Hi, i have a 3 x 3 meters room, and i want to turn it into a live recording room (just for recording, not mixing). i know the room size is bad and its kind of a cube, but thats what i got. also, unfortunately the closet you see must stay there.
all of the acoustic treatment is going to be DIY.
the room is going to be used for acoustic guitar and vocals.
the things you see on the walls with the horizontal lines represent QRD 1 dimensional deiffusers, and the other ones are rockwool absorbers. the diffusers would be with a design frequency of about 700-900Hz.
what do you think about the diffusers? will it help or am i better off with more absorbers instead? also, i can add more absorbers to this plan.
here are the sketches:
In a room that small diffusers probably wont be a good idea: you most likely wont be able to get your guitar and mic far enough away from them to avoid lobing. They might work, but it's a gamble.
What I would suggest you do is to run an full spectrum acoustic analysis of that room, and post the results here. If you have a 3m cube, then you can expect serious issues around 57Hz, 114 Hz, 128 Hz, 140, 160, 172, 181, 190, 207, 214, 229, 237, and many more. Your best bet might be two slot walls tuned around those specific frequencies, and the other two walls with plenty of absorption. The slot walls will give you some diffusion, and plenty of absorption at the problematic frequencies, will also not killing the room with too much absorption.
But first things first: do the analysis and post the graphs, so we can see what is actually happening in that room.
- Stuart -
Soundman2020 wrote:
In a room that small diffusers probably wont be a good idea: you most likely wont be able to get your guitar and mic far enough away from them to avoid lobing. They might work, but it's a gamble.
What I would suggest you do is to run an full spectrum acoustic analysis of that room, and post the results here. If you have a 3m cube, then you can expect serious issues around 57Hz, 114 Hz, 128 Hz, 140, 160, 172, 181, 190, 207, 214, 229, 237, and many more. Your best bet might be two slot walls tuned around those specific frequencies, and the other two walls with plenty of absorption. The slot walls will give you some diffusion, and plenty of absorption at the problematic frequencies, will also not killing the room with too much absorption.
But first things first: do the analysis and post the graphs, so we can see what is actually happening in that room.
- Stuart -
Hi, thanks for replying. can you explain a bit more about the guitar distance you mentioned: "you most likely wont be able to get your guitar and mic far enough away from them to avoid lobing".
i'm using a program called QRDude to determine the design frequency of the diffuser that i want to make. according to it, a design frequency of about 800Hz will provide me a minimum distance of 1.3 meters from the diffuser, which is ok according to the sketch i included (in the sketch, the distances from the mic to the diffusers are even around 2 meters).
i should have mentioned that i'm really a beginner to this acoustics issue, and i don't think i have the measuring tools nor the knowledge to make those tests you mentioned. i guess i want to know what's the best simple solution for acoustic treatment in this room.
i started looking into diffusion because i'm just concerned that my room will be too dead if i'll use only absorption, and i understand that diffusion can make a room sound more alive and give is somewhat of a bigger sound. i've read in a couple of places that a rather live room is important for acoustic instruments.
maybe those assumptions are wrong, does the minimum distance from diffuser that i get from the QRDude is not sufficient enough item of data to rely on?
Stuart gave you a list of frequencies determined by your room modes. These frequencies as you see are well below your design frequency of 800Hz. As the frequency goes lower, the distance increases. You have to design your treatments to address your problems, and you should concentrate on absorption and trapping - this is where you need to make your major investment. A simple diffuser could be added later for handling reflections of higher frequencies in proximity to the mic - but it's not you main concern.
Download the free software REW (Room EQ Wizard) and after perusing the manual you should be in a position to make the suggested tests.
Like BriHar said: Diffusion isn't your problem, the room is. In a cube-shaped room you have serious, serious modal issues, and the easiest way to deal with that is with tuned treatment. Diffusion is not going to help flatten the modal resonance issues: tuned resonators are. To deal with the problematic frequencies, all of which are below 300 Hz, you'd need a huge diffuser, bigger than the room itself! Do the math.
In other words, your diffusion design is not treating the problem: the frequencies you are designing for simply are not issues in that room. You are designing a solution for a problem that you don't have, and not designing a solution for the major problems that you do have.
Your solution is tuned traps, and by far the easiest way of doing that for multiple harmonics of the same basic frequencies, over a very large area, is a slot wall. Each of the slots should be tuned to one of the problematic frequencies (the one whose peak falls closest to that specific position in the room). You can even angle the walls slightly, to increase the bandwidth and make sure that you will hit all the modal frequencies at some point along the slot. That would also help a bit with flutter echo.
As I already said, the slot wall will help to control your massive modal issues, and will ALSO give you high frequency diffusion, plus reflection and absorption. Put two slot walls at right angles to each other on adjacent walls, and you will be doing some really good things to your room. Treat the other two walls with large patches of thick absorption, and you'll be doing even better. I'd suggest at least four full panels of 4" 703 about 4" away from the walls, or maybe two of 4" panels and two 2" panel on each wall. But the thicker ones on the vertical corners, perhaps even straddling the corners (bass trap style).
I would also put a couple of angled hard-back clouds on the ceiling (also with 703), to help with the vertical modal issues, and keep the floor hard, in order to not kill the room.
If you do all that and think that the room is too dead (unlikely) then, and ONLY then should you think about diffusion. In a small room, diffusion is not your best friend, and in a room with such major modal issues as a cube, diffusion is not going to help very much at all. Major problems require major solutions.
That would be my approach to fixing your room. Others might have different ideas, but that's how I would go about it: two adjacent slot walls tuned to the problems frequencies, with each slot carefully positioned close to the physical position of the node in the room. Slight angles to the walls, to increase bandwidth. Checkerboarded absorption on the other two adjacent walls. Hard-backed angled clouds on the ceiling. Hard floor.
But once again, before treating, measure the room! Download REW, get yourself a good measurement mic, and run the tests. It isn't hard to do, really! The hardest part is interpreting the results, but doing the tests is not that hard, and you can post the results here, for us to analyze. The reason why it is so important to do that is to see what your room is ACTUALLY doing. I gave you a list of the theoretical modal problems for a 3m cube, but most likely reality will be different: the real frequencies will probably not be exactly as predicted, because the room most likely is not a perfect 3m cube, and most likely has other things in it that will change the way it behaves acoustically. We need to analyze reality, to see what the REAL problem frequencies are, and design the treatment for those, not what theory predicts. We wan to make sure that the treatment will hit the problems, not make the room even worse by NOT hitting the problems, and on the contrary messing with frequencies that were actually just fine!
So measure the room, post the results, and we'll help you design the slot walls and other treatment. The most important tests are waterfall plot, impulse response and frequency response, focusing attention below 500 Hz. (although full spectrum graphs would be good too!)
- Stuart -
Soundman2020 wrote:
So measure the room, post the results, and we'll help you design the slot walls and other treatment. The most important tests are waterfall plot, impulse response and frequency response, focusing attention below 500 Hz. (although full spectrum graphs would be good too!)
- Stuart -
Thank you very much for this, it's much appreciated.
i will start making the arrangements for the measurements and get the equipment that's mentioned the REW manual (the SPL meter).
some questions i have:
from what materiel will i make the slot walls, wood?
can you send me a link to a picture of one for example, so i can get an idea of what it is?
will the two adjacent walls be fully covered by the slot walls or is it more like panels?
same question for the absorption, will it be panels like the sketch i posted or a full wall coverage?
also, i have easy access to a 60kg/m3 (or more) rockwool in any thickness. i also have access to rigid fiberglass but only in a 36-38kg/m3 density and its harder for me to get. so the rockwool will be fine right?
Thanks again!
Example of a slot wall:
viewtopic.php?f=1&t=226&p=1259&hilit=+slot+wall+#p1259
Yes, it is just strips of wood of very specific thickness and very specific spacing between them, over very specific depth. Those are the three main factors that set the frequency to which each slot is tuned. Basically, each slot is a long Helmholtz resonator, where the slug of air in the slot between each adjacent pair of wood strips will vibrate vigorously every time it "hears" the frequency to which it is tuned. The cavity behind has absorption in it (fiberglass/rockwool/etc). The combination of "vibrating air slug over damped cavity" removes some energy form the room at that specific frequency.
will the two adjacent walls be fully covered by the slot walls or is it more like panels?
The bigger you make them, the more effect you will get! In your case you have a cube, so the modal problems are serious: therefore the treatment needs to be serious too, so make them BIG. Entire wall will give you maximum effect. You want them on adjacent walls, not opposite walls, since you have modal issues on all three axes of the room, so you need to cover at least two of those axes. You could do a "slot ceiling" too if you want, but it might look a bit strange! Hard-backed angled clouds will look far better, I reckon...
:)
same question for the absorption, will it be panels like the sketch i posted or a full wall coverage?
Panels will be fine. I would use full sheets of 703, wrap them in cloth to disguise the "ugly", or put them in cloth-covered frames. Search the forum for threads on how to do this: there are many examples. Just a simple wooden frame (with large hoels cut in the sides) covered with cloth is the most common. Make some 2" thick, and some 4" thick, and set them up so that each panel is opposite a bare patch of wall on the other side. Put the thicker ones closer to the corners, or even across the corners (diagonally), for maximum effect.
i have easy access to a 60kg/m3 (or more) rockwool in any thickness.
That0s a bit too dense for low frequency trapping. 40-50 kg/m3 would be better. If you can't get anything else then it will work, but it won't be as effective as something less dense. Contrary to popular belief, higher density is NOT better for low frequency absorption: lower density is better (within reason!).
also have access to rigid fiberglass but only in a 36-38kg/m3 density
That sounds about right! that should work well.
- Stuart -
Ok i see. well, i wont be able to make such a large wall, there are two windows on two walls, so i cant block them permanently with a new wooden wall. also, i don't have the resources to make such large walls.
maybe i can do something in a smaller scale, can the slot walls be made as panels on stands? so i can move them when needed? i understand that it will be less effective, but will it have
some effect at all?
i'll also do some ceiling treatment with hanging absorption, i didn't include this in the sketch.
here is an example of what i have in mind, so you see what i mean, what do you think?
the slot wall panels wont have to be parallel to the walls like in the sketch, i'll be able to position them as i want because they will be mounted on stands.
i can also make the slot wall panels horizontal instead of vertical, if the wood stripes need to be longer in order to vibrate better..