How do I sound proof a room with a very loud large compressor in it?

I have a large compressor within a 6×10x10 room (sheet rock,tile ceiling, concrete floor) in my building at work. I need to get it quieted down as it is causing staff to have headaches due to the noise. There is no chance of moving the compressor. So I need to find a way do greatly reduce the noise coming out of that room. I have looked at a couple of sites but can’t really make heads or tails for them. I see all kinds of solutions but have no direct knowledge of them or if they will actually work… and thus I ask you all for help!