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Amps/Ohms/Watts Help me Please!


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I was once told that 1200 watts delivered to three speakers is 400 watts to each speaker. That doesn't make any sense when I compare that to ohms. Three cabinets need 800 watts each, or as much as I can get from my QSCPLX2402. I have been told three different things by three different people, all of them I trust. Help me figure this out please!? PD :rolleyes:
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Simple answer - if the Ohms ratings agree between the amp & speakers, then it's theoretically true. Assuming parallel wiring of the speakers, you are dividing the resistance when you add another speaker, so: 8 Ohm speaker + 8 Ohm speaker = 8/2, or 4 Ohms. for 3 speakers: 8 + 8 + 8 = 8/3, or 2.6667 ohms. So, if your amp is rated ot 1200w @ 2 ohms, you will get a bit less than 1200 @ 2.6667, which would divide out to just under 400w/speaker. (FYI - Series wiring has the opposite effect, doubling the resistance of the speaker circuit - 8 + 8 = 16 Ohms.) Of course, this is just theoretical - YMMV. :wave:
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I have 3x800watt peak cabs in a mono cluster. I need to power the puppies so I still have a clear mix over 90db. They are underpowered right now at 425 into one cab and 700 into the other 2 (350). I just want to bridge my amp and pump 2400 into the three of them, but QSC doesn't rate it for that. I know it will do it, but I also want to cover my butt too. I know the crown amps you can drive all day on a 2ohm load bridged, but I have never tried a QSC like this. Thanks for taking an interest. PD :rolleyes:
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Hmmm - if the cabs are rated at 800w peak, my guess is that they're probably rated at 400w program, i.e. continuous level? If so, then the match at 1200w is probably more appropriate, asseming that the QSCs power rating is continuous & not peak. (It shouldn't be peak, but with specs you can never really tell unless they specify. I didn't see it in the user's guide... you should ask them.) If so, then you can actually plug all 3 of these into 1 side of your amp & get ~1200w. But, trying to run them at 2400 continuous is asking to blow them, as well as the amp. (I'd do it with Crown or Crest, but not QSC unless I had no choice...) Maybe you need more/better speakers? That amp seems pretty beefy, at least on paper (I haven't used one myself).
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I have spoken with QSC and EAW. QSC doesn't recommend it, but off the record says it will handle it so long as the output is not running at peak for long periods (which it wouldn't be.) EAW says I should be delivering 600 to 800 watts per speaker to get the results we need. The cabs have been driven far above that in other situations and outperformed cabs with twice the continuous according to the guy at tech supp. I talked to. My only real concern was the abuse on the amp over the next couple years. I hope to scrap it and get a more beefy amp, but don't have the budget. The PLX amps suck for big end sound. I might use it on monitors or a nice vox pa, but not at the levels we are trying to reach. QSC doesn't make an amp which has borders the PLX/CX/ and powerlite stuff. They all jump in price in power so there is no middle ground. Thanks for your input. PD :rolleyes:
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