Subdermal bone conduction headphones?

So, I've been thinking about the modifications I want, and a magnet in the finger doesn't appeal too much to me.  I have some ideas for magnets, but there is one idea that's is much more interesting and nove to mel: subdermal bone conduction headphones.  I've done a little thinking on it but so far everything is very theoretical.

So far it seems like my best bet would be to use some form of flexing piezoelectric element, of which I can harvest a simple one from a Radio Shack buzzer.  Then bioproof it, figure out a way to power it, and then supply it with signal.

But the problem is I want the connection point to be closer to my pocket, where I'm more likely to keep a music player than my skull.  That means in addition to some way to keep the buzzer bioproofed and attached to the skull, I need wiring of some sort.

So basically, I'm just wondering if anyone's done any work on something like this.  Has anyone dealt with anchoring stuff to the skeleton?  My layman knowledge suggests that something like one of those hammer-on wooden beam connectors for a skull, with small holes in the metal stickout prongs that the bone could grow through should be sufficient and not too difficult to make out of biocompatible metals.  But I'm not sure.  And I'm not sure how to get the signal down my body, from each ear.  I need to be able to carry a fair amount of power back and forth.

Any ideas or similar work?


  • As you said, you would need something piezoelectric to vibrate and it would need to be biologically compatible.

    Attachment and power would be problematic, as would would be finding the optimal location within the jaw or skull.

    As for wires, you could always use Bluetooth (the chip or some sort to receive and transmit) to communicate without wires, and the handheld device of your choice that would serve as a processor.

  • Interesting idea, since I always listen to music. The head phones(probably bluetooth) might be ok as a transdermal if the outer part is small enough. Power is a problem though,,, a wire going down the neck is a risky thing to do, but conductive ink seems to be a perfect option, here is the idea:

    I'm a tattoo artist and piercer, so this idea is awesome, will do some experiments...

  • Apparently those buzzers from Radio Shack work just fine, if you strip out the element.  A guy on Instructables built a basic bone conducting headphone with it. 

    I'm not a big fan of bluetooth.  It's great, but the modules take up quite a bit of power and space, both of which are going to be at a premium with a skull-mounted device.  You would end up having to run a power cable somehow anyways just to make everything run.

    As far as placement, I was thinking the lobe behind the ear.  Apparently some scuba diving equipment uses that spot.  Maybe up just a bit.

    That's a really cool circuit idea Ghost!  You going to give it a try?  I'm not a big fan of the transdermal idea, though.  From what I've heard those can get nasty, plus it adds something that can fail catastrophically more easily.  It shouldn't be too hard to use a pair of induction coils to transfer energy instead, though that still leaves the question of how to run the power.

    Any ideas for keeping the element next to the skull?  I'm specifically thinking of how to keep a non-biocompatible element in hard contact with it, rather than through sugru.
  • Worst thing about the wires is the difficulty of implanting them, big procedure, no chance in hell that I would be able to make that procedure on my self...

    Also I'm not very knowlidgeable on induction charging, will put my google-foo in use and do some research, will update with new design asap..

    Element next to the skull?= Silicone coating, thicker on the side faceing the skull?

  • Okay, so I'm going to keep investigating conductive inks, but at this point it just seems infeasible.  An alternate idea: conductive thread and a suturing needle.  Cut part of the way through the skin, suture through the rest and into the flesh.  The cut then heals over the thread.  That sound feasible?

    I think I'm pretty close to building a test unit.  Sometime next week I'll stop by Radio Shack, grab me a buzzer and hack it apart, then assemble it. and surround it in sugru.  I want to know whether I'm going to need a metal plate to place next to the skull or if something flexible will work.

    I think that conductive inks might still play a role in making connections.  Rather than use induction, we could just create a vertical line of conductive material in the skin.  Would that work?
  • BTW, sugru sucks. It lasts for about a year then gets soft and starts falling apart. If you don't want the implant to ever come out, use parylene C. If you want to be able to replace it, I would suggest teflon.
  • Hey, just had an idea relating to this...

    What would sound quality be like with one of those little radio shak buzzers? I know if I was going to have cans in my head I'd want something that would sound amazing!
    Context? I spent the afternoon comparing headphones and amps. At one point I had aboutt $12,000 worth of audio gear between my iPod and my ears... and it was nice.
  • Press the speaker to your jaw, or bite down HARD on it, to get some idea of sound transmission quality.
  • Which is tougher, parylene or teflon?  These won't be in a high impact area but I'm betting that there will be regular pressure.  And by replace, do you mean open up or take the implant out?

    Right now I'm hoping to only use those Radio Shack buzzers to test the feasibility of the design, not to implant.  Something tells me that they have terrible, terrible sound quality.  But it all depends on whether there is another element thin enough to fit between the skin on the skull.  Unfortunately there isn't room to cram $12,000 of sound equipment into my skull, at least not without major surgery.  Bet it was fun, though.  I'll do some experiments and post the results here.  I'm not too harsh about sound quality, so who knows, I might find the music listenable.
  • rdbrdb
    edited August 2012
    The primary difference between parylene and PTFE is that parylene bonds with the tissue around it, whereas PTFE is so slippery that tissue can't bond with it, the tissue will just grow around it.  That makes something coated with PTFE a lot easier to remove than parylene.

    EDIT: sorry, parylene has a low coefficient with friction also, its ability to bond with skin depends on how it's processed.
  • edited August 2012
    Hm, so in this case Parylene is probably more appropriate.  Not just because it would lock it in place better, but because it would keep it against the skull without needing some form of skull-anchored brace.  That sound legitimate?
  • tissue != bone. you.. may want to stay away from bones. having something with a hard shell press against a bone is not really comfortable.
    btw there are commercially available bone-transmitter based headsets for noisy environments. you don' really need a bone anchor for that. nor any implant at all.

    about coating, i think there was that one issue with parylene where the body can degrade it , creating tiny holes in the thin coating. depending on your base material that can be a serious problem.

    i estimate it would have rather high power demand. and probably a horrible response for low frequencies ;) still, worth a try without implanting it at first.
  • edited August 2012
    So it sounds like a PTFE coating is best after all, then.

    Yeah, my first step is to build a working model from things I can get pretty easy and see if the idea makes any sense at all.  I'm aware of those commercial models, but they work by applying a whole lot of pressure.  You're going to have to vibrate the bone regardless.  That was the point of the possible bone anchor: to keep the disk held tight enough to the skull that they act as one.  I assumed that the best sound (and the least power drain) would be achieved with an implant right next to the skull.  If not, that actually poses a problem, since the spot I was looking at is about has very little between the skin and skull.  Perhaps a softer coating would help ease the strain, but then I'm still worried about wear and tear from the vibrating.

    The point isn't necessarily just to have a headset for a noisy environment, but one that is completely invisible and mostly passive.  If properly designed, I could listen to music at any time including in bed without the sound ever leaking beyond my own skull.  I could listen to music without headphones signaling that I am cut off from the world.

    But yes, I'm expecting it will need a fair bit of power.  Hopefully a regular speaker jack will be enough, but if not, well, I'll figure it out from there.
  • For the record, for your purpose you may also want to try or consider this approach, which is significantly less invasive.

    If you're going for an implant, you may want to consider using an induction loop to transfer audio from your music player to your implant instead of using a transdermal connector (which is quite tricky).  It's quite easy to implement (matter of making a few coils) and you may not even need a battery in the implant itself depending on which mechanism you use for playing the audio.
  • Yeah, I think an induction loop would be better than a transdermal.  In all it seems like less of an ordeal.  By the way, you are evil for introducing me to the neurophone.  That will probably consume lots of my time in the future.
  • edited August 2012
    Knocked me together a quick bone conducting headphone:


    And it works!  Findings: doesn't need much pressure to work.  Pressed up against the skin, it transmits sound.  I don't have to press hard.  Bit down on, it transmits a bit louder, but again not much pressure is needed.

    It's not very loud with just headphone power.  I'll need to add a bit more oomph to it if I want this to work.

    Sound quality is quite flat, but only in an FM vs CD sense.  Even with a cheap piezo buzzer from Radio Shack it makes passable noise.

    I'm going to try a smaller buzzer next, but at least the project passes (my) initial sanity check.

    Edit: tried a smaller buzzer, and sound quality and volume goes down.  I need to get an amplifier to see if I can boost it to a usable level.
  • Today I saw this guy:
    and thought it would quite fit to this thread since he is going to have a "bone speaker" attached to his skull.
    Also he is using it as an input to be able to "see" color, so he's really using the brains plasticity.
  • You could get a magnetic anchor and surround it with a coil. Passing current through the coil may transfer vibrations powerful enough to hit the eardrums.

    Also, check out the Neurophone, which supposedly transmits sound through the nervous system from anywhere on the body. I haven't built one to be sure, but some guys on hackaday have.

    Zack Freedman [@ZackFreedman]
  • edited September 2012
    I've been working on something similar with one of these for a while now:  Pretty crystal clear on a tooth, otherwise, positioning takes some work.  Still transmits pretty damn well through silicone, but an amplifier over normal headphone levels starts to become necessary.
  • In medical tests we test bone conduction vs normal hearing via air by putting a vibrating tuning for against skull (top of skull and bone behind ears are two most common testing areas, though almost everywhere there bone is immediately under skin should work) and then when the sound fades enough to not be heard anymore, moving it next to ear to see if it still can be heard this way. In healthy person it should be heard (air conduction has on its way a mechanic amplifier made of eardrum and ear bones 'ossicles' - malleus, incus and stapes while bone conduction is unamplified).
    That method means that any kind of speaker or other vibrating object pressed against the bone could perform well in such use. But to conduct well it might indeed need to be pressed against the bone so that the sound doesn't dissipate in soft tissues.

    Indeed a dental prosthesis could be a very good spot to place such implant (it could house a mic too ;P ) if you can make it durable enough and convince a dentist to put it in your mouth (you don't want to do it yourself for sure), or any implant that could be attached to bone by screws or other method...
    The problem is - operating on bones, especially skull bones at home == bad idea. 'Enjoy your meningitis' to quote one person ;)

    The ways I can imagine as viable is somehow attaching a device to teeth (probably on the lateral, external face (so facing your cheek, not inside of mouth). It is a bit risky though - you need to attach it so well, so that it doesn't detach while you sleep and choke you. Plus you quite probably will damage your teeth unless you are very careful and use proper method for attaching...

    In the imperfect, grinding environment I imagine any speaker placed under skin where it's thin - as in little tissue between skin and bone (possibly behind ear for example, or under hair as close to ear as possible) to have it pressed against the bone quite well by the skin itself. It should work quite well and if you'd need to hear something really barely audible you could press the implant stronger against your bone from outside. Could be unpleasant though and placement would have to be in such a place where it won't hurt you for example when you sleep (hence behind ear could be a good idea too, especially if it's not very big)...

    Also keep in mind, that if it gets infected it can very easily mean huge problems even if it isn't screwed to the bone - infections can spread quite rapidly in this area, and there is quite little space where it won't damage anything important if not treated really quick. And you probably know what most surgeons will tell you when they have to yank the implant out and treat the infection (unless they're like me and would say 'wow, that's awesome, but you totally botched it') ;P
    And well, not everyone may want to have visible implants/scars (I for one can't, at least until I'd be able to make the living from implants, even tats on doctors can be frowned upon, much more such 'selfmutilations' ;P )...
  • It's amazing how many people seem to think that labeling something as "self-mutilation" constitutes an argument against it.

    Actually, tats are becoming more and more accepted; I know quite a few people who hold highly-ranked positions, with visible tattoos.  Of course, there will always be employers prejudiced against any form of body modification, but hopefully those people will end up becoming the minority.
  • Well, hopefully it'll become less and less of a problem in future, but up till now I haven't met a doctor who has a tat in a place that'd be visible from under their clothes unless they reveal it on purpose...
    It probably is frowned upon because of ciminal subcultures used tats extensively first and only later it all seeped into popular culture... But as tats get more and more common, additional piercings in places other than women ears get more and more common, probably the problem will subside...
    Especially when grinding will start seeping into the popculture... They might focus on us instead then though ;P

    P.S. Labeling something 'self-mutilation' is an argument against it, because it's a sign of psychic illness, but most of us are actually quite sane, so most wouldn't fit under the label of self mutilating ;P It's just abusing the label, not the label itself being wrong/not argument against something...
  • Right, but just labeling something doesn't constitute a valid argument.  It would have to be demonstrated that we have some psychological disease, and most people just throw it out there without even thinking about providing evidence of that.
  • I would add that even proving that someone has what is generally considered a mental illness doesn't say anything about the validity of his argument.
  • edited September 2012
    Wow, a lot of new information since I last posted.  I'm going to place an order for that transducer.  I also found some smaller ones, but I'm worried that they won't transmit sound through silicone.  At this point, I'm mostly waiting on funds to become available.  I think we have come up with enough that I should be able to build this thing, though I have yet to build ThomasEGI's connector (side note, have you tried it yet?).  I'm planning for behind the ear and a touch up and just using the skin to keep up pressure, which should also help make the scarring harder to spot.  It also lets my ear keep any pressure of the implant.

    Shaedlaer, in your hypothetical opinion, if one were to go about installing this, how would one minimize the risk of infection without relying on a trained surgical staff?  Unfortunately I know no dentists or surgeons crazy enough to help me with this.
  • Well, pretty much one would make as small incision as possible to place the implant inside without stretching the wound (so just a slight bit wider than the implant's cross-section), this way the wound will heal quicker. The cut should be straight made with a very sharp tool, so a scalpel (they're not THAT expensive) - all uneven ripped parts will have trouble healing quickly.
    And in general keep everything as sterile as possible - all tools sterile, the skin to be cut sterile, the implant sterile, sterile gloves...

    The implant shouldn't be covered by the stitch, but rather one would make a 'pocket' under the skin and insert the implant inside. That's because if the implant would be right under the wound and stitches it would press on the tissues, because that'd cause the wound to heal slower (or not to heal at all).

    With stitches it's also quite important so that they're not too loose nor too tight - the first will cause the wound to not heal fast enough and the latter will cause parts of the tissue to not get enough blood, which in turn may cause the skin around too tight stitch to necrotize/break apart.

    Then clean wound dressing, possibly changed daily.
    One should avoid wetting the area for as long as possible until it's healed, especially first 2-3 days until it's really well clotted and started healing.

    In general anything that makes the wound heal longer will make the risk of infection greater. Assuming that during the procedure the tools, and especially the implant were sterile of course.

    The smaller the interference with the organism, the better, so minimizing the size of implant, minimizing the cut, minimizing the healing time is the way to go. With increasing each of those the risk of infection will be higher.

    Proper surgical cutting and sewing techniques are probably a matter for at least a small book, which might be a good idea getting. Stitching probably should be trained first a bit on something like a piece of meat, especially with the skin, or on a banana skin...
    I know that when I was searching to learn myself I saw some pages and vids about such things, but I don't have any precise links now anymore...
  • For the record, when it comes to making incisions DIY, 5mm piercing needles actually work as well (I've even found that they work better).  Scalpels should work just fine though.
  • Thanks for the info.  I'm probably going to get a friend with some rudimentary medical skills to help me, if she'll let me, so hopefully I won't have to sew myself shut.  How would you recommend that I run the wire?  What I've heard is that basically you pinch the skin, make an incision on either side, then run the needle through.  Then repeat with another small incision a pinch away, repeating till you get to the destination.  At least, that's how I've heard they run those drainage pipes.  The problem is that the skin on the skull is really tight, and I'd be worried while running down the neck.
  • Okay, short update: got some transducers, soldered them up, and gave them a shot.  They work plenty well, though audio quality clearly wasn't a focus.  Pretty cool to play with though.  So, basically I'm wondering if anyone knows anyone who might know of better sounding transducers.

    Next I need to experiment with the cable.  I have everything necessary to make some flat coils and test the signal transmitted that way, so I'll do a short writeup on how I build that.  Should be simple enough and most people will know how to do it, but more technical information is always welcome (I'm guessing).
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