Windows 7 box, Klipsch earbud headphones, 10 ft extension cables bought from Monoprice.com. I bought 10 of them and have tested three so far, each has the same problem. When I plug the headphones in without the extension the sound is fine. I have a multimeter. What could be the issue here, and how do I test it?
Update: You're right there is no single cable for center channel, but there is a way that the two cables encode for the center. audiocheck.net/audiotests_stereo.php using these test files, the right and left sound like the center, and the center is barely audible. I'm playing with the cable at the moment, it seems when I plug the headphones into the female portion of the extension, only slightly out and tilted, the channels test perfectly. I wish I had the ability to easily bisect the metal so I could more thoroughly test it.
Update 2: Okay I just noticed that there are three insulating ring on the male end of the headphone wire, and only two on the male end of the extension wire. That spacer must be to create a different connection for the mic on the headphones. I wonder if there are adapters that will accept a three channel 3.5mm cord but not continue the mic channel in the interest of fitting an extension that only observes the stereo channels.
Solution: I found my solution: http://www.amazon.com/StarTech-com-MUHSMF2M-Position-Headset-Extension/dp/B008DWGLLO/ref=pd_sim_sbs_e_2
I hope this helps someone as clueless as I was >.<