Best Ratios for a Newly Constructed Listening Room

14 X 20 would be nearly ideal (best to avoid square) with the speakers placed along the longer wall about 12 feet apart with the primary listening position directly across (these proportions and dimensions can be played with depending on speakers, furnishing and placement of course).  The placement of the speakers should be biased to one side of the long wall and not centered within the 20 foot side.  In other words, you will end up with one speaker roughly in one corner and the distance between them and the listener should approximate an equilateral triangle as much as possible.

Greg 

Actually Reuben - It just occurred to me after my last post that you might be setting a multi-channel theater system versus 2-channel stereo only for music.  If that's the case then my advice above probably won't work if you're doing a 5.1, 7.1, 9.1, etc.  If the latter is the case, you're going to want to orient the listening room lengthwise so you have room for your side and rear surrounds with your listening position roughly in the center of the room.

Greg

Thanks Greg, but I thought the last thing you'd want to do would be to offset the distance between the speakers and the adjacent walls? Ref. "Cardas listening room"...