If the sound level is too high, they get squashed down flat(er) and don't rise back up to sway as they once did.

One time I read the assertion that horn speakers were all the rage in the 50's because of the returning WWII vets. They went to school on the GI Bill and got good jobs - jobs that afforded them the leisure and money to play with audio. But their hearing was very poor from all the gunfire and large bore weapons they were exposed to - hence the love of horns and high SPL with the available amplification.

Interestingly, Paul Klipsch developed the KHorn while working as a range officer and doing velocity testing on projectiles. He sold a lot of them to his fellow vets.