............My system has has a speaker selector w/ 3 sets of speakers. I'm replacing the OLA's.
All speakers are 8ohm What do I have to do to replace the OLA's with one pair of 4ohm speakers and still keep the other two sets of 8ohms?
That depends.
The simple answer is, don't run the 4ohm pair with either of the others. But things often aren't so simple.
The question is, does the speaker selector combine the speakers in parallel, or in series?
If parallel, then you have the simple answer above. But if series, you can run them in any combination you want, because the impedences will sum, rather than behaving the way they do in parallel circuits.
How do you know if the speakers are being combined in series? A little experimentation: Suppose the 3 pairs are called A, B, and C on your selector switch. Disconnect pair B from the rear terminals. Now, turn on pair A. They still play, right? Now, move your selector switch to "A+B". If the A pair keeps playing, then "A+B" is a parallel connection. If they stop, then it's a series connection. Pair A can't play because without pair B in the circuit, the series circuit is incomplete.
But be warned, I've never heard two pairs sound as good in series as they can in parallel. Remember, the impedences in series are summed. So the amplifiers output is essentially cut in half.
I also think that in a series circuit, the crossovers in the 2 pairs of speakers interact with each other, which should impair the performance of both pairs (but I've never seen a discussion about that).
Small Advents are obviously a prime solution if the 4ohms isn't a problem. One other obvious answer that I forgot in my earlier post is the AR-28.
