Air horn

This article is about the noise maker. For the engine intake component, seeVelocity stack.

Anair hornis apneumaticdevice designed to create an extremely loud noise for signaling purposes. It usually consists of a source which producescompressed air,which passes into ahornthrough areedor diaphragm. The stream of air causes the reed or diaphragm to vibrate, creating sound waves, then the horn amplifies the sound making it louder. Air horns are widely employed asvehicle horns,installed on largebuses,semi-trailer trucks,fire trucks,trains,and someambulancesas a warning device, and on ships as a signaling device.

Steam whistle from asupertanker,in Merseyside Maritime Museum, United Kingdom

Operation

Diagram of a typical locomotive air horn power chamber, showing operation

An air horn consists of a flaring metal or plastichornor trumpet (called the "bell" ) attached to a small air chamber containing a metalreedordiaphragmin the throat of the horn. Compressed air flows from an inlet line through a narrow opening past the reed or diaphragm, causing it to vibrate, which createssound waves.The flaring horn serves as an acoustic impedance transformer to improve the transfer of sound energy from the diaphragm to the open air, making the sound louder. In most horns it also determines thepitchof the sound. When vibrated by the diaphragm, the column of air in the horn vibrates instanding waves.The length of the horn determines thewavelengthof the sound waves generated, and thus thefundamental frequency(pitch) of the note produced by the horn. The longer the horn, the lower the pitch.

Larger air horns used on ships andfoghornsfunction similarly to awhistle;instead of a diaphragm the air escapes from a closed cylindricalresonatorchamber through a precisely shaped slit directed against a knife edge (fipple). The air blowing past the knife edgeoscillates,creating sound waves. The oscillations excitestanding wavesin the resonator chamber, so the length of the chamber determines the pitch of the note produced.

Trucks and buses

In trucks and buses, the air horn is powered with compressed air from the vehicle'sair brakesystem. In trucks, a cord mounted on the ceiling of the operator's cab is pulled or in buses, a valve lever on the side of the dashboard is pushed down or pulled up to open the valve, supplying varying amounts of air to the horn. Thus, an outstretched hand reaching upward and pumping is a signal to the driver of an air horn equipped vehicle, requesting a toot. In modern trucks and buses, the horn is actuated by a button on the steering wheel (just like a normal car horn). Some trucks and buses have both electric and air horn, selectable by a switch on the dashboard. This is to prevent the use of the powerful air horn in populated areas.

Emergency vehicles

Toronto Fire uses air horn while responding

Many fire trucks, ambulances, and other large emergency vehicles operate air horns as a means of warning vehicles to clear theright-of-way.

There are also electronic horns for emergency vehicles, which produce a similar easily recognizable sound. These are typically integrated into the same system as the vehicle's electronic siren, and sound through the same speakers. In the last several decades, electronic sound systems with more widely varying frequencies have been chosen as common supplemental warning systems.

Locomotives

Main article:Train horn

Leslie model S5T five-chime locomotive air horn.

Originally, diesel locomotives were equipped with truck horns. After an accident in which a driver mistook a train for a truck, the need for a unique-sounding train horn became clear.Consequently, North American trains now have at least two horns with different tones forming the airhorn, that sound simultaneously,creating aharmonic intervalorchord.Each individual horn is called a "chime". Three and five-chime configurations are the most common, but two chime horns also exist.

Fifteen to twenty seconds before entering alevel crossing,federal law requires locomotives to sound their horns in a standard warning sequence. This succession consists of two long, one short, and one long horn sounding repeated as necessary until the locomotive clears the crossing. Exceptions to federal law occur in locations with established quiet zone ordinances that prohibit sounding locomotive horns.

In recent years, it has become a fad for bicycle, car, and truck enthusiasts to install large air horns on their vehicles.Some jurisdictions do not allow an airhorn to be attached, whether or not it can be activated.

Cyclist Yannick Read attached a train horn to his bicycle and set theGuinness World Recordfor the world's loudest bicycle horn.

Portable or personal air horns

A small portable air horn used for sporting events, boating, or safety, powered by a can of compressed gas. It is operated by pressing a button on the top.

Portableair horns are also readily available packaged with a can of compressed gas as the air source. These are often sounded by fans atsporting eventssuch asAmerican football,basketball,ice hockey,andassociation football,and at other events such asgraduations,andpolitical conventions.

Small versions are sometimes used asbicycle horns,since they yield a louder warning sound than traditional bicycle bells or bulb reed horns.

Another use is as anon-lethal weaponfor self-defense, mainly as anauditorydistraction to get away from an attacker. For outdoor activities like hiking, hunting, cross-country skiing, canoeing, fishing, an air horn can be handy to frighten away unwanted or aggressive wildlife, signalling for help and to announce one's location.

Additionally, air horns (especially those that containfluorocarbons) have the potential to be abused as a substitute forrecreational drugssince many such refrigerants can beinhaledfor a quick and dangerousintoxication.

Use in sports

The air horn is used for signaling goals, home runs, touchdowns, and other points in various sports:

• Ice hockey
• TheNational Lacrosse League(NLL)
• Major League Baseball(MLB)
• Indoor soccer(Especially in theMISL)
• TheNational Football League(NFL)

NHL arenas normally employ two horns—a high-pitched horn (or a siren, as in the home arenas of theBoston BruinsandMontreal Canadiens) that announces the end of the period (or the start ofinstant replayreviews), and a much louder horn sounded when the home team scores and/or wins a game. Some MLB and NFL stadiums use horns for similar purposes, such as when a member of the home team hits ahome runortouchdown.In many places, air horns are used for signaling the end of the period or quarter on scoreboard systems.

The idea of a goal horn in NHL ice hockey is said to have begun in 1974, whenBill Wirtz,then-owner of theChicago Blackhawks,liked the sound of the Kahlenberg Q-3 on his yacht so much that he had another Q-3 mounted inside of the team's home arena,Chicago Stadium,to be sounded whenever the Blackhawks scored a goal.Since then, every NHL, AHL (with the exception of theChicago Wolves,who instead use a siren and fireworks), ECHL, SHL, and CHL team has picked up a horn, including many more leagues.

Inmixed martial arts,an air horn is commonly used to signal the end of a round as opposed to the bell used inboxingandprofessional wrestling. However,CZW,GCW, and otherindependent wrestling companiesallow air horns, while major companies such asWWEandIMPACT Wrestlinghave banned them.

Use in music

The air horn is a popular sample inreggae music.Jamaican dancehall music was the first musical genre to use the effect, and has been using the airhorn sample for over 26 years, in live shows as well as on mixtape recordings, and in Puerto Ricanreggaeton,a reggae hybrid genre since the late '80s and '90s.The sound effect has recently been used inhip hop musicas well.

The "Air Horn Orchestra" gathered at theNorth Carolina Governor's Mansionevery Wednesday for 30 weeks from April 13, 2016, until November 2, 2016, to protest the state'sPublic Facilities Privacy & Security Act,also known then as House Bill 2, and GovernorPat McCroryby making aloud, disruptive noise.The 30th and final performance on November 2 was expected to set theGuinness World Recordfor the number of simultaneously sounding air horns, having had 342 participants. This was the last performance owing to the gubernatorial election six days later.

See also

• Vuvuzela
• Train horn
• Foghorn