Search

Purpose As the form and size of the external auditory canal determine its transmitting function and hence the sound pressure in front of the eardrum, it is important to understand its anatomy in order to develop, optimize, and compare acoustical methods. Method High-resolution computed tomography (HRCT) data were measured retrospectively for 100 patients who had received a cochlear implant. In order to visualize the anatomy of the auditory canal, its length, radius, and the angle at which it runs were determined for the patients' right and left ears. The canal's volume was calculated, and a radius function was created. Results The determined length of the auditory canal averaged 23.6 mm for the right ear and 23.5 mm for the left ear. The calculated auditory canal volume ( V total ) was 0.7 ml for the right ear and 0.69 ml for the left ear. The auditory canal was found to be significantly longer in men than in women, and the volume greater. Conclusion The values obtained can be employed to develop a method that represents the shape of the auditory canal as accurately as possible to allow the best possible outcomes for hearing aid fitting.

In this paper, methods of predicting the sound pressure at the ear drum are compared to probe tube measurements in 30 human ears occluded by closed ear molds. The methods compared fall into two categories: in one of them, the acoustical source (receiver and tubing) is modeled independently from the individual ear, in the other one it is modeled jointly with the individual ear. Models of the individual ear include modified variants of the phase reflectance and the pressure minima methods and a model of an ear simulator. As a result, it appears that the modified phase reflectance method works best for independent models of source and ear, whereas the modified pressure minima method works best for joint models of source and ear. With these methods, acceptable accuracies can be obtained in the frequency range from 100 Hz to 10 kHz, except for a few extremely large ear canals.

In this paper, a method of predicting the sound pressure at the ear drum, based on an optimized variant of the reflectance phase method and on a method of estimating individual drum impedances is presented and validated by probe tube measurements in human cadaver ears occluded by closed ear molds. It appears that the proposed method works with acceptable accuracy (roughly ±5 dB) in the frequency range from 1 kHz to 10 kHz. At lower frequencies, leakage is responsible for a high variability (up to 20 dB) of the sound pressure generated in the ear canal (and thus at the ear drum as well in this frequency range). In addition, it was observed that predictions based on ear canal models obtained from computer tomography scans were less accurate than predictions based on the method proposed in this paper. As the residual ear canals of the temporal bones used in this study were rather short, these results should be confirmed in vivo.