Terry from Dumfries Gliding Club explains how he communicates when he’s flying gliders.
I am not completely deaf and I normally wear hearing aids but they are forward facing so it is difficult to use them with an instructor behind me. So I use headphones with a Sonido Personal Amplifier which I purchased from RNID (now known as AOHL) for about £40. It has a microphone which can be clipped on the instructor’s collar and works very well. (It has a built in mike as well and a loop pickup, so it can be used in other situations).
You can view the datasheet about the Sonido Personal Amplifier if you want to know more.