Hi there "Luny Tune". Welcome!
This is my plan, and when looking at these drawings, you should know that the side walls are "soft". 95mm high density Rockwool behind speaker cloth.
Why? What is the reason for that? Do you not want to have good acoustic response in there? This is supposed to be a control room, right? So why don't you want to have the correct acoustic response for a control room?
I'm also making a sloped ceiling. From the front wall and to above the middle of the desk with 10cm boards spaced by 8cm across
Here again, I have to ask: Why? That wold create some really strange reflections, diffraction, and frequency response distortion right in the most critical part of the room. Why do you want to do that? What are you trying to achieve? Why not do a more conventional ceiling that is designed to give smooth response?
over the listening position I'm shifting to a membrane type basstrap tuned to the frequency that matches the distance between wall and floor right there.
And one more time: Why? Why would you do that? Yes, you do need to deal with the modal issues in the room, but using a tuned membrane trap for just one part of the ceiling does not seem to be notably useful. Which mode would you tune it to? How would you ensure that there is enough volume in the trap to have a significant impact on that mode? Do you even have enough space up there to get sufficient depth? Low frequency membrane traps need a very deep resonant cavity: can you afford to waste that much height? Why not just go with a more conventional angled, hard-backed ceiling cloud? It takes up much less space, is far more effective, and looks good too.
I'm all up for building more complex contraptions if needed,
Complexity is never a good idea in acoustic treatment of very small rooms. Simplicity is much better. Just do the most simple type of treatment that will accomplish the intended goal. Complex treatment needs a lot of space, is very hard to tune correctly, and very expensive.
and I have a couple of ideas inspired by larger studios I've worked in.
Things that work in large studios do not work in small studios. Acoustics response is not scalable. You cannot take the treatment that you see in a room twice as big as yours and just scale it down to half the size: that would be a disaster. Small rooms have very, very different acoustic needs from large rooms. For example, you cannot use any form of numeric-sequence diffuser in a small room, but in a large room you really do need them. Small rooms need much more bass trapping than large rooms do, proportionally. Etc. There are major differences, so it is very probable that the things you have seen in larger studios would not work at all in your place, or indeed, might make things even worse. Plus, what you can see in most studios is
not the actual treatment: frequently the real treatment is hidden behind the room surfaces, and not visible at all... So what you think you saw is very probably not what was actually there.
I'm building walls to flush mount my monitors in.
Excellent! That is one of the best things you can do in a control room. But your pictures seem to show that the monitors are mounted too low in that wall: you should raise them until the acoustic axis is at or slightly above ear-height.
In the best sounding control room I've ever worked in, there was a zigzag wall of plywood
Once again, that might have worked fine for the room you saw, but it will not work for such a small room, and certainly not at the angles you show. A zig-zag panel like that is basically a tightly tuned diffuser that will exhibit lobing effects. In a large enough room, that would not be a problem, but in a small room you would hear a very different response just by moving your head a bit to the left or right, as you would be in different parts of the lobing pattern.
because it'll be reflecting sound away at a predictable angle
... and it is also a tuned diffuser! Any time you have a repeating pattern of peaks and valleys, you create a tuned diffuser. In addition to the simple reflections, you will also have lobes that change with frequency.
I could maybe use them as membranes for basstraps
How would you tune them? A membrane trap needs a rigid, sealed cavity behind it, but you need that space for the low frequency broad-band absorption. How would you fit both into the same space? And why would you limit your broadband absorption options in favor of tuning to a few specific frequencies? That does not make much sense.
Also, I think it looks good
It does look good, but "looking good" is not a valid reason to chose an acoustic treatment device for a studio. Rather, it must first perform a useful acoustic function, then it secondly it must be made to look good.
The "blanks" in the corners on both sides of the zigzag wall are suppposed to be Superchunks as big as I can make them and still keep them symmetrical in the room.
Superchunks do not need to be symmetrical. They just need to be as big as you can make them. Low frequency sound, and especially modal resonances, are not directional, so treating more on one side of the room than on the other does not make a much difference. Modal issues can be treated either at the point where the particle velocity is at its peak, or where the wave pressure is at its peak. Room corners are the perfect location for the latter.
There are several other major problems with that layout, such as having your head in the exact middle of the room (1.8 m from the front wall, and also 1.8m form the back wall), which is the worst possible location, the speakers are too close to the side walls, there is no treatment on the first reflection points, there is no balance in the treatment, and there is very little isolation between the CR and the isolation booth.
I would suggest going with a more conventional, much simpler design, based on RFZ or CID, ans using the normal, typical, common treatments that are needed in small rooms.
A soft wall of mineral wool surrounding the speakers or (like I've drawn here) a firm wall stuffed with mineral wool creating the "infinite baffle" for the monitors
That would not be an infinite baffle! In order to correctly flush-mount speakers, the baffle must be very solid, hard, rigid, and massive. Most people use several layers of plywood, MDF, or something similar. Some people use concrete. Some use stone. The concept is that the baffle is an extension of the front panel of the speaker, and needs to be just as solid, hard, and rigid, proportionally.
angled to prevent standing waves between the front and rear walls?
You cannot deflect standing waves with angled porous absorption: standing waves (room modes) are always measured to the solid boundary walls of the room, independent of any treatment you put in front of the walls. Mineral wool is just treatment. It does not prevent the waves from forming: all it does is to damp the resonance.
I haven't seen the zigzag plywood wall in any other studios than the one mentioned above and I can't find anything on the interwebnet.
There's a reason for that: Designing a control room with such a rear wall would be rather complex, and there would not be a huge benefit to doing so. It is a lot less complex, less expensive, and less time consuming to do more conventional treatment. It is possible that the studio you mentioned paid a designer to figure out all the issues and get it right, in which case it would have been expensive. Or it might just have been sheer luck that they did the zig-zag thing it it worked anyway!
Does anyone know if this must be a membrane type basstrap
It does not "have to" be anything! When we are designing a studio control room, studios designers first calculate and predict the expected room response, then we look ta possible ways of dealing with each of the many problems, then we start by addressing the biggest problems with the simplest solutions and see if that will work, and what effect it might have on the other problems too. If it has negative effects, then we look for different solutions and try those, or we add secondary treatment to deal with the problems created by the main treatment. Then we repeat the process for each of the problems, and adjust the treatment plan as we go, because adding additional treatment can have an effect on the treatment we already decided to use. So there's a procedure here for coming up with the best solution that will have the greatest impact on the problems in the room.
What we NEVER do, is to start out by saying "I like the way zig-zag plywood looks on the back wall, so I will do that, then figure out how to deal with the additional problem that this would create for me." We also never start out by saying "I like membrane traps, so I'll use them in the ceiling and on the back wall". Or: "I like wood slats so I'll have them on the ceiling above the mix position.". What we do is to find the most suitable solution that works for the room, then think about ways that it could be modified to make it look better. That's why many, many control rooms have large sections of fabric on the walls: the fabric is there to hide the ugly treatment behind it. There might also be slats across the fabric, and they could be there as part of the acoustic treatment, tuned in certain ways to do specific things. Or they might just be there to protect the fabric, so that somebody walking past does not damage it. Or both.
Or could it be simply a sort of diffusor
The room is too small to be able to use diffusers that are tuned to useful frequencies. Tuned diffusers are only suitable for large rooms.
I've seen recommendations to avoid regular diffusing in such a small studio,
Correct. Because the acousticians who came up with the theory about how tuned numeric sequence diffusers work (D'Antonio and Cox) also figured out that they don't work in small rooms, because of the lobing artifacts. In a small room, you cannot be far enough away from such a diffuser that the artifacts are acceptable.
but place the diffusors at an angle so that they direct the sound away
I think you did not understand that post at all! First, what RT-60 time did you calculate for your iso booth? And based on that, what ISDG did you select for your control room? Then based on that, what design did you use for the diffuser, and what frequency range did you tune it to? It has to be Schroeder diffuser for this to work (which yours is not), and it has to be rotated 90° from the normal orientation. That means you would have to put such diffusers on the side walls, well behind the mix position, and then you would need a very long room so that the re-directed scattered energy can be treated further back in the room: Clearly, Jens is assuming that you need a very long ISDG in this case, that cannot be obtained in the usual manner. But it is impossible to get such an ISDG in your room, because it is so small! Jens also mentions that diffusers should never create a specular reflection (which yours obviously does), unless it is tuned to the range 10 - 15 kHz (which yours obviously is not). So basically, nothing in that post applies to your situation.
should I make each panel an individual trap or can I pair them up in three pairs?
How would you make that work? How would you tune such a trap? What fundamental frequency would you tune it to? And why would you tune it to that frequency, instead of another?
can/should I then use two different membrane thicknesses in one trap? (Making it effective at two different frequencies...?)
Once again, if you did that, what two frequencies would you choose, and why?
It seems to me that you are approaching this room the wrong way. You are starting out with some ideas that you saw in very different rooms, and trying to put them into your room, where they won't work, and indeed might make things worse than having no treatment at all. It would be much better for you to approach this from the normal perspective that studio designers use when designing a studio: analyze how the room is predicted to behave then choose the most suitable treatment for dealing with that. If you carry on trying to do it your way, that's like trying to design a car based on some cool wheels that you saw once on one car, and a nice driver's seat that you saw in another, plus a good looking steering wheel and gear stick that was in a magazine picture, and a pretty carpet you show on TV, then working backwards from there to design the rest of the car, and figure out what type of engine it needs, and how the body should be shaped... What you are doing so far makes about as much sense as designing a studio the way you are trying to do it...
- Stuart -
