A little question...

Hi, my name is John.
I would really appreciate if someone could tell me what do the "PA systems" are.
I found that at the end of the 10th paragraph in the Creedence's "History" (in this site, of course...).

The fact is that I'm really interested in the way John Fogerty started to sing. I'm a singer too (not that great...), and I'm learning some of his tecniques by myself. So, when I read that words in the "History" of my favourite band I couldn't understand it completely (because I speak Spanish...). So I want to know what do those poor "PA systems" are. Thanks!

By the way, keep listening to Creedence Clearwater Revival !!!

PS: yeah... you may also listen to John Fogerty-alone.