Not at all, the bells work off of a vacuum valve, sorta like your old automobile windshield wipers, which, by the way, is the same system used on locomotives, vacuum powered wipers. The reason is simplicity. All the thing really wears out are o rings, which are cheap, and its easy to chase down vacuum leaks, as opposed to electrical shorts. If you listen to the bell closely, you can hear the vacuum valve make a hiss and the valve opens. It pulles the clanger back and then the valve releases its vacuum, and gravity makes the clanger, or striker, fall down against the bell. The reason they have a different tempo is due to the age of the valve, and the idle speed of the diesel. Faster idle, slower bell, slow diesel speed, fast bell, due to more manifold vacuum at slow speed. As for the speed of bells in films, well, ever wonder what a Foley artist is? See the credits at the end of a movie. They should call them by their real name, sound effects people. With the exception of dialogue, almost all the sounds you hear in a movie, doors slamming, horns honking, bells ringing, even the sounds of a fist fight, are "dubbed" into the sound track by the foley artist. The reason they record the "live" sound is so the foley people have something to go by.
Watch railroad movies carefully, and you can hear the click/clack of wheels going over track joints, but look, and you see continuiously welded rail, no joints!
And depending on the type of steam loco, well, they use steam to drive the ringer in the bell, and the engineer can adjust the speed by opening or closing the valve to the bell.
Stay Frosty,
Ed
