I have a PA hookup question? I have two Soundtech LT5 speakers with 250w rms 8 ohms and a Peavey XR600C mixer head and it says on the back 210w/4 ohms and 300w/2 ohms It dont say 8 ohms would it work? I dont understand the ohms deal? Thanks

With most solid state amps you can safely use any speakers that are higher ohms than the amp's minimum ohm rating (some Class D solid state amps are picky about both min and max impedances, but the XR600C is a typical Class AB solid state amp). The higher the speaker impedance, the less power the amp will put out (the amp will also run cooler). The XR600C will drop to about 105 watts driving 8 ohms, down to about 52 watts driving 16 ohms.

The XR600C is a mono amp. If you connect one 8 ohm cab to it, the amp can put out 105 watts to that cab. But two 8 ohm speaker cabs daisy-chained in parallel is a 4 ohm total load, so the Peavey can put out 210 watts to the pair of them.

Here's Peavey's manual for the XR600C: http://www.peavey.com/assets/literature/manuals/80300747.pdf
Note that they do list the clipping point for 8 ohms, so it's perfectly safe to use just one of your 8 ohm cabs if you don't need the extra volume.

Thanks for the info but I have a show this week end and need both speakers so is it bad to use both? Will it not have a good output sound? Thanks

Since the Peavey XR600C is a mono amp and you asked about hooking it up to an 8 ohm load, I assumed that for some reason you wanted to use just one of your 8 ohm cabs.

Running both your 8 ohm cabs is fine. Hooked together in parallel that's a 4 ohm total load and the Peavey can put out 210 watts into 4 ohms (105 into each cab).

Thanks again one last question when you parallel do you mean one cable from the back of the amp to one speaker then one speaker to the other? would I gain anything with the biamp input on the speaker or is that different? Thanks

"do you mean one cable from the back of the amp to one speaker then one speaker to the other?"

Yes, that's exactly correct.

The bi-amp inputs on the speakers are indeed something completely different -- for using an electronic crossover to drive separate power amps for the woofer and tweeter.