>I think us being silent in these situations reinforces this kind of behavior.

This is true only if the person is not aware they are being obnoxious. Instead, consider the possibility that the person knows they are being annoying and obnoxious by acting in that anti-social manner, and are looking for a reason to fight with someone.

Any half-socialized person knows that using loud speakers like that is going to annoy others. He knows what he is doing. You telling him about it changes nothing. So don't say anything. Just walk away (and let someone else, who wants a fight and wants the quiet - let those two handle it together).