Horns

Introduction:
 The horn (or audible warning device) is a device which is established to produce a uniform sound. This consequently proves sirens and melody type fanfare horns illegal.

 Properties of the horns:
 

• Most horns draw a large current, so are switched by a suitable relay.

• The standard horn operates by simple electromagnetic switching.

• As current flow causes an armature that is attached to a tone disc to be attracted to a stop, a set of contacts is opened.

• This disconnects the current allowing the armature and disc to return under spring tension.

• The whole process keeps repeating when the horn switch is on.

• The frequency of movement and hence the fundamental tone is arranged to lie between 1.8 and 3.5 kHz.

• This gives good penetration through traffic noise.

•  Twin horn systems, which have a high and low tone horn, are often used.

• This produces a more pleasing sound but is still very audible in both town and higher speed conditions.