Acoustic Treatment for a circular mixing room

Hi everyone, I am new on this forum and I would like to get your advice for treating the acoustics in my room. I know it's not a good shape for mixing but it's the only room available in my house. It is a circular room with a cone shaped ceiling... I heard it is the worst shape possible but I would like to have your suggestions. - Ben

Hi there Benjamin, and welcome! :) Please read the forum rules for posting (click here). You seem to be missing a couple of things! :) You have picked pretty much the worst shape for a control room, so this will be a very interesting thread! :) Before you do any treatment at all, please download the REW acoustic analysis software package from the Home Theater Shack web site. It is free, but you do have to register there in order to get (registration is also free). The use REW to do an acoustic measurement of your room, and post the resulting MDAT file here on the forum, so we can analyze it in detail for you, and figure out what to do about your room.

I heard that circular rooms have the most acoustical problems

Right! About the only thing that could be worse is a sphere, or maybe a circular room with a cone-shaped roof... :shock: - Stuart -

Thanks for your help Stuart. I am currently in the US therefore I will do the analysis in one month (when I get back home). - Ben

Do you know which microphone I should use for the REW analysis? Is it an omni microphone? Thanks, - Ben

Yes, it has to be omni. The best idea is to get a proper measurement mic, such as a PreSonus PRM1, Beyerdynamic MM1, DBX RTA-M, or even a Behringer ECM8000. Or if you want to go really high-end, maybe an Earthworks M23... Do make sure that you calibrate REW correctly before you measure the room, and do make sure that you place the mic exactly where your head is when mixing. The measure that location of the mic very precisely, and keep a note of it: you must be able to get the mic back to that exact same location in the future, for measurements after you install each piece of treatment. If the mic is not in the exact same position, then you cannot validly compare the readings. Even a just 1cm out of place can make a difference: you must get it back to the precise same point every time, accurate to within about 3 or 4 mm. Also, when you calibrate, make sure that both your hand held meter and REW are set to "C" weighting and "Slow" response. - Stuart -

I heard that a circular room is problematic but I did not know it is the worst room shape...

It's the worst shape for many reasons: Firstly, the walls focus sound waves, and the focal point depends on where the sound came from. So depending on where you stand in the room, you will hear very, very different things coming form the speakers. Also, since the "dimensions" of the room are exactly the same in all directions, the modal response is severely skewed, with just a few major modal peaks that are related only to the diameter of the room, and nothing else. You will likely need some type of tuned trap to deal with those, since the peaks will be so sharp, so large, and so well defined. Maybe a couple of membrane traps might do the job. There's also the issue of surface waves, that follow the curved surface of the room, and therefore get back to their starting point to continue around again. If the wavelength happens to be related to the room circumference, then that's an unusual form of modal resonance that only happens in such a room. Not so easy to deal with.

By the way, the biggest room at Avatar is circular with a dome and it is considered as one of the best room (acoustically) in the world: it is well known for drum sounds.

But that isn't a control room... :) Yours is. Control rooms and live rooms have very different acoustic requirements. Major differences. Control rooms are deigned to be absolutely neutral, acoustically, but live rooms are supposed to NOT be neutral: they are meant to have character, "vibe", "style" or whatever you want to call it. Designing the sound of a live room is a bit more complex than for a control room, if you are aiming for something specific. The sound of the room itself should be attractive for the purpose it is to be used for, and for the musicians whose business you are hoping to get. Some people like a "warm" sound, some like "mellow", some like "bright", some like "dark". And some like it to be variable, so they can change the sound as needed for each session. But that would be hard to do with a circular room: it will pretty much imprint it's own sound, regardless of what you do in terms of treatment, simply because the underlying signature of such a room is so powerful. That is very likely why that room at avatar sounds so good for drums: the acoustics of that size circle with that size dome just happen to sound really god with drums. But I'm betting you'd have a hard time recording a grand piano well in there... Late last year I was called in by a church in the city where I live, as they had discovered some major acoustic issues with the new building they were putting up. One of the big issues was that the architect had "cleverly" designed the rear wall of the stage with a circular shape: That's how it looked the first time I saw it: Cast in concrete, and too late to change the shape. And it sounded awful! Here's another view from a few weeks later, with the stage in place and a small band doing a test for me. You can see the acoustic panels that I designed for them, leaning against the curved wall. This was just a test, and the panels were later properly mounted in place. The difference was huge: without the panels in place the band could not even perform well, since they couldn't even hear each other clearly, even though they were standing just a meter or two way from each other! Due to the multiple sharp echos and phasing issues, they found it really hard to play in time, keeping the rhythm, and they felt uncomfortable playing like that. With the panels in place, it sounded great, and they played just fine. But look at the percentage of that wall that I had to treat, to get it sounding good. Nearly 80% of the total surface area of that wall needed treatment... The stage itself is also designed as part of the treatment. And that was just a small section of curved wall, not even a complete cylinder! So yeah, curved walls are a big problem. Been there, fixed that!! :) - Stuart -

thanks

Hey Ben, I checked your MDAT file, but the levels are way too low to be useful: You need to follow the calibration procedure for REW, using a hand-held sound level meter, then do the tests at a level of 80 dB for each individual speaker, then 86 dB for all speakers on at once. - Stuart -