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

DICTIONARY OF ORGAN STOPS. 13I
organ be disturbed by a rise of temperature, it is generally the reeds that
are made the scapegoats, whereas, as a matter of fact, it is the flue pipes
which are mainly responsible for the disparity 01 pitch. For, metal flue
pipes and small wood flue pipes respond to an increase of temperature by
sharpening perceptibly. The effect on reed .pipes is different. A stop
like the Vox Humana will actually flatten, since the pipe exercises but
little control over the tongue, which expands under the influence of the
heat. The Oboe, on the other hand, with its long and slender tube, will
remain fairly well in tune, the rarefaction of the air column compensating
for the expansion of the tongue—the one tending to raise the pitch, the
other to lower it. Between these two extremes lie stops such as the Horn,
Trumpet and Tuba, of larger scale and shorter body than the Oboe.
Deprived of its pipe, a reed will emit a thin, wheezing sound. The
pipe, tube or body (as it is variously called) is superimposed, not for the
purpose of determining the pitch of the reed, but in order to act as a
resonator and to qualify the tone. The pipe is, therefore, so adjusted that
the vibrations of the air column in it shall approximately correspond in
pitch with the note of the reed tongue, though, for various reasons, not
always exactly. Reed stops of an orchestral or imitative character usually
have short-length bodies (see Clarinet, Orchestal Oboe, Vox Humana).
These short-length pipes are employed . as resonators and possibly to
reinforce certain harmonics, but, generally speaking, the determination of
their length rests on traditional and empiric grounds rather than on a
scientific basis.* The curtailment in length of their pipes is one of the
main reasons why such " fancy " stops are so apt to get out of tune, for
the air column in the pipe has no control over the vibrations of the tongue.
In pipes of full length the vibrations of the tongue are, to some extent,
governed by the column of air in the pipe. Should an abnormal rise of
temperature occur, the point at which the pulsations of the resonant air
column and the vibrations of the tongue are no longer able to synchronize
will be marked by the reed "flying off" its note. Large pedal reeds and
Diaphonic valvular reeds, voiced and regulated "close" (i.e., smooth), are
peculiarly liable to this distressing defect. As a temporary remedy, the
recalcitrant pipes may be tuned slightly flat, if the wider opening of the
tuning siot does not prove effectual. Sometimes the "flying off " of a
reed is occasioned by the fortuitous influence of some definite volume of
air enclosed by the boot. It may then be cured by piercing a hole in the
boot, and if the waste of wind be likely to prove excessive, the perforation
may be covered with a leather membrane. For pneumatic starter for 32 ft.
reeds, see trombone.
* The scientific aspect of reed voicing is, nevertheless, dealt with in Pastor Allihn's
edition of "Topfer," in a manner interesting and comprehensive, if now—so far as
modern English work is concerned—somewhat archaic,