– John Coldwell (assistant Keeper to Walt Tansky on Pulteney Point 1969 – 1972)
The diaphone is a unique organ pipe. The theory was based on a design for the Wurlitzer pipe organ invented by Robert Hope-Jones dating from 1895.
A special tone generator in the organ involved a piston vibrating inside a cylinder, which had slots through which air was discharged. The air passing through the slots caused a vibration which when amplified through a long cone (like a megaphone) created a powerful harmonic sound.
Robert Hope-Jones also applied this principle successfully to foghorns, and this then became the most common type of navigational aid in the world.
The ‘F’ type Diaphone apparatus was manufactured by Chance Brothers of Birmingham, England and was able to issue a tremendous blast of sound that could easily be heard at more than five miles (depending on size of horn and volume of air).
An important feature of the diaphone sound was that it was two-toned – a higher pitched note followed by a sound similar to a grunt. This grunt made the horn distinguishable as a land-based foghorn as opposed to a ship’s horn which has a single tone. Listen for the grunt in the sound file below.[audio:http://lighthousememories.ca/wp-content/uploads/2012/04/Lennard_Island_-Diaphone.mp3|titles=F-type Diaphone]
The diaphone was fed with compressed air from a compressor driven by a diesel engine. In the days before electricity the timing and control of the blasts was regulated by a belt drive running off the compressor which turned mechanical timers. Later, when electricty came to the lighthouses, the belt was replaced with electrical solenoids.
An example of how far this sound travelled was shown to me on my first station, Pulteney Point. The senior keeper Walt Tansky was a Ham radio operator and at this instant was talking to another Ham in Alert Bay, 10.5 miles (16.9 kms) away.
“Walt, I can hear your foghorn!” said the friend. Walt disputed this and said it was blowing at the time he was keying the microphone. “No, I heard it from outside the window”, said his friend. He told Walt to hold his mike outside his window the next time the horn blew.
Walt did this and keyed the mike when the horn blew. The man in Alert Bay, upon hearing the foghorn on his speaker keyed his microphone outside his window. Forty seconds later we heard the sound of our foghorn through Walt’s speaker.
For an official version of the operation of the F-Type diaphone please check out the Chance Brothers manual here. This is a PDF file which can be read or downloaded.
For more information on the history of the F-type diaphone foghorn, please see tomorrow’s column.
More information here in Wikipedia.