I suffered total hearing loss in one ear from an acoustic neuroma tumor and while I was in recovery from the tumor removal surgery I was looking to relax via activities involving listening to headphones. I found I could no longer use and enjoy my old normal bilateral headphones in all the ways I was used and while this was expected, I was frustrated to find there were no stereo headphones made by any major headphone manufacturers for people with single-sided deafness (SSD)/unilateral hearing loss (UHL). If you listen to music via normal bilateral stereo headphones some sound is played through the Left channel and some is played through the Right channel of the stereo headphone and if you are deaf in one of your ears you will naturally miss out hearing one of the channels.
I thought a solution to hearing in stereo with one ear were one sided headphones that they describe as "DJ stereo headphones" but I was disappointed because upon introspection those types of DJ headphones are not true stereo headphones due to the fact that if they only have one speaker driver to an ear it is still only mono sound. This realization inspired me to make good use of my Aviation Airframe & Powerplant background and design and create my own stereo headphones that will reproduce stereo into one ear for me and the end result was so successful I started making these headphones that I have dubbed the 2E1 for "Two Ears in One" for others in the single-sided deaf community.