Hearing aids are electrical devices that assist perception of speech or other sounds. Hearing aid users frequently complain about the sound of their own voice. They often say that their voice sounds "hollow", or as if they are "talking in a barrel". This may be due to the occlusion effect.
The occlusion effect results from sound energy produced internally that resonates in the cavity between the ear drum and hearing aid. This causes an increase in sound delivered to the cochlea. The boost in internally generated sound is centered mainly at low frequencies with a peak of around 250 to 500 hz. Thus it provides a low-frequency boost.