I have a iPhone 4S, the cracked back was an accident LONG time ago, the speakers just blew out for no reason today... does my AppleCare (not plus) cover the speaker? I don't care about the back.
Tough to say. Apple could claim that the accident that broke your back also caused the speakers to stop working. I'd take it to Apple and see what they say.
By the book, Apple can easily claim, Cracked screen = drop with enough force to damage something else, BUT members here have claimed Apple is nice enough to fix it anyways, so waste some gas to find out.