[westfalia]

I've got a recording studio along with a friend of mine in a basement- and we were fortunate enough to be able to get help from a professional in wiring the walls up with sound jacks, and the works. But nonetheless, the main key was to keep the sound in there.

Other people have already said some great ways to do this, I just want to add the rest of what I know, if it hasn't already been said: Use two doors in succession between the outside and the inside of the room, definitely take into account that the sound will travel through the ceiling, so acoustic panels are a great idea (already been said, i know). If you're dealing with any glass windows, set two layers of glass in the pane, but do not sit them in parallel to eachother, put them at skewed angles, like / \ or \ / if you see what I mean. I've also found that mounting cloth on the walls (like thick carpet or a nice comforter) does a great job, and is something you don't need to buy. Some acoustic foam panels can be quite expensive, because of their special material properties.

I love it how we can blast our amps at full force at 2 a.m. if we so desire, no worries about waking anyone!