Fig. 16. Estey's Open Bass Pipes—Wood and Metal
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.