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Audio question - running 8 speakers off a 2 channel amp

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Old 01-09-2006, 12:48 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Also, is there a way to figure out power(wattage) that an amp poduces between the 2 and 4 ohms? In other words, if an amp is rated at 720 watts RMS at 4 ohms and 960 watts RMS at 2 ohms how do you figure out what power it would have at 2.67 ohms?
C'mon you experts, you have my wheels turning big time now!
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Old 01-09-2006, 02:14 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

I'm no EE and my math is rusty but I'm coming up with about 805 watts. This is based upon checking out the amps voltage decrease with ohms decrease and figuring out how much voltage will be at its outputs with a 2.67 ohm load. But one doesn't have to go through all this when matching amps to speakers. When in doubt, overpower.
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Old 01-09-2006, 02:26 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

easy formula to follow to figure ohm load in parrallel
2 4ohm speakers in parrallel
1/x + 1/x= eg. (1/ 4ohm + 1/ 4ohm = 0.5ohm =x
divide by 1/.5 = 2ohm load)
1/x

can be used for multiple speakers also
I think that I did that right some one let me know if thats wrong.
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Old 01-09-2006, 02:51 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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I'm no EE and my math is rusty but I'm coming up with about 805 watts. This is based upon checking out the amps voltage decrease with ohms decrease and figuring out how much voltage will be at its outputs with a 2.67 ohm load. But one doesn't have to go through all this when matching amps to speakers. When in doubt, overpower.
It was more of a curiousity thing. I was coming up with 800 watts at 3 ohms so I figured 2.67 would be about 830-840. But I was too lazy to rack my brain and it's been way too long since I have had an algebra class!!!
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Old 01-09-2006, 02:54 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Originally Posted by batty
easy formula to follow to figure ohm load in parrallel
2 4ohm speakers in parrallel
1/x + 1/x= eg. (1/ 4ohm + 1/ 4ohm = 0.5ohm =x
divide by 1/.5 = 2ohm load)
1/x

can be used for multiple speakers also
I think that I did that right some one let me know if thats wrong.
Parallel is easy and series and easy to figure out. It was when combining I was confusing myself! But with the help tyson and this website I think I finally have it figured out!
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Old 01-09-2006, 03:29 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

now all that Engineering school has paid off !!! Thats a pertty cool website lotsa information to learn from.

just becareful with the power of the amps. You dont want to let the smoke out of the speakers!
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Old 01-10-2006, 02:06 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Originally Posted by noboat
It was more of a curiousity thing. I was coming up with 800 watts at 3 ohms so I figured 2.67 would be about 830-840. But I was too lazy to rack my brain and it's been way too long since I have had an algebra class!!!
830 would be a theoretical output. Because this amp, like a lot of amps will not double its power when halfing the ohms, it turns down its internal gain. The Crest PA amps I use call this an IGM circuit. Theoretically this amp should make 1440 watts at 2 ohms but that amount of energy would fry things. Remember that Power is an amount of energy over time. So I figured the voltage out using Ohm's Law with both the 4 ohm and 2 ohm loads. There's about a 10 volt difference. Then using that difference, I assumed that the gain reduction of the amp was uniform so I figured out the voltage of the amp at 2.67 ohms and then calculated power. It's been a while for me on that one, but I'm pretty sure I got it right. Are you doing up a system???
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