Re: A new paradigm?(On pitch and periodicity (was "correction to post")) ("reinifrosch@xxxxxxxx" )


Subject: Re: A new paradigm?(On pitch and periodicity (was "correction to post"))
From:    "reinifrosch@xxxxxxxx"  <reinifrosch@xxxxxxxx>
Date:    Tue, 1 Nov 2011 17:29:33 +0000
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

------=_Part_3270_24575464.1320168573330 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hello Dick, I, too, would like to publicly agree with you. In the past months I have do= ne calculations on (standing) cochlear evanescent waves. These, too, are pr= edicted to occur in strictly ideal (i.e., incompressible) liquids. A common= feature of standing evanescent and traveling surface waves is the fulfillm= ent, in small-displacement cases, of the Laplace equation by the liquid sou= nd-pressure [see e.g. de Boer's chapter in the book "The Cochlea" (1996)]. = Such cochlear evanescent waves (driven by two simultaneous forces, due to t= he basilar-membrane stiffness and to active outer hair cells) may occur dur= ing the generation of SOAEs (spontaneous oto-acoustic emissions), as descri= bed in my just published proceedings paper, "Cochlear Evanescent Liquid Sou= nd-Pressure Waves During Spontaneous Oto-Acoustic Emissions", Canadian Acou= stics Vol. 39 No. 3 (2011) 122-123. With best wishes, Reinhart. =20 Reinhart Frosch, Dr. phil. nat., CH-5200 Brugg. reinifrosch@xxxxxxxx . ----Urspr=C3=BCngliche Nachricht---- Von: DickLyon@xxxxxxxx Datum: 31.10.2011 22:47 An: <AUDITORY@xxxxxxxx> Betreff: Re: A new paradigm?(On pitch and periodicity (was &amp;quot;correc= tion to post&amp;quot;)) At 4:57 PM -0400 10/31/11, Willem Christiaan Heerens wrote: >... I really must remind you to the fact that a mechanical vibration=20 >-- and the sound stimulus is such a vibration -- in a fluid, or in=20 >this case water like perilymph, will always propagate with the speed=20 >of sound, which has typically here the value of 1500 m/s. That is=20 >just one of those constraints dictated by general physics. Willem, No, not "always"; that 1500 m/s wave mode is for longitudinal=20 pressure waves only. Your conception of "general physics" needs a=20 slight extension to cover other types of waves. Then the problem=20 won't be so over-constrained. In the ear, the stapes doesn't couple much energy into this fast=20 pressure-wave mode. A much slower propagating vibration mode is=20 involved in the cochlear traveling waves that use the compliance of=20 the basilar membrane, as opposed to compression of the fluid, as the=20 displacement-based restoring force that leads to the wave equations.=20 This mode has a very different form, doesn't depend on fluid=20 compressibility, requires a membrane with motion in a suitable=20 symmetry across it, etc. This is what the physics describes, and=20 what the models model. Gravity waves on water are a related, but different, example of=20 mechanical vibrations that propagate much more slowly than 1500 m/s.=20 These modes use gravity as the restoring force, and can be put into=20 analogy with what the membrane does in the cochlea (though it's not=20 such a close analogy as to give the same wave equations). Of course, until one acknowledges the basic physics of waves in=20 incompressible fluids, as described by Lamb and Rayleigh and others=20 over a hundred years ago, it will not be possible to converge on an=20 understanding of cochlear models and their traveling waves. The physics and math are pretty simple, relying only on f=3Dma for=20 fluid elements, and conservation of volume for incompressibility, and=20 something to make a restoring force. To get waves, you need=20 something to hold potential energy and push back against displacment,=20 to trade that energy against the kinetic energy of moving fluid.=20 Fluid compression is one such mechanism, but there are others that=20 your approach is ignoring. This is what the membrane is about:=20 springiness, or compliance. The membrane compliance has been=20 measured, and the measurements fit the physical models and the=20 observed wave speeds. Adding some compressibility to the model is also possible, and is=20 needed to get that fast pressure mode as well, which I agree is=20 involved in getting the round window to be pushed out when the oval=20 window is pushed in. But that can be approximated well enough with=20 incompressible and infinite-velocity pressure waves, since the=20 wavelengths are so long, as you point out. These pressure waves=20 don't create any differential pressures around the basilar membrane,=20 and have negligible associated displacements and velocities=20 everywhere (even at the windows), compared to the traveling-wave=20 modes, so they are typically ignored in the discussion of cochlear=20 hydrodynamics, where the motions are what we care about. Sorry to be so long-winded. Dick ------=_Part_3270_24575464.1320168573330 Content-Type: text/html;charset="UTF-8" Content-Transfer-Encoding: quoted-printable <html><head><style type=3D'text/css'> <!-- div.bwmail { background-color:#ffffff; font-family: Trebuchet MS,Arial,Helv= etica, sans-serif; font-size: small; margin:0; padding:0;} div.bwmail p { margin:0; padding:0; } div.bwmail table { font-family: Trebuchet MS,Arial,Helvetica, sans-serif; f= ont-size: small; } div.bwmail li { margin:0; padding:0; } --> </style> </head><body><div class=3D'bwmail'><P><FONT size=3D2>Hello Dick,</FONT></P> <P><FONT size=3D2>I, too, would like to publicly agree with you. In the pas= t months I have done calculations on (standing) cochlear evanescent waves. = These, too, are predicted to occur in strictly ideal (i.e., incompressible)= liquids. A common feature of standing evanescent and traveling surface wav= es is the fulfillment, in&nbsp;small-displacement cases, of the Laplace equ= ation by the liquid sound-pressure [see e.g. de Boer's chapter in the book = "The Cochlea" (1996)].&nbsp;Such cochlear evanescent waves (driven&nbsp;by = two simultaneous forces, due to&nbsp;the&nbsp;basilar-membrane stiffness an= d&nbsp;to active outer hair cells) may occur during the generation of SOAEs= (spontaneous oto-acoustic emissions), as described in my just published pr= oceedings paper, "Cochlear Evanescent Liquid Sound-Pressure Waves During Sp= ontaneous Oto-Acoustic Emissions", Canadian Acoustics Vol. 39 No. 3 (2011) = 122-123.</FONT></P> <P><FONT size=3D2>With best wishes,</FONT></P> <P><FONT size=3D2>Reinhart.</FONT></P> <P><FONT size=3D2></FONT>&nbsp;</P> <P><FONT size=3D2>Reinhart Frosch,<BR>Dr. phil. nat.,<BR>CH-5200 Brugg.<BR>= reinifrosch@xxxxxxxx .<BR><BR></FONT></P> <BLOCKQUOTE><FONT size=3D2>----Urspr=C3=BCngliche Nachricht----<BR>Von: Dic= kLyon@xxxxxxxx<BR>Datum: 31.10.2011 22:47<BR>An: &lt;AUDITORY@xxxxxxxx= A&gt;<BR>Betreff: Re: A new paradigm?(On pitch and periodicity (was &amp;qu= ot;correction to post&amp;quot;))<BR><BR>At 4:57 PM -0400 10/31/11, Willem = Christiaan Heerens wrote:<BR>&gt;... I really must remind you to the fact t= hat a mechanical vibration <BR>&gt;-- and the sound stimulus is such a vibr= ation -- in a fluid, or in <BR>&gt;this case water like perilymph, will alw= ays propagate with the speed <BR>&gt;of sound, which has typically here the= value of 1500 m/s. That is <BR>&gt;just one of those constraints dictated = by general physics.<BR><BR>Willem,<BR><BR>No, not "always"; that 1500 m/s w= ave mode is for longitudinal <BR>pressure waves only.&nbsp; Your conception= of "general physics" needs a <BR>slight extension to cover other types of = waves.&nbsp; Then the problem <BR>won't be so over-constrained.<BR><BR>In t= he ear, the stapes doesn't couple much energy into this fast <BR>pressure-w= ave mode.&nbsp; A much slower propagating vibration mode is <BR>involved in= the cochlear traveling waves that use the compliance of <BR>the basilar me= mbrane, as opposed to compression of the fluid, as the <BR>displacement-bas= ed restoring force that leads to the wave equations. <BR>This mode has a ve= ry different form, doesn't depend on fluid <BR>compressibility, requires a = membrane with motion in a suitable <BR>symmetry across it, etc.&nbsp; This = is what the physics describes, and <BR>what the models model.<BR><BR>Gravit= y waves on water are a related, but different, example of <BR>mechanical vi= brations that propagate much more slowly than 1500 m/s. <BR>These modes use= gravity as the restoring force, and can be put into <BR>analogy with what = the membrane does in the cochlea (though it's not <BR>such a close analogy = as to give the same wave equations).<BR><BR>Of course, until one acknowledg= es the basic physics of waves in <BR>incompressible fluids, as described by= Lamb and Rayleigh and others <BR>over a hundred years ago, it will not be = possible to converge on an <BR>understanding of cochlear models and their t= raveling waves.<BR><BR>The physics and math are pretty simple, relying only= on f=3Dma for <BR>fluid elements, and conservation of volume for incompres= sibility, and <BR>something to make a restoring force.&nbsp; To get waves, = you need <BR>something to hold potential energy and push back against displ= acment, <BR>to trade that energy against the kinetic energy of moving fluid= . <BR>Fluid compression is one such mechanism, but there are others that <B= R>your approach is ignoring.&nbsp; This is what the membrane is about: <BR>= springiness, or compliance.&nbsp; The membrane compliance has been <BR>meas= ured, and the measurements fit the physical models and the <BR>observed wav= e speeds.<BR><BR>Adding some compressibility to the model is also possible,= and is <BR>needed to get that fast pressure mode as well, which I agree is= <BR>involved in getting the round window to be pushed out when the oval <B= R>window is pushed in.&nbsp; But that can be approximated well enough with = <BR>incompressible and infinite-velocity pressure waves, since the <BR>wave= lengths are so long, as you point out.&nbsp; These pressure waves <BR>don't= create any differential pressures around the basilar membrane, <BR>and hav= e negligible associated displacements and velocities <BR>everywhere (even a= t the windows), compared to the traveling-wave <BR>modes, so they are typic= ally ignored in the discussion of cochlear <BR>hydrodynamics, where the mot= ions are what we care about.<BR><BR>Sorry to be so long-winded.<BR><BR>Dick= <BR><BR></FONT></BLOCKQUOTE><BR></div></body></html> ------=_Part_3270_24575464.1320168573330--


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