Bone Conduction

[olsenn]

Does anybody here have any knowledge/experience with bone conduction headphones? I tried some recently and even though I could hear music playing when I plugged my ears, I could still hear the music playing when I removed contact of the headphones from my head (just held close). Do they simply play the music loud enough that the sound vibrations get picked up anyways?

A similar question; if you've ever had a fire alarm go off, and you plugged your ears since it was loud... just to continue to hear the alarm, albeit attenuated, is this an example of bone conduction, or were your ears simply not 100% covered?

[qno]

You cannot attenuate the sound you are hearing 100% just by couvering your ears.
Sound will get to your ears bya your mouth and via  your scull.

Just nock on your head a few times.
When wearing sound proofing headphones open your mouth and you will notis the sound changes.

[djococaud]

99% Of people who read this post has knocked their head !!! 

[kg4arn]

Does anybody here have any knowledge/experience with bone conduction headphones? I tried some recently and even though I could hear music playing when I plugged my ears, I could still hear the music playing when I removed contact of the headphones from my head (just held close). Do they simply play the music loud enough that the sound vibrations get picked up anyways?

A similar question; if you've ever had a fire alarm go off, and you plugged your ears since it was loud... just to continue to hear the alarm, albeit attenuated, is this an example of bone conduction, or were your ears simply not 100% covered?

I don't have any such headphones but I use tuning fork tests in my medical practice to assess for middle ear effusions daily.  This is how the system works.

Sound transmitted through the air vibrates the very sensitive tympanic membrane and this vibration is coupled to the cochlea via the tiny bones (ossicles) in the middle ear.  The cochlea is a transducer that changes the mechanical vibrations to electrical signals which are then transmitted to the appropriate brain centers via the vestibulocochlear nerve.  This is called air conduction.

Since the transducer, the cochlea, is embedded in the skull, it is also stimulated by any vibration in the skull.  This is called bone conduction.

Air conduction is much more sensitive than bone conduction.  Consequently, under normal conditions any sounds transmitted through the air overwhelm and "drown out" bone conducted sounds.  When you plug your ears you attenuate the air conducted sound and any bone conduction becomes easier to appreciate. 

If your tympanum (ear drum) were scarred or missing, or the ear ossicles were frozen, or there was fluid in the middle ear preventing the tympanum from moving in response to sound in the air, then you would still be able to "hear" bone conducted sounds or vibrations in the skull (because the cochlea and the nerve are still working).  If you transmit the vibrations efficiently to the skull, like pressing a tuning fork firmly on the skull at the base of the ear, then the sound power can be very low and still perceived   The trick is to drown out the air transmitted sound energy that usually overpowers the bone conduction system.

[alex.forencich]

Do they simply play the music loud enough that the sound vibrations get picked up anyways?

It's more an issue of coupling than an issue of volume.  The headphones don't really play it 'loud', they just play it with transducers that are able to transfer the sound efficiently into the bone.  They aren't designed to work in air, so you can still hear something, but it won't be very loud as the transducers will not be moving very much air.