I made a guide on how I made an audio Y adapter with 3 stereo jacks.  They don't seem to sell something like this anywhere, so I had to make my own.  This is good if you need to listen to 2 sources with your headphones or something.

Let's begin.  The goal is to have a wire with 3 female headphone jacks & no plugs.  I used 2 headphone splitters for this.

First, I cut the 2 jacks off of one splitter, & then I cut one jack off of the 2nd splitter.  The rest of the 2nd splitter won't be needed, but it should still work as a small extension if I decide to use it for something.  For these Belkin splitters, they used 2 wires for Left & Right, & they used the shielding for Ground.

I decided to test just to make sure all wires are matching.  They do indeed match.  The way headphones are wired is like this: on the plug, the Tip is Left, the Ring directly underneath it is Right, & the Sleeve, or the bottom part, is Ground.  If you look inside the jack, you can see the 2 prongs that will contact the Tip & Ring for Left & Right, & the rest of the metal that you can see sticking out of the top is Ground.  By sticking a probe into the jack & touching the bottom contact that contacts the Tip of the plug, I checked for continuity, & can see that this runs on the red wire.  The next contact, for the Ring, runs on the white wire.  The gold strands are soldered to the Sleeve, & are used for the Ground.

After the soldering is done, you should use heat shrink to cover up the exposed wires & protect them from touching anything else.  However, you have to think ahead & put heat shrink on the wires BEFORE you do any soldering, because once you solder the wires together, you can't take them apart unless you cut them.  It's easy to forget to do this.  So before anything, be sure to put a big piece of heat shrink on the wires that will cover the whole assembly.  I put a 2nd small piece of heat shrink on the single wire just in case I needed more, but in the end, I didn't need it after all.

Since these wires are so small, working with them can be a little tricky.  First, I twisted the 2 red wires together on one side.  Then, I put some heat shrink on the other red wire, & I intertwined & twisted the 3rd red wire with the first 2 wires.  I put a little soldering flux on the wires (I use Chip Quik SMD291), & then I touch the soldering tip underneath the wires & melt solder on from the top of them.  They are very small, so this wasn't too hard to do.  Then, slide the heat shrink over, heat it up so it shrinks, & this is the end result.  Left is now complete.

Now, I do the same for the white wires.  I put some heat shrink on first.  However, now that the red wires are holding both sides together, I can't twist all 3 of them together.  That's OK.  As long as the wires are pushed together & the strands are intertwined, they can still be soldered together quite well.  Just make sure the strands are intertwined & squeezed together nice & tight, & try not to move them while soldering.  This was a bit tricky, as I had to brace them against something, hold them with one hand, & solder them from underneath in mid-air with the other hand.  Since they're so small, you don't really have to apply force with the soldering iron, so that helps.  Heat shrink, & now the Right side is done.

Now for the Ground.  When I started, I didn't quite realize that I would need more length, as the wires on both sides weren't quite overlapping too much.  I probably should have cut the red & white wires shorter on both sides so that the ground wires would overlap more.  I just kept on going anyway.  I intertwined the strands by pushing them together & squeezing them, then soldered them together.  It worked quite well.

That completes all 3.  Now, just slide the heat shrink over everything, heat it up to shrink it, and this is the final result.

It's not very pretty, but the goal has been achieved.  I really wish they would sell something like this.  Oh well.  Time to test!!!

My 2 sources with an extension wire for each...

And success!!!  I can hear both sources perfectly & clearly at the same time.  On each one of them, Left goes to Left, & Right goes to Right, just as it should.  This job is finished, & is a total success!!!