Take a look at Ethan Winer's site for acoustic treatment. http://www.ethanwiner.com/acoustics.html

I made some bass traps for a problem room which worked fine. Normaly bass traps alone will tame a room enough to get good sounds. Any furniture and fittings will take care of the distribution/deflection of the highs.

Bear in mind that there is no perfect room. Some are bright, some are dull, some are just right for the sound you're looking for. The bottom line is that you don't need to spend a fortune to get a good effect. Studios and concert halls have to cater for all types of sounds, whereas the home studio can be tailored to your own sound cheaply.

Egg cartons don't work, and most foam products are not very effective over a large range.
A great plus with high density mineral wool (Rockwool, Isover..etc.) is that it in flameproof!


Chris