Years ago there was a product called "Bone Phones" – they were conductive earphones that laid against the base of your skull and rested down your shoulders, and music played through them was audible only to you. Zero decibels – the music was reproduced by the sound waves vibrating your skull bones, so it was literally all in your head. I always wondered if they came about via Ultra or its kin.
Yes. They didn't last long on the market – people found them uncomfortable, made them feel weird in the head. Can't imagine why….
I had access to a set. I could tolerate them, but after a while I wanted to scrape the inside of my skull with a steel brush.
We prefer "personcunt."