Low Ceiling - what are my options!?!?

[lourudd]

Hi Guys, I'm wondering what you all reckon my best options are for building a studio in my basement which has a low-ish ceiling height. It's 2.5 meters at present, 8 foot 2ins.
I have built studios before about 7 or 8 years ago, using the room within a room or floating room model. We used a floating floor with joists on rubber and then rockwool and plasterboard walls and ceilings, with a good couple of sandwiches of the stuff all the way round for extra soundproofing.
The thing is - if I used the same sort of design for the space I have now, the ceiling height would end up being as little as head height! So I'm wondering if there's new technologies available that would give me a good level sound proofing, with the minimum amount of thickness, so I can retain as much ceiling height as possible. I need to be able to rehearse and record loud bass and drums without disturbing people too much. Any ideas guys? Thanks, really appreciate it

[Soundman2020]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

It's 2.5 meters at present, 8 foot 2ins.

It's not that low! That's above average for basements. Assuming you don't need huge isolation, that's decent, and usable. If you do your isolation properly, then you'd only lose a couple of inches off that, for the acoustic height of the room. (perhaps more for the visual height, but it's the acoustics that matters most).

We used a floating floor with joists on rubber

You probably don't want to hear this, but that was a major mistake: it cost you isolation, it cost you in performance (internal acoustics), and it cost you time and money. All wasted. Here's why: http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

If you avoid making the same mistake again, you'll have plenty of head-room. OK, maybe not "plenty", but still reasonable.

then rockwool and plasterboard walls and ceilings, with a good couple of sandwiches of the stuff all the way round for extra soundproofing.

I'm not sure what you mean by "a good couple of sandwiches", but that sounds a lot like you built a multi-leaf room! If that's the case, you trashed your isolation further, and spent more money than you needed to... as well as wasting space. But maybe I misunderstood what you meant by that comment, so it would help if you could describe exactly what you had there, from outside to inside, mentioning all layers that you put into each "sandwich", including air spaces and insulation. Those air spaces and insulation spaces are very important, in defining the isolation properties of the wall.

So I'm wondering if there's new technologies available

Nope! Not now, and there never will be, either. Because the laws of physics have not changed, and wont change. The laws of physics regarding isolation are pretty well understood: the equations are known to be correct, and accurately predict the isolation of any given construction material or method of putting together various construction materials.

For single-leaf barriers, it's dead easy to calculate using the equation know as "Mass Law", since it describes very well how single-leaf barriers block sound, and the key is simply mass. If you know the mass of the wall (or rather, it's "surface density" to be more correct), then you can predict what the maximum isolation could possibly be under perfect circumstances, then assume that in real life it will be a bit less. You can calculate the exact isolation for any frequency band you choose, or you can use the simplified "empirical mass law" equation, which accurately estimates overall isolation without considering the frequency.

For two-leaf MSM isolation walls, there's a set of equations that give you the answer, once again based heavily on the mass of the wall, but also taking into account other factors that don't apply to single-leaf walls, such as air gap, damping, and various types of resonance that rob isolation from various parts of the spectrum. Using those equations, you can predict the "transmission loss" graph for pretty much any two-leaf barrier. Ditto for three-leaf walls: there's another set of equations, although it gets more complicated here because there are multiple resonances going on that are inter-related. And so on: there are equations for "n" leaf barriers too, but that gets really complex, and any home studio builder who would even consider going multi-leaf is way out of touch with reality in any case, and those equations would be way beyond his/her ability to understand.

So no, there are no new magical materials that can give you more isolation than the laws of physics allow. You can get up to the maximum number predicted by the equations if you use top quality materials and build perfectly, but in real life you will get less isolation that that, because no material is perfect and no construction is perfect. In other words, the equations predict the limit that you could reach in theory, but in practice it will always be a bit less... or a lot less if you don't build it well.

OK, so that answers that actual question that you did ask: There are no new technologies, nor can there ever be. But t does NOT answer the question you SHOULD have asked: "Is it possible to get more isolation than I got before, without losing ceiling height"? And the answer to that is: "Hell, yes! For sure!" Not because technology has changed, but because you did it wrong the first time! It's not really your fault, though: you fell for the hype, myths and legends that surround and pervade the world of home studio building. I'm betting that you did a bit of research and came across a web site or maybe a YouTube video, or perhaps even a misguided magazine article, showing "How I Built My Studio", and there you saw, in all their useless glory, a set of rubber pucks with 2x4s sitting on top of them, then a light-weight deck of plywood or some such going on top of that... and grinning, smiling, happy builders showing thumbs-up at their wonderful accomplishment... so you figured if they did it, and it worked for them, then you should do it too! Truth is, both you and them got suckered into following a myth that is absolutely untrue, totally, useless, very misleading, and doesn't work.

I'm sure you didn't come here to be told that you screwed up, but if there's one thing we do well on this forum, it is to lay out the truth, in al its ugly detail, no holds barred, no punches pulled, no pussy-footing around. Short summary: You were mislead into wasting time and money the last time around, and THIS time you don't need to do that, as you can now learn the truth: And the truth is: it is impossible to improve full-spectrum studio isolation by floating a light-weight deck on joists over rubber pucks. They laws of physics demonstrate that it is impossible, and also demonstrate that it makes things WORSE, not better, for both low frequency isolation and also for room acoustics. For the very simple reason that floating a light weight panel over an air cavity creates a resonant system, and the typical sizes of joists and weights of plywood mean that the resonant frequency is exactly where you DON'T want it for a studio.

Even shorter story: You screwed up last time by building a "floating floor" that didn't float. You can get better isolation this time, and more ceiling height, and less expense, and less wasted time, but NOT making the same mistake this time.

It's basement, so it has a concrete slab floor. There simply is no better studio floor than that! Your floor is done. It's finished already. Nothing more needs doing, if it is a concrete slab on grade. That's it. Complete. If it is in bad shape, or looks ugly, or you just don't happen to like the look of concrete, then lay ordinary laminate flooring on top of it (over a suitable underlay), or maybe ceramic tiles, or some other hard, solid, reflective finish flooring surface. Just make sure that there are no air gaps under it.

that would give me a good level sound proofing, with the minimum amount of thickness,

Acousticians prefer not to use the word "soundproofing", because it describes an impossible goal, and it means different things to different people. We prefer "isolation", as that describes the function better. But isolation does not depend on the thickness of the wall. That's another myth isolation depends mostly on the MASS of the wall, in the sense of "How much does each square meter weigh?". Walls that have the same density will have roughly the same isolation. So a wall made from cardboard that is 79 cm thick would have about the same isolation as a wall made from steel that is 5mm thick, since they would both have a surface density (aprox. 35 kg/m2), and you could get the same isolation from a wall made of lead that is just 3mm thick, or a wall made from concrete that is 20mm thick... It's the mass that matters, not the thickness.

In other words, if you use high density materials, then you can have thinner walls and still get good isolation. But high density materials are generally more expensive than lower density, so then it becomes a question of how much you are prepared to pay in order to save a few cm on each side of the room.

so I can retain as much ceiling height as possible.

Retaining ceiling height is not about thicker or thinner materials, and not even completely about the density (although that plays a big role, for sure). Rather, it is mostly about using the materials intelligently, such that they provide maximum isolation. You can have two sheets of drywall put together in one configuration that gives you 25 dB of isolation if you use them wrong, or you can have the same two sheets in another configuration that gives you one hundred times more isolation, if you use them right. (Yes, I do literally mean 100 times more: 45 dB instead of 25 dB). It's not about thickness: it's about understanding the principles of acoustics and using them to your advantage, instead of fighting against them.

I need to be able to rehearse and record loud bass and drums without disturbing people too much.

Your very first order of business shoud then be to put numbers to those concepts: How many decibels is "loud bass and drums"? How many decibels is "not disturbing people"? One you have those two numbers, then you simply subtract one from the other, and now you know exactly how much isolation you need! And once you know how many decibels of isolation you need, you can look at some of the various types of construction, and construction materials, that will get you that much isolation, then decide which one you will use, based on local availability, laws, and your budget. For example, you light like the idea of lead sheeting, because it is so thin, but then you find that it is illegal to use in your area, and costs way more than you wanted to pay, so you'd have to look for different materials that are legal and that you can afford... but would end up with a thicker wall.

There's a process here. It's not rocket science: Follow the process, do some simple math, and you can arrive at the optimum set of materials and the correct method for arranging them to meet your needs.


- Stuart -

[lourudd]

thanks a lot for the detailed reply, very helpful. I forgot to mention that I want to build a small control room next door to the live room- so if I'm building directly on to the concrete floor will sound not travel straight into the control room?
Last time, I built like so;

within the original 4 walls of a room we;

-built 4 concrete walls to make a new room within the original with a 100ml 'air gap' between walls.
-Then laid struts and joists on walls, ceiling and floor (floor joists on rubber as mentioned earlier)
-filled struts with / joists with dense rock wool
-plasterboard over with x2 skins of different thicknesses and overlapping.

so by sandwich I mean what you call a leaf I think. The ceiling I think we did x2 of these leaves or sandwiches, to make up for the fact that there wasn't a second concrete 'wall' like the rest of the structure.
So you see if I did it this way again (which clearly I won't since you're giving me great information, I'd be left with only a little amount of ceiling height.
The lead sounds interesting - could you actually line the walls and ceilings with lead to get the same sort of isolation as what I've described above?!
thanks, Lou

[Soundman2020]

so if I'm building directly on to the concrete floor will sound not travel straight into the control room?

Not if you build it right, no. It's a basement, so your concrete floor is almost certainly "slab on grade", meaning that it rests directly on the ground, with only a bed of gravel and a plastic membrane in between. That implies that you are using the entire Planet Earth as your damping system... That's hard to beat! Your slab is damped by a hell of a lot of dirt, rock, oceans, cities, etc. OK, so it's only the first few meters that really matters, but it's still a hell of a damping system. If you directly strike the concrete with something solid, then yes, sound can be transmitted into the slab and potentially through into the CR. Which is why you isolate all things that could cause such "impact noise". You'll put your drum kit on a small "drum riser" that isolates it from the floor, and your bass amp can sit on an isolation pad of some type too. Or you could just put isolation pads under the pedals and the feet for the kick and snare... many options. There are designs here on the forum for drum risers. As long as you keep the impact noise out of the slab, you are fine. The airborne noise will not be a problem, as it won't get into the slab. Concrete is very massive, very rigid, and does not pick up air-borne noise very well, due to the huge impedance mismatch between air and concrete. Not much energy gets transferred.

-built 4 concrete walls to make a new room within the original with a 100ml 'air gap' between walls.
-Then laid struts and joists on walls, ceiling and floor (floor joists on rubber as mentioned earlier)
-filled struts with / joists with dense rock wool
-plasterboard over with x2 skins of different thicknesses and overlapping.

So from outside to inside, it was something like this: Original building with brick(?) / concrete(?) outer walls, then an air gap, then concrete "middle" walls, then another air gap, then two layers of drywall (plasterboard). Is that about right? If so, that's a three-leaf system, and therefore has LESS isolation than the equivalent two-leaf system of the same total mass and thickness. That sounds silly, illogical, not intuitive, etc. but it's true. A three-leaf wall will always have less isolation that a two leaf wall built with the same total mass, and the same overall thickness. Laws of physics. Resonance, actually. Resonance will rob you of isolation, because at it's resonant frequency any system will not only fail to isolate, but it can actively amplify the sound passing through it. And with a three leaf wall, you have two thin resonant cavities, whereas you would have had just one deep cavity if your wall only had two leaves. A deep cavity means a much lower resonant frequency, usually so low that it does not cause a problem. But two thin cavities will each have their own frequency, and each of those will be higher up the scale... thus robbing you of isolation at those frequencies, and at all related frequencies.

What you should do in your new place, is just a two-leaf wall. The existing basement wall (I'm assuming brick or concrete block?) is your outer leaf, and it is extremely massive, once again because it has the entire planet behind it. So that's great: it's difficult to imagine that you could make enough noise in your studio to make the entire planet vibrate! So you have your outer-leaf wall already: now you just need to build your inner-leaf walls. One single-leaf wall for each room. Like this:

MSM-two-leaf-WallChunk-conventional-NOT-inside-out--three-room--with-corridor--S04.png

That's the concept, not your specific situation. It shows a three-room studio, plus a corridor or non-isolated area next to them. The entire thing is surrounded by one single wall (in your case, the basement wall), then there's an "isolation wall" that divides the space in to the area that will be isolated to create the studio, and the area that isn't isolated. Then inside the isolated area, there are three individual rooms (there will only be two in your case, but the principle is the same). Each of those rooms is a single leaf, consisting of stud framing with sheathing on only one side of it. That sheathing might be one or more layers of drywall, OSB, MDF, plywood, fiber-cement board, and yes, even exotic and expensive things like steel plate, aluminium plate, or lead sheeting. The key is to calculate how much mass you need on there to get the isolation level you need, then choose materials that add up to that amount of mass (surface density), and check that against your budget. If your selection of materials turns out to be too expensive, then you'll have to go with cheaper, usually thicker, materials. If you think the materials are less expensive than you imagined, and you want to save space, then you can go with higher density, thinner, more expensive materials.

One very important thing here: the inner-leaf of each room is absolutely, totally and entirely independent from the outer shell, and also from the leaf of the other rooms. In other words, they don't touch at any point. No mechanical contact at all. Not even a single nail. This is critical: there can be no solid paths at all between the inner leaf of a room, and anything else: it must be "fully decoupled". Even something as small as a stray nail that accidentally connects one leaf to another leaf will trash your isolation. The leaves are completely self-standing and independent. They all sit on the same concrete slab, but apart from that, there is no contact.

Also, not shown in the above diagram is that each room has it's own individual ceiling, and once again those ceilings rest ONLY on the inner-leaf walls: there is no contact between the ceiling of one room and the ceiling of another, nor with the ceiling of the outer leaf shell that encloses them all.

This is what is meant by "room-in-a-room" construction. Each room is one single leaf, and, they sit inside the outer "room", that is the building itself. That's it. There's a lot of confusion out there about this term, but the above diagram is what it actually means.

Technically, this whole arrangement is referred to as a "fully decoupled two-leaf MSM system". It is the only way to get high isolation at low cost and with use of minimal materials. Single leaf requires mountains more mass to get the same isolation, and 3-leaf, 4-leaf, 5-leaf, n-leaf all have penalties in terms of space and reduced performance. fully decoupled 2-leaf MSM is the optimal system. Which is why the vast majority of studios are built like this!

so by sandwich I mean what you call a leaf I think.

Right. Technically, a "leaf" is just a bunch of mass, and might consist of several layers of materials, to build up the mass to the right level. The most common materials are as I mentioned above:drywall, OSB, MDF, plywood. In most places around the world, plain old drywall is the best value for many: inexpensive, and fairly high density.

The ceiling I think we did x2 of these leaves or sandwiches, to make up for the fact that there wasn't a second concrete 'wall' like the rest of the structure.

I'm assuming there was a roof above that, or something similar, such as the floor of the room upstairs? In that case, once again you created a triple leaf barrier, which performs worse than the equivalent two-leaf barrier.

So you see if I did it this way again (which clearly I won't since you're giving me great information, I'd be left with only a little amount of ceiling height.

Yep! So aren't you glad you came here, and found out the right way to do it, that won't eat up all your height, and will actually do a much better job of isolating? Aren't you glad we saved you thousands of dollars / pounds / euros, and many, many cm of head room, plus lousy acoustics?

The lead sounds interesting - could you actually line the walls and ceilings with lead to get the same sort of isolation as what I've described above?!

You could, yes. Provided that you did it correctly, and intelligently, properly designed, properly calculated.... and that you have a hefty budget! Lead sheeting is not cheap, and might not even be allowed as a construction material where you live, or might be subject to restrictions. But in theory it is possible, and I do know personally of one case where a high-end pro studio was built in a residential building, and lead plates were used in the walls to achieve the required isolation. That happened here in Santiago, where I live, and where it was installed legally and safely. That was back in the 90's, and the studio is now defunct, but as far as I know the lead is still in the walls! And it worked just fine...

- Stuart -

[lourudd]

Thanks again for such detailed info. Just a couple of questions, hopefully don't sound too silly but just to clarify - You mention that the sheathing would be only on one side of the leaf-clearly we would board the inner stud frame work (inside of the room) with plaster or some sort of board with lead lining for example... But would we not also board the back of the frame work which faces the outer shell?
On the diagram I take it the green wall is representing the inside of my basement wall? And if it is- is it green and yellow because it has studs with rock wool on it?
Thanks, Lou

[Soundman2020]

Just a couple of questions, hopefully don't sound too silly but just to clarify...

Not a problem! As one of my high-school teachers used to remind us, more decades ago than I care to remember: "The only silly question is the one you DIDN'T ask!". Everyone is a beginner at something, at some point in time, and the best way to learn and understand it better, is to ask questions... even ones that you might think are silly, but really are not silly at all.

You mention that the sheathing would be only on one side of the leaf-clearly we would board the inner stud frame work (inside of the room) with plaster or some sort of board with lead lining for example... But would we not also board the back of the frame work which faces the outer shell?

Nope! Because that would make it a three-leaf system, and would REDUCE isolation. It's one of those things about acoustics that is not intuitive at all, and sounds illogical until you understand the theory. You think:" But I'm adding more mass to the wall! Surely that must make it better?" But no, it does not necessarily make it better, and potentially makes it worse.

To add to your confusion, consider this graphic illustration:

2-leaf-3-leaf-4-leaf-STC-diagram--classic2-GOOD!!!.gif

All three of those examples use the exact same wall thickness, and same basic construction. All of them are double-framed walls, where each side is a stud frame with sheathing on it. In the first case, each frame has a single sheet of drywall on BOTH sides, and it gets you a rating of STC 44 (not to be confused with 44 dB of isolation, which is not the same thing!). And here's where it gets curious: If you take OUT one of those leaves, by removing a sheet of drywall from one of the frames, the isolation goes UP! You now get STC 53., which is a pretty large jump. The wall now has LOWER mass (since you took out a sheet of drywall, but it isolates BETTER! Not intuitive at all, but true. In the third case, on the right, the OTHER stud frame also had it's second sheet of drywall removed, and both of those missing sheets have now been transferred to sit on top of the drywall on the other side of the studs. You now have the same original mass as the first wall, but arranged according to the laws of physics, not intuition, and you get another 10 point jump in isolation. That wall on the right has the same mass as the wall on the left, and the same thickness, yet is is twenty points better at isolating!

The difference is on how the wall is built, and how the parts of it resonate. The first case, on the left, is a four-leaf wall, and there are three thin air gaps in there: Each of those air gaps has a rather high resonant frequency, and they also interact with each other. A high resonant frequency means that the walls does NOT isolate when it is resonating, and since those resonant points are high up the scale, in the lower mid range of the human auditory spectrum, the wall does not isolate well at all. By removing the layers from inside the wall and transferring them to outside, those three thin resonant cavities have now been replaced by one single, much deeper cavity, that has a much lower resonant frequency. The wall still fails to isolate when it resonates, but now it will only resonate at a frequency that is way, way lower than before, likely below the audible range. So for the audible range, it isolates very well. And not only did you make the cavity much deeper, you also increased the mass on the remaining two leaves: It's the same total mass, yes: still 4 sheets of drywall. But now they are doubled-up, 2 and 2, which yet again lowers the resonant frequency, and improves isolation.

So no, you definitely would not want to put sheathing on the other side of ANY of the walls in the diagram that I posted yesterday: Doing so would trash your isolation, perhaps by as much as twenty points. And when you consider that a difference of twenty points means that the wall is blocking one hundred times less (or more) sound, it all falls into perspective. Because the decibel scale is logarithmic, and the STC rating is loosely based on decibels, each increase of ten points implies ten TIMES the intensity. So an increase or decrease of 20 points is (10 x 10) = 100 times. In simple terms, putting a third leaf inside your wall can cut your isolation to one tenth of what it could have been, and putting a fourth leaf in there cuts it to 1/100th of what it could have been.

Eye opener, isn't it? Resonance is a powerful tool, when used in your favor... and a powerful wrecking ball that destroys isolation, when not planned and used intelligently!

Now you can see why your question was not silly at all: the answer prevents you making a mistake that would have cost you big-time in lost isolation.

On the diagram I take it the green wall is representing the inside of my basement wall? And if it is- is it green and yellow because it has studs with rock wool on it?

Correct. As I mentioned, that's not your exact situation: I prepared that years ago for someone else. But it does represent the principles in play here. You want your build to be ONLY two leaves, never one, never 3 or 4. In your case the outer shell is concrete, since it is a basement, but the inner walls will likely be stud framed, as shown here. The concept still applies the same: only 2 leaf.

There's another twist to this: the initial diagram shows the inner walls built "conventionally", but there's also the option of building them "inside out", like this:

MSM-two-leaf-WallChunk-conventional--inside-out--three-rooms--S04.png

In this case, the sheathing faces the cavity inside the wall and the studs face the room. There are some advantages to doing it this way (and some disadvantages too), but it's a valid and useful tool in the designers toolbox. Many of the studios I design have "inside out" walls, and especially "inside out" ceilings, as there are real space-saving and acoustic benefits to doing it that way. You might want to consider it as an option, especially for your ceiling. It complicates the build a bit, but the advantages outweigh that, in my opinion. It means that your actualy acoustic ceiling height can be much greater, since the sheathing sits on top of the joists, not below them, so you gain the full height of the inner-leaf ceiling joists. The visual ceiling is still at the same height, but the acoustic ceiling is many inches higher, and that's a big benefit. IT also makes the acoustic treatment of the ceiling dead easy: just fill in the bays between the joists with suitable insulation, and you are done!

In all cases, "suitable insulation" is not just any old stuff on the bargain shelf at Home Depot: You do need to get the right stuff for the job in each case.


- Stuart -

[lourudd]

ok, so the orange part in your second diagram is just air - it's not some sort of sound proofing like rock wool... just that it's orange and therefore looks like it represents insulation of some sort.
also on this diagram, we now have x2 stud walls, whereas before it was x1 original concrete wall, then x1 stud wall for each room. is this diagram just to help explain or do we need x2 studs going around ?! and again van you confirm the green in the first and third diagram represents rock wool / insulation. sorry again if this sounds dumb, just wanna be sure I'm getting it!

[lourudd]

ok, so the orange part in your second diagram is just air - it's not some sort of sound proofing like rock wool... just that it's orange and therefore looks like it represents insulation of some sort.
also on this diagram, we now have x2 stud walls, whereas before it was x1 original concrete wall, then x1 stud wall for each room. is this diagram just to help explain or do we need x2 studs going around ?! and again van you confirm the green in the first and third diagram represents rock wool / insulation. sorry again if this sounds dumb, just wanna be sure I'm getting it!

[Soundman2020]

ok, so the orange part in your second diagram is just air - it's not some sort of sound proofing like rock wool... just that it's orange and therefore looks like it represents insulation of some sort.

No. It is insulation, such as mineral wool or fiberglass.

also on this diagram, we now have x2 stud walls,

No. There is only one wall. It consists of two leaves, but there is only one wall. Each leaf consists of a stud frame with drywall on one side of it, just like the other diagram. There's no difference. This is sort of a "zoomed in close-up", to better explain the concept.

whereas before it was x1 original concrete wall, then x1 stud wall for each room.

The original diagram is the same as this one. In both cases it illustrates the CONCEPT, not your specific case. Yes, in your case, one of the leaves is the existing concrete wall of the building itself, assuming that you will be using the entire basement for the studio, with no access paths, stairwells, corridors, other rooms that are not isolated, storage areas, bathrooms, etc.

is this diagram just to help explain

Right.

or do we need x2 studs going around

No. You need your original concrete wall, which will be the outer leaf of the studio. Assuming that you will live permanently in this basement for the rest of your life, never leaving it, ever, due the lack of a stairwell or door to the outside world, then the diagrams show what you will have, and the outer wall in the first diagram is your entire basement, and the entire basement is the entire studio. However, in real life I'm assuming that there must be a stair well, and probably other rooms that are NOT part of the studio, which is why need the dividing wall down the middle of the first diagram, that separates the studio rooms on the right, from the non-isolated area on the left, which is where your stairwell, other rooms, etc will be. The area on the right is the isolated area, and since that dividing wall does not exist yet, you will have to build it. It will tie in to the existing walls of the basement, and the are that it closes off is where your studio rooms will then be built. That dividing wall completes the outer leaf of the isolated area. It is the fourth side. The other three sides are the existing basement walls, and you will need to build the fourth side across part of the basement, to isolate a section of the basement for the studio. You might decide to build a concrete wall there, or a brick wall, or a stud frame with drywall on one side of it: it does not matter what materials you use to build it: what matters is that it creates the missing side of the "outer leaf" for your studio area. Then you build your individual rooms inside that area, as single-leaf structures, made from a stud frame with drywall on only ONE side of it.

you confirm the green in the first and third diagram represents rock wool / insulation.

It's actually yellow, not green, but yes, it represents insulation. It might be mineral wool, or it might be fiberglass, but it is very much needed in there. It acts as an acoustic damper on the wall cavity, damping any resonances that might happen to occur between the leaves.

- Stuart -

[lourudd]

Hey Stuart, sorry I disappeared for the xmas period - just to say thanks for the information it's really helpful and you've provided a lot of insight ahead of my project. Thanks so much again - Lou