Pipe Organ Mixtures - Hammond Model A Manual

CHAPTER II.
ANALOGY BETWEEN HARMONICS AND PIPE
ORGAN MIXTURES.
HOSE familiar with pipe organ design will recognise that the har-
monic control system of the Hammond Organ is simply an extension
of the principle of harmonic corroborating stops or mixture stops
on a pipe organ.
In pipe organ phraseology, the fundamental is of 8-foot pitch, the second
harmonic of 4-foot pitch, the third harmonic of 2 2/3-foot pitch (twelfth or
nazard), the fourth harmonic of 2-foot pitch (fifteenth or super octave),
the fifth harmonic of 1 2/5-foot pitch (seventeenth or tierce), the sixth
harmonic of 1 1/3-foot pitch (nineteenth or larigot), the eighth harmonic of
1-foot pitch (third octave or twenty-second), the sub-harmonic of 16-foot
pitch, and third sub-harmonic of 5 1/3-foot pitch.
The chief difference is that in the Hammond Organ the player is able to
control the precise amount of strength of each rank, which is obviously
impossible with pipes, because a pipe must either be blown or left silent.
To incorporate as many different sizes of pipes for each rank of the harmonic
series as are necessary to control the tone quality by harmonic changes
alone, would require so many pipes that the expense and difficulty of
regulation and maintenance would make it impracticable. The number of
pipes required under such a system would be so large that it is actually
simpler, and requires fewer pipes, to put the harmonics in the foundation
pipes by voicing, and to supply as many ranks of differently voiced pipes
as the user wants or can pay for.
THE HAMMOND ORGAN IS A "STRAIGHT" ORGAN.
Without going into any discussion as to the merits of "extension" in a
pipe organ, it is obvious that this principle cannot be used to reduce the
number of pipes which would be necessary to control the tone quality by
harmonic pipes alone; for in the common case where the same frequency
reappears twice as a harmonic of different order of two notes in one chord,
the single pipe would have to be made to blow twice as hard. This is
plainly impossible because the pipe must either be blown the same way
or not blown at all.
Owing to the fact that it is much simpler to control the amount of electricity
which will flow in an electric circuit than it is to control the amount of
sound that will come from a pipe, it has been possible to design the instru-
ment so that one source of a given frequency can be used to put different
amounts of electric current into the whole. No matter how many times
a certain frequency is called upon to enter into a complex mixture of a
chord of tones of one kind, the same source can be used with increasing
strength and so represents in itself a large number of pipes which would
otherwise have to be available for the purpose. Thus, the Hammond
Organ has none of the tonal failings characteristic of the unit pipe organ.
It is a straight organ with full and equal tonal resources available on both
manuals and pedals.
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