Schmidt, Sebastian

Finite Element simulation of external ear sound fields for the optimization of eardrum-related Measurements

The sound pressure p_Tat the human eardrum has essential advantages asreference signal in audiological and psychoacoustical experiments.Unfortunately, precise pressure measurements very close to the tympanicmembrane are difficult. In practice, the microphone has to be positioned ata certain distance from the eardrum. The measured pressure then has to betransformed to the eardrum. As a ''classical'' approach for the estimation ofthe necessary transfer function, an acoustical network model of the earcanal is developed from geometrical data of the canal (cross-sectional areafunction) which is in turn determined from measurements of its acousticalinput impedance. Such methods, however, do not provide robust results. In this thesis, the concept of one-dimensional models of the ear canal isexamined to find the origin of these errors. For this purpose, the soundfield at the human external ear was analyzed using finite element models.Inside the canal, irregular three-dimensional structures occur that cannotbe modelled accurately using classical one-dimensional network concepts.Upon these findings, an accurate, efficient and highly feasible method forthe estimation of p_Twas developed. Equal-loudness level contours withreference to the eardrum pressure that were measured as pilot application ofthe new method are presented.