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.
[Illustration: 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.