Fig. 30. Diaphone Producing Foundation Tone
The action is as follows. Air under pressure enters the chamber B through the pipe foot A, and passing up the ports C, C1, C2, etc., forces the metal balls D, D1, D2, etc., upwards into the chamber E; the bottom end of the resonator or pipe. The pressure of air above the balls in the resonator E, then rises until it equals or nearly equals the pressure of air in chamber B. This is owing to the fact that the column of air in the pipe or resonator E possesses weight and inertia, and being elastic, is momentarily compressed at its lower end. This increased pressure above the balls allows them to return to their original position, under the influence of gravity. By the time they have returned to their original position, the pulse of air compression has traveled up the pipe in the form of a sound wave, and the complementary rarefaction follows.
The cycle of movement will then be repeated numerous times per second, with the result that a very pure foundation tone musical note will be produced.
The Diaphone is tuned like ordinary flue pipes and will keep in tune with them; the pressure of wind (and consequently the power of the tone) may be varied without affecting the pitch. The form of the pipe or resonator affects the quality of the tone; it may be flue-like or reedy in character, or even imitate a Pedal Violone, a Hard and Smooth Tuba, an Oboe, or a Clarinet.
In closing this chapter, the writer desires to express indebtedness for much of the material therein to the comprehensive "Dictionary of Organ Stops," by James Ingall Wedgwood, Fellow of the Society of Antiquaries, Scotland, and Fellow of the Royal Historical Society (published by the Vincent Music Co., London, England). Although the title is somewhat forbidding, it is a most interesting book and reveals an amount of original research and personal acquaintance with organs in England and the Continent that is simply marvelous. It ought to be in the library of every organist.
[1] Broadhouse, J., "Musical Acoustics," p. 27.
[2] Mr. Skinner has built some of the finest organs in this country.
[3] Much of Roosevelt's finest work is now being improved by various builders by leathering the lips.
[4] The "Harmonic" principle is described in Dom Bedos' book, published in 1780, as applied to reeds, and Dr. Bédart states that this principle was applied to flutes as early as 1804.
[5] That is to say, the pipes are made double the length actually required, but are made to sound an octave higher by means of a hole pierced half-way up the pipe.
[6] Wedgwood; "Dictionary of Organ Stops," p. 150.
[7] Wedgwood: Ibid., p. 153.
[8] Wedgwood: Ibid., p. 151.
[9] Wedgwood: Ibid. p. 153.
[10] "The Hope-Jones pattern of Muted Viol is one of the most beautiful tones conceivable."—Wedgwood: "Dictionary of Organ Stops," p. 173.
[11] The Erzähler, a modified Gemshorn, is found only in organs built by Ernest M. Skinner.
CHAPTER XI.
TUNING.
Having described the improvements in pipes, we now consider how they are tuned, and the first thing we must notice is the introduction of equal temperament.
About fifty years ago most organs were so tuned that the player had to limit himself to certain key signatures if his music was to sound at all pleasant. Using excessive modulation or wandering into forbidden keys resulted in his striking some discordant interval, known as the "wolf." The writer remembers being present at a rehearsal of Handel's "Messiah" in St. George's Hall, Liverpool, Eng., in 1866, when the organ was tuned on the unequal temperament system, and there was a spirited discussion between the conductor and Mr. W. T. Best, who wanted the orchestra to play "Every Valley" in the key of E flat so as to be in better tune with the organ.
The modern keyboard is imperfect. One black key is made to serve, for instance, for D sharp and for E flat, whereas the two notes are in reality not identical.[1] To secure correct tuning and tone intervals throughout, forty-eight keys per octave are required, instead of the twelve now made to suffice.
In what is called the equal temperament system the attempt is made to divide the octave into twelve equal parts or semi-tones, thus rendering all keys alike. To do this it is necessary to slightly flatten all the fifths and sharpen the major thirds. The difference from just intonation is about one-fiftieth of a semi-tone. Although recommended and used by J. S. Bach, equal temperament was not introduced into English organs until 1852.
Much has been lost by adopting equal temperament, but more has been gained. To a sensitive ear, the sharp thirds and fourths, the flat fifths and other discordant intervals of our modern keyed instrument, are a constant source of pain; but the average organist has become so accustomed to the defect that he actually fails to notice it!
The change to equal temperament has on the other hand greatly increased the scope of the organ and has rendered possible the performance of all compositions and transcriptions regardless of key or modulation.
The tuning of an organ is seriously affected by the temperature of the surrounding air. Increased heat causes the air in the open pipes to expand and sound sharp contrasted with the stopped pipes through which the air cannot so freely circulate. The reeds are affected differently, the expansion of their tongues by heat causing them to flatten sufficiently to counteract the sharpening named above. Hence the importance of an equable temperature and the free circulation of air through swell-boxes, as described on page 59, ante.