Many computers, 1 set of headphones. What are the options?

Question

Like many other super users I have many computers both at home and in the office. They are connected together with a KVM. What options exist to combine the audio from many systems so I only need a single set of speakers or headphones.

I want to be able to hear sounds from all the computers at the same time. I want to be playing music, video, or something entertaining on one computer while I am working on another. I want to hear the beeps and sound effects on the system I am working on while music or something is playing on another. So a simple switch really isn't want I want.

Currently I have an older mixer hooked up, but it takes up a huge amount of desk space. I am looking for alternatives.

To sum up, I am looking for:

• a device that will accept two to four stereo 3.5mm line-level audio sources and will merge the audio and provide 1 line level output.
• I don't need individual volume controls for each input, I can control that on the computers.
• I don't want to switch between the audio sources, I want audio from many sources at once.
• I would prefer a product I can buy, instead of something I have to build.
• I want something with a small form factor.

Answer 1

Here's a 4 channel stereo passive (unpowered) mixer, USD 50 at Amazon:

If you can deal with switching between sources, there's a $5 option, 4 input stereo passive selector:

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There's also the daisy-chain option. Since you'll need a bunch of 3.5mm-3.5mm stereo cables anyway, you could run them from one computer to the other and just plug your headphones into the last one.

This assumes you have a stereo line-in on your computers.