B4 II – 75
It would be convenient if tonewheel organs used harmonics to describe the
drawbars settings. However, the terms used for describing the harmonic content
of organs historically comes from pipe organs, where the use of various lengths
of pipe determines the tonal characteristics. Hence, organs have come to use
“pipe length” rather than harmonic number to describe sound settings.
Additionally, it is quite useful to have tones that are not part of the basic
harmonics series to “fatten up” the resultant sound. On the tonewheel organ,
the brown drawbars provide tones which are not natural harmonics of the
fundamental frequency, but belong to the harmonic series starting one octave
below. That’s why they are often called sub-harmonics.
The “pipe length” settings, and their relationship to the natural harmonics,
are described in the following graphic:
Drawbars and their Harmonics
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