A third, evolutionarily younger, function of the basilar membrane is strongly developed in the cochlea of most mammalian species and weakly developed in some bird species. It is the function of frequency dispersion of incoming sound waves. In brief, the membrane is tapered and it is stiffer at one end than at the other. The dispersion of fluid waves causes sound input of a certain frequency to vibrate some locations of the membrane more than other locations. As shown in experiments by Nobel Prize laureate Georg von Békésy, high frequencies lead to maximum vibrations at the basal end of the cochlear coil (narrow, stiff membrane), and low frequencies lead to maximum vibrations at the apical end of the cochlear coil (wide, more compliant membrane). This "place-frequency map" can be described quantitatively by the Greenwood Function and its variants.
The basilar membrane is a pseudo-resonant structure that, like strings on an instrument, varies in width and stiffness. The "string" of the basilar membrane is not a set of parallel strings, as in a guitar, but a long structure that has different properties (width, stiffness, mass, damping, and the dimensions of the ducts that it couples to) at different points along its length. The motion of the basilar membrane is generally described as a traveling wave. The parameters of the membrane at a given point along its length determine its characteristic frequency (CF), the frequency at which it is most sensitive to sound vibrations. The Basilar membrane is widest (0.42–0.65 mm) and least taut at the apex of the cochlea, and narrowest (0.08–0.16 mm) and most taut at the base. High-frequency sounds localize near the base of the cochlea (near the round and oval windows), while low-frequency sounds localize near the apex.
The mathematical model of the mechanical analyzer for non-stationary signal decomposition based on an array of resonators.(Report)
Jan 01, 2008; 1. INTRODUCTION Most of mammalians and therefore also most of humans use mechanical analyzer for decomposition of non-stationary...