John Sayers' Recording Studio Design Forum Archive

Hey everyone, my first post here. I'm planning to build a rehearsal studio slash live room. Currently still very much in the research phase, so I'm digging through the forums, youtube, Rod's book, etc, in order to understand all that I have to take into account.

There is one question that I didn't really see answered anywhere yet, perhaps due to the differences in building approaches between Europe and the US, perhaps due to my subpar Google skills... I plan to build everything from scratch, and there are essentially 2 approaches that I can take where it comes to the building's foundations and the concrete floor.

The "traditional" way would be to build foundation walls, which would support all external and bearing walls, and to pour a concrete slab within the foundation boundary. There would be a small (~1in) spacing between the slab and the walls - XPS or a similar material. All rooms would end up with their separate isolated slabs.

The other approach would be to forego buiding foundation walls, and instead pour a single reinforced concrete slab that would act as a support for all of the building's walls. This would mean no spacing between the slab and the walls, and also would make creating separate isolated slabs impossible.

The question is - is there a noticable difference in how those two floor versions would act when it comes to acoustic isolation? Let's say, assuming a single stand-alone room, a sound source of ~120dB inside the room (loud loud rock band) and a target of ~60dB outside, and assuming that all other parts of the design are not a limiting factor - could one version possibly fall short of the required 60dB of noise reduction? Would one be noticably better and allow for a much higher isolation than the other? If so, what could the ceiling possibly be? 70? 80? Hard to say? Assuming perfect construction of course. Sorry for the lack of widths/heights/etc, that's pretty much a theoretical topic as of now.

The way I see it, having a common slab would result in it acting as a bridge between the two wall leaves, decreasing the overall performance, while the XPS filled spacing would possibly offer a bit more separation, making the whole assembly much (?) more effective. Or is it that the sheer mass of the slab, coupled with the dampening effect of the ground below would make the difference negligible?

BTW the band would not be playing directly on the concrete slab, as there'd be need for some thermo isolation (-10C and counting during the winter). I would need a 5-10cm layer of XPS/rigid glass fiber planels on which the real floor would be built: osb/plywood + an eventual pretty and good sounding top layer. This would isolate some impact noises (so, bass + drums a bit?), but would it act like the dreaded drumhead as in a floating floor? I think not, as the materials I have in mind are not compressible and hence would not act as a spring, but honestly, I'm not sure of anything anymore. Too much reading does that to a man...

Very "sketchy" images of the two options attached, please note that they're absolutely not to scale, and that I've opted to skip drawing stuff like hydroisolation, caulking and wooden framing for clarity.

TL;DR - does as single concrete slab supporting both leaves perform noticably (let's say 10dB) worse than a slab isolated from the foundation?

Hi there "mohard", and Welcome!

Currently still very much in the research phase, so I'm digging through the forums, youtube, Rod's book, etc, in order to understand all that I have to take into account.

Great! But skip YouTube, and just use the forum and Rod's book. There's so much pure garbage about the field of acoustics on YouTube, that the whole thing is just no use. Trying to figure out what advice is good and what advice is bad will take you more time than just learing to do it your self... and is far less confusing!

...there are essentially 2 approaches that I can take where it comes to the building's foundations and the concrete floor.

The "traditional" way would be to build foundation walls, which would support all external and bearing walls, and to pour a concrete slab within the foundation boundary. There would be a small (~1in) spacing between the slab and the walls - XPS or a similar material. All rooms would end up with their separate isolated slabs.

The other approach would be to forego buiding foundation walls, and instead pour a single reinforced concrete slab that would act as a support for all of the building's walls. This would mean no spacing between the slab and the walls, and also would make creating separate isolated slabs impossible.

Both methods are valid, and both are used, in the USA, Europe, and elsewhere. There are pros and cons to both methods, of course. The second one you mention is usually called "monolithic slab on grade", or just "slab on grade", and is the method that I prefer for studios: It is simple, fast, effective, and often cheaper than going with conventional foundation walls plus slabs. However, there are occasions where it isn't advisable, so you should get a soil engineer involved in making the decision. If you have stable ground with good rock base and no permafrost or ground freeze/thaw issues, then slab o grade is probably the best way to go.

The question is - is there a noticable difference in how those two floor versions would act when it comes to acoustic isolation?

There can be, assuming that you need very high isolation, but you are talking about something even more exotic here: You ca, indeed, get extreme isolation if you and don't mind the increased costs for creating a series of rather expensive individually isolated slabs inisde an outer shell which sits on its own, separate isolated foundation...., which seems to be what you suggest...

Let's say, assuming a single stand-alone room, a sound source of ~120dB inside the room (loud loud rock band) and a target of ~60dB outside, and assuming that all other parts of the design are not a limiting factor - could one version possibly fall short of the required 60dB of noise reduction?

You can get 60 dB isolation on a conventional crawl-space foundation system, or from a slab on grade. You can probably get ten times better, but that's about the limit for those two. If you need more than that, then the method you mention is a possibility (multiple individual isolated monolithic slabs, each supporting its own inner-leaf wall), but you can get pretty much the same isolation (arguably, even better) by just having one single slab for the entire building, then building individual floating floor son top of that, one for each room. Both are options... and both are expensive! And complicated.

Big question: do you really need extreme isolation? Related question: do you have deep pockets? Those two always go together: high isolation implies high budget.

You seem to be concentrating only on the floor, but frankly, that's the least of your worries in a studio built for extreme isolation: walls, ceilings, doors, windows, the HVAC system and the electrical system will all let you down long before the foundation comes into place. If you have a slab isolated to 80 dB but your HVAC system is only good for 60, and your doors are only up to 50, then your total isolation is around 50... just a tad higher. If you really do need extreme isolation for your slab, then you need even more extreme care (and budget) in those other areas.

Would one be noticably better and allow for a much higher isolation than the other? If so, what could the ceiling possibly be? 70? 80? Hard to say

I partially answered that above: 70 dB is about the limit for what you can expect from a typical home studio or project studio build. The slab is a part of that, since 70 dB is probably the flanking limit for a typical slab, done either way. Slab on grade will likely get you a bit better than slab-over-crawl-space (because of the crawl space) 80 is likely beyond the limits of a typical home/project studio build Beyond that, you are getting into SERIOUS big money and complexity. The very best isolated recording studio on the planet is arguably Galaxy Studios, in Belgium. They get a tiny fraction over 100 dB isolation, and it cost them 5 years and many millions of dollars to achieve that, as well as the brightest acousticians around (one of whom used to be a member of this forum, but sadly passed away a couple of years ago).

The way I see it, having a common slab would result in it acting as a bridge between the two wall leaves, decreasing the overall performance, while the XPS filled spacing would possibly offer a bit more separation, making the whole assembly much (?) more effective. Or is it that the sheer mass of the slab, coupled with the dampening effect of the ground below would make the difference negligible?

There's too many variables to give a precise answer: For example, soil type, underlying bedrock, permafrost, building materials, techniques, etc. And once again, the slab isn't the biggest limiting factor in isolation. If you open the door at Galaxy Studios in Belgium, then you have no isolation at all....

BTW the band would not be playing directly on the concrete slab, as there'd be need for some thermo isolation (-10C and counting during the winter). I would need a 5-10cm layer of XPS/rigid glass fiber planels on which the real floor would be built:

That's an usual way of doing it! Normally the slab itself is thermally insulated from he ground...
If you don't do it that way, then you lose a lot of building heat through the slab into the ground. It's not just about losing the heat in the room itself through the floor, the way you show, but rather about losing the heat held in the thermal mass of the entire building structure. It costs you a lot of money to generate that heat, so you don't want to lose it through an incorrectly built slab!

Those photos show two examples of how insulated monolithic slabs are usually done. Under all that is the usual gravel base on undisturbed ground, then comes sand (sometimes), then the impermeable membrane, then the XPS, with rebar where needed, and steel mesh where needed.... Then you just pour your concrete into that, level it, smooth it, and polish the surface. Done! The final surface of the concrete slab IS your studio floor. That's all you need. Or if you don't like the look of concrete, then maybe you would put down laminate flooring over the slab, or linoleum, or ceramic tiles. But the slab itself is basically your floor. That's the beauty of monolithic slabs: pour it, and you are done!

osb/plywood + an eventual pretty and good sounding top layer.

It's actually a myth that the solid floor materials have a huge incidence on the "sound" of the room: the room acoustic is governed mostly by the walls and ceiling, and of course by the treatment. The floor is always going to be hard, solid, rigid and reflective, so the material you use for that has very, very little effect on the overall room response. In addition, the floor only represents less than 17% of the entire surface area of the bare room, so no mater what you do to it, it isn't going to affect the room acoustic much (unles you do something dumb, like carpet it!). So don't worry too much about the floor materials, regarding overall room acoustics.

This would isolate some impact noises (so, bass + drums a bit?),

Not really. A think layer of a few sheets of OSB plus finish flooring will make no difference at all to isolation through the slab. That's a function of mass, stiffness (rigidity), and damping. Since your floor will have dozens of TONS of mass, and your OSB will only be a few kilograms, at best, it's not going to have any measurable effect.

but would it act like the dreaded drumhead as in a floating floor?

I'm not sure what you mean: a properly floated floor does not act like a drum head. Floated floors are the best possible solution for very high isolation... complicated to calculate, complicated to build, and expensive, yes, but they don't end up as drum heads, no are the "dreaded"! Maybe you are confusing floating floors with undamped slabs, such as those above crawl-spaces on traditional foundations, or at each level of multi-story buildings? Those are not floating floors, and they really are drum heads.... You wouldn't want to build a studio on top of one of those, if you can avoid it, as you probably WOULD need to add a floating floor to get high isolation...

I think not, as the materials I have in mind are not compressible and hence would not act as a spring,

Ummm.... don't look now, but all of the materials you have mentioned so far are compressible, even concrete. The compressive strength of concrete is a rather important factor wen designing concrete structures. OK, so the actual degree of compression is very slight, but it is measurable. But even assuming, for practical purposes, that concrete is in-compressible, it is still flexible, and will still vibrate. Being flexible, it also has resilience (the opposite of rigidity and stiffness), so it is, in and of itself, a spring. Jump up and down on the thin floor of a cheap office building, and you'll certainly find out that concrete is springy...

I think your point was damping, not resilience. A concrete slab on grade is very well damped, yes, so it does not resonate very well, even at it own resonant frequencies. A slab up in the air, over empty space, is NOT damped, and DOES resonate at its own frequencies. From that point of view, studios should preferably be built on very well damped slabs, such as slab-on-grade. If a studio must be built on an undamped slab, then as I mentioned above, it might be necessary to install a floating floor on top of that slab in order to get usable isolation.

but honestly, I'm not sure of anything anymore. Too much reading does that to a man...

Yup! And even worse, is watching too many YouTube (and other) videos about the field of acoustics, which are totally, horrifyingly, wrong! Many are just plain ignorant, some have a veneer of intelligence but are still garbage, some are unsafe, and more than just a few are illegal. Only a tiny fraction of them are sound, solid, good acoustics. And finding those is like finding the proverbial "needle in a haystack".

TL;DR - does as single concrete slab supporting both leaves perform noticably (let's say 10dB) worse than a slab isolated from the foundation?

No. The isolated slab would perform better, assuming that it was properly calculated and properly built. But having multiple isolated slabs, one for each room, is rare: I have only ever done one studio like that. It is very seldom needed, and complicated/expensive to do. In that one specific case, the contractor who poured one of the slabs screwed up, measured badly (because he didn't understand the concept), poured the slab wrong, and we had to re-design the entire studio around his error, because it was far cheaper to do that than to rip out the slab and do it right...

The basic question here is: how much isolation do you need? In decibels. And what frequencies do you need it at? Once you have decided on that, THEN you can start looking at building materials and techniques that will get you there. You seem to be going about it backwards: first looking at building methods, seeing how much isolation each one gets, then figuring out how much isolation you need, based on that!

- Stuart -

Hey Stuart! Let me start by saying that I really appreciate your reply! Really, your whole work on this forum - every time I read your post I'm amazed with your professionalism and knowledge. And patience! You must have answered some of the questions over a thousand times already! So please keep up the great work! OK, enough sugar for today.

However, there are occasions where it isn't advisable, so you should get a soil engineer involved in making the decision

Yup, definitely. I'd never trust myself to make a correct decision based just on internet knowledge. And, well, I think that'd be illegal over here All non-trivial building constructions are required to have a building project with everything calculated by an engineer, and it must be verified and signed by a licensed official that takes legal responsibility for it. I think geological measurements are a must as well. So don't worry, I won't build something that can't stand on its own - they won't let me

You ca, indeed, get extreme isolation if you and don't mind the increased costs for creating a series of rather expensive individually isolated slabs inisde an outer shell which sits on its own, separate isolated foundation...., which seems to be what you suggest...

I'm not 100% sure we're talking about the same thing, maybe I've over-complicated my description. Have a look at this picture - https://cyfrowymurator.smcloud.net/t/t/m-5785_10151.jpg - that's what I had in mind (sorry about the polish language, it's the prettiest picture I could find, and it sould be more or less self-explanatory). There would be a small amount of XPS spacing between "płyta nośna z betonu" (concrete slab) and "ściana fundamentowa" (foundation wall) that is for some reason not included in this picture, which would provide some decoupling between floor/wall, and hence between leaves.

You seem to be concentrating only on the floor, (...)

Yeah, I'm going through all of the elements of a well-isolated room, and while I feel I understand what needs to be done with walls/ceiling the floor gave me a bit of a headache.

(...) but frankly, that's the least of your worries (...)

And yeah, I get that, and I'm not ignoring those other aspects! It's just that in order to understand the full picture I have to understand the building blocks separately. And the one building block that I currently had the most issues with - was the floor. I will have questions about HVAC as well, eventually, don't you worry!

The slab is a part of that, since 70 dB is probably the flanking limit for a typical slab, done either way. Slab on grade will likely get you a bit better than slab-over-crawl-space (because of the crawl space) 80 is likely beyond the limits of a typical home/project studio build

That's just what I wanted to read!

That's an usual way of doing it! Normally the slab itself is thermally insulated from he ground...

Ah, yes, I may have made one mental shortcut too many. And I'm not 100% sure on the exact building techniques used here tbh, and there are many variations of them, so I may just have had an incorrect image in my mind. Thanks for the pictures.

I'm not sure what you mean: a properly floated floor does not act like a drum head. Floated floors are the best possible solution for very high isolation... complicated to calculate, complicated to build, and expensive, yes, but they don't end up as drum heads, no are the "dreaded"! Maybe you are confusing floating floors with undamped slabs, such as those above crawl-spaces on traditional foundations, or at each level of multi-story buildings? Those are not floating floors, and they really are drum heads.... You wouldn't want to build a studio on top of one of those, if you can avoid it, as you probably WOULD need to add a floating floor to get high isolation...

I don't mean properly floated floors, they're 99% way too much hassle for my needs. I just meant that I don't want the floor to behave like a resonant wooden frame filled with rockwool and "floated" on hockey pucks If you look once more at the picture I've linked above - that's what I'd probably end up having as a floor in case of the "with foundation" approach. So a layer of "rigid" thermal isolation between the bottom slab and the actual floor. Kinda like a whole-room drum riser. I'm just wondering if that's not an acoustical "shot in the foot".
I have now researched a bit more and it seems that foundation slabs are usualy thermoisolated from the bottom side, as in your pictures, so there indeed would be no more layers above them. So no issues there. And I had a look at some concrete floor finishes, wouldn't say no to them.

Ummm.... don't look now, but all of the materials you have mentioned so far are compressible, even concrete

Touché Once again, I meant a layer of XPS thermoisolation between bottom concrete slab and the top floor layer.

Yup! And even worse, is watching too many YouTube (and other) videos about the field of acoustics, which are totally, horrifyingly, wrong!

Haha, at least I already read enough to spot the more obvious blunders Just yesterday I was watching a report from a studio build, and while most of the stuff that was said and done matched the knowledge I got from the forum and Rod's book there were times I was going "Dude... but... that's not how it works!". And I was a quite a bit proud of myself after I've verified that it was ME who was right! So, well, thanks once more for putting the knowledge out there.

The basic question here is: how much isolation do you need? In decibels. And what frequencies do you need it at? Once you have decided on that, THEN you can start looking at building materials and techniques that will get you there. You seem to be going about it backwards: first looking at building methods, seeing how much isolation each one gets, then figuring out how much isolation you need, based on that!

It seems that way because I don't really have any concrete requirements as of yet. It's all theoretical. As in - I don't even have a piece of land to build on right now. As in - my budget is equal to ??? (but somehow I'm pretty sure it's not going to be counted in millions of USD ).
Right now I'm gathering as much data as possible in order to solve what is effectively an optimization problem. How big of a room, with how high acoustical isolation can I build with how much money. With money being the obvious limiting factor, just not set in stone yet.

So I'm trying to calculate if it's financially feasible to build a large enough place in a kinda residential area, where I'd probably shoot for 70dB isolation. And I know it's not *easy* to reach.
Or maybe it would be better to aim for 60dB and use the remaining money to build a bigger place, but in a more industrial location, where it would be acceptable?
Or maybe I should wait a few years and save up some more? To build bigger/better? Or maybe take a loan to build bigger/better and *now*? Or look for a warehouse to adapt instead of building from scratch? Or maybe ditch the plan completely?
I will eventually have to make an educated decision on this, and to make the right one I will have to truly understand what's possible and with what effort.

I know I'm going to house a hard rock/metal band. Drums, 5-string bass (Ampeg SVT-810E cabinet, who the hell thought it's a good idea to design this thing???), let's say 120dB to be safe. About 4-5 people inside at one time. Maybe 10 if it's beer time. Those are my only guidelines as of now. Sorry if it looks like I have no idea what I need, it's because it's at least partially true.

But don't think that I completely ignore the numbers! I already know that if I have an outer wall built of 24cm silicate blocks (2000kg/m2), a cavity filled with fiberglass wool (a=30/b=45cm), and an inner wall build of a single OSB sheet and two more gypsum boards (~5cm at 600kg/m3) I will end up with: f0a=14,92Hz or f0b=12,18Hz; Rf0a=28,30dB or Rf0b=26,53dB; and R~=90dB above 183/122Hz. And I know that it does not really mean anything, because HVAC and doors and flanking are a thing. I'm simply solving this problem one step at a time, and will backtrack if needed.

So, does this seem like I'm doing my job backwards? Well, maybe. Will I get my answers doing it this way? Yeah, I think so. But please feel free to tell me I won't if that's your opinion.

Once again, thank you wery much for your input Stuart, and hope you're having a great weekend!

Hey there, I wanted to confirm some of my TL calculactions, just to make sure I don't go any further on wrong assumptions. (BTW, should probably edit the topic title...)

I'm trying to calculate walls' parameters using MSM equations. The goal, as written in the previous post, is to have ~70dB of noise reduction. (Yeah, I know it's a lot, I will possibly have to live with a smaller reduction if I calculate it's not feasible on my budget, but 70 is the ambitious goal for now).

The lowest frequency I'll have to isolate is A0 == 27,5 Hz (5-string bass tuned one step lower).
So the resonant frequency I'm trying to reach equals 13,75 Hz.

The external wall is going to be built out of 18cm silicate blocks, having 1800kg/m3 density, which yields 324 kg/m2 surface density.
Next is the air gap, filled with fiberglass wool insulation, of 45cm. C == 43.
The internal leaf will consist of 15mm OSB (625kg/m3) + 2 layers of 12,5mm "acoustic" GB (735kg/m3), which yields 27,75 kg/m2 s/d. (The "acoustic" gypsum board costs virtually the same as "regular", but is 25% more dense... definitely much more cost/space effective).

This yields: f0 = 12,68 Hz, f1 = 122,22 Hz, R(f0) = 25,99 dB, R(A0) = 76,22 dB, R(f1) = 89,18 dB.

I would get the required isolation for A0, and greatly overshoot the need for frequencies > f1. I would not have to use Green Glue, which is great as it's pretty expensive here. Also, given the psuchoacoustic curves, it seems that I could do with lower isolation, am I right? 45dB at 27,5 Hz is pretty much totally inaudible, right?
It seems to me this is "a bit" over-engineered, especially given that I'd have to match those parameters for double door assembly and HVAC installation... Aaand there's also the concrete slab flanking
Still, I would be grateful if somebody could double-check my maths.

I'm also wondering if reaching the resonant frequency == A0/2 is really really necessary? I remember Stuart wrote multiple times that the wall assembly does NOT isolate at f0, and only really starts isolating at f0 x 2. But from the MSM equations I get 26 dB of reduction at f0. I mean, it's not much, but it's not ZERO either.

So let's calculate another case for comparison purposes:
Once again - the external wall is going to be built out of 18cm silicate blocks, having 1800kg/m3 density, which yields 324 kg/m2 surface density.
The air gap, filled with fiberglass wool insulation, of 15cm. C == 43.
And once again again - the internal leaf will consist of 15mm OSB (625kg/m3) + 2 layers of 12,5mm "acoustic" GB (735kg/m3), which yields 27,75 kg/m2 s/d.

This yields: f0 = 21,96 Hz, f1 = 366,67 Hz, R(f0) = 30,76 dB, R(A0) = 66,68 dB, R(f1) = 89,18 dB.

Now this is interesting: R(f0) is actually bigger than for the 45cm case R(A0) is still more than acceptable (as 55dB at 27,5 Hz seems to be on the threshold of hearing), R(f1) and above is still awesome. Is my math correct? What am I missing? Maybe those equations don't take possible amplification due to resonance close to f0 into consideration? It just seemed to me that reaching f0 < A0/2 would be a much bigger deal that it shows from those results...
Even removing one GB panel still leaves me with 64,15 dB for A0. Is this because my outer leaf is so massive that it makes other parameters that much less important? But it's not really THAT massive after all...

I have currently halted all design work, because too much stuff depends on the gap that I need to have. Would be extremely grateful if somebody could verify what I wrote!

My work is typically remedial, but I have a cautionary tale from one green field build.
I was not on site, but I would have trusted the builder's experience in any case.
He laid the most perfect slab. Hardly needed polishing.
But it is one giant drum head. I am told there was gravel and sand and some of that hard PUR insulation. Kingspan here.
Perhaps he created a void in some way unknown to himself, but I am told this is a a contiguous sandwich.
Boom. Disastrous really.
DD

(...)
Boom. Disastrous really.
DD

Dang, another horror story :/ Maybe the sand/gravel below wasn't compacted properly and settled irregularly? And I read through Gregwor's build thread recently (fingers crossed Greg!). I have to admit it's a bit discouraging, the number of various ways you can get shafted... Either by contractors, your own lack of planning/knowledge or just plain old Mother Nature...

Well, sorry for spamming so much, but it looks like the more you think on those subjects the more questions you have

How do I tune the double door resonant frequency? Assuming a double door in a 2-leaf wall situation, with one leaf much more dense than the other. See my previous post for numbers.

Example:
Leaf-1 s/d = 324 kg/m2, leaf-2 s/d = 27,75 kg/m2, d = 45cm ==> f0 = 12,68 Hz

Now, should I have the door-in-leaf-1 s/d == ~320kg/m2 ? Because that's pretty much impossible to achieve on any kind of a realistic budget

Or would I rather settle for:
Door-1 and door-2 s/d == 60 kg/m2, d = 75cm ==> f0 = 12,65 Hz (numbers chosen to match the f0)

In short: should I aim to match the door density in each leaf to the respective leaf's density, or rather to match the double door resonant frequency to the wall's f0?

Cheers!

Hardly spamming! I didn't post to scare but rather to prevent it happening to you and any other readers.
I am sure if you can be there to observe and direct you can prevent a void being created.
I was not and the builder was doing such a great job nobody doubted him.
I am just wondering if the type of insulation caused the problem. Perhaps they used a Wall version, not proper rigid underfloor stuff.
DD

I was contemplating insulating under the raft...

I have done both insulation under slab and insulation over slab then screed on top...

Insulation under is better for utilising the thermal mass of the concrete... insulating over is better for underfloor heating as it reacts quicker, heats quicker etc.

In the end both structural engineer and building control officer thought in a raft situation it would be tricky to get the detailing correct of sand blinding for damp membrane and neat insulation without voids.

The Building control guy showed me pictures of a site where they blinded the grade/hardcore with concrete before doing the steelwork... neat but another cost...

I ended up not insulating under...