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Audio question - running 8 speakers off a 2 channel amp

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Old 01-09-2006, 10:36 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

three 8 ohm loads would be
(8 x 8) / ( 8 + 8) = 64/16 = 4

then take that load and parallel it to the other 8 ohm

(4 x 8) / (4 + 8) =32/12 = 2.66666667 is the load for 3 8 ohm loads
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Old 01-09-2006, 10:37 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Originally Posted by Bigyellowcat
the formula is for 2 loads not 3. you have to do 2 loads at a time then you can combine them.
So, how do you do that? To keep it simple say you want to hook up 3 4 ohm subs to a mono channel amp. How do you calculate the ohm load?
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Old 01-09-2006, 10:39 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

Quote:
Originally Posted by Bigyellowcat
three 8 ohm loads would be
(8 x 8) / ( 8 + 8) = 64/16 = 4

then take that load and parallel it to the other 8 ohm

(4 x 8) / (4 + 8) =32/12 = 2.66666667 is the load for 3 8 ohm loads

Whoops you beat me to it! Thank you. It drives me crazy when I can't figure this kind of stuff out!

Last edited by onesickpantera; 01-09-2006 at 10:43 AM.
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Old 01-09-2006, 10:40 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
Now, let's say hypethetically I add two more speakers to each channel and wired those two in series as well for a total of 3 "8 ohm speakers". Now I wire all three in parallel. My brain is telling me 8 ohm load/3 = 2.67 ohm total load. !

just because that worked this time I would always use the formula because, that worked out right that time and some times it will work out easy but usuallly it is wrong if you just divide.
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Old 01-09-2006, 10:43 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Originally Posted by Bigyellowcat
just because that worked this time I would always use the formula because, that worked out right that time and some times it will work out easy but usuallly it is wrong if you just divide.
Right. Thanks for the help.

So in my example 3 4 ohm speakers on a mono amp would be:

(4x4)/(4+4) = 16/8 = 2

(2x4)/(2+4) = 8/6 = 1.33 ohms total?
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Old 01-09-2006, 10:52 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

I guess going to school for degrees in mechanical engineering, electrical engineering and acoustical engineering finally paid off.
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Old 01-09-2006, 11:08 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Originally Posted by Bigyellowcat
I guess going to school for degrees in mechanical engineering, electrical engineering and acoustical engineering finally paid off.
It sure did! So are my above formulas right? 1.33 ohms for 3 4 ohm speakers wired in parallel?
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Old 01-09-2006, 11:27 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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?
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Old 01-09-2006, 11:36 AM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

Quote:
Originally Posted by Bigyellowcat
I guess going to school for degrees in mechanical engineering, electrical engineering and acoustical engineering finally paid off.
Ya but what is the formula for shear
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Old 01-09-2006, 12:26 PM
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Default Re: Audio question - running 8 speakers off a 2 channel amp

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Ya but what is the formula for shear
depends on what kind of shear you are talking about, shear strength, shear force, horizontal shear vertical shear, they are all different actual forumlas.
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