Acoustic feedback tendency in hearing aids for different types and couplings in relation to insertion gain

To make signals audible again for hearing impaired people, hearing aids pick up the sounds with a microphone amplify them and play them back in the ear canal. Parts of the amplified output signal return to the microphone by an acoustic pathway. Depending on the selected amplification, this can result in 'critical feedback', which limits the maximum possible amplification of hearing aids. 
The Insertion-Gain-Related Feedback Path (IFP) was introduced to characterize the acoustic feedback path. It describes the frequency-dependent gain that a hearing aid can provide until a critical feedback condition becomes possible. In addition to the feedback signal, the IFP also takes the Real Ear Unaided Gain (REUG), the Microphone Location Effect (MLE) and the hearing aid transmission to the eardrum into account. Technical measurements were used in this work, including the use of hearing aid dummies and probe microphones. This was used to determine the IFPs in 28 test subjects' ears. This data is freely available.