Open technology hearing aids have some constraints. Thus far, they are only available in a behind the ear model. Most importantly, they will only work for a patient that has a moderate hearing loss. Feedback or the squeaking sound from a hearing aid is caused when the sound energy going into the ear from the unit’s speaker leaks out and back into the microphone. Feedback commonly happens when the hearing aid is not completely down in a patient’s ear canal.
So if that is how feedback happens, how can it be prevented in a style that already has holes in the dome? Won’t the sound energy leak out those holes? Yes it will, and the answer to feedback control happens by software control in the digital circuit but with limitations on the power being put out by the hearing aid. In other words, open technology has to be a lowered powered hearing aid for the internal feedback control function to not be overwhelmed. If a patient has a really severe hearing loss they are not a candidate for open technology.
Common adjustment problems in traditional custom hearing aids are now much easier to conquer than in previous generations of technology so the severe loss patient has greater options to hear better comfortably, but open technology may not be one of those options.
Custom made hearing aids have both the microphone and speaker in the same small space. Behind the ear hearing aids can have a custom made impression on the end of a small tube that connects to the tip or horn of the hearing aid. Sound is broadcast through the tube. Open technology, again, fits discreetly behind the ear with the microphone on the hearing aid and the sound being broadcast through a small coated wire into a miniture speaker covered by a dome with holes that sits comfortable about a quarter of inch from the ear drum. A hearing test would determine if you are a candidate for open technology.