Low frequency resonance will be what will piss off the old lady upstairs the most. In fact, it is the hardest thing to absorb. Any frequency below say 300 is just going to go through foam, mattresses, what ever. What you need is none resonating walls, and some dead space to absorb low freq's.
To attenuate 50db, here is what you will need.
All walls must have a layer of 1/2" particle board, 1/2" firtex, and 1/2" sheet rock. This must be done on both sides of the wall, with 2X6 framing, and 2X4 studs. The studs must be offset, meaning that there will be a stud every 8", but the first one will be for supporting one side, the next one for the other, and going back and forth for the whole wall.
More low end absorbtion can be obtained by doing this, the building another wall inside the room. If you are only after say 75db of attenuation, then the next wall only needs all of those materials on one side. There should be at least 6" between the walls.
You can go ahead and try all the other solutions, but, I can tell you from experience that what is described above is the only real solution for absorbtion. A friend of mine a few years ago built a "jam room" (basically a garage) and spent $11,000 on it. He decided to try all sorts of funky things to absorb sound. When it was all said and done, the very first time that his band rehearsed there, a neighbor about 4 houses down could hear the low end in his living room, and called to cops. My friend does not use that space for rehearsing any more, and he kicks himself in the butt for not following advice that came from much research into this.
What about you???
As far as refections, there are only a few things you need to consider, unless you are trying to build a very flat sounding room.
Make sure that you do not have opposing walls that are 180 degrees from each other. This means that you will need to build a funky room. If you don't, you will experience significant standing waves that will cause phase cancellation. This will make the room very weird sounding.
Next, NO 90 DEGREE ANGLES ANYWHERE!!! All corners need to be broken from a 90. You can buy that corner foam stuff, but since you are going to build, why not just break the corner with wall material.
Wood and tile both make excellent sounding reflecting surfaces, but very different sounds to them. You could play with making part of the room one material, and the rest the other. Variety will serve you well.
Good luck.
Ed Rei
Echo Star Studio
www.echostarstudio.com
