And so it came to pass, on 01-08-97 12:44,
   that Hung Cao spake unto All :
 HC> I need some information.  I have a reciever that I can hook up to 4
 HC> spkrs to in twos sets (A & B).  It says "A or B, 4ohms minimum per
 HC> speaker"  "A AND B, 8ohms minimum per spker."  I have a pair of
 HC> Polks in there right now which are 8ohms but I also have a set of
 HC> car spkrs i would like to add.  I think the car spkrs are 4ohms
 HC> though although it doesn't say so, i heard somewhere that most car
 HC> spkrs are 4 ohms (correct me if i'm wrong).  Can someone explain to
 HC> me about what ohms are and what would happen if I connect my car
 HC> spkers to the reciever with the Polks? 
In a nutshell, ohms are a units of measurement of electrical resistance (or 
more correctly in this case, impedance).  There's lots of good reading out 
there on the subject, so I won't take up bandwidth by rehashing much more 
than that here.
Basically, your amp isn't designed to have a load of less than four ohms 
across the outputs.  The A and B speaker terminals are actually just wired in 
parallel, I would guess with a switch or switches to select which ones are 
used, if not both.
When connecting speakers in parallel, the total load they present to the amp 
is reduced; if both are the same impedance (say, eight ohms), then the total 
load is cut in half (to four ohms).  Thus, you could have the amp driving one 
set of four-ohm speakers, or two sets of eight-ohm speakers in parallel... or 
any other combination whose total load does not go below four ohms.
Car speakers are typically rated as four ohms; putting them in parallel with 
the eight-ohm speakers would give you an average impedance of 2.7 ohms.  You 
could do it as long as you don't turn the amp up very much; on the whole, I'd 
recommend against it.
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Love, luck, and lollipops...
Matt


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