When purchasing hearing aids there are two types of domes you are presented (really 3 with custom molds) with. Before we get into that lets first clarify what a "dome" is. A hearing aid dome is the small plastic bell-shaped piece at the end of the tube. This is the actual physical piece that is inserted in your ear. A proper fitting dome can make a huge difference in both comfort and quality while wearing your hearing aid.
An Open Style dome has openings for sound to pass through from outside of the hearing aid. This helps people from experiencing what is called the occlusion effect. The occlusion effect can give the experience of hollow or booming like sounds from their own voice. Very similar to sticking your fingers in your ears and listening to yourself talk. For individuals with lower level hearing loss this can at times be a distracting experience. Open domes can also sounds more natural for some people as they are still receiving some sound through the ear unimpeded.
A Closed Style dome is meant to reduce the sound from outside the hearing aid so it can more aggressively boost the sound level. Closed domes can also boost the low frequency (usually below 500HZ) sound pressure in the ear canal 20dB or more. Often closed domes are the better answer for people suffering for a more severe level of hearing loss. Custom molds are, for the most part, closed domes that have been fitted specifically for an individual allowing a more comfortable fit (albeit at a much higher cost).
If you have any questions on what dome is best for you, please contact us and let us know!
The "Occlusion Effect" -- What it is, and What to Do About it, http://web.archive.org/web/20070806184522/http://www.hearingresearch.org... by Mark Ross, January, 2004 in Hearing Loss. Accessed 25 Nov 2007