The Leslie speaker is a combined amplifier and loudspeaker that modifies the sound of an electric musical instrument by rotating a baffle chamber (drum) in front of the loudspeaker. A similar effect is provided by a rotating system of horns in front of the treble driver. It is most commonly associated with the electric Hammond organ, though it was later used for the electric guitar and other instruments. A typical Leslie speaker contains an amplifier, a treble horn and a bass speaker—though specific components depend upon the model. Some models have two speed settings, known as chorale and tremolo.
The speaker is named after its inventor, Donald Leslie, who began working in the late 1930s to get a speaker for a Hammond organ that better emulated a pipe or theatre organ, and discovered that baffles rotating along the axis of the speaker cone gave the best effect. Hammond was not interested in marketing or selling the speakers, so Leslie sold them himself as an add-on, targeting other organs as well as Hammond, beginning in 1941. The sound of the organ being played through his speaker received national radio exposure across the US, and it became a commercial and critical success, becoming popular with jazz organists. In 1965, Leslie sold his business to CBS who, in 1980, sold it to Hammond. Suzuki Musical Instrument Corporation subsequently acquired the Hammond and Leslie brands.
Because the Leslie is a sound modification device in its own right, various attempts have been made to simulate the effect using electronic effect units. These include the Uni-Vibe, the Neo Ventilator, and Hammond-Suzuki's own simulator in a box.
History
Donald Leslie worked as a radio service engineer at Barker Brothers Department Store in Los Angeles, which sold and repaired Hammond organs. He bought one in 1937, hoping it would be a suitable substitute for a pipe organ. He was disappointed, however, with the sound in his home compared to the large showroom where he originally heard it. Consequently, he attempted to design a speaker to overcome this. He initially tried making a cabinet similar to Hammond's, but soon concluded that pipe organs produced a spatially varied sound because of the different location of each pipe. He set out to emulate this by making a moving speaker. He tried various combinations of speakers and speeds, and discovered that a single one running at what's now known as the "tremolo" speed worked best. After further experimentation, he decided that splitting the signal into a rotating drum and horn helped accentuate bass and treble frequencies.
By 1940, Leslie decided his prototype was ready to market, and went to the Hammond Organ Company to demonstrate it. Laurens Hammond, however, was not impressed with Leslie's attempt to better his own organ design, and declined to market it. The company even changed the speaker interface on their organs to make them "Leslie-proof," though Leslie quickly worked around this. Leslie began manufacturing the speaker in 1941—initially under a variety of names, including Vibratone, Brittain Speakers, Hollywood Speakers, and Crawford Speakers. He returned to the name "Leslie Vibratone" in 1947. To counteract Hammond's slogan "Music's Most Glorious Voice," Leslie added a similar slogan, "Pipe Voice of the Electric Organ" to the plates. He eventually owned nearly 50 patents on the speaker.
Leslie manufactured the speaker to work with other organs besides Hammond, including Wurlitzer, Conn, Thomas and Baldwin. He never particularly liked Hammond organs, once remarking "I hate those damn things."
In 1965, Leslie sold his Electro Music company to CBS, which had also acquired the Fender guitar company. In 1980, the Hammond Corporation finally bought Electro Music and the Leslie name from CBS. After Hammond went out of business in 1986, a former engineer re-established Electro Music, licensing the name from Noel Crabbe, who had acquired the rights to Hammond. It was subsequently sold to Suzuki in 1992, who continue to manufacture the speaker.
Features
A Leslie speaker consists of a number of individual components. The audio signal enters the amplifier from the instrument. Once amplified, the signal travels to an audio crossover, which splits it into separate frequency bands that can be individually routed to each loudspeaker. Different models have different combinations of speakers, but the most common model, the 122, consists of a single 15" woofer for bass and a single compression driver and acoustic horn for treble. The audio emitted by the speakers is isolated inside an enclosure, aside from a number of outlets that lead towards either a rotating horn or drum. Electric motors rotate both horn and drum at variable speeds. The Leslie uses a dual horn; its symmetry is used for mechanical balance, however one of the horns is audibly blocked.
The only control common to all Leslie speakers is a dial that controls the master volume. This is normally set up once and then left, since the organ's expression pedal normally controls the volume. Leslie recommended playing the organ at full volume with all stops (drawbars) pulled out and adjusting the volume just before distortion occurs. However, the distorted sound of an overdriven vacuum tube amplifier can be a desirable sound, to the extent that modern Leslie simulators have an explicit "overdrive" setting.
The Leslie speaker' output is normally controlled by a switch mounted on the instrument featuring two settings, "chorale" and "tremolo". Some early models were limited to "off" and "tremolo", and some later models had all three settings. The switch can be used while notes are being played, and the sound of changing between the two settings is part of the characteristic sound. On both settings, the treble horn rotates slightly faster than the bass woofer; about 50 revolutions per minute (rpm) for "chorale" and 400 rpm for "tremolo", compared to the woofer's 40 rpm and 340 rpm respectively.
Unlike most popular music amplifiers, that use jack plugs to connect to instruments, Leslie speakers use an Amphenol connector to interface directly to an organ via a console connector. The type and design of the connector depends on the organ and model of Leslie speaker.
Older models that used tube power amplifiers use a variety of six-pin connectors, while later models use nine-pin connectors. In all cases, for a single organ–Leslie configuration, the AC power, audio and control signals are all carried on the connector, and the design of the pin layouts varies between organs and speakers. Care is taken when attempting to service them since an incorrectly or poorly wired cable can cause permanent damage to the organ or speaker, or result in electrocution. It is also possible to connect multiple Leslie speakers to a single organ, by using a power relay that provides the necessary AC current.
A separate device, known as the combo preamp, is necessary to connect a vintage Leslie to another instrument such as a guitar. This combines a separate AC input and line level input onto a single Amphenol connector, and provide a footswitch to select between the speeds of the Leslie. 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 11-pin interfaces that are safer to service, as AC power is carried separately using standard IEC connectors. The Hammond-Suzuki Leslie 2101 also includes line in and line out jacks, so a combo preamp is no longer required. Its settings can also be controlled via MIDI.
Models
Single speed The initial models of Leslie speakers did not have the "chorale" setting. The control switch was simply a choice between "off" and "tremolo". The first model of Leslie produced was the 30A. It emulated Hammond's DXR-20 tone cabinet, which used moving drums but only produced amplitude modulation, not frequency modulation. It contained a drum and the power amplifier was housed in the top of the unit, to allow easy repair. This was superseded between 1947 and 1949 by the 31H, also known as the "Tall Boy". It was similar in appearance to the 30A, but contained additional louvres along the top of the cabinet. Also, reflectors were placed on the end of the horn, to allow the treble signal to exit the unit through the sides, rather than on the top.
The next models Leslie produced were the 21H and the 22H, which had a cabinet in a similar styling to the better known 122, with the same dimensions and louvres. They were powered by a 40 watt tube amplifier.
Dual speed
The 122 is the most popular Leslie. It was specifically designed for the Hammond organ and is the model most commonly identified with it. It is high, offers two different speeds for chorale and tremolo, and has a 40 watt tube amplifier. The 122 is the most adaptable to being recorded, as it has a balanced signal which eliminates AC hum and other noise. The 122RV was the same model, but with an additional reverb amplifier, which fed through to a separate static speaker. A slightly smaller version, the 142 was available. Hammond-Suzuki currently manufacture the 122A, a straight reissue of the 122, and the 122XB, which contains a modern 11-pin adapter, an IECC AC adaptor, line-in, and a jack socket for a footswitch to control the speed. This eliminates the need for a combo preamp.
The 147 is the "universal" version of the 122, designed for many organs, and has a different amplifier input and motor speed control, but is otherwise identical. The signal input is unbalanced, allowing a simpler connection to organs that have a built-in speaker system, such as the Hammond A100, or a Wurlitzer. The motor speed switching uses a separate AC signal, rather than the DC voltage control of the 122. In operation, the 122 has a lower susceptibility to induced noise, and a delay between operation of the speed control and the actual change in speed. As with the 122 and 142, the 145 is identical to the 147, except that it is housed in a cabinet, and thus slightly easier to move. As with the 122, Hammond-Suzuki manufactures a modern replacement, the 147A. The model X-77, released in 1968, was designed to accompany Hammond's new tonewheel / transistor organ, the X-66. It contained seven different tab controls and six speakers. It has a completely different interface from other Leslies, using a 12-pin amphenol connector.
Pro-Line
By the late 1960s, gigging musicians were finding that older Leslies like the 122 were not loud enough for large venues, which led to the introduction of the "Pro Line" series. These Leslies had louder solid-state power amplifiers, and were mounted on casters for ease of portability. The first models Leslie manufactured were the 900 and 910, which contained a 100 watt, three-channel power amplifier. Both could split into two sections. The most popular version of the Pro-Line series was the 760. It was a smaller version of the 900 and 910, and contained a 40 watt treble and 50 watt bass amplifier. A smaller, more portable version of the 760 is the 820. It is a solid-state cabinet like the 760, and it connects to the organ with a 9-pin connector as well. However, it is only high and has only a single rotor with a full-range 12-inch speaker.
The Pro-Line series was durable and fault-tolerant, with many models lasting for years. However, because they used solid-state amplifiers, they are not as highly regarded as the older tube-based Leslies, because they lack the characteristic sound when the amp is overdriven.