EAR CANAL IMPEDANCES OF CHILDREN AND ADULTS – INVESTIGATIONS WITH SIMULATION AND MEASUREMENTS

Acoustic impedance measurements of the human ear canal enable us to understand the function of the middle and the inner ear as well as to recognize possible dysfunctions. Additionally, the ear canal impedance is an important parameter which has to be taken into account when hearing aids are adjusted. Hearing aids for infants, children, and adults are all fitted using only a few standardized couplers (i.e. 2 ccm coupler (IEC 60126). The measurement of individual real-ear-to-coupler differences (RECD) is required since these couplers yield insufficient data as far as children are concerned. However, couplers suitable for different age groups can be developed for an improved fitting process if the knowledge about ear canal impedances and the ear canal volumes of infants and children is increased. Two different methods to obtain ear canal impedances will be discussed in this article. The first one is a classic measurement technique in which a one-microphone-impedance probe is used. Different coupling techniques have been tested with regard to repeatability and measurement uncertainty. Later on, the impedance probe is tested on adults and on children. The second method is the simulation of the ear canal impedance using FEM (Finite-Element-Method). The required CAD-models are generated with the help of CT-scans (computed tomography) of young children and adults