Confused on some specifics

Hey everyone, I have done a ton of research into my studio design and have tried answering as many of my questions as I can, but I can’t seem to find answers to these specific questions.. I need help! When considering both a desire for isolation and good acoustics, I’m not sure if the walls finished over the foundation walls are insulated. If they are not, do I need to tear them down, insulate, and put drywall back up? Furthermore, I know they have not sealed in between the floor plate and the concrete floor.. So do I need to just tear down and rebuild this wall anyway? Remember, in this case, I am referring to the finished walls over the foundation, not the double studded two leaf walls I will build for the interior walls. Is it true that when constructing a double studded wall, that using different stud spacings and leaf masses for the two different walls is the right thing to do? If it is necessary, what is the best way to seal between the bottom stud plate and the floor to isolate? Is it necessary to seal between two layers of drywall on the same leaf using a product like green glue or a regular bathroom/kitchen caulk? I am really confused about how to construct my ceiling. First of all, I will unfortunately have air ducts running down the LONG way of my control room (my listening position is faced parallel with the ducts) on the ceiling, one all the way to the left, and one all the way to the right. So I have to drywall around the ducts..but how should I finish the middle of my ceiling? The ceiling joists are 7’3” from the floor. Should I drywall underneath the ceiling joists making a ceiling of about 7’1” or try to create the inner leaf up inside in between the ceiling joists? I am trying to decide about my control room dimensions and how to calculate what is best. The width will be 10’ approximately , for sure. The ceiling will be about 6’4” under those ducts, which will take up about 1/3 of the ceiling sq ft. The middle of the ceiling will be about 7’1” if I drywall underneath the ceiling joists, and that will of course cover about 2/3rds of the ceiling sq ft. And I have about 21’ of length that I can use. I would love to use all of it for space reasons, and because I can achieve about 1500 cubic feet of space. But first of all, how does that ceiling situation factor into my proper room dimension calculations? Also, can I get away with using all of that 21’ of length for the control room? Just a note, I wanted to make the back wall entirely absorbent with like a foot of insulation. So will that take away any problem making the room this long when the width and height are proportionately much smaller? I want to construct soffit mounts, but what if I get monitors that are a little bigger in the future..can I build the speaker cavity in the soffit mount a little bigger than my current monitors to accommodate a future purchase, or do the monitor cavities need to be a tight fit for monitors? When measuring room length if you have soffit mounted speakers, do you measure from the face of the soffit mount or the normal wall behind it? Eric

Hi Eric, and welcome! :) You ask a lot of interesting questions. Many of them have been answered before in different ways on the forum, but I'll give you a brief summary answer here in any case, since there's a lot of them in your post, and it might be useful to others in the future:

I’m not sure if the walls finished over the foundation walls are insulated. If they are not, do I need to tear them down, insulate, and put drywall back up?

Basic answer: Probably, but "it depends". You didn't say how much isolation you need, in terms of real-world decibels, so no-one can say if you need to do that or not. But assuming that you need to isolates something like acoustic drums, or you live in a typical city or suburban house with other people, then yes, you will need insulation in your walls. If all you need to isolate is voice-overs (ordinary speech) and you live alone in a silent concrete bunker, then most likely it isn't necessary. However (and more on this below), if those "finished walls" are built as normal stud-framed walls with drywall on both sides, and you want to build a proper two-leaf MSM isolation system, then you have no choice: one side of those walls must come off, and stay off, leaving the studs exposed, and if there is no insulation, then you will need to install some.

I know they have not sealed in between the floor plate and the concrete floor.. So do I need to just tear down and rebuild this wall anyway?

You don't need to tear it down just for that reason, but you do need to get to that joint and seal it. Sealing is critically important for good isolation. No seal = no isolation.

Remember, in this case, I am referring to the finished walls over the foundation, not the double studded two leaf walls I will build for the interior walls.

This is what I mentioned above, about the "more on this below": You already have a wall with at least one leaf on it, possibly two leaves. So why would you ALSO need an ADDITIONAL double-studded two leaf wall? You only need an additional SINGLE stud frame with a leaf on ONE side. And if the existing "finish walls" already have drywall on both sides, then you have to REMOVE the drywall from one side, in order to end up with a grand total of two leaves, only two leaves, and nothing but two leaves. If you build a double-studded wall next to your exiting finish wall, then you have a FOUR leaf wall! :shock:

Is it true that when constructing a double studded wall, that using different stud spacings and leaf masses for the two different walls is the right thing to do?

No it is not true, and it would be pretty darn hard to do for anything but a very short wall. If you have different stud spacing on either side, it wont be long until the studs start coinciding... What you should do is choose either 16" OC or 24" OC spacing for your new wall. But you DON'T need to build a double studded wall in any case! Sea above...

If it is necessary, what is the best way to seal between the bottom stud plate and the floor to isolate?

Acoustic sealant, or common flexible caulk. Or if the floor is very uneven, then perhaps a rubber strip under the bottom plate.

Is it necessary to seal between two layers of drywall on the same leaf using a product like green glue or a regular bathroom/kitchen caulk?

Caulk, no, Green Glue, yes. But Green Glue is NOT a sealant, and nor is it glue. It is a visco-elastic polymer that acts as constrained layer damping between the two layers. Very different thing, acoustically. I have an appointment outside right now, so I'll get back to you on the rest later, but I did want to give you the above to get you started. - Stuart -

I am really confused about how to construct my ceiling. First of all, I will unfortunately have air ducts running down the LONG way of my control room (my listening position is faced parallel with the ducts) on the ceiling, one all the way to the left, and one all the way to the right. So I have to drywall around the ducts..but how should I finish the middle of my ceiling?

IF the ducts cannot be moved, then you have two options: Built rectangular soffits around them (perhaps as part of your wall), or angle your ceiling on both sides, to a peak in the middle (gable). Neither is a fantaastic choice, acoustically. Each has it's pros and cons.

I am trying to decide about my control room dimensions and how to calculate what is best.

There are a number of good room mode / room ratio calculators around, many of them linked from the "stickies" right here on this forum. Stay away from the bad ratios, get close to one of the many good ones, and you'll be fine.

But first of all, how does that ceiling situation factor into my proper room dimension calculations?

You'd probably be OK just using an average for the height dimension. The mode calculators will not give you accurate answers if your room is not rectangular, but at least you'll get a ball-park idea.

Just a note, I wanted to make the back wall entirely absorbent with like a foot of insulation. So will that take away any problem making the room this long when the width and height are proportionately much smaller?

If you have the space, I'd use hangers at the back. When calculating ratios and modes, you still measure the room length the the actual physical walls, not just to the face of the treatment.

I want to construct soffit mounts, but what if I get monitors that are a little bigger in the future..can I build the speaker cavity in the soffit mount a little bigger than my current monitors to accommodate a future purchase, or do the monitor cavities need to be a tight fit for monitors?

Barefoot once posted a design here for a soffit mount system where it is easy to replace the speakers in the future. That's also here on the forum. - Stuart -

Thanks Stuart, I'm much clearer on those things now.

if those "finished walls" are built as normal stud-framed walls with drywall on both sides..

No, I am not referring to any of the interior walls, I am talking about the walls installed 4" over the perimeter of the foundation. If you look at my attachment, I am specifically referring to the right side of the control room (east side), the front of the control room, and the north side of the live room. Those walls are already built, I am just not sure if they are insulated, and they are not decoupled or sealed at the floor plate of course.

No, I am not referring to any of the interior walls, I am talking about the walls installed 4" over the perimeter of the foundation. If you look at my attachment, I am specifically referring to the right side of the control room (east side), the front of the control room, and the north side of the live room. Those walls are already built, I am just not sure if they are insulated, and they are not decoupled or sealed at the floor plate of course.

I guess maybe you didn't understand my previous post too well, so I'll try again. You never mentioned how those walls are built, or what they are made of. So like I said, if they are built as stud frames with heavy surfaces on each side, such as drywall, siding, OSB, plywood, MDF, etc, then they are already two-leaf, so adding additional walls means that you will have 3 or 4 leaves. You did say that you don't know if those walls are insulated, which implies that you do know they are hollow but don't know if the interior cavity has any insulation in it. Therefore, it is logical to assume that they are two-leaf walls already. If not, then please explain what you meant by not knowing if they are insulated. Put another way: The only reason why you'd be unable to know just by looking at them, is if you can't see inside them. For example, if they were brick or concrete walls, then it would be absolutely obvious if they are insulated or not, as you'd see the insulation right there, attached to the wall. So the simple fact that you said you don't know if they are insulated does imply that they are stud-framed, and you can't see what is inside since they have surfaces on both sides. And finally, since you also specifically asked: "If they are not, do I need to tear them down, insulate, and put drywall back up?", it seems more than reasonable to assume that they are, in fact, stud framed walls with drywall on one side and "something" on the other side. So I don't get why you said "No, I am not referring to any of the interior walls, I am talking about the walls installed 4" over the perimeter of the foundation" when those are the very walls under discussion! I don't see what other walls we could be talking about, and I thought in my post it was pretty clear I was referring to the same walls you are referring to. So, assuming that they are stud-framed walls, as implied by your post, then as I said before, they are already two leaves. So if you were to build another wall next to them, then you would have at least three leaves, perhaps four. Since you did not show any construction details at all on your rough outlines, and didn't supply any further details in your post, there's no way to know what you have there, or what risks you are running. Perhaps you should spend the time to build a detailed SketchUp model of what you have right now, and also what you plan to have, so we can better understand the situation. After all, we are not there and cannot see what you can see. Unless you either show us or tell us, then we just don't know. Photos would be useful too.

I am specifically referring to the right side of the control room (east side), the front of the control room, and the north side of the live room.

So am I! So why do you think I'm confused about which walls you are talking about?

Those walls are already built, I am just not sure if they are insulated, and they are not decoupled or sealed at the floor plate of course.

You already said that, and I already answered: If those walls are stud-framed with surfaces on both sides, then you WILL need to remove the drywall facing the room, and you WILL need to leave that drywall off, regardless of whether or not the wall is already insulated. You WILL need to do this because those existing walls already have two leaves on them, so in order to avoid building a 3-leaf system, you MUST remove one leaf. Then you would build a SINGLE stud frame a few inches away from those walls, and put drywall on just ONE side of that single stud frame, thus creating a 2-leaf wall. You do NOT need to build an additional double-stud wall, which is what you said you planned to do, in your first post. If you were to do that, then once again you would be be building a 3-leaf or 4-leaf wall, which is a bad idea in general, especially if you need to isolate low frequencies. I don't know how to explain it any more clearly than that! You never did explain what type of instruments / music you need to isolate, and you never did state how much isolation you need, so it's impossible to say what else you'd need to do, how much gap you'd need between the existing stud frame (once you take off the drywall) and the new stud frame, nor ho many layers of drywall you'd need on each leaf, nor if you might need to beef up the existing wall from the inside (between the studs), nor numerous other things. That's why the initial page of this forum specifically asks for all of these details, since it is impossible to provide accurate help without them. We can assume certain things about your build, guess at others, and read be between the lines a bit, and therefore give you some basic advice, but unless you provide all of the details asked for, that's all we can do.

... and they are not decoupled or sealed at the floor plate of course.

They don't need to be decoupled, since they are your OUTER leaf, and will not be touching your inner-leaf walls at all. But they do need to be sealed, regardless of whether they are inner or outer leaf: Everything must be sealed! So if you can't see if they are sealed, or can't get to parts that need sealing, then you need to figure out how to do that: sealing is fundamental to isolation. - Stuart -

Thanks again Stuart..Sorry to take so long to get back to you, I was out of town! Sorry about the confusion, I know why we weren't on the same page.. I was mistakenly referring to the wall in between the control room and live room as a "Interior" wall while in that case you were thinking I was referring to the walls that were already built along the foundation walls when I was talking about building a double studded double leaf wall. Anyway, I know now that I need to tear down and rebuild the walls up against the foundation anyway, so I will put the proper insulation there! ..and of course rebuild by adding only one new leaf. Also, sorry about not posting pics and giving more info on my circumstance.. I had just posted a thread called "basement studio Detroit area" a couple days before where I did include all kinds of pictures and more detailed info.. So I shouldn't have assumed that the connection would be made between this thread and that one. And I took your suggestion about building a detailed model in sketchup! I will be posting that soon!