The Continuing Story of the Leslie Rotating Speaker Cabinet

You would know the Leslie rotating speaker’s sound even if you didn’t know about the device itself. The Leslie lent swirling, highly ethereal sounds to many a soulful Hammond organ line and pioneering guitar lick on legendary recordings, especially in the '60s and '70s.

How exactly did the Leslie create its signature warble? The speaker cabinet operates on the same physics as a police siren changing in pitch and volume as it whizzes past you. This is the Doppler effect, or the phenomenon of sound changing in pitch as it grows nearer or farther away.

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The Leslie speaker accomplishes the Doppler effect with a stationary unit through clever engineering. Even though the Leslie is commonly referred to as a “rotating speaker,” it really has two speakers and only one rotates. Across multiple models throughout the years, the Leslie speaker relied on the same basic mechanics.

A treble speaker sits high in the unit, rotating on a fixed pivot point. A bass speaker is mounted lower in the unit, inside of a rotating drum with a narrow aperture for sound to escape.

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Fluctuations in pitch and loudness are ultimately the result of the treble speaker’s and drum aperture's distance from the listener. The rotation causes sound sources themselves to grow nearer to and farther from the listener, even while these sound sources are housed in a stationary cabinet.

Those speakers’ rates can be varied to make the effect more or less intense, with the faster setting giving the Leslie its most distinct sound.

The Origin of the Leslie Speaker

In the late 1930s, Donald Leslie brought an electric Hammond organ home. As fascinating as the technology was, Don was ultimately disappointed by the organ’s sound. He wanted that massive, quivering sound he heard on pipe organs in churches and movie halls.

Channeling his experience in mechanics and electrical engineering from his stint at the National Research Laboratories in Washington D.C. during World War II, Leslie started tinkering with a design for a new type of amplification system that could emulate that warble.

Inside a 1971 Leslie Speaker Model 147

By 1940, he had a prototype of his rotating speaker system and approached the inventor of the Hammond organ, Laurens Hammond. Leslie suggested that Laurens market the speaker alongside his own organ, but Laurens didn’t much like the sound of the speaker. He thought it lacked a desirable sound or obvious application.

Little did Laurens realize, organists would adopt the Leslie far and wide, no matter what brand organ they played. Likewise, the Leslie speaker would go on to become a constant companion to the Hammond organ on studio recordings and live performances.

Leslie went ahead and started his own company, Electro–Music, to manufacture the speakers. He started selling them under a variety of brand names in 1941 and started marketing them under his own name in 1947.

The speaker was selling so well that Leslie had no need to advertise. Word of mouth had left him barely able to cope with the demand.

Laurens Hammond grew disdainful of the device and its sound. He went as far as designing a proprietary connector to make it more difficult to run a Hammond organ through any third party speaker and coerced his dealers into agreeing not to sell Leslie speakers.

Eventually, though, Hammond took the “if you can’t beat ‘em, join ‘em” route and tried to buy Electro–Music in 1957. But Don Leslie, successful in his own right and maybe a little bitter, refused to sell.

Playing the Leslie

The Leslie used an Amphenol multi-pin connector for its input instead of the ¼” telephone jack that was largely becoming standard for electric instruments. This added an obstacle to using the Leslie for something other than an electric organ.

The Leslie also required a line level signal, meaning that passive instruments needed a signal boost in order to sound through the speaker. Modifications with a pre–amp were necessary in order to use the early Leslie models with a guitar or microphone.

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It’s important to stress that the Leslie speaker isn’t a “hi–fi” speaker like a studio monitor. It was meant to color and affect an audio signal, much like a guitar amplifier or effect pedal.

The most popular models—the Leslie 122, 145, and 147—used low–wattage amplifiers that could be easily overdriven, primed for the thick and dirty organ sounds made famous in the rock ‘n’ roll era by The Band’s Garth Hudson and Deep Purple’s Jon Lord.

The Leslie were easily and often hot–rodded: drivers could be disabled, crossovers re–installed, the amplifier disengaged or replaced. All of this modification proves that the Leslie was part of a stream of innovation in amplified sound, not an end point.

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By the 1960s, with the availability of cheaper circuitry and better mass production techniques, several companies were having a go at making their own smaller, and therefore more portable, Leslie emulations.

These emulations would let musicians take the sound out on the stage without worrying about maintaining and operating the delicate and, sometimes, cumbersome equipment.

The Many Leslie Pedals

The delicate nature of the Leslie made it somewhat unreliable for studio work and its bulkiness was the bane of the of the regularly gigging organist. Self–contained Leslie–style effects were quickly welcomed, with their controls and and functionality providing a good substitute for the burdensome speaker cabinet.

In one relatively small effect, you could directly control the signal’s gain or use an expression pedal to manipulate the effect’s rate. While there are a massive amount of pedals emulating the Leslie speaker, these are just a few of the more interesting ones.

Companion Psychedelic Machine

This device housed two effects that would eventually become the standalone Uni-Vibe and Super Fuzz units. The Psychedelic machine gave you greater control over the sound than the later stand–alone versions of the Uni–Vibe. It offered separate Vibrato and Tremolo modes with adjustable repeat time, intensity, and volume. There was a nasty fuzz circuit, too.

The original version, issued in 1967, was called the Honey Psychedelic Machine. The second edition was called the Companion Psychedelic Machine, adding a Duet setting that combined the Tremolo and Vibrato. The Honey is capable of more flanger–type sounds, while the Companion sounds a bit smoother.

Shin-Ei and Univox Uni-Vibe

The Uni–Vibe is the most iconic Leslie simulator. Jimi Hendrix would juice its 4–stage phaser circuit and external expression pedal to make it one of the most legendary effects pedals ever built, period.

With both the “Chorus” and “Vibrato” modes, players could control the speed of the effect using the expression pedal. The incredible variations this allowed for were best demonstrated on Hendrix’s opus, “Machine Gun.”

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Roland AP-5 Phase Five Jet Phaser

Roland’s foray into the Leslie emulation game led to the creation of this very interesting effect pedal. The unique CC “Continuous Control” and TC “Touch Control” modes set this pedal apart from the flock. The CC mode tethers the phasing settings to the settings of the LFO wave that creates the effect. The TC circuit responds to the dynamics of the input signal, giving a gentle or harsh response depending on how the instrument is played.

Neo Instruments Ventilator II

A high–end modern take on the Leslie, the Neo Ventilator, accurately emulates the Leslie 122 sound while giving you control over every single parameter that effects the vibe. And while this stompbox carries a high price tag, it’s much cheaper and more reliable than the Leslie 122 that it replicates to a canny degree of accuracy.

Boss RT–20

Leave it to Boss to come up with a high–quality, versatile circuit at a reasonable price. This double pedal gives you control over the same kind of settings as a Uni–Vibe, while expanding on that sonic territory with four available modes, overdrive control, and separate slow and fast settings.

Hammond Leslie G

While designed like your typical guitar pedal, the Hammond Leslie G is a standalone version of the digital Leslie simulation present in Hammond's SK series of portable organs. This pedal rivals the Neo Ventilator for accurate imitations of the rotating speaker sound while giving the user unique control over the dry and wet feeds.

Electro–Harmonix Lester G

In typical Electro–Harmonix fashion, this rotary speaker emulation wins on tweakability, making it the most versatile on the list. The Lester G gives you complete control over compression and tube–simulating overdrive circuits. There is also a knob to affect variation in speed (as opposed to having just a fixed rate) and an expression pedal input for controlling rotation speed, in the vein of the Uni–Vibe.

Pigtronix Rototron

The Rototron is designed to specifically emulate the Leslie 122 and 147 cabinets. While many of Pigtronix’s contemporaries provide a number of parameters to expand on the idea of a Leslie, the Rototron has that authentic Leslie sound in spades. It’s a modest goal, well executed.

DLS Effects RotoSIM

The DLS RotoSIM is a fantastic emulation of classic Leslie sounds. You can fine tune the levels of both the tweeter and the bass rotor using specific knobs relative to your amp setup, as well as set two speeds and the ramp up/down time between them creating dynamic swell effects. The inclusion of a toggled overdrive circuit is fantastic for adding character and grit to the emulation.

T.C. Electronic Viscous Vibe

The Viscous vibe is not an emulation of the Leslie. Instead, it’s an emulation of an emulation of a Leslie. T.C. Electronic designed this pedal to replicate the sound of the Shin–Ei Univox, bringing a faithful recreation of that beloved pedal's sound down to a price point that’s around a 20th of the original’s current market value.

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