oak No 20'.
About the roto-sonics
Since most players and technicians, including myself, find the roto-sonic Leslie models less valuable, these are listed in a separate section. Some of these speaker models may be used as is, or they can be converted into more Hammond friendly models or simply serve as parts donors for other more valuable Leslie models. Electro Music tended to use the same parts in as many applications as possible, so a good many parts from, say, a model 710 may be used to restore a model 122. If you happen to prefer the more theatre organ-like sound of the roto-sonic Leslie speaker, by all means - you are just lucky to like the more inexpensive alternative.
About the speakers still in production by Hammond-Suzuki
Models 122, 147 and 770 are still in production as model 122A/122XB, 147A and 771/971 respectively. They are updated in the technical design, but the basic functionality is the same as the vintage speakers. For a while model 145 and 142 were being produced as 145A and 142A. A vintage speaker in immaculate condition may fetch a higher price than a new Leslie, especially for the tube models. If you are a church or a professional business, consider investing in a new Leslie from a local dealer that will support you. Old cabinets often don't come with a warranty or a service organisation, and Mr. <insert name here> from three towns over will most likely not help you with a replacement Leslie for Sunday service, because the 1971 Leslie he sold you broke down at band practice Saturday afternoon. If you are looking for a dealer of new Leslie speakers, a few of them are listed in the links section of this website.
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Model 302C
Model 302C
The 302C is a Hammond Suzuki Leslie utilizing a real rotating horn and simulated bass rotor. It also is a 2 channel cabinet with both a rotary and stationary channel.
It features both an 11 pin interface (for XB series instruments) and a 1/4" input jacks for use with other instruments.
It has an internal preamp so only a "standard" foot switch is needed to switch speeds and there are no cumbersome Leslie cables.
This site and it's content, unless otherwise noted, are the property of Speakeasy Vintage Music, Inc. All Rights Reserved. Use of this site is governed by our general disclaimer.
Maryland Organ Service is a Service Mark of Speakeasy Vintage Music, Inc.
Hammond™; and Leslie™; are registered trademarks of Hammond Suzuki USA, Inc.
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"Unearthing The Mysteries of the Leslie Cabinet"
UNEARTHING THE MYSTERIES OF THE LESLIE
CABINET
by Clifford A. Henricksen Community Light & Sound
First published in Recording Engineer/Producer magazine, April 1981.
The Leslie Rotating Tremolo Speaker System has produced the same unmistakable sound for so
many musicians that it has become an international institution for the recording and performing musical arts. Everything from the venerable Hammond B-3 organ, to human voices and electric guitars, have been processed by the Leslie Sound, and have ended up on countless hit records. This article is an attempt to unearth the mysteries of its operating principles, and includes a discussion of the Leslie Cabinet's practical use in both stage and studio situations.
My love-hate relationship with Leslie Speaker began with the purchase of a Hammond organ during the mid-Sixties. The salesman told me I would probably end up buying a Leslie for it, a statement that I dismissed as the usual sales banter. Besides, at the time I had no idea what a Leslie was anyway. The Hammond was purchased because that's what the Animals' organist, Alan Price, used on all the group's early hits, especially "The House of the Rising Sun." I saw the band live in Schenectady, New Youk, where they put a Hammond M-102 direct into a Fender Bandmaster Amp, and I had to have this sound. I soon discovered, however, that my new musical heroes had better sound. It wasn't long before I knew that Booker T. Jones, Felix Cavaliere, Gary Brooker and Billy Preston (and many others) were all using Leslies. This was The Sound!
My first Leslie, a single-speed Model 45 with a 40-watt tube amplifier sounded great, but it literally got lost in the
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"Unearthing The Mysteries of the Leslie Cabinet"
roar of the Boston-based rock and roll band in which I was then playing. Two big Leslie Speakers were cumbersome to move, they weren't a big improvement in level (plus 3 dB), and the high-frequency drivers broke. From then on, it was guerilla speed shop tactics (mill the heads, oversized pistons, etc.), to the point where I could finally be heard over any guitar player. As a result, I became an expert at Leslie repair, modification and special use, occasionally even letting a few guitar notes into my beloved machines. I've spent the past 15 years in and out of the Music Business, both in studios and on stage. The significant part of this time was spent in some way dealing with Leslie Speaker Systems. As you might guess, this is a rock and roll story. I might as well show my bias here and now. With this in mind, here's what I have learned over the years.
PRINCIPLES OF OPERATION
First and foremost, the Leslie Rotating Speaker is designed as a sound modification device. It is not a "Hi-fi" speaker, but rather a part of a musical instrument. You buy a Leslie to change the sound of an instrument, not to reproduce it.
The Leslie Speaker System, thoughtfully named after its inventor, Don Leslie, operates on a simple principle: a directional sound source is rotated at constant (or variable) speed around a fixed pivot point.
At a listening point some distance from this whirling affair, three things happen. First, because the source is directional, the intensity of the sound will be at a maximum when it points at the listener (or microphone), The sound intensity will increase as the rotating source approaches dead center, and decrease as it rotates past this point. The resultant effect is called amplitude modulation (AM), which is no big thing, and is a feature on any guitar amp with a "vibrato" or "tremolo" feature. By moving closer to the rotating speaker, the inverse square law will increase the modulation effect.
However, the big deal is the Leslie's ability to create frequency modulation (FM). As the source rotates toward the listener, its relative velocity will increase the pitch of any tone it produces; as it rotates away, the pitch well be lowered. This is exactly the same Doppler effect that causes a train whistle (or any other sound on the train, such as grunting pigs, or shrieking passengers), to rise and then fall in pitch as the train approaches and then passes.
Lastly, if you are listening in a room with any significant reverberation, a complete spatial modulation of the sound will happen, as sound is "shot" all around and goes through multiple reflections.
If you want a real treat of all kinds of bizarre whirling horns and things, order copies of Don Leslie's original U.S. Patents: RE#23,323 and 2,622,693, available from The United States Patent Office, Washington, D.C.20231, for a fee of 50 cents per copy. These patent specifications are incredibly entertaining documents, and a must for any Leslie fan.
The Real-Life Leslie
A practical and commercial manifestation of the Leslie principle may take on many forms. Indeed, the manufacturer of Leslie Speakers, Electro Music, Inc. (now a division of Hammond Organ), produces a wide variety. These include models with reverberation, triple channels, and rotating-cone speakers. However, any Leslie afficionado will tell you that the Leslie Models 145, 147, and 122 are the ones with "The Sound". All three Models share the same basic innards: a 40-watt monophonic tube amplifier; an 800 Hz 16-ohm passive crossover; a rotating treble horn and a rotating bass speaker. Both rotating speakers are available with slow and fast A.C. induction motors. (Older Models 45, 47, and 22 are identical, except for having single-speed rotors.)
Furthermore, these Leslie models are similar in that they all have components mounted in a three-compartment cabinet. The top compartment houses the rotating high-frequency horn; the middle "box" the highand low-frequency drivers and crossover (and which also acts as a vented box for the low-frequency driver); and the bottom compartment the low-frequency rotor and amplifier. Louvres located in the top and bottom compartments let out treble and bass sound respectively. All the above speaker systems are virtually identical in terms of their use and sound quality. (The larger Models 147 and 122 allegedly have a better low-end.) Both highand low-frequency speakers operate on the same principle: a stationary driver (loudspeaker) and a rotating acoustic
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"Unearthing The Mysteries of the Leslie Cabinet"
"projector".
The "Treble Rotor"
The Leslie's high-frequency unit is largely responsible for the "Leslie Sound". Some organists actually find that the bass rotor's slower response to speed changes is distracting, and will actually disconnect the bass rotor drive - especially when playing a bass line. The treble unit consists of a stationary 3/4-inch throat Jensen compression driver, connected to a vertical tube that acts as a thrust bearing (Figure 1). A twin-bell, molded black bakelite horn, which starts vertically but flares horizontally, sits on this bearing/tube, and rotates via a two-speed A.C. induction motor fitted with three (selectable) drive pulleys. This motor drives the treble horn at fast or slow speeds via drive belt and belt tension spring. Direct current is sometimes applied to the "fast" motor so that it will slow down more quickly; this is called a "D.C. brake". The treble horn actually looks like two horn assemblies; in fact, only one is operable as a horn. The other side, a "dummy", acts as a counterweight or dynamic balancer, providing symmetric air drag at high speed. The resulting structure rotates smoothly and without eccentric "wobble" forces.
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"Unearthing The Mysteries of the Leslie Cabinet"
At the mouth of the horn is diffuser cone, which is supposed to widen the dispersion of the horn and make a "more musically pleasing tone". Actually, it does work. Figures 2 and 3 show typical polar response charts of a Leslie Horn with and without the deflector; the results are dramatic. The "without" curve of Figure 2 is typical of a "beamy" straight horn, with a lot of sound concentrated on-axis and very little sound off-axis. The "with" polar response curve of Figure 3 is almost omnidirectional; note, however, the "lobing". As the horn revolves, the sound will actually rise and fall a number of times, giving it an even more characteristic sound.
The horn's so-called coverage angle is taken from polar response charts such as these; it is the included angle between -6dB points from the horn's on-axis level. Figure 4 and 5 show such coverage angles, compiled from a series of third-octave polar response curves. Note how the beamwidth gets smaller and smaller without the deflector. This means that if the deflectors are removed the sound will be much hotter on-axis, but much softer off-axis. Therefore, the AM portion of the Leslie Sound will be much more severe and "choppy", as many a rock and roller will tell you. Many Leslies played in clubs are faced backwards, with the top and bottom rear panels and deflectors removed, because the sound "cuts" better; an effect that translates as, "You can hear it better over the guitar player".
This beaming process will actually raise the on-axis sensitivity of any driver, as can be seen from the frequency-response curves of a University ID-40 driver (a respectable, but typical 3/4-inch throat PA unit) mounted on a Leslie horn with and without deflectors (Figures 6 and 7). It is interesting to note the extra sensitivity above 1.5 kHz available without the reflectors in place. (Note also that the low-end - 800 Hz to 1.5 kHz - response isn't affected by removing the reflector, and that the response is ± 5 dB from 400 Hz to 10 kHz. This latter range could be made even flatter with a real-time analyzer and an third-octave equalizer in the studio.)
Now, this entire discourse is based on the treble horn measured in an anechoic or non-reflecting, highly absorbent room. In real life, the horn mounted in a louvred wooden box, which means that the picture changes somewhat with resulting internal reflections. The diffuser cone does another important thing: it shifts the apparent sound source position on the horn. With the cone in, more of the entire range of the horn will appear to come from the mouth of the horn; with it out, however, while lower frequencies still appear to come from the mouth, higher and higher frequencies will appear to come from progressively further down the throat. They therefore appear to be rotating at a smaller radius, which results in less frequency
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