At what level is their deafness? If it is just ear drums that are damaged, and the Hair cells are OK, then using something like “Aftershokz” bone headphones could be used.

Originally I experimented with transducers and a small 1 watt amp and streamed mp3 through it then applied the transducer to parts of my scull and even my teeth to find where the best sound would be obtained, if any. I found that the idea was working, so I did some research on bone headphones, bought a pair and found they really helped. Since then I have upgraded to Cochlea bone implants., fantastic for streaming from my piano into my head, no one else can hear my lousy playing………(except for the tapping on the keys).

BIB 2018 Pro, Win 7, Win 10