Mine were raised on NPR! (Yes, liberal Massachusetts chickens...) When the coop was being finished after they had already moved in, that's all my husband would have on the radio he plugged in there to keep himself entertained. Whenever he's working outside nowadays, he leaves the radio on, with hard rock playing. I don't think they like that so much - they're slightly agitated with it playing. When I change it to softer, more melodious music, I swear they mellow out.
When they were chicks and still living in the basement, both kids would visit them throughout the day and sing to them, and always sing the same songs to them that they'd learned at school just as they were about to turn out the lights for the night. It was their bedtime routine, and the birds quieted right down. They still sing those same songs to them sometimes when they lock up the coop at night. The chickens seem to really like it.
My daughter sometimes brings her guitar out into the run and plays for them. I honestly think the birds enjoy the sound.