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Re: mechanical cochlear model

Dana is pointing to a demonstration in which a closed tube displays
resonance, whereas Christian would like to constuct a chamber in which
traveling waves are generated.

The pertinent question, of course, is: on which principle does the real
cochlea operate?

I have written a paper that compares traveling waves and resonance in the
cochlea, and it is available at


I believe that resonance is the preferred principle because it is more
sensitive: it allows energy to build up over many cycles. The
Exploratorium's demo giving a startling example of what can happen.

The problem with the traveling wave is that it is relatively inefficient.
It is hard to transfer acoustic energy from the fluid to the partition. In
the physical models I have seen (including Békésy's), the model is
compromised by having fluid in the bottom half and air in the top - this
is sort of cheating in that it is not the situation in the real cochlea,
which is filled totally with liquid. Chris, I challenge you to produce a
traveling wave model with fluid in both upper and lower halves!


Andrew Bell
Research School of Biology
Australian National University
Canberra, ACT 0200

On Wed, March 3, 2010 4:00 am, Dana Massie wrote:
> Look at the marvelous exhibit from the San Francisco Exploratorium:
> Visible Effects of The Invisible:
> http://exs.exploratorium.edu/exhibits/visible-effects-of-the-invisible/
> This is the most vivid example I have seen of standing waves in a tube. I
>  wonder how differently this tube would behave if it were conical.
> Dana Massie
> From the web site:
> Visible Effects of the Invisible graphically demonstrates resonant
> frequencies. A horizontal, clear glass tube is partially with clear fluid.
>  Sound generated by a speaker housed at one end of the tube causes the
> air in the tube to vibrate and geysers appear in the fluid where the
> motion of air is greatest. The geysers are generated at various sections
> of the tube by the adjusting the resonant frequency of the speaker which
> causes pressure differentials.
> On 3/2/10 5:41 AM, "Christian Kaernbach" <auditorylist@xxxxxxxxxxxx>
> wrote:
>> Hi everybody,
>> I ponder whether I should have our workshop build a mechanical cochlear
>>  model, filled with water, made from acrylic glass, in a simple
>> box-like arrangement (no coil, rectangular cross section), with oval and
>> round windows covered with latex foil (such as the middle division
>> screen, i.e. the "basilar membrane") and some crank lever and maybe a
>> gear transmission that would allow to enter mechanical waves at
>> different frequencies. I would use it in the lecture room to illustrate
>> the Békésy's travelling wave model. (I realize that he had build such a
>> model himself, which was not meant for class room use as I understood
>> it.)
>> Is there anybody out there who has / knows such a model and could give
>> advice as to dimensions and material?
>> Best,
>> Chris
>> ------
>> Christian Kaernbach
>> Allgemeine Psychologie
>> Institut für Psychologie
>> Christian-Albrechts-Universität zu Kiel
>> Olshausenstr. 62
>> D-24098 Kiel
>> Germany
>> www.kaernbach.de
> --
> Dana Massie
> Director of DSP Architecture
> Audience, Inc.
> +1 (831) 295-0079 mobile
> dmassie@xxxxxxxxxxxx