Chapter X The Production of Organ Tone
We now come to the department of the organ which will be of more interest to the listener, viz., the various organ tones. The general shape and construction of the pipes now in use, judging from the earliest drawings obtainable, have not changed for hundreds of years. The ancients were not wanting in ingenuity and we have pictures of many funny-looking pipes which were intended to imitate the growling of a bear (this stop was sometimes labeled Vox Humana!), the crowing of a cock, the call of the cuckoo, the song of the nightingale, and the twitter of the canary, the ends of these pipes being bent over and inserted in water, just as the player blows into a glass of water through a quill in a toy symphony. Then there was the Hummel, a device which caused two of the largest pipes in the organ to sound at once and awake those who snored during the sermon! Finally there was the Fuchsschwanz. A stop-knob bearing the inscription, “Noli me tangere” (touch me not), was attached to the console. As a reward for their curiosity, persons who were induced to touch the knob thereby set free the catch of a spring, causing a huge foxtail to fly into their faces—to the great joy and mirth of the bystanders.
In order to understand what follows we must make a short excursion into the realm of acoustics. We have already remarked upon the extreme antiquity of the Flute. The tone of the Flute is produced by blowing across a hole pierced in its side; in other words, like a stream of wind striking upon a cutting edge. It is possible to produce a tone in this way by blowing across the end of any tube made of any material, of glass, or iron, or rubber, or cane, or even the barrel of an old-fashioned door key. The primitive Flutes found in the Egyptian tombs and also depicted on the ancient hieroglyphics are made of reed or cane, about 14 inches long, possessing the usual six finger-holes. The top end is not stopped with a cork, as in the ordinary Flute, but is thinned off to a feather edge, leaving a sharp circular ring at right angles to the axis of the bore. By blowing across this ring a fair but somewhat feeble Flute tone is produced.
The six holes being closed by the fingers, the ground tone of the tube is produced. On lifting the fingers in successive order from the bottom end, we get the seven notes of the major scale. Closing the holes again and blowing harder, we get the scale an octave higher. By blowing still harder we get an octave higher still. In other words, we are now producing harmonics.
It is possible to produce from a plain tube without finger-holes or valves, such as the French Horn, by tightening the lips and increasing the pressure of the player’s breath, the following series of harmonics:
The harmonics of a pianoforte string can be easily demonstrated by the following experiment: Depress the “loud” pedal and strike any note in the bass a sharp blow. On listening intently, the 3d, 5th, and 8th (the common chord) of the note struck will be heard sounding all the way up for several octaves. In this case the other strings of the piano act as resonators, enabling the harmonics to be heard.
Coming back to our Flute again and applying the knowledge we have gained to an organ pipe, we observe:
1. That the pitch of the sound depends on the length of the tube.
2. That the pitch of the sound also depends on the amount of wind pressure.
From this last will be seen how important it is that the pressure of the wind in an organ should be steady and uniform. Otherwise the pipes will speak a harmonic instead of the sound intended—as, indeed, frequently happens.
When a stop is labeled “8 ft.,” that means that the bottom pipe, CC is 8 feet long and the pitch will be that of the key struck. A “16-ft.” stop will sound an octave lower; a “4-ft.” stop an octave higher. These measurements refer to pipes which are open at the top and are only correct in the case of very narrow pipes, such as the stop called Dulciana. Wider pipes do not require to be so long in order to produce 8-ft. tone.
“If a tube * * * open at both ends be blown across at one end, the fundamental tone of the tube will be sounded; but if the hand be placed at one end of the tube, so as to effectually close it, and the open end be blown across as before, a sound will be heard exactly one octave below that which was heard when both ends of the tube were open. One of these pipes was an open pipe, the other a stopped pipe; and the difference between the two is that which constitutes the two great classes into which the flue pipes of organs are divided.” [1]
Thus by stopping up the end of an organ pipe we get 8-ft. tone from a pipe only 4 ft. long, 16-ft. tone from a pipe 8 ft. long, and so on, but with loss of power and volume. The harmonics produced from stopped pipes are entirely different from those of the open ones; their harmonic scale is produced by vibrations which are as 1, 2, 3, 4, etc., those of a stopped pipe by vibrations which are as 1, 3, 5, 7. All these harmonics are also called upper partials.
The Estey Organ Company claim to have discovered a new principle in acoustics in their Open Bass pipes, of which we show a drawing opposite. This invention (by William E. Haskell) enables the builders to supply open bass tone in organ chambers and swell boxes where there is not room for full-length pipes.
Referring to the illustration, it will be seen that the pipes are partly open and partly stopped, with a tuning slide in the centre. The builders write as follows:
“The inserted tube, or complementing chamber, in the pipe is such in length as to complete the full length of the pipe. It is, as will be noted, smaller in scale than the outside pipe. The effect is to produce the vibration that would be obtained with a full-length pipe, and in no way does it interfere with the quality of tone. In fact, it assists the pipe materially in its speech. This is most noticeable in a pipe such as the 32-foot Open Diapason, which when made full length is quite likely to be slow in speech. With this arrangement the pipe takes its speech very readily and is no slower in taking its full speech than an ordinary 16-foot Open Diapason.
“We have worked this out for all classes of tone—string, flute and diapason—and the law holds good in every instance.”
Helmholtz was the first to demonstrate that the quality of all musical tones depends entirely upon the presence or absence of their upper partials. In the hollow tone of the Flute they are almost entirely absent; in the clanging tone of the Trumpet many of the higher ones are present; and if we take an instrument like the Cymbals we get the whole of the upper lot altogether.
The different qualities of tone of the organ pipes are therefore determined: (1) By the material of which the pipes are made; (2) by the shape of the pipe; (3) by the amount of wind pressure; (4) by the shape and size of the mouth, the relation of the lip to the stream of wind impinging on it from a narrow slit, and the shape and thickness of the lip itself. The manipulation of the mouth and lip to produce the tone desired is called voicing and calls for considerable artistic skill. The writer recollects an instance of a clever voicer (Gustav Schlette) taking a new organ in hand, which was not quite satisfactory, and on the following Sunday he hardly knew it again.
Another kind of harmonics must now be described, called combinational or Tartini tones (from Tartini, a celebrated Italian violinist of the XVII century, who first described them). “These tones,” says Helmholtz, “are heard whenever two musical tones of different pitches are sounded together loudly and continuously.” There is no necessity for giving a table of all of their tones here; we select the two most useful. If two notes at an interval of a fifth are held down, a note one octave below the lower one will be heard. So organ builders take two pipes—one 16 feet long (CCC) and one 10 2/3 feet long (GG)—which make the interval of the fifth, and, by sounding them together, produce the tone of a pipe 33 feet long (CCCC). This is the stop which will be found labeled “32-ft. Resultant.” Hope-Jones makes a stop which he calls Gravissima, 64-ft. Resultant, in his large organs. Many contend that this system produces better results than if pipes of the actual lengths of 32 or 64 feet were employed. Indeed, a pipe 64 feet long would be inaudible; the human ear has its limitations and refuses to recognize tone lower than 32 feet (just as we cannot lift water by a suction pump over 32 feet)—but, these great pipes produce harmonics which wonderfully reinforce the tone of the organ. Therefore their use is worth while.
The other combinational tone to which we refer is that produced by the interval of a major third. It sounds two octaves below the lower note. The writer is not aware that this has ever been used as an organ stop, but it is found written in the organ compositions of Guilmant and other first-rate composers. It will be seen that a skilful organist, with a knowledge of these tones, can produce effects from small organs not available to the ordinary player.
Reverting once more to our Flute, whose tube is shortened by lifting the fingers from the holes, it is not generally known that this can be done with an organ pipe; the writer has met with instances of it in England. The two lowest pipes of the Pedal Open Diapason were each made to give two notes by affixing a pneumatic valve near the top of the pipe. When the valve was closed the pipe gave CCC. When the organist played CCC sharp, wind was admitted to the valve, which opened, and this shortened the pipe. The device worked perfectly, only that it was not possible to hold down both CCC and CCC sharp and make “thunder”! The organist of Chester Cathedral had been playing his instrument twice daily for ten years before he found this out, and then he only discovered it when the pipes were taken down to be cleaned. It is an admirable makeshift where a builder is cramped for room.
Organ pipes are divided into three families—Flues, Reeds and Diaphones. The flues are subdivided into Diapasons, Flutes, and Strings, and we now proceed to consider each of these groups separately.