I haven't been able figure him out with regard to sound. If anything, I thought he was underreactive to sound. We had him on the beach for 4th of July for a couple of hours with fireworks and it didn't bother him. One time at home, the smoke alarm went off, and he said "I want to hear it again" For awhile, he could not stand to hear a baby cry, but he seems to have gotten over that. Lately though, he has been sticking his fingers in his ears to plug them, but it is mainly when he doesn't want to listen to what I am saying. LOL! He did seem a bit scared the other day at the park when we used a new bathroom. He did not like the fans that were in there. His teachers say that he gets distracted by others in the classroom. So in answer to your question, I am not sure how sensitive his ears are. He has never seemed to mind being in a crowd.