Finite Element simulation of external ear sound fields for the optimization of eardrum-related measurements
153 pages, year of publication: 2009
price: 35.00 EUR
Hörakustik, Audiologie, Messtechnik, Finite Elemente, Psychoakustik
The sound pressure pT at the human eardrum has essential advantages as
reference signal in audiological and psychoacoustical experiments.
Unfortunately, precise pressure measurements very close to the tympanic
membrane are difficult. In practice, the microphone has to be positioned at
a certain distance from the eardrum. The measured pressure then has to be
transformed to the eardrum. As a ``classical'' approach for the estimation of
the necessary transfer function, an acoustical network model of the ear
canal is developed from geometrical data of the canal (cross-sectional area
function) which is in turn determined from measurements of its acoustical
input impedance. Such methods, however, do not provide robust results.
In this thesis, the concept of one-dimensional models of the ear canal is
examined to find the origin of these errors. For this purpose, the sound
field at the human external ear was analyzed using finite element models.
Inside the canal, irregular three-dimensional structures occur that cannot
be modelled accurately using classical one-dimensional network concepts.
Upon these findings, an accurate, efficient and highly feasible method for
the estimation of pT was developed. Equal-loudness level contours with
reference to the eardrum pressure that were measured as pilot application of
the new method are presented.