Claus Nielsen

Research Audiologist

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Making a Completely-In-the-Canal (CIC) hearing-aid seal in the bony part of the ear canal can reduce the occlusion effect. Measurements on test subjects confirmed this, but subjectively-perceived occlusion problems were something we failed to predict.

Measuring the occlusion effect

Seven test subjects participated in a series of objective measurements of the occlusion effect. Three different CIC shells were made with a microphone mounted in the tip, and these shells were fitted binaurally.

 - Bony-seal: full seal in the bony part of the ear canal.
 - Bony-anchored: in contact with the bony part of the ear canal on half of the circumference.
 - Taper-tip: same length of shell as above, but without contact to the bony part.

Each test subject was seated in the anechoic chamber and the occlusion effect was measured while they were reading aloud. A two-channel measurement technique1 was employed, using the non-test ear as reference. This made any variations in vocal level immaterial. The results revealed that the bony-seal CICs produced the least occlusion effect, while the bony-anchored and taper-tip CICs produced similar results. This implies that the greatest contributor to the occlusion effect must be the vibration of the soft part of the ear canal. We also discovered a large variation in occlusion effect, as well as bony-seal benefit (reduction of occlusion effect) among ears.

Relating measured occlusion effect to perceived occlusion problems

The seven test subjects also participated in the second study-phase, where subjectively perceived occlusion problems were assessed by self-report. All test subjects had ski-slope hearing losses. They used identically programmed bony-seal and taper-tip CICs for three weeks each, in a crossover fashion.

At the end of each trial period they filled in a 47-item questionnaire probing physical comfort, hearing abilities, and perception of own voice. While the bony-seal CIC was rated best for perception of own voice, there was a surprisingly weak relation between the objective measures of the occlusion effect and the self-reported measures of own-voice perception. This observation eventually developed into specific studies of the hearing-aid users own voice.

Further reading

1 Carle R, Laugesen S, Nielsen C (2002). Observations on the relations among occlusion effect, compliance, and vent size. Journal of the American Academy of Audiology, 13(1), p. 25-37.