[nerme]

It is like a bugle or any of the brass instruments. The tone produced is dependent on the vibration of the player's lips as well as the length of the tube.

I haven't played one, but I'm sure you could play numerous overtones like you can on a bugle.

They seem to be mass produced, resulting in most of them having the same length. That, along with the fact that the average sporting fan probably doesn't have much embouchure, would explain why there's a single tone that is much louder than any others.