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Claus Nielsen

Research Audiologist

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mail@eriksholm.com

In the middle of the 1990s, Completely-In-the-Canal (CIC) hearing aids created a surge of interest within the industry. As well as being cosmetically attractive, this style has several promising acoustic properties. However, CICs are challenging to produce due to the limited physical space in the outer ear.

Two lines of work

At Eriksholm, the interest in CIC hearing aids developed into two different lines of work. The first was concerned with the acoustic potential of CICs, while the second focused on describing the geometry of the outer ear.

cic

The sound of soft tissue

The emphasis of our acoustic investigations was on the CIC’s alleged potential for eliminating the occlusion effect. This effect was found to be mainly due to vibrations of the outer soft-tissue (cartilaginous) part of the ear canal. Making the CIC sit deeply in the ear canal – with a complete seal in the inner bony part – should prevent vibrations from the soft part from reaching the eardrum.

Models of the outer-ear geometry

This work has provided insight into the shape of the ear canal and its variation across the population. Prototype software tools were developed for automated production of CIC hearing aids and for assisting the mechanical development of CIC components.

Further details of outer-ear anatomy were studied, and models were developed of the dynamic ear-shape variations due to yawning etc. Finally, a software tool and a database were made for rendering the position of the junction between the soft and the bony part of the ear canal.