I just moved into a different home, and as I was setting up the new studio, I found I was in a smaller room, with square walls, wall to wall carpeting, and all of the walls were Sheetrock/plaster ,and hard reflective surface. I did the hand clapping test and noticed significant ringing and an increase in low bass when transferring to a different room location for playback.

  I don't have any formal training in studio design so I started to research what to do and came up with few good informative web pages about this. I thought I would share them with bandamp so maybe some others might
benefit from their expertise
http://www.ethanwiner.com/acoustics.html
http://www.tweakheadz.com/recording_studio_accessories.html

personally, I it depends on what type of sound your going for.  ie) hallow, rich, bright  -- so figure determine what your looking for in your recordings.

yes agreed , The main thing I was working on was the room I do my mixing in. The freq peaks need to somewhat under control for a more even mix. 

As far as recording rooms . I use everything from recording outside to the tiled bathroom. Whatever works best for what I am trying to do.