A PA system can actually backfire, because it can encourage people to talk away during the music, Or even bellow, if the sound is turned up. Then, when there's has a quiet bit, and there's nothing coming through the mike, the bellow roars out very noticeably. Quite comic somertimes, but irritating.

There's the old saying that the best way to quieten a noisy crowd down can be to sing something quiet that people want to hear.

Why the crack against librarians though? Ordinary people doing a valuable job, what's wrong with that?