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Phase cancellation problem
Phase cancellation problem
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Old 16th June 2010, 02:55 AM   #1
Fonic is offline Fonic  Canada
diyAudio Member
Join Date: Jun 2009
Question Phase cancellation problem

I've got some Sennheiser MX51 earbuds that have some strange issues (I know these are hardly hi-fi, but I'm a broke student and this is about as close as it gets for me.)

At one point, the jack quit working. I tried fixing it myself - I bought a 90-degree jack at a local electronics store and soldered it on. After this I was getting center cancellation when I using it on my iPod or my computer, but not when I tried miscellaneous other headphone things. I eventually figured out that the jack was slightly longer than normal, so in some plugs the ground connection must be connecting to the ring instead of the sleeve.

I then tried a different jack that, as far I can tell, is a normal size. It worked great for about 2 weeks, then it started center-cancelling again. If I pull the jack out slightly, I get only one channel coming in-phase out of both sides. I figured it had to be a wiring problem since it worked fine for 2 weeks before crapping out. But I just took a look at them now, and from what I can tell, the wiring is fine. This time, it only has problems on the iPod. The weirdest part is I measured the headphones' resistances and got around 70 ohms from right to ground and left to ground, and about 140 ohms between right and left, which seems to make sense to me. I also tried this while connected to the iPod (since the iPod jack itself seems to be what is shorting it) and got approximately the same readings - which seems to indicate nothing is shorting. And it's not a busted iPod jack; I tried a different pair of headphones (which, as far as I can tell from eyeballing it, have the same size of jack) and it worked fine.

Anybody have any idea what would cause this, or more importantly how to fix it? I don't really want to just buy new headphones because I don't want ones any cheaper than this, but I'm also a job-less student and so I don't really want to buy ones better than this either.
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Old 16th June 2010, 03:42 AM   #2
Don Hills is offline Don Hills  New Zealand
diyAudio Member
Join Date: May 2009
Location: New Zealand
"Centre cancellation" implies that the ground connection (sleeve) of the headphone jack isn't making contact with the ground connection in the iPod socket.

- Bad match between the jack and the socket. Fix: Change the jack or the iPod.

- Poor quality jack. The connections between the solder tabs and the jack components are often only riveted, and the heat of soldering loosens the rivet. Fix: Change the jack.

- Break in the shield wire in the cable, near the jack. This is the usual cause of the original jack failure. Fix: Cut a couple of inches off the end of the cable and re-solder.
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