No experience yet but I have been thinking about building a closet for my Supercell, which is my biggest noise generator, so that I can concentrate the soundproofing on a smaller space. It will need some powered ventilation to send the heat it generates outside but I figure that will also help with the sound levels and heat build up inside the shop too.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.