The Diaphone Fog Signal

The Diaphone Fog Signal by Jeff Laser

reprinted with permission from Terry Pepper and his website

Diaphones were a once familiar sound heard throughout the Great Lakes from the early 1920s until the late 1960s / early 1970s when most lighthouses were automated. 120 such installations existed on both U.S. and Canadian waterways in the 1950s. The two most commonly heard Diaphones were the “Standard” Diaphone, which gave a full steady upper tone that terminated in a heavy “grunt” tone, and the classic two-tone Diaphone that produced an upper tone followed by a full steady low tone of equal or greater duration than the upper tone.


Robert Hope-Jones

In 1895, Robert Hope-Jones, an English pipe organ designer and builder, developed a special tone generator for his famous WURLITZER organ; the WURLITZER was a popular musical instrument in the days of silent movies and live stage performances. The new tone generator consisted of a casing that contained a slotted cylinder with a similarly slotted piston. Air was channeled through the casing in such a way that it caused the piston to reciprocate within the cylinder. The major portion of the air was discharged through the slots in both the piston and cylinder as the piston stroked back and forth in the cylinder. As the air passed through slots in the piston, it was “chopped” which caused a vibration that was amplified though a long cone shaped trumpet. Hope-Jones labeled this new tone “diaphonic” (meaning two or more tones”). The new tone had a full, powerful harmonic structure that could be heard over some of the other tones on the pipe organ. He called his new tone generator a Diaphone. Continue reading

‘F’ Type Diaphone Foghorn c. 1969

– John Coldwell (assistant Keeper to Walt Tansky on Pulteney Point 1969 – 1972)

Lennard Island diaphone - photo Chris Mills

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. Continue reading