Here we have the base audio amp and speakers from the bottom of an old Dell CRT. We're going to add an additional input to this so that we can push through sound from our MCU projects and other things that a stereo jack is too cumbersome for.
You have to remove the two back feet to access the last two screws and get the cover off.
Step 2: Soldering
Here you see the soldering job. Two tips: I marked the three wires with dashes of marker (not visible) to make certain I knew which was which; the other tip is to just strip away the top layer of plastic with the blade of a regular screwdriver. Then, you just solder the wires on, adding a little extra solder to the joints. You might want to tape the wire down, as I did, just to get it out of the way when you put the lid back on.
Step 3: Routing
Those "sound tubes" that come out of the back are actually good for something! In this case, I routed the wire right through this one.
Step 4: Reassembly
Be careful to keep the wire out of the way, and put the screws and feet back in.
Step 5: Fin
There you have it! A simple modification that allows a great deal more flexibility for sound sourcing! Have fun!