spl is correct. as far as keeping the neighbors happy you're not going to get what you're after by using egg cartons, foam, etc. You'd need floating floors, hanging ceiling, a lot of insulation, an air-tight room within a room (dead air is the key), etc....you're talking about at least 10K to make it right. The best you can do is try to soak up the low freqs by focusing on limp mass but without well-designed bass traps (in combination with good designs in the rest of the room) you're still going to experience very minimal success. There are books on designing studios and rehearsal spaces -- I bought a couple when I designed my studio space. Since I couldn't afford to do it "right" I just schedule all my drum and bass times around when my neighbors are not at home.