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Ok, you need to run your amp evenly so swap to a 12 and an 8 on each side. You're into ohm's law here. Also unless you mixing in mono and senting the same feed to all the speakers your stereo will be buggered, as you have 2 x 12 on one channel (say Right), and 2 x 8 on the the other (Say Left). If you have mixed them up then you are REALLy buggering things up..
Set them up in one of the ways below, though read the whole article as to why this may not be such a hot idea..
If you wire the speakers in series you get a 12 ohm load (add them). Below.
Speaker Speaker
Amp Red _____+12-______+8-_______Amp Black
If you wire them in parallel then you'll wind up with a 3 ohm load. this load will be much louder than the series setup, but may not be wise as you will be getting 4x the current for a given output.
R= 1 (1 / ((1/R1)+(1/R2)) = 3
---------
1 1
--- ---
12 8
Amp Red Amp Black
| |
| Speaker |
|___+12-___|
| |
| Speaker |
|___+8-____|
Now, neither of the above takes into account frequency crossover. Low frequency drivers naturally filter high frequency sounds, but High frequency (tweeters) will blow if you put bass through them (The much more power usually in the low frequency leads to melted driver coils pretty quickly). Though you just mention 8" and 12" speakers are they just drivers or whole cabinets with multiple other speakers in there (Tweeters, mid range etc?)
It's also generally a bad idea randomly slinging speakers together, but if it makes you happy....
Now back to your question, look at your amp's specifications and it will give you a range for the load, usually something like 4 - 12 ohms. I you run at 3ohm in this case watch your levels, as you are likely to blow output transistors / valves or what have you as the current flowing through the speakers is beyond what the amp can take.
If 12 or 3 is in your amp's range then go which one is, If both are try and see whic sounds best, but pay attention to the still more boring stuff below..
V=I*R where V is voltage, I is current, and R is resistance
at one volt with a one ohm resister you have a one amp current. This is all for DC btw, as you actually have an AC circuit going things get more complex, but I'm simplifying for now. You can rearrange the above to give I=V/R, so as R gets smaller I rises.
Many people think that if you have speakers rated to 120W and you have a 50W amp then you can't blow your speakers. This unfortunately is DEAD WRONG. If you drive the 50W amp flat out until is starts to clip it can produces some very unpleasant signals that can destroy your speakers pretty easily. You are actually in many ways better off with an amp that is MORE POWERFUL than your speakers rating as its transient response at a senseible listening level is likely to be much better.
How this helps..
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