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Diaphones

A third type of pipe found in many Australian theatre organs is the diaphone. This was invented by Robert Hope-Jones, who discovered the principle by accident. Diaphones are not unlike reed pipes, but in place of the reed is a kind of valve, which opens and closes rapidly as air passes around it, sending air pulses into the resonator. The frequency of these pulses determines the pitch of the pipe.

Diaphones are used only in the lowest octaves (below 8 ft. bottom C) of Diapason ranks extending to 16 ft. or 32 ft. pitch. Their significant advantages over flue pipes are great clarity of tone and pitch, immense power (when needed) and promptness of speech. Flue and reed bass pipes tend to take a comparatively long time to speak, and the burst of energy given to the air column by a diaphone's valve significantly reduces the time needed to set the large column of air in the pipe in motion. For rhythmic playing, diaphones give a very prompt bass response as soon as the pedal key is depressed.

Because of their immense size (one can, even if built on the generous scale, easily climb inside them), the 32 ft. octaves of diaphone pipes were not located in the organ chambers, but were placed separately above theatre roofs (as at the Regent Theatre, Brisbane), or under the auditorium floor (as at the State Theatre, Sydney). It is very difficult to identify the precise source of such low-frequency sounds (16-32 Hz), so audiences would not have been aware that these sounds were not coming from the same location as the rest of the organ. They create considerable vibration, and were thus unpopular with those in properties adjoining theatres in which they were installed. However, their deep rumbling roar, literally shaking the building, provides a moving and unforgettable experience.

In Australian theatre organs, Wurlitzer's 32 ft. diaphones invariably had wooden resonators, as did 16 ft. diaphones on the larger instruments (fifteen ranks and above). Metal diaphones were used in smaller Wurlitzers (where the stopkeys were labelled "Bass 16") and in Compton and most Christie organs.

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