Ideal room dimensions for great system sound?

Golden Ratio: The ratio of depth, width, and height based on the Greek Golden Rectangle. Often applied to speaker boxes or listening room design. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W. The ratio of depth, width, and height based on the Greek Golden Rectangle. Often applied to speaker boxes or listening room design. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W.

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The best listening room I've had the pleasure of being in was a custom designed room using the Cardas Golden Ratio for its dimensions, as Davetherave describes. The dimensions of this room were: 16' wide x 26' deep x 10' high.

If I were designing a room from scratch with no limitations, these are the dimensions I'd start with. At the same time, I've been in many listening rooms that had excellent sonics but were far removed from any of the various "ideal" dimensions. The main ingredient to success always seems to be in preventing the dimensions from being multiples of each other as much as possible, even if this means making the room a bit smaller in one dimension or another. It also helps to get as much depth as possible to support the bass. My current room is 14.75 x 26 x 8 and I'm delighted with the sound of this room. Also, be aware that it is possible to make the walls too rigid. It can be surprising difficult to tame excessive bass nodes in a room, particularly in a basement with concrete floor and exceptionally rigid walls. Often it's better to let those walls flex to naturally dissipate the bass from the room.

As I recall, the additional build specifications for the first room above included: floated concrete slab floor, interior walls isolated from exterior walls (shell construction), doubled interior sheetrock walls on z-bar, dedicated HVAC designed for low air flow and exceptionally low noise, electrical system separate from the rest of the house with each outlet on a dedicated isolated-ground line. The interior used very minimal acoustic treatment, relying mainly on half-height record shelving along the side walls, wool carpets and furniture.
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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.