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Organ Talk

The Drawbar System



If imitation is a form of flattery, the Hammond Organ Company must be pleased to note how drawbars have increasingly been fitted to other makes of organs — even the home-constructed variety—over the years. Of course, manufacturers borrow each others ideas freely and even Hammond is in this category, but the drawbar system has been in use for 45 years and is still very popular.

Despite the system having its limitations, the modern instrument may well incorporate drawbars as part of the many facilities available. As there is a tendency for the newcomer to 'grab a handful' of drawbars without knowing the principles on which they are based, this article will attempt to provide a better understanding of their use.

In the very early days of modern science, Robert Hooke discovered that musical tones could be created by holding a piece of card against a cogwheel. Doubling the speed of the revolving wheel raised pitched by an octave, a discovery he made in 1618. Over two centuries later, other scientists were experimenting with toothed wheels, magnets and electric motors and at the beginning of the present century, the Telharmonium was playing music to telephone subscribers in New York, its tones derived from alternators.

Tone-wheel



Laurens Hammond, a man of greatly inventive mind, had developed a number of ideas - electric motors, stereo movies, a radio power pack and electric clocks - before turning his designing to music and the organ. His first organ appeared in 1935 and worked on Hooke's principle but used an electromagnet in front of the toothed wheel.

A single Hammond tone-wheel generator produces a very good sine wave, but the sound of a pure waveform is uninteresting to the ear. Consequently Laurens Hammond decided to provide additional pitches so that harmonics could be added to the fundamental. However, rather than using tabs or drawstops, he decided upon individual volume controls for each pitch: these were engraved with numbers from 0-8 for setting the required harmonic content of a given timbre. He named these 'drawbars' or 'tonebars', the classic Hammond system having sets of nine drawbars.

The CTV screen's phosphors are of three primary colours only (red, green and blue) but mixtures of these will give an almost infinite number of hues. In the same way, the primary or fundamental tones available from each drawbar are mixed: with nine primary musical colours, the variations again are almost infinite. During the last decade, the Hammond mechanical generator was replaced by LSI devices, but sine waves are still produced and mixed as hitherto.

Harmonics



The drawbars are related to each other harmonically and for the system, to work properly the waveforms must be pure sine. The set of nine drawbars have coloured knobs for controlling these harmonics of the fundamental and appear as in Figure 1.

Figure 1
Brown Brown White White Black White Black Black White
Sub Octave Sub Third Fundamental 2nd 3rd 4th 5th 6th 8th


If all of the nine drawbars are pulled out to their fullest extent (i.e. set to 8 in each case), the registration is written down as:

88 8888 888

The nine figures are split into three groups partly to make the registration easier to read. A more important reason for this grouping is to remind the user that:

88 — the first group of two Brown drawbars controls the suboctave content of the timbre.
8888 — the central group sets the basic tone.
888 — the top three drawbars add brilliance.

Brown drawbars give sub-octave sounds, white denotes consonant (even) harmonics and black dissonant (odd) harmonics. The second brown drawbar provides 5⅓' pitch, which is dissonant, but its use adds a sub-octave character because of difference frequencies it provides when other pitches are in use.

Basic Tone



Drawbars in the central group have their own characteristics. Taking each in turn we find that:

00 8000 000 (the first white drawbar) adds fundamental power to all unison 8' sounds but requires the addition of other drawbars to establish a sense of pitch. Reducing volume allows the upper harmonics to be more incisive.

00 0800 000 adds brightness and clarity without brilliance. At low volume it imparts a delicate effect to any tonal family.

00 0080 000 is dissonant, adding Quint tone necessary for strings and woodwinds. If too powerful will thicken the registration.

00 0008 000 provides brilliance and aids the sense of pitch definition.

Using just these four drawbars, we can try a few permutations. If the sound is pleasing but too loud, a 'mini' version of the same registration is obtained by pushing each drawbar in by the same number of notches. Given a good amplification system, quiet registrations are often more effective than fortissimos:

00 7656 000 8' Diapason — mainly consonant with some third harmonic.

00 8020 000 8' Tibia Clausa — fundamental with some third harmonic content.

00 4763 000 8' Oboe Horn — weak fundamental.

00 8888 000 8' Tuba — loud and fairly bright.

00 8740 000 8' Horn — a very smooth registration.

00 8605 000 Flute Chorus (consonants only).

Brilliance



The top group of three drawbars adds 'seasoning' to the central group, as shown in these examples:

00 6888 000 8' Trumpet becomes 00 6888 543

00 8888 000 8' Tuba becomes 00 8888 866

00 2354 000 8' Salicional becomes 00 2354 321

00 7373 000 8' Clarinet becomes 00 7373 430

Lastly, we can add small quantities of the first two brown drawbars for sub-octave and chorus registrations:

52 8888 542 Full Great

34 3576 421 String Chorus

47 5430 000 16' Oboe Horn

64 3322 000 16' Diapason

Artists like Jimmy Smith and Groove Holmes took to the Hammond because of the 'dirty sound' that it could produce — aided by the use of plenty of 5⅓ drawbar and percussion of second/third harmonics. Hammond's old B-3 organ was so popular in this respect that an almost identical LSI version of the tonewheel model was produced recently — the B-3000. Drawbar registrations do not necessarily need to be imitative and the 'blues' player might well use registrations (with or without soft percussion) such as:

68 0800 006, 88 8800 000
66 0880 000, 88 8000 008

An extra black drawbar with red spot is sometimes encountered on Hammond organs. This controls a mixture of tenth and twelfth harmonics, giving extra 'fizz' to any registration.

It is worth noting that settings which involve plenty of dissonant harmonics are best reserved for solos whilst accompaniments and block chords should employ consonant harmonics mainly. Where reverse colour presets are fitted (the lowest octave of a six octave keyboard), Hammond usually preset these so that accidentals (white keys) give solo voices and the naturals (black keys) more consonant voices intended for chords. This is a reminder that dissonant harmonics must be used with care — depending on the type of music being played!

Writing down any favourite tone-colour discovered is well worth while as otherwise its registration will soon be forgotten. Yes... I know what I said earlier about grabbing drawbars! With an understanding of the principles, memorising the pattern made by the protruding drawbars will help when making quick changes in registration. In effect, the pattern is equivalent to a bar graph/frequency spectrum, allowing the player to see the harmonic content at a glance. In very general terms the patterns will be:


Not all drawbar systems will conform to the specification mentioned but the same ideas can be applied provided that pure waveforms (perhaps described as 'Flute') are being processed. In strict theory, nine Hammond drawbars will give at least 80 million different timbres — according to the blurb. I'll settle for far less than this, but it should be possible to hear the effect of tiny changes in registration if the instrument is worth its salt and the reader not too senile!



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Working with Video

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Hot Wiring Your Guitar


Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.

 

Electronics & Music Maker - Jun 1981

Feature by Ken Lenton-Smith

Previous article in this issue:

> Working with Video

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> Hot Wiring Your Guitar


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