Middle ear model

SIMPLE COUPLED ACOUSTIC-STRUCTURE EAR MODEL

Leonardo Molisani1 and Daniel Carmona1, Ricardo Burdisso2
1Mechanical Engineering Faculty of the National University of Rio Cuarto
Rio Cuarto,Argentina,
Email: lmolisan@vt.edu, dcarmona@ing.unrc.edu.ar
2Mechanical Engineering Faculty of the Virginia Polytechnic Institute & State University
Blacksburg, USA,
Email: rburdiss@vt.edu

SYNOPSISAn ear model under headphone load is presented in this effort with focus in the middle ear. The main function of the middle ear is to compensate the impedance from a system of low impedance, such asthe external ear, to another of high impedance, such as the cochlear fluid in the internal ear. The ossicles system works amplifying the pressures due to the surface size differences between tympanicmembrane and oval window. The pressure amplification is in the order of 27 dB. Experimental data from the middle ear has shown that the pressure amplification decreases above 1000 Hz. The decreasedoes not depend of the cochlear load for every frequency. The tympanic membrane (TM) and stapes footplate (FP) displacements were measured using double laser interferometers in human ears. Themeasurements supported by previous experimental studies indicate that there is slippage in the ossicles lever system above 1000 Hz. The reduction thought to be caused by the translational motion of theossicles rotation axis. The full model is a structure-acoustic cavity coupled system.

INTRODUCTION

The conventional behaviour of the human middle ear is known as an impedance adaptor system. The systemcompensates the sound energy loss from low impedance field such as the external ear to relative high impedance at the cochlear fluid. A mechanical analogy is usually performed to explain the pressuretransformation done by the tympanic membrane (TM). The area and lever ratio in the middle ear helps to recover about 27 dB of sound pressure (Lara Saenz, 2004). Experimental measurements of the...