Principles of Small Control-Room Layout

I’ve been working on control rooms for a bunch of years, now, and have designed and/or built more than my fair share. Also, I’ve been studying wide-dispersion speakers since 1982, and have learned an unfair amount about acoustics and psychoacoustics from that crazy effort. Also from that work plus a lot of studio work and management, I’ve come up with a basic room topology that I’m satisfied works very well, suitable for a broad range of speakers, either mounted in the wall, on the meter bridge or both. The best thing about it is that it is pretty simple, cheap and user-friendly. With full apologies to all those whose ideas I’ve, er, appropriated, and in the hopes that it may help me become absurdly famous, I’ve christened it “The Moulton Room.” How’s that for ego?

The Basic Principles for the Moulton Room:

Assuming a shoe-box, or rectangular, room (the cheapest kind):

1. The room dimensions should have “non-consonant” ratios to smoothly distribute low-frequency room modes. In musical terms, think of, for instance, the intervals of root-tritone-major ninth, or 1:1.41: 2.245 for relative height, width and length – with an 8-foot ceiling that would result in room width of 11’4” and a length of 17’11”. Root-fifth-tenth – 1:1.5:2.5 (8’ high by 12’ wide by 20’ long) – would be not good, because the room modes would tend to bunch together, reinforcing each other. Other nice ratios include root-tritone-minor seventh and root-tritone-major seventh.

2. The median plane between the loudspeakers should also be the median plane of the long axis of the room.

3. The reverberation time should be roughly the same at all frequencies between 60 Hz. and 8 kHz., and it should be quite short (ca. 80 to 200 ms.).

4. The lateral early reflections (those that arrive at the mix position within 50 ms. of the direct sound from the side walls) should be as loud and spectrally and temporally accurate as possible (i.e. no RPG-type diffusers and no Sonex® or other wall treatments). Floor and ceiling early reflections should be damped/diffused as much as is reasonable.

5. The monitors should have as broad horizontal dispersion as possible at high frequency. A good specification would be 3 dB down at 10 kHz at +/- 60° off-axis. A great specification, which I’m trying to get with my speakers, is 5 dB down at 16 kHz. at +/- 90° off-axis. Such performance yields spectacular tonal quality and imaging.

6. The monitors should be approximately 30° off the median plane to the left and right at the mix position.

7. The front wall, this is, the wall behind the monitors should be seriously absorptive from 60 Hz. to 20 kHz.

Take a look at the approximate layout of such a room in Figure 3.

	Dave’s 8’ x 11’4” x 17’11” control room, with monitor shell/absorber fitted. Speakers with a beamwidth of 60° shown. I personally think 60° beamwidth is way too narrow.

Naturally, in real life, you can hardly get room dimensions ‘n stuff that are exactly the way you’d like. Usually, you’re faced with an existing space that you are trying to adapt to some sort of ideal. The trick is to get as much symmetry as you can, as long a median plane as possible, and dimensions that are not, repeat not, consonant ratios. To accomplish this, you reduce the length and/or width (by building an inner wall) just enough to get yourself away from really nasty ratios.

Using these fairly simple and straightforward principles, you can construct a playback room that really sounds quite decent, and accepts quite a range of loudspeakers successfully. Also, if you are brave, there are some cylindrical diffuser/absorbers you can fit at the back and side walls that will make things even better. The nitty-gritty about how to design/build such a room has to be left for another article or two.

Using Multiple Sets of Monitors

The final thing to worry about is multiple sets of monitors. I’m a firm believer in listening to your work over a variety of monitor systems as a fundamental part of the production process. As Tom Bates puts it, “You aren’t done mixing until your mix sounds really good over every speaker available, not just your favorites.” For me, this means switching over to Auratones (which I think are obligatory) and whatever else I’ve got lying around (right now, Paradigms and Apogees), in addition to my custom wide-dispersion superspeakers.

It also means, and I think this is the more important part of it, taking the mix into different environments, like cars, living rooms, etc. Further, it helps to play your mix for other people over a range of systems. This sort of focus-group marketing study is absolutely essential, and it is one of the most important parts of the production process. You simply cannot reasonably expect one person listening to one set of speakers, in one location, in one room, to accurately predict the response of all listeners listening to all speakers in all locations in all rooms. So plan on a test listening phase in your production schedule.

Check your mixes all over the place, and remix them until they really travel well. The secret isn’t to get it right the first time (that only happens with dumb luck), but just to get it right. Your decently laid out control room (a Moulton room will do fine!) with decent monitors can really help you, by reducing the number of remixes and shortening your postproduction time, without absurd expense.

Fun ‘n Profit Time

You can make a very nice control room that is rectangular and that doesn’t have much in the way of wall treatments. And you can fit that room with some fairly inexpensive loudspeakers that will sound really nice, while giving you a lot of information about your recording. You need to maintain symmetry (within a few inches), a long and clear median plane, some really serious (but not expensive) sound absorption on one end of the room, and a small array of different loudspeakers. With such a space, you can hear and make some really nice recordings!

Happy masters!