A sound wave will enter the hearing aid, get A to D converted, adusted, then D to A converted and enter the ear via the speaker/dome (e.g. Oticon OPN). Meanwhile that original sound wave is also hitting the ear itself. Does the dome block this sound? If not, wouldn’t this sound wave now be out of phase with the hearing aid processed version, resulting in some cancellation?
Yes, this presents some problems in open fittings in mid and lower frequencies. There’s a collision of the output of the hearing aid and incoming sound which can lead to addition and subtraction points.
Most modern Aids include a balancing function which takes the form of a comparator circuit between the final stage to the mic and the input. This comparator also ‘knows’ the phase delay of the of the mic and receiver, so can make changes on the fly to smooth the output.
Excellent answer - thank you. So what the brain gets is the net effect.
The combined effect of the comparator signal, the ambient sound energy and the amplification of the aid are delivered to your eardrum.
Real ear measurement allows this signal to be observed in relation to your hearing loss and output needs.
This passes through your hearing system to be decoded by your brain.
thanks for the summary!