I think the concussed brain can develop a sort of PTSD from such loud startling noises. It can take a while for this sound sensitivity/anxiety to settle down. I don't think it is damage, just a startle response action. We become protective of the sounds as our brain considers them almost trauma.

I would expect exposure techniques would help. Watching fire crackers go off when you see them and expect the sound can help you brain put the sound into proper perspective. I know that I do much better with loud noises when I can see the source and anticipate the sound.

My best to you.