The Red Light District
Beatmag’s regular technical columnist James Spectrum (AKA Jari Salo of Pepe Deluxe)
Johann Christian Andreas Doppler (1803-1853) was an Austrian mathematician and physicist best known for research into the effects of motion on acoustic pitch, known as the ‘Doppler effect’. Doppler knew of the existence of sound waves, and he also knew that the pitch of a sound is dependent on the length of those waves. If a source is moving toward the listener, he supposed, the waves in front of the source would be squeezed together, creating a higher frequency. A sound source moving away from the listener would create a lower frequency. It is important to realize that the frequency of the sounds that the source emits does not actually change: it is the wavelength which is affected and as a consequence, the perceived frequency is also affected.
In 1845, to substantiate his theory, Doppler arranged for his colleague CHD Buys Ballot (1817-1890) to conduct what would be one of the most unusual scientific experiments in history. Ballot arranged for a locomotive to pull an open car full of trumpeters playing a single sustained note while, to the track’s side, a group of musicians with perfect pitch listened. For two days the trumpeters were towed back and forth while the listeners recorded the changing pitches of their instruments. This nerve-wrecking experiment did provide absolute confirmation of the theory, though apparently the local dairy managers noticed a serious drop in milk production and some of the cows avoided the fields adjacent to the rail line for years
While it’s neat that you can apply the principle of Doppler’s effect to several things ranging from blood flow to temperature measurement and radar to measuring the size of the universe, mankind had to wait almost a century until Mr Donald Leslie (1911-2004) came up with THE application. This invention (first one built in 1940) went by many different names including ‘Vibratone’, ‘Brittain Speaker’ and ‘Hollywood Speaker’, before settling for the final and rather obvious ‘Leslie Speaker’. A fan of church and theatre pipe organs, Leslie had become enamoured with the compact electric Hammond organ shortly after it was introduced in 1935. The small electric organ, Leslie thought, had sounded much like a theatre or church pipe organ in the vast furniture showroom where he first heard the instrument. But once he got it home he was disappointed with its sound in confined spaces. He started experimenting with devices to make the instrument sound like labyrinthine pipe organs.
Similar to many of the best inventions, Leslie Speaker operates on a simple principle. A directional sound source is rotated at constant (or variable) speed around a fixed pivot point, and this leads to three things. First, because the source is directional, the intensity of the sound will be at a maximum when it points at the listener, the sound intensity will increase as the rotating source approaches dead center, and decrease as it rotates past this point. Second, this movement will ‘shoot’ the sound all around the room you’re listening in, creating a complex modulation of the sound as it goes through the reverb and multiple reflections. Last (and the big deal) is the Doppler effect caused by the movement of the sound source.
The manifestation of Leslie’s idea comes in many flavours and sizes, but the most important ones share the same basic technology: a (tube) amplifier driving a rotating treble horn and a rotating bass speaker. The speakers have two speeds and the bass rotor has a slower response to speed changes. The art of timely speeding up and slowing down of the Leslie rotors while holding single notes and letting the Leslie provide the dramatics in rotor acceleration is often more exciting than anything synthesizer players have ever come up with. In fact the combination of Hammond organ with a Leslie Speaker was and still is so powerful, that it’s probably the only modern well-known musical tool that has never needed any advertising at all: Leslie Speakers were so popular they literally sold themselves. However, they did get free advertisement from a very unlikely source: Hammond inventor Laurens Hammond never liked the Leslie-effect and his on-going anti-Leslie propaganda actually increased interest in the speaker which improved sales! By late ‘60s Hammond-Leslie combination was recognized as the coolest and usually most expensive instrument money could buy. Instead of cows the Doppler-effected was now driving hippies to the edge of sanity… and often beyond. Not limited to psychedelic organ freak-outs only, Leslie Speakers were applied to everything ranging from vocals (‘Tomorrow Never Knows’ by The Beatles) to drums ( ‘In-A-Gadda-Da-Vida by Iron Butterfly).
Like King Willie said on ‘Predator II’, “There’s no stoppin’ what can’t be stopped.” In 1980, seven years after Laurens Hammond had passed away the inevitable marriage finally happened: Hammond Corporation bought Electro Music, the manufacturer of Leslie Speakers and the Leslie name from CBS. Today Donald’s invention is still the undisputed Champion of musical effects, and the only thing that can seriously challenge it is two (or more) Leslies.
Hammond organ thru a ring modulator and a beat up Leslie
