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.