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Re: underwater listening - bone-conduction

Hi Mike. Thanks for your answers. Yeah, I thought I would get a bit more o replies, because I?m sure that are guys out there (or not) doing research into this, however besides you I got one more reply by Jan Schnupp (among others that before had emailed me), which was quite helpful.

My source for assuming the fact that our perception of underwater sound is realized through bone conduction is John Maurer?s paper http://ccrma-www.stanford.edu/%7Eblackrse/h2o.html How in turned is based on Michel Redolfi thoughts, which seem not to have any references.

I?m not sure that our perception of sound underwater is done entirely by bone conduction, at least perceptually, it gives the impression that most of the hearing is done through that mechanism. What seems to makes sense from the two factors that you refered. I had already though of these fluid to air to fluid translations might stop or reduce the normal (airborne) process. However it never occurred to me that bone transmission would be higher, due to the reduction of impedance mismatch between skull and the surrounding environment.
It seems to make sense, just hope I can sustain it with refrences in my essay, because right now just seems in bits and pieces of separate information which I have to relate and nothing very solid. Hopefully your references are going to help, unfortunately is a bit difficult to get access to JASA (only found it in the British Library), but I?ll manage to do it.

I?ll be delighted to tell you know any interesting results (I think I?m getting somewhere, quite interesting and unexplored, is scary and fascinating). Many thank.

All the best.


From: Mike Ravicz <Mike_Ravicz@xxxxxxxxxxxxxxxx>
To: Andre Castro <andre_castro83@xxxxxxxxxxx>
CC: AUDITORY@xxxxxxxxxxxxxxx
Subject: Re: underwater listening - bone-conduction
Date: Wed, 5 Apr 2006 11:11:11 -0400

Hello Andre,

Sorry to see that no one has answered your inquiry yet... There are other folks out there who will probably have more to say on this, but here's some info:

One thing that has been fascinating me is the fact that our perception of underwater sound is realized through bone conduction.

I don't know that for sure, but it seems plausible - what are your sources for this?

For what I could gather by relating different sources is that when inside water the impedance matching/communication from the ear drum (air) to the inner ear (fluid) through the ossicles is stopped. As a result our air conducted listening is also stopped.

The middle ear has apparently evolved to reduce the impedance mismatch between the air in the ear canal and the liquid-filled inner ear. When the head is immersed, there's another water-air interface in the ear canal (I think that the ear canal doesn't fill with water, so there's a bubble near the eardrum), so there's another impedance mismatch there without any mechanism to compensate for it, and sound transmission through the ear canal is reduced.

On the other hand, the impedance mismatch between the surface of the skull and the surrounding fluid (air or water) is reduced when the head is immersed, since water has a much higher specific impedance than air. In air, sound transmission through the head is 40-60 dB lower than through the ear canal; in water, sound transmission through the head is likely to be considerably higher and may be higher than through the ear canal.

Another factor is that, at least at low frequencies, sound perceived by "bone conduction" is conducted through the head to the ear canal and (apparently) causes the ear canal wall to vibrate, setting up a sound signal in the ear canal near the eardrum that is conducted to the cochlea in the usual fashion. At higher frequencies, other mechanisms seem to be dominant. (See Shyam Khanna's work for this - ref. below.)

And of course sound can be conducted to the head through the body. A paper we put out a few years ago suggests that the body-conduction mechanism is less efficient than conduction through the head, but not by a lot. The old "Bone-Fone" loudspeakers worked this way - you'd wear them draped over your shoulders. (I never tried them out though.)

David Mountain and Darlene Ketten have done a lot of work, especially recently, on hearing and sound conduction in marine mammals - you might look up some of their recent papers (and maybe this post will spur them to weigh in).

And it raises the question: How well do people with a conductive hearing loss hear underwater? Is their hearing underwater comparable to that of normal-hearing people?

Please let us know what you find out.
	- Mike Ravicz

Khanna et al., "Mechanical parameters of hearing by bone conduction," J. Acoust. Soc. Am. 60: 139-154 (1976).
Ravicz et al., "Isolating the auditory system from acoustic noise...," J. Acoust. Soc. Am. 109: 216-231 (2001) - has references to a lot of the early work.

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