How to off TV screen when listening to music

I used to be able to tune to a music channel then turn off the TV. I would hear the music through my sound bar that’s connected to the cable box. I do not need to use power to see the “art” on the TV screen. Now when I turn the TV off, the cable box goes off so the music goes off too.  What do I need to do now to turn off the TV but keep the cable box on?