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I am building an installation with two screens and two computers that will not run sound simultaneously. Is there a standard component I can buy to combine two minijacks into one, or can I just solder this myself?

Are there any risks involved?

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migrated from Jan 15 '13 at 18:22

This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.

This really should not have been migrated from EE stack exchange - there it might have had meaningful answers based on typical circuit topologies, here it will receive mostly speculation and anecdotal advice. Please consider sending it back to EE stack exchange, where proper answers such as resistive combiners can be discussed. – Chris Stratton Jan 15 '13 at 18:59
@ChrisStratton It is asking for a purchasable unit for consumer electronics, not design and the only answer here is one that is from EE.SE, not one an Super User user wrote. meta.SU or meta.EE is the place to discuss this. – Kortuk Jan 15 '13 at 19:24
@Kortuk - factually untrue! The poster explicitly mentions willingness to solder something together, hence there's an openness to the design of a proper mixer circuit. Dumping the question to superuser where it is limited to moderately unsuitable off-the-shelf widgets does a real dis-service. – Chris Stratton Jan 15 '13 at 19:26
@ChrisStratton they offer to solder, never a device, ask them though. They are specifically looking for an off the shelf and have 0 questions about design. You could post an answer on how to put together a mixer here, but I have a feeling someone who wants a solution or a little soldering means, "Can I just solder the cables together?" – Kortuk Jan 15 '13 at 19:27
I was asking about both. I can solder, and I can solder audio cables, but I don't understand what the impact/result/risk/hazards are, which is why I asked in electronics. If soldering doesn't do the trick, there's probably a more advanced/invasive solution I would like to know about. – joon Jan 16 '13 at 2:53

If you're not outputting audio simultaneously from the laptops, you can safely use a splitter as a combiner:

3.5mm stereo splitter

Such a splitter is less than $1 at Monoprice.

If you do happen to output audio from both laptops simultaneously, you will potentially be overdriving the input on the amplifier. If the speakers/amp has protection built in, you'll probably just get clipping. If not, you may damage the preamp.

You can make one of these yourself using 3.5mm plugs and jacks, but for the price, it's not worth the trouble.

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I knew these existed, but hadn't considered using this in the opposite direction. What's your guess on computers having said protection? – joon Jan 15 '13 at 18:19
A laptop audio output shouldn't have any problem with there being audio from another laptop present on the line, especially if it's off. – JYelton Jan 15 '13 at 18:21
This is a relatively poor answer, with a lot of assumption as to how connected components would behave. I'd be more worried about the output stages tied together than overdriving the input. – Chris Stratton Jan 15 '13 at 19:00
can you provide more info on this, or point me in the right direction? I can't find any google results, which seems weird as I can't believe I'm the first person who wants to try this. Maybe I'm not using the right search keywords – joon Jan 15 '13 at 19:16
@Kortuk Move the question back to the site where such an answer would belong, and we can make some progress. – Chris Stratton Jan 15 '13 at 19:29

There are two ways to approach this question. I am assuming that the output is going to some sort of amplifier or an amplified speaker. An answer that will work for all situations, but cost some money, is to buy stereo plug to RCA cables and plug them into a mixer. Then plug the mixer output to the amplifier. However, if the output device is an amplified speaker, it would be cheaper to buy a second amplified speaker.

Another solution makes an assumption about the hardware. One can buy a stereo plug to stereo plug cord. That cord can be plugged from the output of one computer and into the line in of the other. The other computer may then play a mix of its own sound and the other computer's sound.

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I‘m assuming that only one computer will be on at a time, and one set of speakers with a small built-in amp. You can use a splitter as a combiner. Also stereo shouldnt be a problem either. To repeat previous cautions - dont over drive your speakers. :-)

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