The only place I've ever NOT been able to hear was Via Napoli.
I have a hearing loss. 3 years ago I got hearing aids. Best decision ever. It gives me the full richness of sound, and makes it easier for me to hear in places I thought I wouldn't be able to hear in. It doesn't just turn up the bad volume and make it harder. It gives me back most of my hearing. (I have "mild to moderate" loss in both ears, though with my last hearing test we found that it's a "profound" loss in my left ear at 3 of the higher registers)
If he hasn't been to one yet, I strongly suggest finding a good audiologist and considering a hearing aid if they say it can help. If the hearing is absolutely gone, Phonak makes an intriguing hearing aid set where you wear them on both ears, and it takes the sounds from the side you cannot hear on and sends it to the hearing ear, so you're hearing everything.
Also, and this just happened with my son, see if a chiropractor can check out his TMJ/mastoid area. My son was having sudden hearing loss, and we had already done the audiologist appointment, he was on prednisone in case it was inflammation behind his eardrum, and he has an MRI scheduled along with a hearing aid appt. He went to our chiro (full disclosure, I'm a retired chiro and know that modern day chiropractic started BECAUSE of a deaf man regaining his hearing after a certain set of circumstances caused him to lose the hearing), mentioned his ear. Our chiro did a couple adjustments (similiar to what they can do with babies/toddlers to help them stop getting ear infections) and he had his hearing back instantly. It's worth a try.
