Subject: Evanescent waves in the cochlea. From: "reinifrosch@xxxxxxxx" <reinifrosch@xxxxxxxx> Date: Thu, 29 Apr 2010 10:17:33 +0000 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>------=_Part_1544_22605787.1272536253092 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Dear colleagues, =20 Better late than never: evanescent (standing) liquid-sound-pressure waves a= ppear to play a fairly important part in the cochlea. In my paper "Old and = New Cochlear Maps", Canadian Acoustics Vol. 37, No. 3 (2009) 174-175, I int= roduced a "BMR map" defined to yield, for a given distance-from-base, the r= esonance frequency of the local basilar-membrane (BM) resonator, calculated= under the assumption that the liquid "above" and "below" the cochlear part= ition is absent. As explained in the just mentioned paper, at that resonanc= e frequency the imaginary part of the local BM impedance vanishes. With liq= uid, however, evanescent waves generated by the oscillating BM decrease the= local BM resonance frequency, by typically half an octave, so that the loc= al with-liquid resonance frequency is about equal to the "characteristic fr= equency" (CF), i.e., the frequency which in a healthy cochlea yields, at th= e considered distance-from base, the maximal travelling-wave BM excitation = by low-sound-level sine-tones. For non-human mammals, the well-known Greenw= ood maps [JASA 87 (1990) 2592-2605] in my opinion yield approximately that = characteristic frequency. =20 Conjecture: spontaneous oto-acoustic emissions are caused by with-liquid BM= R oscillations; at given (assumed) frequency, these oscillations occur near= the "characteristic place", so that the emissions can be transported to th= e stapes by slow retrograde travelling surface waves. I plan to add a chapt= er on these evanescent-wave effects to my (almost finished) book "Introduct= ion to Cochlear Waves". The following observation is probably relevant: the= tapping of a full or submerged wineglass yields a short click if the water= is disturbed. A nice tone of a duration of a second or so results only if = the water is quiet. =20 Reinhart. Reinhart Frosch, Dr. phil. nat., r. PSI and ETH Zurich, Sommerhaldenstr. 5B, CH-5200 Brugg. Phone: 0041 56 441 77 72. Mobile: 0041 79 754 30 32. E-mail: reinifrosch@xxxxxxxx . ------=_Part_1544_22605787.1272536253092 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; font-size: 12px; margin:0; padding:0;} div.bwmail p { margin:0; padding:0; } div.bwmail table { font-family: Trebuchet MS,Arial,Helvetica; font-size: 12= px; } div.bwmail li { margin:0; padding:0; } --> </style> </head><body><div class=3D'bwmail'><P>Dear colleagues,</P> <P> </P> <P>Better late than never: evanescent (standing) liquid-sound-pressure wave= s appear to play a fairly important part in the cochlea. In my paper "Old a= nd New Cochlear Maps", Canadian Acoustics Vol. 37, No. 3 (2009) 174-175, I = introduced a "BMR map" defined to yield, for a given distance-from-base, th= e resonance frequency of the local basilar-membrane (BM) resonator, calcula= ted under the assumption that the liquid "above" and "below" the cochlear p= artition is absent. As explained in the just mentioned paper, at that reson= ance frequency the imaginary part of the local BM impedance vanishes. With = liquid, however, evanescent waves generated by the oscillating BM decrease = the local BM resonance frequency, by typically half an octave, so that the = local with-liquid resonance frequency is about equal to the "characteristic= frequency" (CF), i.e., the frequency which in a healthy cochlea yields, at= the considered distance-from base, the maximal travelling-wave BM excitati= on by low-sound-level sine-tones. For non-human mammals, the well-known Gre= enwood maps [JASA 87 (1990) 2592-2605] in my opinion yield approximately th= at characteristic frequency.</P> <P> </P> <P>Conjecture: spontaneous oto-acoustic emissions are caused by with-liquid= BMR oscillations; at given (assumed) frequency, these oscillations occur n= ear the "characteristic place", so that the emissions can be transported to= the stapes by slow retrograde travelling surface waves. I plan to add a ch= apter on these evanescent-wave effects to my (almost finished) book "Introd= uction to Cochlear Waves". The following observation is probably relevant: = the tapping of a full or submerged wineglass yields a short click if the wa= ter is disturbed. A nice tone of a duration of a second or so results only = if the water is quiet.</P> <P> </P> <P>Reinhart.<BR><BR>Reinhart Frosch,<BR>Dr. phil. nat.,<BR>r. PSI and ETH Z= urich,<BR>Sommerhaldenstr. 5B,<BR>CH-5200 Brugg.<BR>Phone: 0041 56 441 77 7= 2.<BR>Mobile: 0041 79 754 30 32.<BR>E-mail: reinifrosch@xxxxxxxx . </P></= div></body></html> ------=_Part_1544_22605787.1272536253092--