Occlusion effects caused by earmoulds

Many people use earmoulds every day (e.g. hearing aid or hearing protection). Unfortunately, occlusion of the ear canal changes the perception of one's own voice. This 'Occlusion effect' is a major annoyance.
In the PhD project it was showed that the experienced annoyance is correlated with the sound pressure in the occluded ear canal. The sound pressure generated from one's own voice is up to 30 dB greater in the occluded ear canal than in the open ear canal.
The second part of the project has been concerned with the physical mechanism causing the occlusion effect. The ratio between the sound pressure generated by airborne sound and the sound pressure transmitted through the body has been determined in a related MSc project by Carsten Bremmelgaard. Experiments with foam plugs contra hard acrylic moulds showed that soft plugs reduces the occlusion effect. The results have been used to develop a computer model of the occlusion effect from one's own voice.
The project is an industrial PhD project with Oticon A/S as the industrial partner.