ok thanks. so when running things in parallel is the formula to divide by 2? so like the example above, i had 12ohm on 3 speakers in series, 12ohm on the other 3, then running in parallel i divide 12 by 2 = 6ohm? or is this not always the case? thanks
Lest we confuse the open, he never mentioned running all the speakers parallel or even in two groups of parallel. The 4/3 ohms configuration isn't what he asked about, although it is another option he could consider.
Assume we want to parallel two sets of three 4 ohm speakers in series. Three 4 ohm speakers in series gives us 12 ohms. The impedance when two sets are paralleled is:
1/(1/12 + 1/12) = 6
That happens to be 1/2 the impedance of one set in this case (divide by two as OP noted), but that is not always the case. In fact, you can count on it not being the case most of the time, unless you are paralleling two sets with the same impedance.
Sure. Of course I never tried to describe the math, I just gave him the correct answer.
For most cases, the math can be shortened to the following, which may be useful to the op:
For series, add the resistances together.
For parallel, dived the resistance of one by the number being wired in parallel.
That holds true for cases where all speakers are the same impedance rating, or you are working with groups of speakers where all groups have the same effective impedance and you treat the group as one effective speaker. Which covers the majority of cases, including this one.