The picture was a bit of a joke but I'm working on it. It's just not a high priority for me at the moment. It's from our firetruck at work. I've cut it down to make it a bit shorter so it can be hidden behind the bumper. I'm getting an actuation valve, on board compressor and small air storage tank from JC Whitney. This thing needs 60 psi to 100 psi to really honk.

 

60 psi, damm, how big is the back up tank, my friend has a train horn on his F250, and he has a 6 gallon resovoir tank, its huge.
That thing when he rips it shakes the ground. Crazy loud.

In my eyes its excessive, but hey, to each his own.

 

I only would do a small tank (1/2 to 3/4 gal.). This would be good for about a 10 to 15 second blast or a bunch of short blasts. It's more of a novelty and not as a real horn.