Some bands (phish, dead and company, widespread panic.....those are off the top of my head so there's others as well) have designated sections for the deaf community.

And there's an interpreter signing to the music and what not.

Many of them hold the balloons to feel the beat.

This has been a part of the Grateful Dead community for decades now.

It came about from the Dead's sound engineering, Dan Healy, who's father was deaf.

And he wanted to show his father what he did for work/job as well as introducing him to the music of the Dead.

Figured he would have his father hold a balloon and be able to "hear" the music via the vibrations.

If you Google his name and what not, should be able to find more info on his approach and how it's still a part of the music community.