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Author Topic: Series-Parallel Wiring My PA  (Read 1470 times)

Daniel Mock

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Series-Parallel Wiring My PA
« on: December 21, 2012, 05:58:22 am »

So I have a Crown MA-12000i
that outputs 4500w per channel at 4ohms.

And eight TSW-721s
1200 program (8ohms)

I want the amp to see a 4ohm load per channel so that it outputs 4500w,
and I want each driver to receive 1125w.

Is the diagram below the accurate way to achieve this?


Thank You


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Steve O'Connor

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Re: Series-Parallel Wiring My PA
« Reply #1 on: December 21, 2012, 07:28:46 am »

So I have a Crown MA-12000i
that outputs 4500w per channel at 4ohms.

And eight TSW-721s
1200 program (8ohms)

I want the amp to see a 4ohm load per channel so that it outputs 4500w,
and I want each driver to receive 1125w.

Is the diagram below the accurate way to achieve this?


Thank You

The top row of speakers are in series with each other. Each speaker is 8ohm so the equivalent impedance of that row is 8+8 = 16ohm
The second row is also 8+8 = 16ohm
The top row and second row are in parallel with each other therefore 1/16 + 1/16 = 1/R so the impedance seen by the channel is 1/(1/8) = 8ohm

The only combination with 8x8ohm drives to achive a 4 ohm load on each channel would be 2 8Ohm drivers in parallel on each channel.

Or if you put a block of 4 parallel drivers in series with another block of 4 parallel drivers but then that wouldn't be what you want either.
« Last Edit: December 21, 2012, 07:31:25 am by Steve O'Connor »
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Brad Weber

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Re: Series-Parallel Wiring My PA
« Reply #2 on: December 21, 2012, 08:36:38 am »

I want the amp to see a 4ohm load per channel so that it outputs 4500w,
and I want each driver to receive 1125w.
As Steve noted, what you shows is a net result of two channels with 8 Ohms per channel.  2,100W per channel over 4 speakers is 525W per speaker.
 
You could keep the four 16 Ohms series pairs shown and wire all four pairs in parallel, a total 4 Ohm load, and then run the amp in bridge mode for 7,500W over 8 speakers or 937.5W per speaker.
 
Compared to 1,125W, 937.5W would be -0.8dB and 525W would be -3.3dB.
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David Parker

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Re: Series-Parallel Wiring My PA
« Reply #3 on: December 21, 2012, 08:51:06 am »

So I have a Crown MA-12000i
that outputs 4500w per channel at 4ohms.

I had the same situation years ago, and realized I couldn't do what I wanted. I was using a Crown MA3600. As it turned out, it performed beyond my expectations with the 8 ohm load per channel, so I had mine wired exactly as your drawing and was very pleased. The MA 3600 was  a strange bird though, rated almost 1200 watts per channel at 8 ohm, and then only 1600 at 4 ohms and 1800 at 2ohms.
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Ivan Beaver

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Re: Series-Parallel Wiring My PA
« Reply #4 on: December 21, 2012, 08:56:20 am »

As Steve noted, what you shows is a net result of two channels with 8 Ohms per channel.  2,100W per channel over 4 speakers is 525W per speaker.
 
You could keep the four 16 Ohms series pairs shown and wire all four pairs in parallel, a total 4 Ohm load, and then run the amp in bridge mode for 7,500W over 8 speakers or 937.5W per speaker.
 
Compared to 1,125W, 937.5W would be -0.8dB and 525W would be -3.3dB.
Brad's way would be the best way.

Or you could wire it a different way-this may be easier.

Run 4 speaker in parallel, then another 4 in parallel.  Then run those 2 sets in series.

How you do it depends on the particular setup.  If you are going to run a home run from each cabinet back to the amp rack and do the series parallel there-then the original wiring would be best.

But if cable is limited, then running each set of 4 in parallel may be easier.

HOWEVER-because of the 2 ohm load this presents-the damping factor and possible loss over the wire (depending on the length) might be to much.

Of course you could put a "wiring box" behind each set of cabinets and plug everything into that-and then run a single 8 ohm cable to the amp rack.

This would be the best way (in my opinion).  The higher impedance would make for less line loss and higher damping.

But more information is needed to arrive at the best for the OP situation.
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Ivan Beaver
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David Parker

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Re: Series-Parallel Wiring My PA
« Reply #5 on: December 21, 2012, 09:13:09 am »

Brad's way would be the best way.

Or you could wire it a different way-this may be easier.

Run 4 speaker in parallel, then another 4 in parallel.  Then run those 2 sets in series.

How you do it depends on the particular setup.  If you are going to run a home run from each cabinet back to the amp rack and do the series parallel there-then the original wiring would be best.

But if cable is limited, then running each set of 4 in parallel may be easier.

HOWEVER-because of the 2 ohm load this presents-the damping factor and possible loss over the wire (depending on the length) might be to much.

Of course you could put a "wiring box" behind each set of cabinets and plug everything into that-and then run a single 8 ohm cable to the amp rack.

This would be the best way (in my opinion).  The higher impedance would make for less line loss and higher damping.

But more information is needed to arrive at the best for the OP situation.

that chart is wrong. The 4ohm bridged and 8 ohm bridged numbers are backwards. It would be 9000 at 4 ohms bridged.
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Mac Kerr

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Re: Series-Parallel Wiring My PA
« Reply #6 on: December 21, 2012, 10:53:41 am »

Is the diagram below the accurate way to achieve this?

No. You have 2 8Ω speakers in series making a 16Ω load. You then have 2 of these 16Ω loads in parallel, making an 8Ω load. The only way to make those 8Ω loads into 4Ω loads is to have 4 of them, each consisting of 2 8Ω loads.

Mac
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Steve Anderson

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Re: Series-Parallel Wiring My PA
« Reply #7 on: December 21, 2012, 07:17:04 pm »

that chart is wrong. The 4ohm bridged and 8 ohm bridged numbers are backwards. It would be 9000 at 4 ohms bridged.

Are you suggesting the entire chart is wrong? The 4 ohm bridged number is twice the noted 2 ohm single channel number, and the 8 ohm bridged is twice the 4 ohm single channel number. Exactly as I would expect.

The limiting factor here is the power supply in the amp, there are quite a few amps that put out less power at 2 ohms (or 4 ohm bridged) than at 4 ohms. [I have no direct experience with the MA12K, just saying the chart looks right to me]

Simple mistake... in my greener times I used to wonder why all amplifiers didn't put out twice as much power into 4 ohms as into 8 ohms! Or for that matter 4 x as much into 2 ohms! (not suggesting you think that David)

Cheers!
« Last Edit: December 21, 2012, 07:23:48 pm by Steve Anderson »
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Ivan Beaver

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Re: Series-Parallel Wiring My PA
« Reply #8 on: December 21, 2012, 07:34:51 pm »

Are you suggesting the entire chart is wrong? The 4 ohm bridged number is twice the noted 2 ohm single channel number, and the 8 ohm bridged is twice the 4 ohm single channel number. Exactly as I would expect.

The limiting factor here is the power supply in the amp, there are quite a few amps that put out less power at 2 ohms (or 4 ohm bridged) than at 4 ohms. [I have no direct experience with the MA12K, just saying the chart looks right to me]

Simple mistake... in my greener times I used to wonder why all amplifiers didn't put out twice as much power into 4 ohms as into 8 ohms! Or for that matter 4 x as much into 2 ohms! (not suggesting you think that David)

Cheers!
There have been only a very few-I mean VERY few amps that were rated at twice the power into 4 ohms as 8 ohms.  Or very close twice anyway.

It should "theoretically" be twice the power-but in reality it is not.
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Mac Kerr

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Re: Series-Parallel Wiring My PA
« Reply #9 on: December 21, 2012, 07:41:59 pm »

As Steve noted, what you shows is a net result of two channels with 8 Ohms per channel.  2,100W per channel over 4 speakers is 525W per speaker.
 
You could keep the four 16 Ohms series pairs shown and wire all four pairs in parallel, a total 4 Ohm load, and then run the amp in bridge mode for 7,500W over 8 speakers or 937.5W per speaker.
 
Compared to 1,125W, 937.5W would be -0.8dB and 525W would be -3.3dB.

Or, just use the amp in stereo with 4 speakers in parallel for 2Ω on each channel, for the same 9000W total. This would eliminate the whole series/parallel scheme which can be a PITA, and presents the same load to the amp.

Mac
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