Positive Feedback's ongoing article on room treatments makes interesting reading...
Part 1: http://www.positive-feedback.com/Issue21/gordon_rives.htm
Part 2: http://www.positive-feedback.com/Issue32/asc.htm
Part 1: http://www.positive-feedback.com/Issue21/gordon_rives.htm
Part 2: http://www.positive-feedback.com/Issue32/asc.htm