re: Noise reduction from inside to outside the shop…

at the company i worked for we sold Roxul which is a product of Rockwool. it is made from volcanic lava. one demonstration they showed us was the guy put a load siren inside a box lined with roxul closed the lid and you could just barely here it. and it was ear piercing loud ! also fire resistant. if your walls are open it would be easy to install. the insulation alone would kill most of your noise issues.