Actually, it's important to note that untreated square rooms are a bigger problem than rooms with different dimensions. Why? Because rooms with the same LxW (and sometimes even height) have exactly the same resonance characteristics at exactly the same spots along their axis. For example, let's say you have your speakers' tweeters a foot away from the sidewalls and a foot away from the rear walls in a room that is exactly the same LxW and your resonant mode along that specified point at the length axis has a +3 db bump at 200hz;  double that for the width axis and now you have a +6db increase at 200 hz--simply because you have your speakers a foot away from each wall. Moreover, even in a treated room, there will still be significant peaks/nulls above/between frequencies that are normally affected by bass traps and/or acoustic treatments, which is why it is recommended to have your speakers properly positioned first and use bass traps/wall panels for the smoothest in room response.

Hope this helps!

Oliver