It depends on the power amp and the ohmage of the speakers. Some can power down to 2 Ohms of speakers, most will do 4 Ohms easily. Most speakers are 8 Ohms. 2 of those together are 4 Ohms and 4 are 2 Ohms. So you have to check the amplifier specs and the speaker specs to make sure.

And, of course, make sure everyone realizes if you're only using 1 amplifier with 2 separate inputs and outputs, you're only going to have 2 mixes.

So then what you're saying is that a typical power amp (with enough power) could possibly power 8 8ohm speakers.

Does it matter if I am running 4 ohms on one side and 2 on the other?

Again, it depends on the amp. Some like balanced loads and some don't mind. What amp are you using? And I wouldn't say a "typical" amp can do 8 8 Ohm speakers. A good one "might" be able to.

I'm thinking about getting a Carvin DCM 1504L. I think that should be enough to power 5 monitors (all 8 ohms).

I'm leaning towards Carvin because of price. Any thoughts?

Nope, I wouldn't put more than 2 speakers on each side. Just look at the specs, if it doesn't say 2 Ohm, then it's not going to do 2 Ohm. Unless you want no sound and a little extra smoke anyways.

Yeah, wow! I didn't even see that. Ok then. I need to look a bit closer.
Thanks for your help. What are your thoughts on Carvin? Or any other suggestions?

The list of what I consider good power amps is (in no particular order): QSC, Crest, Crown and EV. Again, check the specs, not all of them will do 2 Ohms. The ones that will will probably be more expensive. It might be cheaper to get 2 amps, though, and then you can also have more mixes - and you'll probably be using your amps a bit easier too.

Thanks again.

As to your question regarding Carvin power amps, they are no better than, say, Peavey. In fact, Peaveys are probably a bit better in the long run, reliability-wise.

Your best bet for that setup is two power amps. 2 perside on one and one with the amp mono'd or bridged. Use this one for your lead singer if you have one. In this situation you wont need as big of an amp wattage wise as in bridged you're using both sides of the power amp.

It is NOT a good idea to run an unbalanced load on an amp which doesnt have separate power supplies for each half of the amp. Besides, your power will be higher in the lower ohmage side and in a monitor system this means certain feedback loops.

Davedog absolutely has the right idea. Two reasonably priced amps will give you 4 channels of amplification and much better sound quality. You can't go wrong with any amp on Spase's list.

An amp running at 2 ohms sounds like garbage and it will significantly shorten the life-span of the amp. Even an amp that claims it can run at 2-ohms, will be running extremely hot - if pushed very hard it will be running on the verge of thermal shut-down. Heat kills electronics.

We need to know the exact monitor speaker to make the call. It is best to have every monitor on it's own amp channel with it's own EQ and processing. If you guys do not require discrete mixes, then you can share, assuming that your monitors are no lower than 4 ohms in parallel. You could always wire them in series, but there would be some performance trade-offs. Then next thing to consider is power. Will you have sufficient AC power (2x 20 amp circuits) to power your two amplifiers. Most clubs don't have that for the whole room. If your monitors aren't efficient, they will require more power. That is something else to consider.

I'll second Davedog's suggestion of getting another amp, but I'd use the bridged/mono amp for the drummer. You will want at least one channel of decent eq (1/3 octave, good brand) per mix. If you don't have all matched wedges you should at least use matched types on shared amp channels and have separate eq for each type.

For example, say you have a pair of matching 10" monitors, a pair of matching 12s and one 15, and two monitor mixes. You need three amplifier channels and three eq channels. I'd put the 15" wedge on the drummer with his own mix and eq into the bridged amp, the pair of 10s on one side of the front line and the 12s on the other side. The 10s and 12s would share a mix but have separate eq and amp channels for each type of wedge.