I have my room dimensions and info listed in my other post but I'll include the basic stuff at the bottom of this post.
It's better to keep all your posts about your build in one place, in the same thread. That helps you to keep track of where you came from and where you are going, but it also helps others in the future who might be following your thread, because they have a similar situation and want to learn what you did, and how it turned out.
In dark brown I have shown my "shell" wall which is the sound isolating single leaf wall for each room
I'm just wondering why that shell follows the same line as the speaker soffits at the front of the CR. There's no need to do that, and it just complicates the build: better to go straight across with that wall.
Also, I'm assuming that the outer-leaf will be completed around the other two sides of this area? It looks like these rooms will be in a corner of your basement, and the basement walls will therefore provide two of the outer leaf walls, but you also need to add the other two walls, to create the complete envelope. It would help if you show those on your diagrams, to clarify the "big picture".
The question is should I keep front my "shell" walls (dark brown studs in photo) rectangular? Or should I angle them as I have shown?
Looks like I already answered that above!
I'm assuming you are talking about the angles where the speaker soffits are? Not needed. Keep that walls straight to simplify construction, and also to improve the acoustics inside the soffits.
I'm actually assuming my design is wrong and an actual rectangle might give me better bass-trapping area.
Yup!
I's alo worth noting that I'd rather have a good shaped/sized room than a hang out area - so if I need to push back the rear wall and booth and lose some space back there I'm ok with that.
Here too it would help if you show the outer-leaf dividing wall that goes between the rear wall of the CR and that green room area. Right now, it looks like the green room is inside your MSM wall cavity!
If you add the missing walls in there, the overal design is a lot clearer.
Anyway I'm assuming that theres only so much I can do in term of predicting what the room WILL/MAY sound like - and the actual room treatment should be determined after I run REW in my new finished space; speakers in soffits, room untreated.
Yup! Exactly. Start by taking some very careful base-line measurements, one speaker at at time then again in combinations, then again with all of them running, so you have basic data against which you can compare each round of treatment. That helps you see what is working, what isn't, and what you still have to do to get the room good.
My question is - is there any room treatment that I will undoubtedly need - and that I could incorporate into my sketch up design?. I have 2 corners with plenty of space toward the rear of the room which I'm assuming will need bass trapping.
yup again! bass traps will be needed for sure! Big ones, and lots of them, because the room is small.
You will also undoubtedly need some for of control at your first reflection points: that might be angled reflectors, or absorbers, or both. With such huge speakers, that's going to be a major issue for you, since the first reflection "points" won't actually be points at all: they will be areas, or zones.
But beyond that, I don't know what frequency(s) need attention. I can use room simulator in REW to predict the problem frequencies - but is it too early for me to start designing/planning treatment for those frequencies? Or os it best to wait until after I analyze my room?
You are doing an RFZ style room, that is more than just a simple rectangular box. So all calculators that consider the room to be a box will not give you accurate predictions. Even if you did have a perfect rectangle, the predictions would still not be 100% accurate, since there's no such thing as perfect building materials, nor perfect building technique. The actual result will not match the predicted result, so it's best to just do design in the minimum that you will need without any doubt, then leave plenty of space to add other devices as needed, when you do the REW analysis.
There are two schools of though here: one is to design the room to be as live as possible, then slowly add treatment to "kill" it down to the required level. The other is to design the room as dead as possible, then add devices to liven it up as needed. Personally, I prefer the second option: Start with a really dead room (inside-out walls and ceiling, filled deep with good insulation) then cover that up with tuned treatment, reflective areas, diffusion, or even more absorption, as the case may be for each part of the room.
Should I use a Cloud for overhead/ceiling treatment or design an Angled ceiling in the the "Shell"?
Both ways work, but from the point of view of actually building it, it is far easier to have a flat ceiling then hand an angled cloud below it. That way, you also get to adjust the angle if you need to, just by making the chains longer or shorter. It's hard to adjust the angle of a purpose-built ceiling!
I usually only do angled ceilings where there's a real need for that, such as if there is a structural beam, HVAC duct, or something else that can't be moved up there anyway.
(financially that is - I'll probably have to cut many corners physically to make this work).
very true! lots of corners to be cut in building a soffit, and most of them have to be cut at strange angles...
I know my speakers are way big for the room. I know I need that wall massive to make it work right and Im thinking of even incorporating concrete into the design,
Right on all three counts!
Before I ask too many questions or do too much research into a design which may not be ideal for this room - I was wondering if anyone had any suggestion about how to construct this soffit?
I can OM you something about that, if you want, but I can't put it out in public on the forum, as it's a paid design I did for one of my customers, and he hasn't yet given me permission to release it, only to show it in private. PM me if you are interested.
Before I ask too many questions or do too much research into a design which may not be ideal for this room - I was wondering if anyone had any suggestion about how to construct this soffit?
Given the size and power of those things, you are going to have to build even more rigidly and massively than most people. I'd seriously consider brick or concrete stands inside the soffit to support them, then a decoupling system to keep them "floating" off that, and also a concrete front baffle for the soffit. The rest of the soffit can be wood (framing and finish), but the support and baffle would be good in concrete. One of my customers did a concrete front baffle for much smaller speakers than yours, and it worked out great. If you do decide to tilt your speakers down, then you are going to been very hefty tie-downs to keep them in place. That's a BIG box, with lots od vibration when run at high power: that has to be kept tightly under control, but also decoupled...
There are also subwoofers which I'd like to tuck up underneath the build-out somehow but I pretty sure these don't need to be "soffit" mounted per say acoustically - I'd like to get them flush with the wall for aesthetic purposes.
Right: just put them on the floor, close up the real front wall, below the center section of the soffit, and make that deep enough that you can hide them behind a cloth panel or some such. That's what I often do for subs. PM me about that too.
I'd prob do 2 layers of gypsum there as my "massive"? baffle wall.
Not nearly enough for those massive things. I'd want a lot more mass on the front baffle. Consider using really thick fiber-cement board, which can be cut fairly simply with a masonry blade in a circular saw, or using an angle grinder (lots of dust!). Your speakers are rectangular, so cutting the hole isn't too much of an issue, but it does have to be fairly accurate: you need to leave a small gap between the speaker cabinet and the baffle, for decoupling...
How important is it to match the mass of the existing subfloor to my new 2 layer gypsum ceiling?
The basic concept is that the surface density all around the entire leaf, on all sides, should be about the same. If you have one area that is substantially lower surface density, then that's a weak spot, for isolation, so you should concentrate on that area. On the other hand, if you have one area that has substantially higher surface density than the rest, then you wasted money on that part! (Unless it already was there, of course).
One major point here: get a certified structural engineer to sign off on anything you do to that sub-floor above you. That's dangerous stuff, to be adding lots of mass to that above your head. There are limits to what the structure can handle, in terms of additional live load, so make sure that you stay within those limits, regardless of how much mass you "need"! If you really do want very high isolation, then you might need to beef up the structure of that floor with additional joists, beams or pillars, but only a qualified structural engineer can guide you on that.
Am I to calculate the mass of each of these areas and then add only the amount of drywall to the underside as to match the new ceiling mass?
Yes!
Would it be a dire mistake to mindlessly just put two layers of gypsum without using MATH!
YES!
But don't try to do the math yourself: Get that structural engineer to come in and do it for you! This is one area of building where you cannot skimp, and where it is very dangerous to go it alone. Don't do that. Call in the expert. He'll charge you a couple of hundred bucks to inspect the place, do some magical incantations on his computer, and give you a signed piece of paper telling you exactly what you can do with what you have, and also what additional things you might need to do to get where you want to go. That's the smartest money you can invest in your entire build. Well worth every cent.
now onto to researching vapor barriers…oh the joy.
General rule: they go up against the warmest side of the wall cavity, INSIDE the cavity. For guidance beyond that, check your local building code, and ask your contractor about how he normally does it in your area.
The room is going to be used for mixing hip hop and reggae and pop mostly, and occasional rock bands. So accurate low end monitoring is a must!
Then make your bass traps HUGE! And also leave lots of space on the rear and front walls for additional tuned treatment, if it turns out to be necessary. Modal issues and SBIR can be a bitch to control in small rooms, especially with massive speakers that go very low...
One general comment: You don't seem to be leaving much additional area around your speakers: the front baffles of your soffits are not much bigger than the speakers themselves. I'd try to make them bigger, if you can.
- Stuart -
What is the primary purpose of s studio? To only look cool? Or to make good music 
