A while ago I liberated these headphones from the front seats of a Delta Flight. I wanted to have some over the ear headphones, and they were being left behind because they were the complimentary headphones and had a weird headphone jack (2x 3.5 mm prongs)
Step 1: Choosing an Approach
The first thing that I did was take the end of the cord and cut it odd to see what the pinout was like because there was no pinout I could find online. I figured that there were two options -- the first one was to solder a new tip onto the current cord -- the other option was to install an entirely new cord instead and solder it into the PCB on the headphones. Eventually, I decided to do with the second option because it looked cleaner and didn't look like it would hold very well.
Opening up the headphones, there were 6 inputs and 8 outputs -- the six inputs were SR, SL and S- and ML, MR and M-. The outputs were SR+, SR-, SL+, SL-, MR+, MR-, ML+ and ML-. The S looks like it stands for speaker, and the M stands for microphone. Interestingly enough, it looks like in order to make the headphones sound canceling they routed the microphone signal back into the media center that the headphones plug into where the signal processing is done. Then the signal is inverted and added back into the speakers. This explains why the headphones have 2 3.5 mm prongs -- the standard wouldn't accommodate enough separate signals for Left audio, right audio, and right microphone and left microphone.
I decided that I didn't need the sound canceling functionality, so I desoldered all of the wires on the input side and replaced it with an AUX cord that I stripped one end off of.
Step 3: Finishing Touches
Finally, I added a bit of hot glue to the hole that the cord comes through because I didn't want to have anything yanked out or broken too badly. All in all, it was fun to do this project, and I got to learn a little bit about the design considerations behind making these. One thing that I'd like to change is to get a little extender so I have a bit more range, as now the cord is only about 3 feet long or so. =They're not the greatest headphones, but for 2 dollars in parts, I can't complain.