I have just completed a room based on the Fibonacci Series which is related to the Golden Ratio. In this series, each number is the sum of the previous two numbers starting with 0, 1, 2, 3, 5, 8, 13, 21, 34 etc. The ratio of each number to the previous one approaches the Golden Ratio as the series approaches infinity. For example, 13/8 = 1.625, and 34/21 = 1.6190476190 etc.
In theory, a room built using these ratios would spread the first order modes such that they were not directly additive at any point. The room modes are what they are depending on the distances between walls, and you can not change that, however, you can spread them out. This would minimize the constructive and destructive interferences and make the room response as smooth as possible.
I chose the dimensions of 8H, 13W and 21L which required building a new rear wall. You can also compute the room size for different sizes by using the ratio. For example, if you had a 10 foot ceiling, the width would be 10*1.618 = 16.18 and the length would be 16.18*1.618 = 26.17924.
Currently, I am in the process of measuring the room using both a RS Meter and a computer based system which generates a sweep and computes the frequency response and waterfall chart. Preliminary measures confirm the fact that the response is within +/- 3 db and there are three peaks corresponding to the primary modes generated by the floor/ceiling, front/back walls, and side walls.
So far I am very pleased with the outcome, as I put many hours into the construction of the room and would have been very disappointed if this turned out to be sub optimal. There are many approaches to room design, and I can recommend this one based on my experience.
I also did some additional things to the room, including a floating ceiling (ISOMAX sound clips, RC channel and Green Glue) for isolation, dual sound lock doors, and a hemholtz resonator built behind the back wall. As soon as I get some time, I will post my system with pictures and more detail.