A comprehensive dictionary of organ stops - Allen Organ Studio of ...

DICTIONARY OF ORGAN STOPS.
A.
Acoustic Bass Harmonic Bass; Resultant Bass; also,
Gravissima (q.v.); Gravitone (q.v.) ; Tonitru (g.v.) ; comprising also.
Acoustic Violone, and Quintatbn, 32 ft. tone. 32 ft. tone, rarely
64 ft. tone.
Resultant Bass is a permissible synonym, but the use of the term
"harmonic" is open to objection, owing to its well-nigh exclusive appli-
cation in organ-building to a particular method of generating tone, as
exemplified in the Harmonic Flute.
The phenomenon variously known as resultant, combinational, vibra-
tional, acoustic and (in a limited sense) differential tones was discovered
by Tartini, circa 17 14, and, subsequently, independently by Sorge in 1740.
It was first introduced into the organ by the Abt Vogler (1749-1814),
as a feature of his " Simplification System." Acoustic Basses are indeed
but sorry substitutes for real 32 ft. stops, and, contrary to the worthy
Abbess expectations, have not ousted them ; nevertheless the Acoustic'
Bass forms an economical compromise available for instruments of no great
pretensions.
A resultant tone is an acoustical illusion produced by the periodic
coincidence of particular vibrations emanating from two or more pipes (or
other tone generating agents). Such periodic synchronizations reinforce
one another, and are therefore involuntarily isolated and synthesized by
the ear. They thus appear as vibrations produced by some independent
agent, the pitch of the illusory note being determined by the
frequency with which the synchronous vibrations occur. This frequency
is dependent upon the interval separating the pipes. If, for instance, the
interval amount to a major third, the resultant tone will be heard at the
pitch of two octaves below that of the lower of two pipes ; if a fifth, at one
octave. Thus a 16 ft. pipe and a Quint io| ft. when simultaneously
sounded, give rise to a resultant tone of 32 ft. pitch.
Let a represent the 16 ft. pipe, b the Quint pipe. Adopting the
recognised scientific standard of pitch, in 1 second a will give rise to 32
vibrations, b to 48 vibrations. Reducing this to the simplest dimensions