Figs. 25, 26, 27. Diaphone in St. Patrick's Cathedral, New York
Referring to Fig. 25, the chamber WW is supplied with air under pressure whenever the organist presses a key or pedal calling into use this particular note. The pressure of air enters through the circular engine supply port S, thus raising the pressure in the chamber C and forcing in an upward direction the aluminum piston P through the medium of the division D (colored black), which forms a portion of the aluminum piston.
When the lower edge of the piston has risen a certain distance it will uncover the circular engine exhaust port E, and will allow the compressed air to escape into the atmosphere. At this moment the rise of the piston will have closed the engine supply port S.
The momentum acquired by the piston (see Fig. 27) will cause it to travel upward a little further, and this upward travel of the division D will cause a compression of air to take place at the foot of the resonator or pipe R. This compression will be vastly increased through the simultaneous opening of the eight circular speaking ports SP.
The pressure of the compressed air at the foot of the resonator E will now by acting on the upper surface of the division D depress the aluminum piston until the engine supply port S is again opened.
By this time the compression at the foot of resonator R will have traveled up the pipe in the form of a sound wave, and will have been followed by the complementary rarefaction. This rarefaction on the upper side will render more effective the pressure of the compressed air again admitted through the engine supply port S on the underside of division D.
It will be seen that this cycle of operations will be repeated as long as the organist holds down his pedal or key admitting compressed air to the chamber W.
As the aluminum piston P is very light and is in no way impeded in its movement or swing, the speed of its vibration, and consequently the pitch of the note emitted, will be governed by the length of the resonator or pipe R.
The tone given by this particular form of Diaphone possesses a peculiar sweetness in quality, while the power is limited only by the pressure of air used to operate it.
