The air horn is a device designed to create an extremely loud noise. It is usually composed of a pressurized air source coupled to a horn through a valve which allows the device to be turned on and off. Air horns have been installed on large semi-trailer trucks, fire trucks, and some ambulances for many years. It is also used on trains as a warning device, and on ships as a signalling device.
There are also electronic varieties of "air 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. There are also air-horn only systems available, which some states allow for use by volunteers in their personal vehicles.
More recently, some individuals are adding truck air horns (and even louder train horns that sound a minor-seventh chord rather than the major chord of truck horns) to their personal autos as a hobby or addition to the culture of bigness exemplifed by SUVs. It should be noted that the use of a train whistle in an automobile could cause an accident. Some jurisdictions do not even allow an airhorn to be attached, whether or not it can be activated.
Original 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 train horn became clear Consequently, North American trains now have at least two "horns" forming the airhorn, that sound simultaneously, creating a chord. Three and five-tone configurations are the most common, but two-tone configurations also exist At a grade crossing, the usual sequence is two longs, one short, and one long, except in locations where airhorns are not allowed to sound due to quiet ordinances. Train mounted airhorns are called train whistles or air chimes.
A list of air horns used on various railroads with audio samples can be found here
It is a common game among schoolchildren (especially on field trips, which are more likely to involve travel on a major highway) riding a school bus to pump their fists, imitating the motion of a truck driver operating an air horn, in order to request that passing drivers sound their horns. If the driver obliges, the passengers will generally respond with great amusement, sometimes despite chastisement. Such chastisement is more likely to come from teachers or fellow students, as bus drivers are generally used to distractions. Air horns are also sometimes used as retaliation toward telemarketers or other harassing callers to deter future calls.
The airhorn is also a popular sample in reggae music. Jamaican dancehall music is the first musical genre to use the effect, and been using the airhorn sample for over 26 years, in live shows as well as on mixtape recording. The effect has recently been used by hip hop mixtapes as well as reggaeton, a reggae hybrid genre.
In recent years it has become a fad for car and truck enthusiasts to install large air horns on their vehicles. A popular web series called "Terror On The Streets" depicts drivers of such vehicles startling unsuspecting pedestrians while driving through urban areas Even police officers are not immune to these audio assaults and are shown being startled while on duty.
In Arrested Development, Buster blows an air horn and his mother refers to it as her "rape horn."
In Jackass The Movie, one stunt involved blasting an air horn at unsuspecting golfers.
The rock band, Oppenheimer , has become famous for their legendary Air Horn solos which are incorporated into all of their shows.
Portable air horns are also readily available, utilizing a small aerosol spray can as the air source. These are often present at sporting events such as football, hockey and soccer, and at other outdoor events. Small versions are sometimes used as bicycle horns.
In the Jackass television series and movies, air horns are occasionally used to frighten people. Many people amuse themselves by driving around blasting air horns at others, or using them in other ways. Youtube has many videos about such events. A very common and popular undertaking with the air horn is the accordingly named "golf course airhorn", where the Jackass team blows an airhorn just as an unsuspecting golfer is coming down with their swing.
Some people use air horns to deter prank callers. Those who receive harassing calls may sound off an air horn instead of saying "hello" to make it less desirable for the caller to call back.
The airhorn has also had a large role in ice hockey, especially in the NHL. There are normally two horns; a small high one that announces the end of the period, and a much louder, lower horn that is sounded when the home team scores and/or wins the hockey game.
Some air horns are used for signaling the end of the period or quarter on scoreboard systems. Although not technically air, the Federal 55 (used in these applications) is an electric horn which uses a coil to move a diaphragm, in turn, causing the diaphragm to resonate a column of air , which produces the musical note you hear. Notably, most arenas use two horns, although by themselves the horn can achieve sound pressure levels of 106DB. These horns are used over the standard Federal 350 horn (used on high school and smaller gym scoreboards) so that the signal can be heard over fans, the band, and other noise at sporting events by officials. "Federal" is Federal Signal Corporation of Illinois.