I tried to soundproof my music room at home, b/c the sound was aggravating my wife. I play guitar, harp, bass, keys, and drums... and they can get quite loud when I get everything looping. A local liquidation store had 2 foot square rubber backed carpeting tiles for sale for $1, so I bought a bunch of them, and covered the walls with them (did not do the ceiling, as there is no one above us, just an attic). The carpet tiles are all different colors and have all sorts of different designs on them, so it looks really cool. As for the sound... The carpet helps with echoes, so it's good for recording in the room. And the rubber helps with noise suppression, keeping it from getting out of the room. I can play guitar and harp to my heart's content, and my wife can go to sleep or watch tv just fine. Cost me $100. However, it does nothing for bass frequencies... bass and drums just blow on through, so I have to keep the volume very low for them. I really don't get to play drums at all, except when my wife is gone out... I can record the drums into a looper, and the recording is fine, but the real drums are too loud (I kind of wish I had just bought an electronic drum kit).
To stop bass frequencies, you have to have heavy mass. I thought about building a cage for my drums, so I can practice... apparently it can be done fairly cheap... you build a double-walled cage of drywall, making sure there is space between the 2 walls, and the cage is raised off the floor. Some of the bass frequencies will still get through, but it would be greatly reduced. Others for for the room-within-a-room approach... I considered it, but didn't go with it because I wanted something that could be easily removed (I don't own the house). And I haven't built a cage b/c we're thinking about moving... maybe the next place I live I'll actually get around to building one.