[FRIAM] what complexity science says ...

[David Eric Smith]

I wonder a bit about the image of waves reflecting etc. 

Speed of sound in water is (say) 1500 m/s
Upper range of hearing for most young people is about 20kHz
100 cm / m

So the shortest wavelength one would get in a fluid in the skull should be about 
100 *1500 / 20000 = 7.5  (cm)

I read somewhere that the length of the cochlea unrolled is about 3cm.  Double it for a round trip.

So the extreme upper range of what most young people can hear just fits one wavelength long-wise in that fluid, assuming its wrap around the membrane makes a waveguide (probably not a great assumption).

I assume that means that for most of the range of sounds people hear, the fluid motion is —not “laminar”, that isn’t the right word, but — but effectively infinite wavelength.  If that is not very wrong, then much of whatever motion there should be should come from elastic response of the enclosing vessel, between pressure sources input on one side, and an essentially ambient pressure reference on the other.  So almost as if there is a long reed-like drumhead between two long cylindrical fluid volumes, one made to oscillate in pressure relative to the other.  Where there is strong response should I guess be governed by the shape and elasticity of the reed and some kind of incompressible flow condition in the two fluid volumes.

I guess all this has been modeled to death, but I never learned any of it.

Eric


> On Feb 9, 2021, at 5:47 PM, <thompnickson2 at gmail.com> <thompnickson2 at gmail.com> wrote:
> 
> Steve,
>  
> The cochlea is a small piece of meat, unlike the boney snail it is enclosed in.  It is moved by the relative densities of the fluid on both sides including back waves, arising from the motions of the lower window, and also motions carried to it via direct boney conduction from the outside world.   I am still wondering about the fluid dynamics of spirals.  I imagine that most of the deceleration is happening at bone side, rather than in the middle and that the reflect wave from the walls of the spiral keeps meeting the direct wave from the upper window. When you add the fact that the diameter of the  channel is increasing and that there is some reflection back from the lower window, there must be some important transformations of the signal that would make tonotopic representation seem unlikely. 
>  
> N
>  
> Nick Thompson
> ThompNickSon2 at gmail.com <mailto:ThompNickSon2 at gmail.com>
> https://wordpress.clarku.edu/nthompson/ <https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fwordpress.clarku.edu%2fnthompson%2f&c=E,1,zC7L3ZV3zN4dFInSdfjczIqHTNbvh0VxP_F6nO5hHM1lXqjgeqQY88xMBLKzIcrRshE96rhSwqF1U44JM1hzOoUmMjP0ZVSOsXPfEvfuAT5PMw,,&typo=1>
>  
> From: Friam <friam-bounces at redfish.com> On Behalf Of David Eric Smith
> Sent: Tuesday, February 9, 2021 3:58 PM
> To: The Friday Morning Applied Complexity Coffee Group <friam at redfish.com>
> Subject: Re: [FRIAM] what complexity science says ...
>  
>  
>> On Feb 8, 2021, at 10:31 PM, <thompnickson2 at gmail.com <mailto:thompnickson2 at gmail.com>> <thompnickson2 at gmail.com <mailto:thompnickson2 at gmail.com>> wrote:
>>  
>> That’s nifty Stephen, 
>>  
>> So we potentially have at least two sorts of motion that the haircells can detect: motion of the fluid in the channel and motion of the cochlea itself. 
>  
> ?  
>  
> Motion of fluid relative to whatever reference surface anchors the hair cells?  I only see one relative motion available.
>  
> ?
> 
> 
>> How do the cells tell the difference.  And why a spiral. 
>  
> https://www.whatsinside.info/bose-wave-radio-3/bose-wave-radio-iii-opened-waveguide-design/ <https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fwww.whatsinside.info%2fbose-wave-radio-3%2fbose-wave-radio-iii-opened-waveguide-design%2f&c=E,1,JOsCMFp2NklyUXjM3Xf3uQ7jIPt9bSQLo8qbuilh0RKtvPTqm2UFr5VzvMbhuxjNyLGM37Eo-pnD_Lm_ss7el_FPuscwuBCV-ZpDBSKDpDn7EOjrRv7ozQ,,&typo=1>
>  
>  
> Eric 
>  
>  
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