Flue pipe
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A flue pipe (also referred to as a labial pipe) is a sound-producing component of the pipe organ that is driven by a ducted flue/windway against a labial ramp, thereby generating oscillations near the mouth. In contrast with reed pipes, flue pipes contain no moving parts.
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[edit] Construction
A flue pipe is comprised of two main portions: the foot and the resonator. The foot is the bottom portion of the pipe, and contains the toe hole at its base, through which wind enters the pipe. The length of the pipe foot does not affect the pipe's pitch. Thus, organ builders vary the foot lengths of their flue pipes depending on several factors, including the desired shape of the pipes in the façade, the height of the rackboard in which the pipes are seated, and the weight of the completed pipe.
The mouth/voicing, vibrates at the desired pitch and the resonator supports this generated frequency. The voicing (frequency generator), the length of the resonator and the resonator's cubic volume combined, determine the fundamental pitch of the flue pipe. The conical taper of the pipe will determine the overblown pitch (if used). If the pipe is metal, a tuning sleeve or tuning collar may be attached to the top of the resonator, which can be raised or lowered to change the length of the resonator, thereby changing the pitch produced. At the joint between the foot and the resonator, one side (and sometimes the side opposite as well) is flat, and an opening almost spanning the diameter of the pipe is cut at the base of the joint. This opening is called the mouth. A flat piece of metal or wood called a languid is affixed inside the pipe, completely dividing the resonator and the foot, except for a small slot/windway parallel to the mouth. This creates a chamber inside the pipe foot. Flat pieces of metal or wood (called ears) may be attached to the sides of the mouth for tuning purposes, and a horizontal dowel (called a roller or a beard) may be affixed at the pipe mouth to aid in prompt pipe speech.
[edit] Actuation
When wind is driven through the foot of the pipe, a column of air is focused by the slot/windway across the mouth to strike just above the edge of labium ramp. This creates a Bernouli, or "siphon effect" causing a low pressure area to be created just below the mouth. When this low pressure area reaches a critical stage, it "flips/pulls" the airstream below the labium edge, filling the vacume and then pressurizeing to the opposite of the previous state. von Karman vortex street. The column of air in the resonator then vibrates at the tuned frequency/tone determined by the mouth/voicing. [1]
[edit] Tonal groups
Flue pipes are divided into three broad categories: flutes, diapasons, and strings. Ranks of all three tonal groups may be either stopped or open, and may be made of either metal or wood. Metal pipes are normally round in cross section, while wooden pipes are most often square.
Flutes are generally the widest-scaled flue pipes and produce the tone with the most fundamental of all flue pipes. They are so named because they sound like the flute (though most flute ranks are not intended to imitate the orchestral instrument, they produce a similar sound). A stopped flute, such as the Gedackt (German for covered), produces a more muffled sound, while an open flute, such as the Waldflöte (German for forest-flute), produces a rounder, open sound. The Flûte harmonique (French for harmonic flute), of which the great nineteenth century French organ buillder Aristide Cavaillé-Coll was a proponent, is a metal flute pipe of double length with a hole punched in the center, which causes the pipe to speak at its first partial with a very round, intense sound. The Rohrflöte (German for pipe-flute; often called Chimney flute in English) is a stopped flute rank with a small pipe built into the cap.
Diapasons (often called principals) represent the primary sound of the pipe organ. They are medium-scaled and are often prominently featured in organ façades.
Strings are the narrowest flue pipes, thus they produce the richest harmonics. Their tone is thin and stringy.
[edit] Undulating stops
Often, an organ will feature two similarly-voiced string stops, one tuned slightly off of the other. When these stops are played together, a unique undulating effect results. Examples include the Voix céleste (French for celestial voice), typically tuned slightly sharp, and the Unda maris (Latin for sea waves), typically tuned slightly flat. This is typically done with string stops, though some builders have made undulating flute stops (notably Ernest M. Skinner's Flute celeste), and rarely an organ may feature an undulating diapason.
[edit] Labial reeds
Some flue pipes are designed to produce the sounds of reed pipes or to imitate the sounds of orchestral instruments which are approximated by reed pipes. The sound is generally more mellow and sweet than that of a true reed pipe. Examples include the Saxophone, the Muted horn, the Clarinet flute, and the Echo oboe.
[edit] Methods of tuning and voicing
[edit] Variations in timbre
For flue pipes, the scaling is of primary importance. The wider a flue pipe is scaled, the more fundamental will be present, and the fewer harmonics will be created. Thus, the tone becomes richer and fuller as the pipe's diameter widens from string scale to diapason scale to flute scale.
The material out of which the pipe is constructed also has much to do with the pipe's final sound (this also affects the shape of the pipe, as shown below). While recent scientific studies have shown that the nature of the metal used in making the pipe has little or no effect on the final sound, organ builders agree that a tin/lead alloy, for example, creates a very different tone than does zinc or copper metals or spotted or frosted alloys. Wooden pipes have a softer-edged, more mellow sound than metal pipes.
For reasons of ease of manufacture, the shape of the pipe is determined primarily by the material out of which it is made: if the pipe is metal, it will usually be cylindrical or conical; if the pipe is wood, it will usually be square or rectangular (some builders experimented with a triangular flute in the twentieth century, but this did not catch on). In addition to end construction, which is discussed above, the presence or absence of a chimney (a small pipe fitted in the cap of a stopped flute pipe) and the taper (or inverse taper) of the pipe body result in different sounds.
[edit] References
- ^ Arther H. Benade, Fundamentals of Musical Acoustics. See also The physics of the organ, by John Mainstone, in The Cambridge Companion to the Organ (1998), edited by Nicholas Thistlethwaite and Geoffrey Webber, p. 31–41. ISBN 0-521-57584-2
See also this organ site; http://www.organstops.org/
