People who don't have hearing loss often make the assumption that once a deaf person has a hearing aid, their problem is solved.
It doesn't actually work that way – hence the need for solutions such as radio aids and streamers. Hearing aids are set to work optimally at a fixed distance of two metres, and they can only work with the residual hearing of the user. A radio aid is essentially a transmitting microphone and a receiver (most often a neck loop) which works with the hearing aid, enabling the user to listen to conversations; TV; music; mobile phone – lightweight and portable, they can go wherever needed.
Streamers work with hearing aids that have a built-in receiver, and stream sound received from another transmitter.
You can read more detailed information from iHear, here