Reed Pipe Construction |
Just as flues have two primary elements in their
construction, reed pipes
(usually called simply
reeds) have both lower and upper parts, in this case called boot and
resonator respectively. However, reeds differ from flues both in the timbre
of their sound
and in the way that sound is produced. The chief difference lies in the presence of a
vibrating body
- - the tongue - - in reeds. Flues produce sound through the creation of turbulence
in a stream of
wind, and that turbulence resonates in the body. In a reed, however, there is
actually a part of the
pipe that vibrates to produce the sound.
Reed resonators
are usually made of metal, although wooden resonators may be found. Metal resonators
may be
found in a variety of shapes, but they are usually circular in horizontal cross
section. The
photograph to the left shows the three most common shapes for resonators.
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When resonators are made of
wood, they most often are square in horizontal cross section. In an approximation of
the
cylindrical and conical shapes of metal resonators, they may be built with near
parallel sides, or
they may be flared outward as they extend from the boot. The photograph shows a
Krummhorn
with a wooden resonator made of mahogany.
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Organ pipes are usually placed
in an upright position on a windchest, but one exception should be noted. Some
trumpet stops
are placed in a horizontal position, so that the top end of their resonators actually
face the listener.
Reed stops placed in this manner are usually called en chamade reeds, and
their
appearance can be quite striking. The photograph shows a Trompette en chamade with
brass
resonators and turned open ends made to resemble the bells of orchestral trumpets.
20.
A deviation from the practice of making pipes with straight resonators is seen in mitered resonators. Mitering of reed resonators can be done in order to accomplish one or both of two goals
The photograph to the right
shows a typical mitered resonator that has been formed so that the resonator
continues upward
from the block.
34 The full length of the
resonator in effect curves around the mitered joints, but the pipes has a shorter
overall length than
it would otherwise have. This pipe is from an installation that does not have enough
space for the
pipe to be made with a straight resonator for its full length.
The pipe in the photograph to
the left is a hooded Trumpet. The end of the resonator has been mitered to allow the
sound to
project forward (in this case, to the left) rather than straight up. Hooded trumpets
are sometimes
used when the direct sound of an en chamade reed is wanted, but there is no
appropriate
place to display a reed in that way.
Reed boots are usually made of
metal and are hollow cylinders which contain all the moving parts of the reed pipe.
In the case of
larger reeds, particularly those found in pedal divisions, the boot may be made of
wood. Wooden
boots are usually square, and they may be fastened to the toeboard to prevent any
movement that
could result from the very strong low vibrations found in pedal reeds. The
photograph shows a
wooden boot from a pedal Fagott and a
metal boot from a Krummhorn.
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The actual working part of a reed - - the part that produces the sound - - is hidden in the boot. A strong brass tube, the shallot, is attached to the underside of the block, opening into the same hole that leads to the resonator on the upper side. The shallot and the tongue - - a thin strip of brass that can vibrate freely - - are held in place with a wooden wedge. One additional part also connects from boot to resonator: the wire, which holds the tongue against the shallot and is used for tuning. The photograph shows these parts both separated and assembled.
When wind is admitted through the bottom of the boot - - the toe hole, as in flues - - it can exit only through the shallot and resonator. As it enters the narrow passage between the tongue and the shallot, the tongue vibrates, producing a sound wave in the air column of the resonator. The tongue must be carefully adjusted in its position against the shallot in order to be free to vibrate without leaving so wide an opening that no vibration takes place at all.
© 1998, James H. Cook