a students' magazine / music

Hammond organ – harmony

In the previous articles about the Hammond organ we introduced the basic features of this instrument: the internal engine, the tonewheels, the Leslie amplifier with rotary effect (and its different speeds), the two manuals, the vibrato/chorus effects and the pedalboard.

In this last article we’re going to explain the true sound-shaping theory and mechanics of the harmonic drawbars.

We have already described the drawbars as “virtual pipes” for the electric organ, but if the classic church organ can be managed with a great variety of registers, the Hammond only counts nine drawbars for regulating its timber – and that’s all we need for sure!

 The drawbars are in the shape of small levers positioned in a row, generally in front of the upper manual. Each lever has a particular number written on it, which indicates the hypothetical length of the virtual cane assigned to that drawbar.

The fundamental drawbar is the 8′ (eight feet) and it gives the basic sound for the instrument. The other levers are used to add sounds with different pitch to the fundamental tone: the 16′ drawbar plays a note which is one octave lower than the fundamental, the 4′ plays one octave higher, while the 2′ plays two octaves and the 1′ three octaves (in a nutshell if you “split the cane” in a half it will play one octave higher). The other drawbars are the 5 1/3‘, the 2 2/3‘, the 1 3/5‘ ad the 1 1/3‘, all of which play at different intervals with “non-octave” relations to the fundamental, such as fifths and thirds.

 Numbers from 1 to 8 are also written along the levers: if I pull a drawabar out I’ll have an idea of how strong the sound for that harmonic is. The more I pull it out, the higher the number. Drawbars that have been left inside won’t give any sound.

 Additionally, the drawbars are grouped by colours: white for the “octave-by-octave” harmonics, black for the “mutations” (fifths and thirds) and brown for the “sub-octave” harmonics.

Ok, here we have an exception: though the 5 1/3‘ harmonic actually plays a fifth ABOVE the fundamental 8′, it has been included into the sub-octave category, that’s why it is brown and placed before the 8’.The reason? Well it’s really uncertain but… who cares? 😉

There’s plenty of possible combinations of the nine harmonics, so that the performer can manually modify the resultant sound by simply pulling/pushing one or more of the drawbars at his own discretion. The musician can change the sound in real-time by directly acting on the drawbars, but managing to do this while performing a fast piece may become a bit complicate… we’ve only got two hands! That’s why every Hammond model is endowed with a series of buttons called “presets”: we can pre-register a specific harmonic combination by assigning it to one of those presets buttons, so we’ll just have to press a key to get the desired sound whenever we want. A piece of cake! 🙂

On the classic Hammond models A, C and B3 (the most famous) we can see that the first 12 keys have the colours inverted – smaller keys in white and bigger keys in black: they’re the 12 preset buttons. Brilliant, uh?

from Wikipedia

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