Train Horns Part 1
It it designed as a warning sign for pedestrian and motorists a like. It's a good warning sign at that! They can also be used to signal other trains as well. Even to the railway station and station masters.
In vehicles and and in trucks, air horns are used, but nothing quite as exciting as that train whistle. It really does stir the imagination like no other sound I know of. Trains in general evoke a feeling of nostalgia, but the sound of a train whistle always reminds me of the train trips I took as a kid. I grew up near a railway station, my grandfather was a station master for 40 odd years.
Just like with anything, there are people or hobbyists who collect all the different types of train whistles from all the different types of trains that have been around. There is actually quite a big market for this sort of item. There are clubs as well.
Air horns for all intensive purposes all work the same sort of way. The best way to explain how they work is like this. Picture a megaphone in your head. You know what they are. They work by way of magnets, a voice coil and a diaphragm. Once it is turned on, the diaphragm starts to vibrate and that causes the loud sound waves.
The air horn is a type of speaker as well, but it pushes air out instead. The air pressure causes the diaphragm (it has one as well) to open quickly and shut quickly. This happens many many times a second. This is then heard by our ears as the steady tone we all know.