AISA: An AccUrAte method for Assessing the AcouStIc EffEct of the EARmould

IntroductIon One of the cornerstones of hearing aid fitting is acoustic accuracy. Without control of the sound at the eardrum, there is a risk that hearing aid users are insufficiently or overly compensated for their hearing loss, and well-substantiated and optimised hearing aid signal processing features may lose power. Ultimately, deficient management of the acoustics may therefore negatively impact the hearing aid user’s performance and satisfaction. A major challenge in fitting hearing aids is to ensure that the actual gain applied at the individual eardrum matches the gain prescribed by the fitting rationale. This is not a trivial matter, since the sound pressure at the eardrum depends on the anatomy of the individual ear and, particularly, on the degree of openness of the acoustic fitting. When wearing a hearing aid, the sound pressure level at the hearing aid user’s eardrum is not only determined by the output of the hearing aid, but is also influenced by the effect of any ventilation (vent) present in the hearing aid’s shell or mould, or leakage between the earmould and the walls of the ear canal. The vent affects the sound pressure at the eardrum in two ways. Firstly, the sound from the hearing aid loses intensity at lower frequencies, resulting in a “tinny”