I sheathed the interior of my shed with Homasote today, and put a noisy oilless compressor in it to test it. I was quite disappointed - there was hardly any difference between door open and door closed. The walls were vibrating strongly on the exterior, so I think the Homasote just transmits the vibration right to the studs. I'm now thinking I should have gone with just the insulation and screen. I'm definitely going to have to build a secondary, smaller enclosure for the compressor.