Are you building a new studio and wondering how to figure out the ideal room dimensions and ratios for it?
Maybe you’ve stumbled across advice that you need to optimize the shape of your room because the ratios of the width, height and length will affect how good the sound and the acoustics will be.
Maybe you’ve read that you need to build your room to the golden ratio, or have had numbers thrown at you, like “2:3:5” or “1:1.26:1.59”.
As usual, there is some truth to it, but to figure out what you should actually do, you need to look at the larger context.
And as it turns out, for us home and project studio guys, the importance and usefulness of optimizing room dimensions is way over-exaggerated.
Why Optimize Room Ratios?
It all dates back to the research of R.H. Bolt from 1946 who was the first to categorize the affect of the spread of room modes on the frequency response.
Simply put, he found that, as long as the room modes are spaced evenly across the low end, you could get a balanced bass response. No two modes would sit on top of each other, giving a bump in energy, or would be missing, to let the energy drop.
He found a whole set of ratios that met his criteria, which he collected in a diagram that is known as the “blob”.
Since then many more have studied the impact of room dimensions on good sound and have come up with their own criteria, ratios that meet them, and ways to calculate them. Most notably Bonello.
Some Fundamental Problems
But they all make assumptions that don’t hold up in reality:
- No room is a perfect rectangle with 100% reflective walls.
- All room modes are never excited at the same time.
- All room modes are never equally audible by the listener.
- Room modes don’t all carry the same energy.
When you are checking the room dimensions of your new studio, the first in the list causes the biggest issue.
Walls, doors and windows all affect the pattern of room modes.
Toole confirms this by saying that “… even within the low-bass region wall flexure can introduce phase shift in the reflected sound sufficient to make the “acoustic” dimension at a modal frequency substantially different from the physical dimension.”
Or in simpler words:
The room dimensions cannot reliably tell you how your low end will sound.
This used to drive me crazy. For room after room that I treated, I would calculate the room modes and compare them with my measurements. Every time it would baffle me that they never really matched. Occasionally they would coincide for one, maybe two dimensions. But even then it was more of a guestimation.
And the more nooks and crannies a room had, the more puzzling the game got.
Now I usually choose to ignore any room mode calculations altogether and directly focus on what is actually happening in the low end instead.
Toole goes so far as to say “… that there is nothing that can be done in advance of building or setting up a room that has a high degree of certainty of achieving good bass. Probabilities may be improved in some respects of acoustical performance, but not all respects. There is no “magic bullet”.”
So what what does that mean for you in practice when you are building your next room?
- If your room isn’t rectangular you can safely ignore the topic completely.
- If your room is rectangular, you can use the calculator to increase your chance for good bass.
- Using a simple criteria like the “Bolt-blob” is good enough, given the accuracy and effort involved.
- Don’t get hung up on making the ratios perfect, chances are that it won’t predict reality reliably anyway.
Now, if you still want to figure out what dimensions and ratios work best for your room, I’ll show you step-by-step in the video below using the Amroc Room Mode Calculator:
R. H. Bolt, “Note on The Normal Frequency Statistics in Rectangular Rooms,” J. Acoust. Soc. Am., vol. 18, pp. 130–133 (1946).
O. J. Bonello, “A New Criterion for the Distribution of Normal Room Modes, “J. Audio. Eng. Soc., vol. 29, pp. 597–606 (1981).
 Toole, F.E., 2008. Sound Reproduction: Loudspeakers and Rooms. Focal Press.