Connecting two PCs to one pair of speakers

[malloc]

This is probably very trivial, but is it possible to connect two PCs to one pair of speakers? By that I mean using 3.5 mm TRS output from two PCs, connect both of those outputs to an Y split, take the other end of that Y split and connect to a pair of speakers.

What will happen if I do this?
Can one sound card get damaged when the other starts sending audio, since the other card is connected directly to it?
Assuming it works at all and doesn't hurt either card, will it create additional noise or other artifacts?

Is there a better or "right" way to do this? I know some KVM switchboxes support 3.5 mm audio, but I would rather not have to buy one.

 

[misterT]

https://www.epanorama.net/circuits/linesum.html

 

[KeepItSimpleStupid]

I do think we have to be careful here with terminology. We are probably talkibg about "powered speakers".

And there could be two options:

1. Is to sum the signals passively or actively. Which is what happens when you try to watch two videos at the same time on a single PC

2. Detect the audio and switch based on that with one source being primary.

Commercial products - they probably exist.

 

[ChrisP58]

Do you intend to have both sources active at the same time? Or only one at a time?

If both, then the proper way to do this is with an audio mixer. If only one at a time, then with a switch to select which source the speaker should 'listen' to. The switch can be either manual or automatic.

The output impedance of a sound card is very low, typically less than an ohm. But they expect to drive a relatively high impedance load. Either a headset with a typical impedance of ~32 ohms, or an amplified speaker that's probably >10K ohms. Tying two low impedance outputs directly together probably won't damage them, but the one will attenuate the output signal of the other.

 

[picbits]

The way I do it in my workshop is to connect the speakers to one PC then use the line out of the other PC to feed the line in of the PC with the connected speakers.

Only works if both PCs are on but it works well enough.

 

[unclejed613]

if the outputs are driven by op amps on the sound cart, doing a "wired-or" with two sound cards might not work well. you would be better off using a 2 input mixer, so a)the output stages of the sound cards don't interact, and b) you can control the levels independently. the only question that comes to mind, is how will you know which computer the audio is coming from?

 

[Ian Rogers]

The way I do it in my workshop is to connect the speakers to one PC then use the line out of the other PC to feed the line in of the PC with the connected speakers.

Only works if both PCs are on but it works well enough.

Yep!! That's how I do it aswell.... I have a 4:1 KVM and one set of speakers.. all the sound cards are linked..

 

[malloc]

Thank you all for the replies. To answer one question:

Do you intend to have both sources active at the same time? Or only one at a time?

Yes, I intend to have both sources active at the same time, it would be nice to have that option, e.g. hearing a message notification on one computer while doing something else on the other -- both using the audio output.

However, before I start cutting up 3.5 mm TRS cables, I'm wondering if this is really a good idea? I have some bad experience with cables like that, sometimes they come with one of the leads (ground?) wrapped around the other, almost like a coaxial cable of sorts, and they are really a pain to work with.

 

[KeepItSimpleStupid]

Make connections in a little box using jacks.

With this type of coax wiring, you don't un-braid the coax. You open it up and "pull" the center conductors though a made hole in the shield.

 

[malloc]

Make connections in a little box using jacks.

With this type of coax wiring, you don't un-braid the coax. You open it up and "pull" the center conductors though a made hole in the shield.

Forgive my lack of knowledge about this. I looked at this again, and I have no idea what you mean, could you provide a picture, description or video?

 

[KeepItSimpleStupid]

By jack, I mean something like this: **broken link removed**

It's a 1/8 mineature phone jack.

By project box, I mean somehting like: **broken link removed**

You can also get feet for them, stick on or screw.

The 2nd post here: **broken link removed** from AFLG describes the process of separating a coax cable into two wires.

I can't find a pic or a video and don;t have time to do one. It's not too bad to do on an cheap audio cable.


Stripping a cable to use the ends should look something like thiis: https://i1.wp.com/make-images.s3.amazonaws.com/ToE3bsWVW3FeDujH.jpg?resize=620,465

The inner wire is brought through a made hole in the braid near the end of the outer jacket. If you've never done it, it is moderately difficult. I could not really find anything on the web.

 

[finfertech]

it works theoretically, I don't whether you can make it

 

[Menticol]

Working with these cables is not terribly difficult, here are some tips

https://cocodrilabs.wordpress.com/2012/04/12/headphone-plug-repair/

If you are willing to try Picbits and Ian's approach you could even reuse a pair of damaged headphones, removing the speakers and soldering the cables together