The diaphone was a noisemaking device best known for its use as a foghorn: it could produce deep, powerful tones able to carry a long distance. Diaphones were also used at some fire stations and in other situations where a loud audible signal was required.
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, head of the Northey Co. Ltd. of Toronto, Ontario, Canada, which manufactured pumps and small gasoline engines. Northey 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. The entire horn apparatus was driven by a compressor.
To manufacture the new equipment, Northey set up the Diaphone Signal Co. at Toronto in 1903. It manufactured a range of diaphone models: the large "Type F", which created a tone of about 250 hertz, found worldwide use as a fog signal, especially in lighthouses. The mechanism of the diaphone created a noticeable low-frequency "grunt" at the end of each note produced, caused by the speed of the piston reducing as the air supply was cut. As this low-frequency sound could carry further, Northey's son Rodney redesigned the "Type F" model to sustain the second low tone, creating the familiar two-tone fog signal which was commonly used in lighthouses and lightvessels in the United States and Canada (as well as in a famous series of radio commercials for Lifebuoy soap). Installations in Europe generally used single-tone diaphones.
Rodney Northey sold the Diaphone Signal Co. in 1932, when it was bought by a Buffalo, NY company, Deck Brothers, working under contract for the United States Lighthouse Service. This company still exists, although it no longer manufactures diaphones. The European manufacturing rights were obtained by Chance Brothers of Birmingham in the United Kingdom, already a major supplier of Fresnel lenses and other equipment to lighthouse authorities.
The majority of diaphone installations were removed or became disused when lighthouses were automated during the 1960s and 1970s, though a few survive in working condition in lighthouses around the world.
The Gamewell Diaphone
This considerably smaller device was produced by the Gamewell Corporation, of Newton, Massachusetts, for use as a municipal alarm, especially at fire stations, to alert firemen and the public during emergencies. Many Gamewell diaphone systems remain in use today. The Gamewell diaphone has a range of about six miles (9.7 km) under optimum conditions.
Working diaphone installations
The following installations are still functional and are demonstrated from time to time as tourist attractions.
- Duluth South Breakwater Lighthouse, Duluth (MN): the F-2-T (two-tone) diaphones at this lighthouse were reinstated after a campaign by residents, and reactivated in 1995.
- East Brother Light Station, Richmond, CA
- Grand Traverse Lighthouse, Michigan
- Portland Bill Lighthouse, Isle of Portland, United Kingdom: A Type F diaphone decommissioned in 1996, but restored in 2003 for the benefit of visitors.
- Low Head Lighthouse in Low Head, Tasmania possesses the only working Type G diaphone (one of the largest models constructed) in the world. It has a range of up to 20 miles.
- Lindesnes Lighthouse in southern Norway. The last Sunday of July, Fog Horn Day is held at the lighthouse.
- Seeing the Light: "The diaphone fog signal" by Jeff Laser
- For the patents of Hope-Jones' diaphones that were used as foghorns, see:
- Hope-Jones, R., "Sound-producing apparatus suitable for sirens, organs, etc.," British patent 26,738 (Dec. 31, 1901). See: Patents for Inventions: Abridgements of Specifications … Period -- A.D. 1901-4. (London, England: Patent Office, 1907) page 122.
- Robert Hope-Jones, "Sound-producing device suitable for sirens, etc.," U.S. patent 702,557 (filed: Nov. 26, 1901 ; issued: June 17, 1902).
- For further information about John Pell Northey and the Northey Company of Toronto, see:
- Northey's patents for diaphones:
- John Pell Northey, "Sound-producing device suitable for sirens or like instruments," U.S. Patent 736,428 (filed: Nov. 22, 1902 ; issued: Aug. 18, 1903). This patent mentions a second source of high-pressure air which caused the slotted piston to reciprocate.
- John Pell Northey, "Sound-producing device," U.S. Patent 973,960 (filed: June 5, 1908 ; issued: Oct. 25, 1910).
- John Pell Northey, "Sound-producing device," U.S. patent 976,682 (filed: June 5, 1908 ; issued: Nov. 22, 1910).
- John Pell Northey, "Sound-signaling installation," U.S. Patent 1,619,585 (filed: June 8, 1926 ; issued: March 1, 1927).
- John P. Northey, "Sound-producing device," U.S. patent 1,799,387 (filed: March 1, 1929 ; issued: April 7, 1931).
- Laser, J. Seeing the Light accessed 03-09-08[vague]
- Rodney V. Northey, "Sound-producing device," U.S. patent 1,844,226 (filed: March 27, 1931 ; issued: February 9, 1932).
- Fox, F. Diaphone at Douglas Head Lighthouse accessed 03-09-08[vague]
- Laser, J. Seeing the Light accessed 03-09-08. Northey sold the company as he required money to marry his fiancee.
- The history of the Gamewell Diaphone, accessed 03-09-08[vague]
- Gamewell Diaphone Technical Information, accessed 9 September 2008
- Duluth South Breakwater Light, Seeing the Light, accessed 04-09-08. Note: as of 2006, the diaphones have been removed and stored.
- The East Brother Diaphones, accessed 04-09-08
- "Blast from the Past". Bournemouth Daily Echo (Bournemouth, Dorset, England: Newsquest Media Group). 27 August 2003. Retrieved 2011-01-16.
- Findlay B (2001). "The Low Head Fog Horn". Low Head, Tasmania: Low Head Progress & Heritage Association. Retrieved 2011-01-16.
- Animation of the operation of the Hope-Jones diaphone: Gamewell Diaphone