Continuing this series on the families of pipe organ tone, I will now look into the wonderful world of flutes. A flutist might certainly be amazed at what the organ world calls a flute, since some of them are taller than a house, weigh many times what an orchestral flute does, could never be blown by mouth, and have no visual similarities with their orchestral namesake. What is it that allows us to call a 16' long, 200 pound wood pipe a flute?
The answer to this question is not so much a matter of size, shape, or material, but rather of comparative tone color. A pipe organ flute is not a principal. reed, or string, and that is about the best way to categorize it. It is something other than those easily recognizable organ voices. It is true that some flutes border on principal tone, and vice versa, and we get around that problem by calling them Flauten Principals, or some other hybrid name. To avoid that issue, let us focus on the details of what makes a pipe organ flute.
Since tone is our choice of delineation, I suggest that flutes are simply sounds of limited harmonic development. This compares to the principals, reeds, and strings which are rich in harmonics. Thus, flutes have only a few upper harmonics or partials, and some are audibly devoid of any harmonics above the fundamental. Indeed, these subtle differences in the relative power of the few harmonics present separate one type of flute from another.
In construction, there is a bewildering array of flute shapes, sizes, and material. Some are fully capped (Bourdon, Gedackt) or partially capped (Rohrflute, Koppelflute), while others are fully open (Harmonic Flute). Some ranks might even have two or three differing types of construction from bass to treble in order to create a specific tonal progression.
Along with the possibilities of being capped, half capped, or open, there are variations in the shapes of the resonators, many of which are ancient in origin. Pipe organ flutes may be cylindrical, square, rectangular, triangular, tapered, reverse tapered, spindle shaped, with chimneys, cones, holes, or a combination of any of the above. There appear to be no limitations, only the limitless desire and inventiveness of the organbuilder to find the sounds which will work for each instrument.
There have been attempts in the past to imitate the orchestral flute and recorder family with organ pipes, but these were never completely successful. The experiments, however, expanded the number of types of pipe organ flutes, and the builder's endeavors to bring other familiar sounds of nature and the orchestra into the pipe organ, though never exact copies, were responsible for generating many of the sounds which the pipe organ has today.
Pipe organ flute stops have a variety of tonal and musical purposes. One of the virtues of the flutes is their ability to combine with other families of tone (strings, reeds, and principals) in endless possibilities. Lacking strong harmonic structure, they add subtlety to other voices and blend into other combinations with ease. This alloying of sounds can also be avoided if academic restraint is sought or if one's musical taste is offended by such mixing.
The pitches available for organ flutes are many and ancient. From 32' on up, there has been endless experimentation with combinations of pitches to achieve various ensembles and solo lines. It is with flutes that the most beautiful mutation colors develop. The Cornet is a special and important voice usually of five ranks pitched at 8', 4', 22/3', 2', and 13/5'. To this may be added the flat seventh (11/7'). The Quintflute 11/3' and Nazard 22/3' (both playing fifths) are wonderful colors when used with 8', 4', or 2'. The rarely found 51/3' and 31/5' can be flute voices of pungency, and when used in the pedal will give clarity and articulation to the large slow-speaking basses. Where space and funds are inadequate for a real 32' stop, mutations at 102/3',62/5',51/3',44/7', etc., will credibly "fake" the effect.
The true glory of the flutes is their ability to combine in endless ways at every possible pitch of the harmonic series to create magical beauty and color for the organist. Fortunate is the organist who has beautiful flute voices over a wide range of pitches to work with.
Over the centuries, flutes have been made from a wide variety of materials. In soft-wood, a flute will sound mellow, somewhat imprecise, distant, or meditative. In hard-wood, the sound will become more firm and precise, chiffy and bright. When made from heavy lead-rich metal, the sound will be full and somewhat dark. When less dense tin-rich metal is used, the sound may be lighter and brighter. Some ancient organs have flutes made of ivory (mostly for show) or other exotic woods and metals, but this is now rare. The descriptions of sounds as related to the materials used for construction are only relative, since it is possible to produce a wide range of tone character by changing the wind pressure, voicing technique, scale of the pipe, thickness of the wall, placement in the organ and the acoustical environment.
As with other organ voices, styles of flute sounds come and go in favor and number. The Melodia, Concert Flute, and Flute D'Amour, which were popular earlier in this century, have now been replaced by other types of flutes revived from even earlier instruments. A recent reappearance of the Harmonic Flute signals renewed interest in 19th-century concepts, but it may be some time before this favorite of Cavaillé-Coll and Franck reoccurs in the multi-rank dominance which it once had in each instrument.
Many organists and builders would agree that for sheer beauty of tone, the flute family has a special place in the organ. The contrasts which are possible between the flutes and the other stronger voices provide essential musicality and variety. The architecture of the organ will continue to evolve, and flutes will continue to be a vital part of that development.