We have an old PA system that we use only for vocals. The speakers each have a 15", 2 piezo tweeters and 1 horn. The crossover in one of the speakers is fried and the 15s are mismatched. I was considering replacing the 15s with a matching pair but wiring the cabinet in series. Since these speakers only cover vocals I think It should sound fine but I was wondering about the impedence.......won't wiring all the speakers raise the impedence and decrease the power amps output? What would the effects of this wiring be or is it just a bad idea?