My dad has had some rather substantial hearing loss and usually uses totally-in-the-ear hearing aids. Recently, he has been dealing with a fungal ear infection in both ears and cannot use his hearing aids while treating the ear infections. However, he still does need to hear and do stuff. Are there any devices similar to hearing aids that can temporarily improve hearing, but which do not need to go into the ear? I have been looking at personal hearing amplifiers and personal FM microphones, etc., but I was not sure which of these are the best temporary hearing aid substitute.
This is a very pragmatic question and I would like give you an explicit answer. Unfortunately I think that there is only so little objective information which hearing aid is the best.
As said when the best aid is considered it is a very subjective matter. There is no clear comparative studies about different hearing aids, especially if those without ear canal implant are used. If your father suffers from fungal infection is is natural that aids figured below are not pleasant due to ear canal irritation:
Many choices of hearing aid styles are available, including the following: completely in the canal (A), in the canal (B), in the ear (C), behind the ear (D), receiver in canal or receiver in the ear (E), and open fit (F).
As so, Personal Sound Amplification Products (PSAP) may seem appropriate as a temporary aid (FDA). It is however, important to notice that these aids are not as powerful as actual hearing aids.
I would recommend to consult an audiologist to get some insight to PSAPs. Also I would seek a brick-and-mortar shop which sells these aids, since most likely the sellers have valuable consumer info on these aids and can help deciding the right aid.
I would like to also remind that it is extremely important to get the fungal infection treated and return to use the ordinary aid, since hearing loss can severely reduce the quality of life.
Bone Anchored Hearing Aids (BAHA) do not require having anything in the ear. Rather, they are placed behind the ear and work based on bone conduction. Commercially available BAHAs are both expensive and typically require surgery (outpatient procedure with local anesthesia), but they can be used without surgery. For example, at John Hopkins they let you test one out with a headband during your appointment. Oticon sells a headband to be used with a BAHA.