anyone know of a simple sound proof setup that doesn't require venting air outside?
I don't know, They're so loud I can hear it on the second floor from the basement. It's intolerable.
There are good YouTube videos on silencing Antminers. Two options, use a cooler or just get a large plastic tub at Home Depot/Hardware store. Use insulated ducting to suck air in and exhaust out. Pack enclosure with fiberglass or acoustic foam. Do put some type of filter on the air intake. I had to scramble to get one put together yesterday but it really cuts down on noise.