When is a closed dome recommended for fitting?

A closed dome is recommended for fitting when maximum low-frequency gain and feedback control is desired. This design effectively seals the ear canal, which allows for enhanced amplification of low-frequency sounds, making them more accessible to the wearer. Additionally, this seal helps minimize the chances of feedback, where amplified sound leaks out and re-enters the microphone, creating unwanted noise and distortion.

In contrast, a dome that allows for maximum venting would not achieve the same levels of low-frequency amplification and feedback control since it would permit sound to escape and reduce the effectiveness of the hearing aid. Similarly, passing low-frequency sounds naturally to the tympanic membrane (TM) tends to be a feature of open fittings, which contradicts the purpose of a closed dome. Lastly, maximum low-frequency reduction is typically achieved with dome designs that allow for more sound to escape rather than keeping it contained and amplified, thus further illustrating why the closed dome is best suited for enhancing low frequencies and controlling feedback.