A few months ago, I got a new desk for my computer. Before I had the desk, the living room was like this (1337 Paint skills are following): EDIT: Looks like I forgot to put the subwoofer in the images. It doesn't really matter though.



I used to sit at the armchair and the monitor and the TV were in front of me.

Now, I've put a desk (which is now where my computer is) between the R and the RR channels:



As you can see however, the audio channels are now messed up due to this change!
So, I was wondering, is there any way to make the audio channels like this?



Physically switching the cables is not an option, since there are times where I want to sit on the armchair and watch something from the computer on the TV.

I was wondering if it is possible to create a hardware-based solution that where I would be able to select which channels setting I want with a rocker switch or something similar.
The device would have 3 female 3.5mm audio ports which would be connected to the computer via 3 line in cables. The output would be another 3 female 3.5mm audio ports where the cables that are connected to the speakers would be plugged in. Depending on the state of the rocker switch, the device would either "send" the audio as it was received (which means that I'm sitting on the armchair, watching TV), or "send" it to the "correct" speakers (L->R, R->RR, RL->L, RR->RL, C->?? (possibly R and RR?)).
Is that even possible?


Thanks

Offtopic: Here's a picture of the desk:

Bump. Anyone?

I've also drawn two small schematics to show you what I mean by the hardware-based solution.

When the switch/button is into position 1 the setup for watching TV will be used:



When the switch/button is into position 2 the setup for using the computer will be used:



Would that work?

I'm in the same kind of situation (surround speakers positioned properly for TV, but incorrect when using the PC. Wondered the same too, and if you do find an affordable solution I'd like to hear it, but didn't put too much effort into looking for it myself.

The things is, while all my audio from my PC comes through my surround speakers, not much audio from my PC actually is surround sound. None of the music, none of the regular applications, movies are mainly played on the TV screen, high-end games I play on Xbox (TV)... simple games generally don't do surround. So yeah, PC mostly does stereo (x2) where it doesn't that much how speakers are positioned.

Also: If you really want proper surround sound on your PC you also have the center speaker to deal with where by far most of the sound comes from. Watching a movie or playing a game where all of the dialog comes only from the left side gets tiring quickly.

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Originally posted by Menthix
Wondered the same too, and if you do find an affordable solution I'd like to hear it

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Originally posted by Menthix
The things is, while all my audio from my PC comes through my surround speakers, not much audio from my PC actually is surround sound. None of the music, none of the regular applications, movies are mainly played on the TV screen, high-end games I play on Xbox (TV)... simple games generally don't do surround.

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Best bet is probably going to be to just have a box where you route the connections through and you can throw a switch that would throw a set of relays setup to make the connections.

Seem like the best option to me.

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Originally posted by wj
and you can throw a switch that would throw a set of relays setup to make the connections.

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If you can find a decent 6PDT switch, it's very possible it would work. The alternative is to essentially build a 6PDT out of relays. Though I'm pretty sure you don't need to switch the subwoofer, so you would only need a 5PDT.

The following information may make it clearer, it may make it worse. if you don't fully understand I don't blame you, just disregard it. There's no real solution here, just some background on relays.

Most relays have a NC and an NO contact. NC being normally closed and NO being normally open. The common pole is connected to one or the other depending on if power is applied or not. NC and NO are based on when there is no power applied to the relay.

Basically this means when your switch is off (open), there is no power applied to the coil of the relay. When there is no power applied to the coil of the relay the Normally Closed output leg is closed (on), and at the same time the Normally Open output leg is open (off).

When you apply power to your relay coil. the NO leg is closed (on) and the NC leg is OPEN (off).

So in your case you would have the input coming into the common leg, and one set of outputs connected to the NC and one set to the NO.

I would highly suggest NOT combining your center and left/right speaker channels. It's typically not expected when the receiver company builds the receiver and you don't know what will happen when the power is coming/going from different channels.

My solution would be to add an additional center channel speaker and switch between the two instead of trying to mix the audio signals. If you're only using 2 channel audio you may not even notice that you don't have it..

EDIT: To answer your question in the other forum, yes you would need a power source to operate your relays. An old 5V wall charger from a cell phone would probably be your best bet.

6PDT will work if you can get your hands on one, I've never really seen them available to be honest, but they certainly exist - might be worth noting it could well be a cheaper and less confusing (debatable) to use multiple smaller relays, ie 2 x 3PDT or even 3 x DPDT.

You'd have a circuit with a DC battery (voltage depandant on what relays you end up choosing) running through the relays and a switch inline. As for the relays, you simply wire up the two possible inputs and outputs. Here's a sample relay wiring diagram on a single DPDT for just the L and R inputs of your PC:



Note: I'm not entirely sure if this'll work with audio, If there are multiple cores carried through a 3.5mm cable, or if combining channels is the best idea, I use relays all the time for robotics but that's just to redirect power, not actual signals...

EDIT: dammit... Lizard.boy sneaked in there while I was constructing my reply

I know in a standard 3.5mm audio cable there are two channels and a common return. You could think of them as +R, +L, and -both.  I don't know if mixing return paths between the 3 outputs on the motherboard is acceptable or not, so it's quite possible that you would need to factor that into your design.

My first instinct would be to place the device between the receiver and the speakers, instead of the PC and the receiver, and switch the "grounds" at the same time as switching the channels.

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Originally posted by lizard.boy
If you can find a decent 6PDT switch, it's very possible it would work.

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Originally posted by lizard.boy
Though I'm pretty sure you don't need to switch the subwoofer, so you would only need a 5PDT.

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Originally posted by lizard.boy
The following information may make it clearer, it may make it worse. if you don't fully understand I don't blame you, just disregard it. There's no real solution here, just some background on relays.

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Originally posted by lizard.boy
I would highly suggest NOT combining your center and left/right speaker channels. It's typically not expected when the receiver company builds the receiver and you don't know what will happen when the power is coming/going from different channels.

My solution would be to add an additional center channel speaker and switch between the two instead of trying to mix the audio signals. If you're only using 2 channel audio you may not even notice that you don't have it..

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Originally posted by lizard.boy
EDIT: To answer your question in the other forum, yes you would need a power source to operate your relays. An old 5V wall charger from a cell phone would probably be your best bet.

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Originally posted by stoshrocket
might be worth noting it could well be a cheaper and less confusing (debatable) to use multiple smaller relays, ie 2 x 3PDT or even 3 x DPDT.

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Originally posted by lizard.boy
My first instinct would be to place the device between the receiver and the speakers, instead of the PC and the receiver, and switch the "grounds" at the same time as switching the channels.

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Originally posted by Mike

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Originally posted by lizard.boy
If you can find a decent 6PDT switch, it's very possible it would work.

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Define "decent" please

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Originally posted by lizard.boy
Though I'm pretty sure you don't need to switch the subwoofer, so you would only need a 5PDT.

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Do these even exist? A Google Image search for 5PDT shows irrelevant images, but does show some pictures of 6PDT switches when searching for 6PDT.

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Originally posted by lizard.boy
The following information may make it clearer, it may make it worse. if you don't fully understand I don't blame you, just disregard it. There's no real solution here, just some background on relays.

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Thanks, now relays make more sense

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Originally posted by lizard.boy
I would highly suggest NOT combining your center and left/right speaker channels. It's typically not expected when the receiver company builds the receiver and you don't know what will happen when the power is coming/going from different channels.

My solution would be to add an additional center channel speaker and switch between the two instead of trying to mix the audio signals. If you're only using 2 channel audio you may not even notice that you don't have it..

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Alright, thanks, I'll keep that in mind. I'll see if I can add speaker on the desk.

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Originally posted by lizard.boy
EDIT: To answer your question in the other forum, yes you would need a power source to operate your relays. An old 5V wall charger from a cell phone would probably be your best bet.

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Bah!
Having a power source seems weird since I will only be rerouting the signals
Is there any reason to prefer relays over a standard switch?

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Originally posted by stoshrocket
might be worth noting it could well be a cheaper and less confusing (debatable) to use multiple smaller relays, ie 2 x 3PDT or even 3 x DPDT.

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Can you create an example diagram please? I can imagine how the diagram for using a 5PDT/6PDT would be, but I'm not sure about this one

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Originally posted by lizard.boy
My first instinct would be to place the device between the receiver and the speakers, instead of the PC and the receiver, and switch the "grounds" at the same time as switching the channels.

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Hmmm ... that would be hard because I use two different receivers (one for the L/R channels and another one for the rest of the channels).

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I thought I already posted this, but guess I just wrote it and never hit "post".

You can re-wire a VGA or parallel switchbox, a mechanical one like this.  It will provide a suitable switch as well as a housing.

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Originally posted by lizard.boy
I don't know if mixing return paths between the 3 outputs on the motherboard is acceptable or not, so it's quite possible that you would need to factor that into your design.

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Originally posted by lizard.boy
My first instinct would be to place the device between the receiver and the speakers, instead of the PC and the receiver, and switch the "grounds" at the same time as switching the channels

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NB: Example of multiple relays wiring:



(Sorry about the slightly wierd overlapping wiring on the relay side, it's basically three relays in parallel but showing them side by side too too much room...)

This will act in the same way as a single 6PDT in place of the 3 DPDT, but in my experience this way would be cheaper and less confusing only switching the 2 channels per relay. If it turns out you end up not switching central and SW then you can obviously remove the bottom relay (or just use a single 4PDT).

As for 5PDT, I'm pretty sure they'd exist, it's not like you need an even number of inputs, 3PDT are quite common. However, I'd still stick down the multiple DPDT route, it'll just make things easier, I've personally never seen anything larger in a simple pin format, from the amounts of times I've wired something wrong with a larger relay I've just ended up thinking it's not worth the hassle!

So let me get this straight... If I take the relay route (which looks like is what I'll be taking), I'll have to build the following circuit, right (sorry for the crappy diagram)?



Also, I should be able to use power from a USB port, right?

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Originally posted by Adeptus
You can re-wire a VGA or parallel switchbox, a mechanical one like this.  It will provide a suitable switch as well as a housing.

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Originally posted by Mike
Also, I should be able to use power from a USB port, right?

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So, to sum up, I will need:

-A construction box to house my project
-6 female 3.5mm audio ports
-3 line-in cables
-3 DPTD relays
-Some way to draw power from USB (I cut an extension cord for this purpose)
-A switch
-Lots of wires

By the way, should I go with a solid state relay? Is there anything more I need to ask for the relay at the store (example: voltage), or asking for "3 DPTD relays" is enough?

Thanks

EDIT: I was reading this:

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Originally posted by http://www.geofex.com/Article_Folders/relays/relays_for_switching_audio_signa.htm
There are some other things you need to know. Those coils in the electromagnets  - they act like (and are!) inductors. When you set up current in them to make the relay switch positions, you are loading up an inductor with current. When you try to turn it off, the inductor responds by reversing its voltage to try to keep the current flowing. This happens as fast as you can cut the current off, so inductors can make very fast, sharp voltage spikes. Since inductance varies as the square of the number of turns on a coil, it usually happens that many turns of very thin wire on a higher-voltage (and hence, lower current) version of a relay will have much larger inductance than the same-physical-size relay in a lower voltage (hence, fewer turns of larger copper wire) version. The coil inductance directly slows down the build up and ramp down of current in the coil when you apply a voltage, so in general, higher voltage relays take longer to operate.

The fast, sharp voltage spike that comes from the relay coil reversing its voltage to try to keep the current flowing can kill your driver transistor. You have to protect the device from the voltage spike. This is usually done by placing a diode in parallel with the relay coil, but in a direction where the diode does not conduct when the relay coil is turned on. The diode only conducts when the relay coil reverses the voltage across it at turn-off. This clamps the voltage spike to only one diode drop more than the power supply voltage.

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In this case you're not driving the relay with a transistor, so the reverse diode isn't quite as important. It is important to make sure you're using a relay with the correct coil voltage.

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Originally posted by lizard.boy
It is important to make sure you're using a relay with the correct coil voltage.

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