Hi jhadbaisley, regarding the comments about carpets, egg cartons and curtains, these do act as absorbers of sound but at specific frequencies.
A quick example: the room you are wanting to treat will have some inherent problems because of its size because its dimensions will have a mathematical relationship to certain frequencies. If you leave this untreated, you will hear a boom, an echo, an exaggeration of this and related frequencies, causing you to EQ your mix to compensate, which will now sound wrong when played in a room with different sound characteristics. Carpet, curtains and egg boxes will absorb some sound but how do you know that the frequencies thex absorb are the frequencies you need to treat? I hope you are not confused by that but see the need to follow the wise advice above.