I need someone to explain this to me.

Repairing Bose Active Noise Cancelling Headphones

QC15 Disassembled

[Mansour] was disappointed to find out that his Bose QC15 headphones had a dead right channel. These headphones have active noise cancelling, which uses a microphone to capture ambient noise and digital signal processing to insert an out of phase signal. Since they’re quite expensive, [Mansour] was determined to resurrect them.

First, he determined that the right speaker had died, so he found a replacement on eBay. These were designed for a different set of headphones, but matched the impedance of the original Bose part. After replacing the driver, it seemed that the repair was a failure. The sound cancelling wasn’t working, and a the playback was high-pitched. As a last attempt, he potted the speaker with glue, to match the original construction. Much to his surprise, this worked.

The problem was that the new driver didn’t have sufficient sound isolation from the microphone, which is meant to pick up passive noise. This feedback likely caused issues with the noise cancelling DSP. A little glue meant a $20 fix for a $400 pair of headphones.

Comments

  1. hojo says:

    not to nitpick, but I kind of doubt those use a DSP. Probably just an inverting amp. All those caps and inductors suggest analog signal processing to me. I could be wrong…

    • SparkyGSX says:

      I could be just as wrong, but those capacitors and inductors could be parts of two (or more) switchmode power supplies, to create a symmetrical power supply from an asymmetrical supply like a battery, and possibly a separate supply for the digital circuit.

      I’d think it would be fairly difficult to suppress the local feedback from the speaker back to the microphone, and to provide just the right amount of power and phase shift to cancel external noise, over a large frequency spectrum, with just analog processing. Even with a decent DSP, it doesn’t exactly seem trivial to me.

      • fiveseven says:

        Well, presumably that’s why they cost so much. I have a pair of QC3s and after 5 years of fair use the fine plastic parts just crumbled and the pads skinned horribly, Still usable, though. Have had some problems with feedback and my phone not recognizing them probably because they present a higher-impedance load than passive headphones. So I’m thinking about modding them so I can bypass the fancy active electronics when needed.

        • Stoneshop says:

          You could build an adapter cable with a 3.5mm jack and socket connected straight through, with 33 ohm resistors between the signals and ground. That should provide the load your phone wants to see.

        • Erik says:

          You can sew the earpiece covers on some models… QC2 perhaps? Not sure what model I have. Anyway, a few pictures of the process: http://people.renci.org/~escott/bose_headphone_repair/index.html . I’ve had to sew pretty much every inch of mine back together. And of course, the usual failure mode is that the plastic fails where the headband comes into the top of the cans. All in all, a pretty junky product for the (outrageous) price. Sure, they were a gift, but…

          • Chris says:

            I just replaced my worn out earpiece covers for about $10 (ebay) and 5 minutes (following a Youtube instruction).

            Intermittent cutting out of the right side of my QC15s brought me here, I have to tap it to get it to work.

      • juno says:

        First link, caption under that photo:

        “All the IC goodies are on the reverse side.”

  2. ERROR_user_unknown says:

    could you not just use the inverse of the input?? a hight speed not gate ?? why shift phase ?? I have little electrical engineering experience so I’m probably overlooking some obvious reason that would fail.

    • Greenaum says:

      Shifting the phase 180 degrees is almost exactly the same as inverting the signal.

    • Stoneshop says:

      The ‘not gate’ you refer to is digital, but you’re dealing with analog signals. Also, you want to cancel out the ambient noise, i.e. what’s picked up by the microphone somewhere in the headphone shell. With that microphone signal the signal processor performs some trickery so that the result is a signal that is roughly the inverse of the amount of ambient noise that would pass through the headphones to reach your ears.

  3. robomaniac says:

    I would have contact BOSE customer service first.
    Then fix it myself if that does not work.

  4. bothersaidpooh says:

    Nice, its amazing how much useful stuff gets needlessky trashed these days because it needs a 2 dollar part.
    I acquired some nice wireless headphones a while back because it had the “special” AAA batteries with conductive collar a third of the way along whose absence prevented the headphones from charging. Fixed:-)

  5. Steve says:

    As something between trashing it and fixing it, Bose will give you a new pair of QC15 headphones for $100 plus return of the old ones, at any time.

  6. Whatnot says:

    You know, if you are going to sell headphones for 400 bucks, you’d better make replacement parts available I say. It’s basic stuff.

  7. IFE Engineer says:

    Hack-a-Day-ers,

    I’m an engineer for a company that provides In-Flight Entertainment systems to commercial airlines. The full-up system – servers, video displays, handset controllers, audio jacks, everything but the headphones because those are throwaway. Part of our system is an active noise-cancelling module. It works at least as well with $3 Chinese headsets as the Bose headphones on their own. It is all analog. No need to add DSPs other than to make it appear that the headphones are “worth” the $400 price tag.

    • Carlos says:

      I guess designing specifically for airplane noise can boost the performance of the system, but I find it hard to belive that a $3 headset can be very much effective in active noise cancelling. Would you be able to share any details about this In-Flight systems… like what is the perceived noise attenuatinon for each frequency range, where is the power supply located, MICs, etc.

  8. Martin says:

    Thanks for the info. I used the same technique to repair US Army Bose Triport Tactical (also with noise cancelling):
    http://www.martinmelchior.be/2014/01/repairing-bose-triport-tactical.html

  9. Annie Johnson says:

    Hi there, I wonder if anyone can help me. I am repairing a pair of this headphone where the negative terminal in the battery compartment was broken off so I wanted to know if someone knows where the wire from negative terminal enters the main earpiece unit. I would be grateful for any description or a close-up picture showing the wire going in from negative battery terminal.
    Kind regards
    Annie

    • Mansour says:

      In the photo on this page, look at the series of colored wires that are soldered on the right side of the board. The solder blob on the top right of number “2″ is the battery’s negative.

  10. KK says:

    Hi there,

    I was recently travelling and noticed, what appeared to be, my battery had exploded within my headphones. I tried to clean it out first with a q-tip and then a q-tip with some rubbing alcohol on it, but when I insert the AAA battery – my headphones no longer work :(

    Does anyone know what I can do to troubleshoot this or maybe even replace that whole unit? Or will I have to replace my headphones… :(

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