Horn

Automobile horns are usually electric klaxons, driven by a flat circular steel diaphragm that has an electromagnet acting upon it and is attached to a contactor that repeatedly interrupts the current to the electromagnet. This arrangement works like a buzzer or electric bell and is commonly known as "Sounding ones horn". There is usually a screw to adjust the distance/tension of the electrical contacts for best operation. A spiral exponential horn shape (sometimes called the "snail") is cast into the body of the horn to project the sound effectively. Sound levels are approximately 107-109 decibels, and current draw 5-6 amperes.

Horns can be used singly, but are often arranged in pairs to produce a chord consisting of two notes, sounded together; although this only increases the sound output by 3 decibels, the use of two differing frequencies with their beat frequencies and missing fundamental is more perceptible than the use of two horns of identical frequency, particularly in an environment with a high ambient noise level. Typical frequencies of a pair of horns of this design are 500 and 405-420 Hz (approximately B4 and G#4).

Some cars, and many motor scooters or motorcycles, now use a cheaper and smaller alternative design, which, despite retaining the name "horn", abandons the actual horn ducting and instead relies on a larger flat diaphragm to reach the required sound level. Sound levels are approximately 109-112 decibels, and current draw 2.5-5 amperes. Again, these horns can be either single, or arranged in pairs; typical frequencies for a pair are 420-440 and 340-370 Hz (approximately G#4-A4 and F4-F#4) for this design.

Truck horns may be electromagnetic klaxons of similar design, but often are purely acoustic, driven by air from an air compressor which diesel trucks have already on board to operate the air brakes. Such air horns are often used as trim items, with chromed straight horns mounted on top of the cab. This design may also be installed on customized automobiles, using a small electrical compressor. Usually two are used, sometimes more. The frequencies vary in order to produce a variety of different chords, but in general are lower than those of automobile horns; for instance 125 through 180 Hz (approximately B2-F#3). Sound levels are approximately 117-118 decibels.

Usage and function
Basically,horns are used for reminding a driver that does not drive properly.In developed countries like Indonesia,horns are used for expressing anger,telling other drivers to give up a way,showing superiority,calling friends.Most drivers in Indonesia honk for something that is not necessary.