Use the parallel out for the second speaker, which will give you a 4 ohm total load, giving you the needed 250 watts. But remember you'll only be using one channel on the amp, and running an amp with a 4 ohm load is going to make it work harder than it would with a 8 ohm load. It should work ok, as long as you're not pushing it too hard. You've also turned your rig into a mono setup....which is actually what most sound people prefer. But don't go thinking you can do any cool stereo effects, or even put a different EQ on each side.
Just how big is this room anyways? Do you even need the second pair of speakers?
BTW, as I understand it, an amp's impedance will change according to the impedance on the speaker. Impedance is resistance, measured in ohms. If the speaker is 8 ohms, then the amp will output 8 ohms. A lot of people think that if the amp only has specs for 8 ohm loads then it can't handle a 4 ohm load. I could be wrong about this, but I'm pretty sure that's how it works. The only problem is when you get to too low an impedance, like a 2 ohm load. Only higher end amps can handle that low of an impedance. But you won't ever have 8 ohms going into a 4 ohm speaker, because the speaker is what's causing that resistance. The spec you get on the amp is just telling you that with that much resistance from the speaker, you can output x amount of watts. And generally for every halfing of the impedance, the amp's output will double. That's not 100% exact, but it's a good guideline. When in doubt, read the manual. Even if you know it can put out 250 watts, you need to know how they measured that spec. Is it peak, RMS, program? There's a difference in all 3.
This is why you should learn how to use the gear before jumping into live sound. I'm not big on people teaching themselves how to use the gear, because you usually end up missing out on a lot of important information. Sure you may know how to use a board, but if something goes wrong, you need to know how to fix it, and fast.
Yamaha's sound reinforcement handbook. Get it. Read it cover to cover. Keep it with you at all times until you know it. In my opinion, it's the soundman's bible.
|