Well I had never heard of a Diaphone before! Why didn’t they call it a foghorn, which is
what it is in form and function? Anyway,
the plans revealed a ‘Diaphone Turret’ on the roof of the superstructure, just
in front of the lantern mast. The structure is about 10ft tall overall and 5ft
diameter. As it is called a turret, I assume that it rotates, although I am not
sure why. It would explain the ‘MOTOR DRIVEN TURNING GEAR’ label inside the
turret – assuming I have interpreted the rather indistinct third word
correctly.
The Diaphone can be seen (just) in the 1950s photo of the
Lady Dixon on station near Carrickfergus.
I found a photo of an up-to-date
version, which has the ‘deflector’ at the business end, although the
noise-generating end has a 90°
bend.
The diaphone horn was based directly on the organ stop of
the same name invented by Robert Hope-Jones creator of the Wurlitzer organ.
Hope-Jones' design was based on a piston which was closed only at its bottom
end and which had slots, perpendicular to its axis, cut through its sides; the
slotted piston moved within a similarly slotted cylinder.
Outside of the
cylinder was a reservoir of high-pressure air.
Initially, high-pressure air would be admitted behind the piston,
pushing it forwards. When the slots of the piston aligned with those of the
cylinder, air passed into the piston, making a sound and pushing the piston
backwards to its starting position, whence the cycle would repeat. A modification of Hope-Jones' design was
patented by John Pell Northey, who added a secondary compressed air supply to
the piston in order to power it during both its forward and reverse strokes and
thus create an even more powerful sound, which carried for miles. The entire
horn apparatus was driven by a compressor.
There is unfortunately nothing remaining of this
wonderful sea organ, but that is probably a good thing as the temptation to try
it out would be overwhelming.
David
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