The Recent Revolution in Organ Building / Being an Account of Modern Developments

by George Laing Miller

THE UNIT ORGAN.

The Unit organ in its entirety consists of a single instrument divided into five tonal families, each family being placed in its own independent Swell box. The families are as follows: "Foundation"—this contains the Diapasons, Diaphones, Tibias, etc.; "woodwind"—this contains Flutes, Oboes, Clarinets, etc.; "strings"—this contains the Gambas, Viols d' Orchestre, Dulcianas, etc.; "brass"—this contains the Trumpets, Cornopeans and Tubas; "percussion"—this contains the Tympani, Gongs, Chimes, Glockenspiel, etc.

On each of the keyboards any of the stops, from the "foundation" group, the "woodwind" group, the "string" group, the "brass" group and the "percussion" group, may be drawn, and they may be drawn at 16 feet, at 8 feet, and, in some instances, at 4 feet, at 2 feet, at twelfth and at tierce pitches.

Arranged in this way an organ becomes an entirely different instrument. It is very flexible, for not only can the tones be altered by drawing the various stops at different pitches, but the various groups may be altered in power of tone independently of each other. At one moment the foundation tone may entirely dominate, by moving the swell pedals the strings may be made to come to the front while the foundation tone disappears; then again the woodwind asserts itself whilst the string tone is moderated, till the opening of the box containing the brass allows that element to dominate. The variety of the tonal combinations is practically endless.

The adoption of this principle also saves needless duplication of stops. In the organ at St. George's Hall, England, there are on the manuals 5 Open Diapasons, 4 Principals, 5 Fifteenths, 3 Clarinets, 2 Orchestral Oboes, 3 Trumpets, 3 Ophicleides, 3 Trombas, 6 Clarions, 4 Flutes, etc., etc. In the Hope-Jones Unit organ at Ocean Grove effects equal to the above are obtained from only 6 stops. The organist of Touro Synagogue, New Orleans, has expressed the opinion that his ten-stop Unit organ is equal to an ordinary instrument with sixty stops.

SYMPATHY.

A strong reason against the duplication of pipes of similar tone in an organ is that curious acoustical phenomenon, the bête noir of the organ-builder, known as sympathy, or interference of sound waves. When two pipes of exactly the same pitch and scale are so placed that the pulsations of air from the one pass into the other, if blown separately the tone of each is clear; blown together there is practically no sound heard, the waves of the one streaming into the other, and a listener hears only the rushing of the air. That the conditions which produce sound are all present may be demonstrated by conveying a tube from the mouth of either of the pipes to a listener's ear, when its tone will be distinctly heard. In other words, one sound destroys the other. Helmholtz explains this phenomenon by saying that "when two equal sound waves are in opposition the one nullifies the effect of the other and the result is a straight line," that is, no wave, no sound. "If a wave crest of a particular size and form coincides with another exactly like it, the result will be a crest double the height of each one" (that is, the sound will be augmented). * * * "If a crest coincides with a trough the result will be that the one will unify the other," and the sound will be destroyed.[1] That is why in the old-style organs the builder, when he used more than one Diapason, tried to avoid this sympathy by using pipes of different scale, but even then the results were seldom satisfactory; the big pipes seemed to swallow the little ones. In the big organ in Leeds Town Hall, England, there was one pipe in the Principal which nobody could tune. The tuner turned it every possible way in its socket without avail, and at last succeeded by removing it from the socket and mounting it on a block at a considerable distance from its proper place, the wind being conveyed to it by a tube. This is only one instance of what frequently occurred.

In the Hope-Jones organ the usual plan of putting all the C pipes on one side of the organ and all the C# pipes on the other, is departed from. The pipes are alternated and in this ingenious way sympathy is largely avoided.

[1] Broadhouse: "Musical Acoustics," p. 261.