Stereo pair conversion to mono - AVS Forum
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post #1 of 15 Old 05-10-2012, 08:14 PM - Thread Starter
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I know this topic is mentioned in many threads and I think I've read about all of them but still don't know the best solution to my setup so I need some assistance.

I currently have two outdoor speakers wired as a stereo pair, driven by an AudioSource 100 amp. I have an apple airport express connected to the amp and I use the system for airplay while on my deck.

The problem is that the sound from the stereo pair is (obviously) only good when standing in the middle of the speakers. Both seating areas on the deck are off to the sides near one speaker only so it doesn't sound great.

Can I somehow rewire things at the amp so I could use both speakers as mono? The amp doesn't have a stereo/mono switch. I know you can use the amp in bridged mode but I don't know how to use this to drive 2 separate speakers both in mono.

Due to budget, I can't buy another amp, different speakers, or run more wires. I already paid an electrician buddy of mine to help me run the wires. They are long runs from our basement to the outside and up to the speakers.

Therefore, I'm looking for a solution centering around the wiring at the back of the amp.

Thanks for any help.

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post #2 of 15 Old 05-10-2012, 08:38 PM
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What's the impedance of the speakers? If memory serves, that amp will run bridged into 8-16 ohms, so if the speakers in parallel or series would equal >8 ohms, it should drive them in parallel or series (notice I keep saying "or" - one will halve impedance, one will double) while bridged.

Otherwise, you can create a mono summing network (http://www.rane.com/note109.html), and feed the same mono signal into both channels of the amplifier and leave the speakers connected as-is. This will be the cleanest solution, and it would let you run whatever speakers the amp will normally support in stereo (and if memory serves, that amplifier has A+B operation as a choice), and give you individual level controls on each channel. Will take a bit of time to create the little box though.


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post #3 of 15 Old 05-10-2012, 09:25 PM - Thread Starter
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The amp does have the ability to drive two stereo pairs, labelled as Speakers A and B. It can drive them simultaneously if you choose A+B mode. I currently have my stereo pair wired to Speaker A left and Speaker A right.

The instructions in the manual describe how to use bridged mode to power a single mono speaker but I'm not clear how to translate it to two mono speakers.

The manual says (and I quote):
For bridged mode playing Right and Left together as mono output, use a Y cable adapter to connect Right and Left RCA signal to the Right (red) input at LINE IN.
Place the MODE switch in the BRIDGED position and use both red terminals to connect to the speaker. Connect the speaker's negative (black) terminal to the amp's left channel positive (red) terminal, and the speaker's positive (red) terminal to the amp's right channel positive (red) terminal. NOTE: Only one zone (A or B) can be bridged. Do not attempt to bridge both A and B speaker terminals. This may result in a lower impedance than the amp is designed for and may damage your amp. The minimum impedance for the total load connected in bridged mode is 8 ohms.


My speakers are the Polk Atrium 7.

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post #4 of 15 Old 05-10-2012, 10:08 PM
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What a dreadful user manual - almost no specifications!

Anyways, what I could pick out of it was 8 ohm impedance, so if you put these speakers in series they would present 16 ohms and you could probably get away running the amplifier bridged. I probably would just build the summing circuit and leave things hooked up as-is though.


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post #5 of 15 Old 05-11-2012, 04:34 AM
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Maybe I missed something...

The back of the speakers have two wires, correct?

The back of the amp has four speaker connections, correct?

Why can't the left speaker be "A" on the amp, and the right speaker be "B" on the amp?

Then just run "A+B" and be done with it.

You probably aren't using the Amp at full tilt, so you wouldn't loose much, I don't think.
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post #6 of 15 Old 05-11-2012, 06:09 AM
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Quote:


Therefore, I'm looking for a solution centering around the wiring at the back of the amp.

Why don't you just sum the line level inputs to mono?
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post #7 of 15 Old 05-11-2012, 06:13 AM
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Rather than trying to find a way to get your amp to drive two speakers as one, perhaps there's a way to get your source to feed a mono signal to the amp in the first place. I'm not familiar with the air play or your amp, so I'm having a hard time figuring out the best way to do it, but there might be a way, either through settings on the device or by using some combination of y-cables, to get a mono signal that your amp just "thinks" is in stereo.
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post #8 of 15 Old 05-11-2012, 08:01 AM
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Quote:


Rather than trying to find a way to get your amp to drive two speakers as one, perhaps there's a way to get your source to feed a mono signal to the amp in the first place.

Great idea!

Quote:


so I'm having a hard time figuring out the best way to do it,

You take the L and R line level source, through two series resistors (about 4.7K will do) and connect them to both left and right inputs on the amp.
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post #9 of 15 Old 05-11-2012, 08:05 AM - Thread Starter
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Quote:
Originally Posted by underminded999 View Post

Maybe I missed something...

The back of the speakers have two wires, correct?

The back of the amp has four speaker connections, correct?

Why can't the left speaker be "A" on the amp, and the right speaker be "B" on the amp?

Then just run "A+B" and be done with it.

You probably aren't using the Amp at full tilt, so you wouldn't loose much, I don't think.

I've thought about this approach but each "zone", A and B, have both a left and right output. So, I'd have to choose to have one speaker as "A left" or "A right", and the other as "B left" or "B right". But, each speaker would be missing half the sound then, right? Or, will amps sense that there's only one speaker hooked up and output everything to that one speaker?

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post #10 of 15 Old 05-11-2012, 08:14 AM - Thread Starter
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Quote:
Originally Posted by SAM64 View Post

Why don't you just sum the line level inputs to mono?

I'm not sure how to do this. Airport express (AE) has only a digital out. The amp is analog only. So, I'm using a cable which on the AE end has a standard digital audio 3.5mm connector and on the amp end has standard red/white RCA male connectors which go into the LINE IN on the amp.

Advice?

Is there a different kind of audio cable which could be used here?

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post #11 of 15 Old 05-11-2012, 08:24 AM
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Quote:


Airport express (AE) has only a digital out. The amp is analog only. So, I'm using a cable which on the AE end has a standard digital audio 3.5mm connector and on the amp end has standard red/white RCA male connectors which go into the LINE IN on the amp.

A cable cannot convert a digital signal to analog.

A 3.5mm trs is not a 'standard digital connector'.

So, I will assume that the AE 3.5mm output is analog. These two analog signals should be connected together through series resistors. Do you know anyone who can solder?
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post #12 of 15 Old 05-11-2012, 08:31 AM - Thread Starter
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Quote:
Originally Posted by SAM64 View Post

A cable cannot convert a digital signal to analog.

A 3.5mm trs is not a 'standard digital connector'.

So, I will assume that the AE 3.5mm output is analog. These two analog signals should be connected together through series resistors. Do you know anyone who can solder?


Sorry, right. I typed before I thought. It's analog to analog. Duh. That's why I purchased this setup. My bad.

Anyway, no, I don't know much about soldering.

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post #13 of 15 Old 05-11-2012, 08:46 AM - Thread Starter
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I was able to figure out how to get my source to output in mono!

I also searched the apple forums and surprise....hidden in the settings>general>accessibility section on both my iphone and iPad there is a selector to switch the audio to mono. I tested it and it works fine. Both speakers will output identical mono feeds now.

I just have to remember to switch back to stereo when listening on my nicer listening zones inside the house. Not a big deal...I just have to remember to switch it back.

Wow, it's strange that apple would have that setting hidden in that menu and not also in the music settings...or in the AE settings or airplay settings. Oh well. This is certainly the easiest solution for me.

Thanks so much to all of you who chimed in and tried to help. That's why this forum is so great.

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post #14 of 15 Old 05-11-2012, 12:09 PM
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Oh cool, nice to see a digital component able to do something simple like that. Now you don't have to build anything (which is always a nice time saver!) .


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post #15 of 15 Old 05-12-2012, 03:15 AM
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An easy solution that doesn’t require soldering skills - only a bit of cash – would be to get something like the Behringer ZENYX 802 mixer. You could plug the AE into Inputs 1 and 2. If you keep the “Pan” control straight up for Inputs 1 and 2, you’ll get a mono signal from the L/R Main Outputs.

Regards,
Wayne A. Pflughaupt





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