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I'm designing a small PA system. I currently have the following setup (stereo main mix into 2-channel amp with 4 speakers [front and rear in parallel]):

+------+           +---+           +------+
|LF-Spk|<------L--+|Amp|+--R------>|RF-Spk|
+------+           +---+           +------+
    +               ^ ^               +
    |               | |               |
    |               | |               |
    |               L R               |
    v               + +               v
+------+         +--------+        +------+
|LR-Spk|         |Main Mix|        |RR-Spk|
+------+         +--------+        +------+

The problem I am encountering is that this setup does not allow me to adjust the volume of each speaker independently. I can adjust the volume of the left and right on the mixer, but I would like to adjust the volume of each speaker independently. There is no apparent way to do this while my speakers are in parallel.

My current plan is to get an additional 2-channel amp for my rear speakers and set up my system like this:

+------+            +----+             +------+
|LF-Spk|<----LF----+|Amp1|+----RF----->|RF-Spk|
+------+            +----+             +------+
                     ^  ^
                     |  |
                  +--+  +--+
                  |        |
+------+          | +----+ |           +------+
|LR-Spk|<----LR----+|Amp2|+----RR----->|RR-Spk|
+------+          | +----+ |           +------+
                  |  ^  ^  |
                  |  |  |  |
                  L  L  R  R
                  F  R  R  F
                  +  +  +  +
                +------------+
                |  Main Mix  |
                +------------+

The problem is that my mixer only has a 2 channels out (L and R). I would prefer to not buy a new mixer. In fact, I sort of need the opposite of a mixer: something that takes two channels in and adjusts its volume for multiple output channels. Are there products that do this? Or is there a better way to tackle this problem entirely?

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2 Answers 2

up vote 3 down vote accepted

All newer Home Theater Receivers offer an option to balance the sound coming from your speakers, which will optimize the surround sound experience. Using the setup menu on many Home Theater Receivers, the user can set speaker distance, speaker size, and speaker channel level in relation to the listening position.

http://hometheater.about.com/od/hometheaterbasics/a/trouble.htm

So one way to solve this without changing your mixer is to use a single 5+1 home theater receiver instead of adding another 2 channel amp. It's possible to get pro-quality units at a reasonable price, like this one.


If you need real-time control over the speaker channels, you can get a "splitter mixer," like this one: http://www.rane.com/sm26s.html#gpm1_2, and configure it as a splitter according to the manual:

As a splitter, place one or both input signals into the LEFT and/or RIGHT MASTER INs. Select the Input(s) to be placed at each of the six MONO OUTPUTS by rotating the MIX / PAN control to the proper position. Set the individual channel LEVEL controls for proper output level. The MASTER INPUT LEVEL control adjusts both Right and Left Input signal levels together.

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That would work great if this were a small setup. Unfortunately I'm dealing with a live-audio PA system. –  Joseph Sturtevant Nov 14 '11 at 23:21
    
You said it was a small setup in your question. How big is it really? Do you need more than 100 watts per channel? –  Robert Harvey Nov 14 '11 at 23:23
    
Come to think of it, your second amp already has a volume control on it. What are you trying to accomplish? If you really do need real-time control over each channel, and don't want to change out your mixer, then you need something like this: rane.com/sm26s.html#gpm1_2 –  Robert Harvey Nov 14 '11 at 23:28
    
Yeah. I guess by small I meant 'small for a PA/SR system'. I think we're currently at 300-500 watts/channel. –  Joseph Sturtevant Nov 15 '11 at 0:03
    
While it is possible to adjust the volume on the amp, the amp is behind the stage so there is no practical way to adjust volume during an event. –  Joseph Sturtevant Nov 15 '11 at 0:04

Daisy chaining the inputs of your existing amp with the inputs of an additional 2ch amp would be the simplest fix.

With out more details (types of physical connections) on the mixer and amp you have now, it’s hard to give an exact answer.

I would personally avoid using a home theater piece of equipment, as it is unlikely to have balanced connections and could give you issues of noise or interference.

Not being able to adjust the A vs. B volume from the back should not be an issue. Once you get an initial setting and tweak it a bit over a few weeks, you should be fine.

Another option is to get a 4CH amp, or run a mono setup and use A for front and B for back.

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