21' 13' room: long wall vs. short wall placement

Bob suggests a great loacation....the positioning well into the room is extremely important and something many audiophiles do not recognize (it will reduce comb filtering in bas frequencies)

Nsgarch has a valid point for keeping the speaker well away from side walls.

As long as the difference is at least 7 milliseconds (if my memory still works

Bob Katz (recording engineer for Chesky) recommends about 5 millisecs....so in practice between 3 and 4 feet of distance between speaker and side wall is a good rule of thumb.....if this means you need a long dimension then it may be the way to go.