I have restored several period horns and had a nice little Klaxon 8-C on my car. It is about the size that seemed good for a T and it worked fine for several years. It has a small single brush motor and always made enough noise to get smiles from people. Recently I finished rebuilding an EA Labs 6 volt horn that has a more robust 2 brush motor and larger diaphragm. I fabricated a mount so it could at least me mounted in the factory location for 26. It fits in there well just under the coil box and slightly ahead. I just about dropped it when I tested it out as it was so much louder than the old horn had been. There is no doubt this horn will be heard. May scare animals and small children so I will have to use it more responsibly.
I like blowing at animals to see their reaction. Some have no reaction. Some turn and look. I have had calves take off running. I kinda felt bad about that.......but I got over it.
I have a Model T battery horn on mine. I've used it on animals such as geese, sheep, squirrels, horses and goats with little to no effect. Cows are a different story. That horn always gets their full attention. The whole field drops what it's doing to stare which is amazing considering the way cows normally are. I guess it sounds like a cow. Try it sometime.
Rest assured, I will. All in the interest of science of course.