2.85 L, 2.45 W, 2.05 H.
OK, so your first three axial modes are at 60.4 Hz, 70.3 Hz, and 84 Hz. Then you have three tangential modes at 92.7 Hz., 103.5 Hz, and 109.5 Hz. And yes, those are all in the area where your kick drum might have a fundamental, depending on how you have it tuned. 70 Hz to 110 Hz, is common for kick tuning.
OK, want to see something interesting? Take a careful look at your the graphs that you posted earlier, and and see if you notice something happening those six frequencies I just mentioned...
All six of those are pretty clear on your results! Your room is doing exactly what theory predicts.
And here's some more interesting theory that matches your reality very well: According to theory, your room modes are dominant between 60 Hz and 180 Hz. In other words, that's the range of frequencies where simple standing waves (modes) are a big problem in your room. Then, from 180 Hz to 720 Hz, the biggest issues are diffraction and diffusion (not so much modes in that range). Above 720 Hz, you are into a pretty diffuse, even zone, where things aren't so bad any more. That's where you might need diffusion, but I doubt it. I think you'll be fine just with basic treatment, as this is only a rehearsal room, not a tracking room.
It's nice when reality matches theory so neatly! Your room is performing almost exactly as theory predicts, and even though your graphs aren't calibrated or accurate, the effects are obvious.
Fortunately, as it turns out, your room dimensions are not too bad at all. Your room ratio is 1 : 1.19 : 1.39, which is very close to a really good ratio, called Sepmeyer's ratio, which is 1 : 1.14 : 1.39. So you have a reasonably smooth distribution of modes. OK, it's a small room, so "smooth distribution" is relative! But your ratio is about as good as you could possibly expect. So you lucked out there!
Finally, something good happened for you, by chance!
Damn, i thought so...how deep? 30-40cm would be OK?
Your superchunks are your main bass traps. Make them as wide across the front face as you can fit into your room reasonably. If you can make them about 80cm or so across the front, that would be good. They don't have to be equilateral triangles: If you want, you can stretch one side and make the other side fatter, if that would help. This is a rehearsal room, not a control room, so symmetry doesn't matter either: If you build one in each corner of the room, you can make them different sizes and different angles, if you feel like it. Or you can make them all the same, if that is easier.
I'd do those superchunks first, then measure the room again when they are finished, and we'll see how they are doing, before deciding on the next step.
Sorry...forgot to mention it. The classic panels with wooden frame, rock-wool covered with some type of fabric. Broadband absorbers, right?
OK, great. You'll need some of those, for sure! Yes, broadband absorbers is the right name.
OC 703 no. Rock-wool is used mostly and lately this one is used instead of rock-wool 'cause it's eco/health-friendly, but unfortunately there are no acoustic specs for that. It is the same as rock-wool and it's density is around 40kg/m3
That stuff should work just fine. They don't publish detailed acoustic specs, but there's one number they did give: the gas flow resistivity, which is important. It's a bit low, but plenty good enough for what you need. So that stuff should be good. Maybe you could call the manufacturer, and ask if they have more detailed acoustic specs that they can send you? They might have more data that isn't on the web site.
- Stuart -