Audiometric notches at different frequencies, by Marshall Chasin Dr Chasin writes, "Have you ever noticed when testing a musician or even a teenager who walked into your office that the patient has a slight 4000 Hz notch in one ear and a 6000 Hz notch in the other ear. From a strictly “asymmetrical hearing loss” perspective, this may fulfill the requirements for a retrocochlear investigation, which should be pursued. But I wonder if there are some acoustical reasons for this finding." ▬▬ ▬▬ ▬▬ ▬▬ MY REPLY: One theory involves perilymphatic fluid flow and turbulence past the basal turn of the cochlea (located at approximately 5-6mm from the oval window), at the points approximately 8-10mm in. See the Greenwood chart at: twitpic/d5rfmk It is further posited that the shear forces from this turbulence act to literally rip out the outer hair cells in this region. There are basically three states of this fluid flow: Laminar flow when the Reynolds Number Re is under about 2400, turbulent fluid flow when Re is greater than 4000; and the transition region when Re is between 2400 & 4000. The Reynolds Number is a dimensionless number that gives a measure of the ratio of inertial (kinematic) forces to viscous forces for given gaseous and liquid fluid flow conditions. To determine the actual fluid flows inside the cochlea, one would first model the inside of the organ and then solve the Navier-Stokes Equations: twitpic/d5rhyp …using finite element analysis software, such as COMSOL Multiphysics. For more on the Reynolds number, please see for a visual demonstration: youtube/watch?v=kmjFdBxbV08 and for the equations, please see: grc.nasa.gov/WWW/k-12/airplane/reynolds.html For more on the Navier-Stokes Equations, please see: https://grc.nasa.gov/WWW/k-12/airplane/nseqs.html ORIGINAL ARTICLE: Audiometric notches at different frequencies hearinghealthmatters.org/hearthemusic/2013/audiometric-notches-at-different-frequencies/
Posted on: Wed, 31 Jul 2013 21:43:51 +0000
Trending Topics
Recently Viewed Topics
© 2015