In 1894 the British electrical engineer and organ builder Robert Hope-Jones took out a patent for a new invention which produced qualities of tone he described under the names Diaphone, Diaphonic Diapason. and Diaphonic Horn.
This form of pipe is open at top and of singular construction; its tone is created by pulses or vibrations in its resonator by the rapid motions of a disk-shaped pallet called a clapper (beater) actuated by pipe wind.
The clapper, or beater, is part of an apparatus in the clapper (beater) box, or boot, of the pipe containing an apparatus which is so connected as to admit a regular succession of puffs of compressed air through an orifice and into the air cavity of the resonator above it; the clapper is a disk valve faced with felt and leather which is held against its seat by a spring which simply opens and closes the lower orifice of the pipe acting in the same way as a striking tongue in the cavity of an ordinary reed pipe.
The Diaphone pipe differs from an ordinary striking reed pipe in that it has no tuning wire and is tuned like any other ordinary labial pipe; it also differs in that, within limits, when blown by different pressures of wind, its power and to a lesser extent its quality of its tone may be altered without any change of pitch.
Hope-Jones carefully tuned Diaphones to pitch pipes and varied wind pressure by as much as 800 per cent without being able to detect the slightest variation of pitch; when passed beyond these limits however the Diaphone went out of tune with the pitch pipe.
This is a high pressure stop voiced on 15 inches or more of wind; most commonly the resonator is made of quadrangular wood of inverted pyramidal form but also may be made stout zinc of inverted conical form; the resulting tone is full and commanding, and evidently, by using different wind pressures, it seems that, within limits, just about ANY strength of tone may be obtained from the Diaphone.
In addition, the pitch of the Diaphone may be made to be independent of the period of a resonator; Diaphonic valves have been made to speak with half length tubes, or without any tubes at all.
Hope-Jones was of the opinion that, when properly made, he did not think that Diaphones should fail to wear well; however, bearing in mind the rapidity with which this piece of mechanism has to act to produce a musical tone, one has reason to question its durability and remaining in good working order for any length of time; this has tended to work against a general introduction of the Diaphone.
Hope-Jones first began inserting this stop in the Pedal divisions of the organ at Worcester Cathedral in 1895 and at McEwan Hall in Edinburgh in 1896 where, in both cases, it could be drawn of 32-foot and 16-foot pitch.
NOTE: The Midmer-Losh organ in the Atlantic City Boardwalk Hall auditorium possesses a unique stop in the organ world -- the 64-foot Diaphone-Dulzian in the Right Pedal Division housed in the right stage chamber, one of only two true full length open stops of this grave pitch in the world (the other is the monster 64-foot reed stop labeled Contra Trombone in the Pedal division of the Hill organ in the Town Hall in Sydney, New South Wales); voiced on 35 inches of wind, this Diaphone-Dulzian stop is mitered in its bottom octave with the tops of the resonators pointing forward like an upside down "L", its bottom 22 pipes are of Diaphone construction, and its remaining pipes are striking reeds -- but because of the way these Diaphone pipes are voiced the transition from Diaphone to reed pipes cannot be detected; and, since its very slow and powerful rhythmic vibrations sound like a helicopter circling overhead it is seldom used, but many more organs including the Saint Louis Scottish Rite Cathedral Kimball (See Photos 3) also have a 64-foot stop in their stop list -- these are acoustic fakes however, created by combining a covered stop of 32-foot pitch (often a Contra Bourdon of Tibia Clausa construction) with a 21-1/3-foot extension situated very closeby in the same chamber and standing at the interval of a perfect 5th above it (the extension often formed of less assertive covered pipes of Lieblich Gedeckt tone) which, by generating the differential tone when both are sounded together, gives a faint 64-foot impression.
When the Rudolph Wurlitzer Manufacturing Company of North Tonawanda, New York bought the Hope-Jones firm in 1910 and acquired all of the Hope-Jones machinery, tools, materials, designs, and patents, the Diaphone continued to be constructed and inserted in Wurlitzer organs all through the heyday of the cinema/theatre organ (c.1910-1930) -- primarily at 16-foot and 32-foot pitches in the Pedal and at 16-foot pitch in the main manual.
NOTE: the photo shows the 12 pipes and clapper (beater) boxes of the bottom octave of the 32-foot Diaphone inserted in the 4-manual Wurlitzer theatre pipe organ Op. 558 originally installed in 1922 in Shea's Hippodrome Theatre in Toronto, Ontario, Canada; when Shea's was demolished in 1958 the instrument was moved to Maple Leaf Gardens and then to Casa Loma in 1970 where it remained in storage until its installation was completed in 1974.