Hammond organ

The Hammond organ is an electric organ which was designed and built by Laurens Hammond in April 1935. While the Hammond organ was originally sold to churches as a low-cost alternative to the pipe organ, it came to be used for jazz, blues, and to a lesser extent rock music (in the 1960s and 1970s) and gospel music. It was widely used in United States military chapels during the Second World War, and returning soldiers' familiarity with the instrument may have helped contribute to its popularity in the post-war period.

Tone generation

In imitation of a pipe organ, with its banks of pipes in multiple registers, the Hammond Organ used additive synthesis of waveforms from harmonic series to generate its sounds. As in Thaddeus Cahill's earlier Telharmonium, the individual waveforms were made by mechanical 'tonewheels' which rotated beneath electromagnetic pickups. Although they are generally included in the category of electronic organs, strictly speaking, because the waveforms are produced by mechanical tonewheels rather than electronic oscillators, original Hammond organs are electromechanical rather than electronic organs.

The component waveforms can be mixed in varying ratios by using 'drawbars' mounted above the two keyboards. The drawbars, which operate like the faders on an audio mixing board, allow the performer to vary the volume of each notes' fundamental tone, the octave below it, and the octaves and harmonics above it. Other features added to Hammond organs included an electromechanical vibrato and, by the late 1950s, a reverb effect which simulated the reverberation of a large church hall. The distinctive 'key click' that was originally a design flaw rapidly became part of the 'Hammond sound', which modern imitations of the Hammond organ try to reproduce.

Speakers originally designed by Don Leslie were widely used with the Hammond organs, though at first, Leslie was a competing company that Hammond sought to drive out of business. The Leslie speakers had a rotating horn and a stationary bass speaker with a rotating baffle that produced a vibrato effect. As well, the Leslie speaker cabinets', the valve amplifier gave the Hammond's tone a warm, natural 'overdriven' sound, which could be varied from a mild 'purr' to a heavily overdriven growl. Soon, the Leslie speaker cabinet's signature sound became a de facto requirement for Hammond enthusiasts.

The tonewheel system

The sound reproduction system is based on tonewheels. There are one of these wheels for each of the ninety-one tones the organ can produce. Each key on the keyboard can control up to nine tones, depending on the drawbar settings or drawbar presets. Each tonewheel has a number of bumps along its edge. The number of bumps and the rotation speed of the wheel determines the tone's frequency. A synchronous motor turns the wheels through a set of axles and gears. The gear ratios determine each wheel's rotation speed. The entire gear train rotates continuously. An electromagnetic pickup is placed next to each tone wheel. The bumps in the edge of the tone wheel cause the magnetic field of the pickup to vary, generating a periodic voltage change in the pickup's coil—a tone. The organist selects these tones via the drawbar circuitry and the keyboards while playing the organ. The resulting tones are ultimately amplified and converted to sound by a loudspeaker.

Keyboards and pedalboard

The lightweight construction of the 'waterfall'-style keyboard for the upper manuals allows for very rapid passages to be executed with more ease than on a weighted keyboard, such as a piano or pipe organ.

Most Hammond organs do not have a full, 32-note American Guild of Organists pedalboard going up to a G (3rd leger line of the bass clef) as the top note. Instead, to reduce the cost of the instrument, or the size of the bass pedalboard, 25-note (with a C on the 1st leger line of the bass clef as the top note) or 30-note (with an F on the 2nd leger line of the bass clef as the top note) bass pedalboards are often used. Several Hammond 'concert' models, the RT-2, RT-3 and D-100 had 32-note AGO pedalboards, in addition to a 'Solo Pedal Unit' which provided several 32', 16', 8', 4' voices on the pedal. The solo pedal unit used oscillators, similar to those used in Hammond's 'Solovox'.

The drawbars

The drawbars add harmonics to the original note that each key produces. This is mainly fifths and octaves, and one major third.

Pipe Pitch	Scale interval	Stop name	Note name
16'	Sub-octave	Bourdon	C (octave under root)
5 1/3 '	5th	Quint	G (fifth over root)
8'	Unison	Principal	C (root)
4'	8th	Octave	C (octave over root)
2 2/3'	12th	Nazard	G
2'	15th	Block-flute	C
1 3/5'	17th	Tierce	E
1 1/3'	19th	Largiot	G
1	22nd	Sifflote	C

Types of Hammond organs

The model B-3 was, and still is, the most sought-after model, though the C-3 differs only in cosmetics. Hammonds can be divided into two main groups: the 'Console' models such as the B-3, C-3 or A-100 which have two 61 note manuals and the smaller 'Spinet' models that have two 44 note manuals such as the M-3, L-100 and the M-100. Hammonds' serial numbers are not sequential from one production lot to the next, which can make it difficult to determine the date of manufacture of a Hammond organ.

Not all Hammonds used tonewheels and drawbars; the Hammond company produced a number of cheaper organs which used a simpler electronic way of producing sound, such as the model J100, but these instruments do not have the distinctive Hammond sound. By 1975, synthesizer technology had reached the point where the unique Hammond sound could be fairly closely simulated electronically. However, accurate imitation of the Hammond sound with simple electronic circuitry was difficult, because the subtly-changing phase relationships between tonewheels could not be easily replicated.

Playing the Hammond organ

Pianists and synthesizer players who begin playing the Hammond soon realize that authentic performance practice involves a lot more than playing the notes on the keyboard. Hammond players vary the timbre of both manuals in real time through a combination of changing drawbar settings, engaging or disengaging the vibrato/chorus effects or percussion settings, and changing the rotating Leslie speakers' speed setting. As well, performers obtain other effects by increasing the Leslie speakers' volume to add natural overdrive or 'growl' for certain passages, or by switching the Leslie speaker's run motor off for a brief moment, which produces a wobbly pitch-bend effect.

There are playing styles that are specific to the Hammond organ, such as palm glisses, rapid repetition of a single note, tremolo between two notes a third apart (typically the 5th and flat 7th scale degree of the current chord), percussive drumming of the keyboard, and playing a chord on the upper manual, then sliding your hand down to duplicate the chord on the lower manual. Artistic use of the foot-controlled expression pedal, which controlled the Hammond's volume level, and bass pedals are also important facets of the art of the Hammond. Pianists making the transition to Hammond organ have to learn to use their feet to perform basslines on the bass pedalboard. Although the pedalboard can be used in a very simple fashion (for sustained or slow-moving bass notes), professional-level Hammond players typically develop the ability to perform fast-moving basslines on the bass pedalboard.

'Clones' and emulation devices

Due to the difficulties of transporting the heavy Hammond organ, bass pedalboard (a B-3 organ, bench and pedalboard weighs 425 pounds/193kg) and Leslie speaker cabinets to performance venues, and due to the risk of technical problems that are associated with any vintage electromechanical instrument, there was a strong demand amongst musicians for way of recreating the Hammond sound in a more portable, reliable fashion. Some early emulation devices were criticized for their unrealistic imitation of the Hammond sound, particularly in the way the upper harmonics were voiced, and in the simulation of the rotary speaker effect. Refinements to Hammond emulations eventually led to the development of relatively light electronic keyboard instruments such as the Roland VK-7 and the KORG BX-3 and CX-3 that produce a fairly realistic re-creation of the Hammond tone.

By the 1990s and 2000s digital signal processing and sampling technologies allowed for better imitation of the original Hammond sound, and a variety of electronic organs, emulator devices, and synthesizers provided an accurate reproduction of the Hammond tone. Some sophisticated emulation devices have algorithms that recreate some of the characteristics of the vintage Hammonds, such as the 'crosstalk' or 'leakage' between the tonewheels, and digital simulations of the rotating Leslie speaker cabinet's sound. Nonetheless, an article entitled Clonewheel Heaven in Keyboard Magazine that reviewed electronic simulations of the traditional Hammond sound claimed that some aspects of the vintage electromechanical Hammonds' sound are not accurately reproduced by clones and emulation devices.

Current interest in Hammond organs

Despite the availability of relatively lower-cost, reliable digital 'clones' and emulation devices, there is still a strong interest in vintage Hammond organs. Even the difficulties of finding spare parts and trained repair personnel for such a complex instrument has not dissuaded musicians from continuing to use vintage Hammonds. Original electromechanical Hammond organs are prized by musicians from jazz, blues, rock, gospel, and other musical styles for the look and feel of their varnished wooden cabinets and 'waterfall'-style keyboards, and their vintage, traditional sound. Although the last electromechanical Hammond organ came off the assembly line in the mid-1970s, it is a testament to their over-engineered design and high-caliber construction that thousands are still in daily use.