Concrete basement, new studio, ceiling question

[lathqe]

Hello smart people,
This is my first post here, so I'll try to make sure to cover all the "dozen simple rules"

Recently I was given the opportunity to build my first project studio in the basement of a non-profit agency. The only stipulations are that they want some large, built-in shelving and good isolation from the floor above.

We are located in Central Asia, which means:
- our climate is like Denver, mountainous and semi-arid with -10c winters and +30c summers
- all existing buildings, floors, ceilings, internal and external walls, etc are made from concrete
- pretty much everything is DIY (and no fun products available like green glue, OC 703, resilient channel, mlv, or pre-made acoustic... anything)
- we have access to drywall, studs, batt insulation, and compressed mineral wool

I have the time and skills. I'm excited about this project, because in our city it will be the first educational studio to teach people how to use more than just a keyboard and Fruityloops.

The whole building is concrete, including the floor/ceiling. The basement has two rooms which will be connected with a window, and right now I am focused on the control room which is 5.7m x 5.7m x 2.5m tall (18'6" square and 8'2" tall)

I have finished the framing for a room-within-a-room using 2x6's, not touching the sides or ceiling at any point. The bottom of the ceiling is now at 7'2"

I am still puzzling over a few questions about the final product. I have read a bunch of threads and Rod Gervais' book (several times), but I can't seem to find the answer to these three, and I have to deal with them before I move on to the next phase (ie, it's easy to re-do framing while it's still just a skeleton...)

Question 1, regarding isolation:
The floor above (ie, my ceiling) is 8"-thick concrete ("pleetka" for those familiar with Soviet construction methods). This space is used for an office, hence the need for isolation. I am very concerned with the nasty room nodes that occur with low ceilings, so I have been planning on acoustically "killing" it by installing 12" of insulation and having just cloth on the underside (similar to what can be seen in Ethan Winer/Doug Ferrara's video here: http://realtraps.com/video_ultimate.htm ). I've never been in such a room, but it seems a legitimate method. (I'll use the walls for diffusion and trapping to keep some room ambiance).

My question is about how this relates to isolation. Clearly I will not have MAM. From the top down it will be: concrete floor -> air gap -> 12" insulation -> cloth -> me. Will this provide any significant isolation?
As I see it, my options are:
a)continue as planned,
b)attach OSB/plywood/drywall/whatever on the TOP side of my framed ceiling, which will leave me about 5" for compressed rockwool and then still just put cloth on the underside (which will be the ceiling that I see)
c)put drywall on the underside, make the standard MAM and then have to deal with a horrid-sounding space. As much as I want isolation, I want a good-sounding room even more!


Question 2: (it's shorter)
Similarly, the 4 walls. These will not touch the outside walls, 3 of which are just external foundation walls. What is my best practice here? From the inside-out, it will be: drywall -> batt insulation -> air gap -> foundation wall. This leaves a 2" air channel going up to the concrete ceiling above. Do I need to change this? Where does a vapor barrier go in this process?


And, finally, one question about acoustic treatment and room shape:
3) I am open to suggestions on where to build the closets. I will build them floor-to-ceiling and consider them to be "walls" for acoustic purposes. They will open with big, sliding doors made out of plywood which will have appropriate acoustic treatment the same as the walls will. Construction-wise, the easiest is to build it on one wall, but I fear that would mess with my stereo image. If I build closets on both walls, I run into the doorway, so I need to make them not run the whole room length. This turns the room into a "T" shape instead of a rectangle. Do those "wings" make a mess of resonances?
The attached images should help clarify my dilemma. Thoughts?

Thank you for reading this excessively-long introductory post. I would be delighted to have any input.

[Soundman2020]

Hi there " lathqe", and welcome!

- our climate is like Denver, mountainous and semi-arid with -10c winters and +30c summers

So HVAC is going to be a very important part of this build! That should be your first priority: Do all your HVAC calculations, to see how big your silencer boxes will need to be, then design the rooms around those.

- all existing buildings, floors, ceilings, internal and external walls, etc are made from concrete

Excellent!

control room which is 5.7m x 5.7m x 2.5m tall

Ummm.... it is SQUARE! That needs to be fixed, urgently. Before you do anything else, fix that.

I have finished the framing for a room-within-a-room using 2x6's,

Whoooaaaaa!!! You have FINISHED the framing, and you don't yet have a design? How did that happen???? This does not look good....

And why did you use 2x6 framing? That's wasting a LOT of space, unnecessarily. Your room is much smaller than it needs to be. 2x4 framing would have been fine for this: your ceiling is not high, there's not a huge load on it, so there was no need to use such large framing.

The bottom of the ceiling is now at 7'2"

Why? You said the original room was 8'2 tall, so why did you need to take up 12" of height for the ceiling? And why did the ceiling end up so low? If you build an inside-out ceiling, the actual acoustic ceiling would be at around 7'11". ....

Did you check your room ratio using a room mode calculator, to see what the modal response of your room will be? Is it even in the Bolt area at all?

(ie, it's easy to re-do framing while it's still just a skeleton...)

Yes it is, fortunately! You are still at a point where the issues can be fixed.

I am very concerned with the nasty room nodes that occur with low ceilings,

I think you mean "modes", not "nodes", but they are not due to having a low ceiling: the modal response of the room is due to ALL of the dimensions, taken as a set, not just the height. 8'2" is not a low ceiling. It's not high either, but it's not too low. 7'2" IS a low ceiling. Too low.

so I have been planning on acoustically "killing" it by installing 12" of insulation and having just cloth on the underside

This is not making sense: You say that the original ceiling height was 8'2", and that you put in joists that are not touching the outer leaf, and the ceiling is now at 7'2". That implies that you used 10" joists, left a 1" gap above them, and then put a couple of layers of drywall under your joists. I can't see any other reasonable way you would have ended up with a 7'2" ceiling. If you now add ANOTHER 12" of insulation to that, your visual ceiling will be down to 6'2" That's REALLY low, and very claustrophobic. I would not do that at all. I would do an inside-out ceiling, and then put 6" to 8" of insulation in the joist bays, leaving a couple of inches gap above it, then put fabric on the joists as the actual ceiling surface. But I would do that 10" joists, (maybe even 8", if you can get the right lumber), so the visual ceiling will be at about 7'3" to 7'5", but the acoustic ceiling will be about 8', or a bit less.

My question is about how this relates to isolation. Clearly I will not have MAM. From the top down it will be: concrete floor -> air gap -> 12" insulation -> cloth -> me. Will this provide any significant isolation?

I don't get it. Your descriptions are confusing. You said that your ceiling is already 7'2", but now you are saying that is isn't? That you don't actually have a ceiling at all? Then why are you wasting all that money on putting up framing? I'm not understanding this at all. If you have no ceiling, then why have walls? If you don't want any isolation then why frame anything? I just don't see any logic at all here....

If you do not want any isolation, then don't build any frames! No walls, no ceiling. Just hang your acoustic panels on the walls, directly.

b)attach OSB/plywood/drywall/whatever on the TOP side of my framed ceiling,

And how will you do that, if you already built it? Or is it NOT true that you built it? And if you have not yet built, how do you know that it will end up at 7'2"? This gets more and more confusing....

So let's clarify: Exactly what is it that you have built so far?

In the photo, I see a fully framed ceiling, yet you are talking about putting drywall on top... How would you get up on top to nail it in place?

which will leave me about 5" for compressed rockwool and then still just put cloth on the underside (which will be the ceiling that I see)

Why?????? Why would it be only 5", if you already put 12" joists up there???? Confusion.... Nothing here makes sense at all. The numbers do not add up.

c)put drywall on the underside, make the standard MAM

Why would you not be able to have "standard MAM" with the drywall on top? What would prevent that from working?

and then have to deal with a horrid-sounding space.

Why would it sound horrid? It would only sound horrid if you did not design it right, and did not treat it right.

What is my best practice here? From the inside-out, it will be: drywall -> batt insulation -> air gap -> foundation wall.

IT would be much better to do your walls inside-out as well.

This leaves a 2" air channel going up to the concrete ceiling above.

Why? I don't understand the connection. You are talking about how your walls will be built, in the horizontal direction, so how did that end up defining the vertical direction?

3) I am open to suggestions on where to build the closets.

Build them outside the room, not inside it. Closets are hollow resonant chambers that can grossly distort the acoustics of the room. Do not even consider putting closets inside the room. That would be a mistake.

I will build them floor-to-ceiling and consider them to be "walls" for acoustic purposes. They will open with big, sliding doors made out of plywood which will have appropriate acoustic treatment the same as the walls will.

If you want to consider them as "walls" for acoustic purposes, then you'll have to make them massively heavy (the same mass as a wall), and have multiple high quality seals on them, all around the perimeter, such that they are perfectly sealed air-tight. That would be very expensive, and very complicated with sliding doors. It is much, much simpler and cheaper to just have them outside the room.

This turns the room into a "T" shape instead of a rectangle. Do those "wings" make a mess of resonances?

Yes. They mess up the room acoustics, in several, ways.

In both of your diagrams, the room is facing the wring way. You CANNOT have it facing the window.side of the room, because it would be impossible to set up the speakers correctly like that, and also impossible to put the treatment in the correct location. The room will have to face the opposite direction, towards the blank wall on the right. That's the only feasible orientation.

There's just so much that is wrong, confusing, or unclear here, that I would suggest taking it down again, and first designing it properly, including the HVAC system, and also taking into account the room ratio, modal response, theoretical acoustic response, correct geometry, and initial basic treatment. Then, once the design is completed, you can actually start building the room. Proceeding the way it is going right now is pretty much doomed to failure.



- Stuart -

[Soundman2020]

Just wondering how this is progressing? Any news? Updated design?

- Stuart -