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UNDER CONSTRUCTION

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THE DIAPHONE

HEAR THE SOUNDS

Type B by Gamewell
(No Grunt)

Type CC (With Grunt)

Type F by Diaphone Signal Company (With Grunt)

Type F2T by Deck Brothers
2-tone)

Originally invented as a deep-toned pipe organ stop, the diaphone was reinvented in the early 20th century to become one of the most widely used fog signals around the world.

Though long ago replaced by modern technology, many still know the sound - even if they've never heard it in person.

After its reinvention to an air horn, the diaphone was organized by size, known as "type." Throughout the 20th century, different variations were made to suit different purposes.

"Type A" was the smallest - though rarely used, and the massive "Type K" was the largest - only ever being used at one light station in California.

The most popular diaphone size for fog signal use was the "Type F" and later (US Only) the improved Type F, known as the "Type F2T" (2-toned).

The both the F and F2T featured a loud and powerful tone which ends in a heavy "grunt." The grunt at the end of the tone made it instantly identifiable as  a fog signal. Only used in the US, the "Type F2T" was able to sound in the "standard" way, or it could be adjusted to turn the grunt into a second, sustained note. This is the "BeeeeeOoooooohhh" sounding fog horn many are familiar with.

Learn about the Evolution of Fog Signal Technology

From the first fog signal at Boston Lighthouse in 1719 until the present day, noise making technology has evolved from gunpowder to steam, to air, and electricity.

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Read about the evolution of lighthouse fog signal technology and hear some of these signals yourself.

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Basic Definitions

Cubic Foot - A unit of measurement for volume that indicates how much space an object takes up in three dimensions, or length, width, and height. It is defined as the volume of a cube with sides that are each one foot long.

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Frequency - The rate at which a vibration occurs that constitutes a wave, in a material (as in sound waves), or in an electromagnetic field (as in radio waves and light), usually measured per second. Directly related to pitch in sound. Higher frequency = higher pitch. Lower frequency = lower pitch.

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Motor Air - Compressed air supply which drives the oscillation of the diaphone's piston inside the cylinder during the sounding cycle.

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Pitch - The quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone. Directly related to frequency in sound. Higher frequency = higher pitch. Lower frequency = lower pitch.

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Speaking Air - Compressed air supply which is forced in between the corresponding slits of the diaphone piston and cylinder. As the piston oscillates, powerful puffs of compressed air are pushed through these slits, giving the horn its voice

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Volume (Air) - The amount of space air occupies. In this situation, it's measured in cubic feet.

Modern & Historic Diaphone Photos

Side-By-Side

(Gamewell) Type B Diaphone fire horn &
(Diaphone Signal Co.) Type F Diaphone fog horn

Side-By-Side

Various diaphone pistons
(Left to Right)
Type F, Type B (Aluminum), Type F2T, Type G

Parts of the Type F Diaphone Fog Horn Assembly

How does it work?

What makes the diaphone better than a whistle? Or a simpler type of horn?

Comparing steam (or air) whistles to the diaphone, the biggest advantage the diaphone has is its reduced air consumption. A whistle requires an incredible volume of air to sound. A whistle does not make efficient use of the compressed air or steam - instead essentially venting 100psi of compressed air out of a 2-1/2" diameter pipe opening - with much waste. It takes a lot of air (volume) at a high pressure in order to blow a whistle.

The diaphone on the other hand uses a relatively large volume (quantity) of air to sound, but at a much lower operating pressure. (35-45psi)

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The two real advantages of the diaphone lie in the power of its blast and the characteristic "grunt." The sound is generated by the chopping action of the speaking air as the piston oscillates. This chopping of air is the actual process which generates sound.

As the slotted piston is driven forwards and backwards inside the slotted cylinder, powerful puffs of "speaking" air are forced through the slits as they pass by each other. Each one of these slits provides its own "voice" - meaning that each slit generates its own sound. This causes the final sound emitted from the resonator to be far more dynamic, rich, and powerful. The added power of the blast allows it to carry further and penetrate a wider range of atmospheric conditions compared to a whistle or simpler air horn - which only generates its sound from one orifice. 

A siren, with its slotted, spinning "rotor" and similarly slotted immobile "stator" generates sound in a similar way. Air is forced out in "puffs" as the siren spins and the holes of the rotor and stator pass by each other. A siren's tone is similarly powerful due to each slot or hole also providing its own "voice" to the tone. The diaphone's increased power over sirens is mostly due to the puffs being forced through the slits at a higher pressure.

"How loud was it in the lighthouse when the horns were sounding?"

Hear for yourself!

Here we see the two Type F2T diaphones and the associated air supply and timing plumbing inside the Duluth South Breakwater (Outer) Lighthouse. The resonator for the right (south) horn can be seen exiting the outer (white) wall. This video was taken by diaphone expert Jeff Laser in the late 1990s to show how to properly disassemble and clean the cylinder and piston to avoid damage.

Side note: the horns you see in the video were previously used inside the Kewaunee Pierhead Lighthouse!

The electric air compressor can be heard running in the background. By this point in the video, the compressor is running "unloaded," meaning the massive air tanks are already filled to 40psi and the compressor is not actively compressing air.

In the video, the in-service horn is the left (North) horn. Only one horn is sounded at a time. These horns were in-use until 2006, when the three-phase power for the air compressor failed.

In-service, the compressor would run constantly when the horns were needed. The horns themselves would sound (or "honk") at a set interval. In Kewaunee, this was every 30 seconds in poor visibility.

Overtaken by Technology

Not only did the technology in the lighthouse advance, but so too did the technology aboard ships. With the advent of radar, radio beacons, and LORAN, it became easier for captains to know their ship's precise location, and to avoid danger. 

The sound signals weren't relied on as heavily as they were in the past, therefore didn't need to be as powerful. Powerful signals were replaced by smaller diaphragm horns - which use air passing between metal discs (known as diaphragms) to generate sound. These horns consume far less air by volume and are much simpler to operate, though in most cases not as powerful.

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The 500 lb diaphone assemblies were removed from lighthouses and either scrapped or thrown into the lake. In rare instances, horns have been saved and were lost in storage for many years (As was the case of the DeTour Reef diaphone) or far more rare, left in place. (As is the case of Outer Island, WI)

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Today, mariners sound fog signals on-demand by keying their marine radio on a designated frequency.

For more information about a specific light station, click the link to view the LighthouseFriends.com bio for that light.

Operational Diaphone Fog Horns

Existing (but inoperational) Diaphone Fog Horns

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