John Sayers' Recording Studio Design Forum Archive

Dear acoustic wizzards,

let me first thank you for your efforts in providing those of us who have a passion for acoustics but who lack the experience and knowledge to fully grasp it with your invaluable guidance. It's been said many times, but this forum really is one of a kind.

With that out of the way, I'd be stoked if you found the time to go over my current progress and advise me on how to best move forward from here.

OVERVIEW
What am I doing?
For about two years now, I've been conceptualizing and planning to convert a small fortune I've received about 10 years ago (due to a climbing accident) into a small, but (hopefully) sophisticated recording and production studio in the basement of my new home, while also planning the house itself. I studied as much as my brain could comprehend, spoke with as many experts and potential clients as I could, and went through many plan-iterations before I landed on my final design.

At that point, I had a basic understanding of room modes and how they relate to the room's dimensions and found a very pleasant size for the live room with 7,86m x 5,15m x 3,31m (3,50m raw, with another 19cm screed/insulation) (LxWxH). I based the rest of the building around those dimensions, which unfortunately led to less than ideal proportions in the Control Room. At the time I thought (for some reason) that modes are less of a problem in the control room because it would have more treatment applied than the live room anyway, which was obviously a misconception. I have since learned from other threads on this forum that it can be quite a challenge to treat a control room of unfavourable dimensions, which in my case are 5,04m x 5,23m x 3,31m (LxWxH).

But that was the plan, at any rate. Once I had a good enough idea of what I wanted to build, I went to a professional (and renowned) acoustic consultant to help me understand potential problems in terms of acoustic isolation between rooms, from and to the outside, as well as from and to the private living areas above the studio. His advice didn't exactly come cheap, but it was well worth the money as the studio can now be completed under fairly solid and ultimately favourable conditions.

We split the foundation of the basement into three segments, one for the live room, one for the control room, and one for the general area. The three segments are entirely separated by a 20mm thick cork mat. We used iron rods wrapped in sylomer to lock them into one another akin to decoupled dowels. We then poured the outer walls, again separating the three outer wall segments in such a way that the three areas never truly connect using cork and thick rubber ribbons (I'm not sure what they'd be referred to in English. It's "Dehnfugenband" in German). Finally, the ceiling slabs were poured in three stages, again separated by 20mm of cork. The ceiling slabs contain a bunch of AC-Ducts, all leading directly to the "boiler room", where they will pass through mufflers and all that. And when they cross from one slab into the next, we used a kind of rubber flange to break the path of any vibration that may be present. (I have since realized that the embedded ducting tubes in the ceiling slab reduce the slab thickness along the ducts by about half, which likely leads to a bit of otherwise avoidable Sound Transmission.)

The rest of the house was then entirely put on top of cork mats (10mm) so that no wall-knocking or foot-stepping from the ground level could flank down into the studio walls. The live room and the control room are effectively separated by a 30cm concrete wall, an 8cm airspace and another 25cm of a cinderblock wall filled with concrete. The same construction isolates the live room from the general area, which in turn is separated from both sensitive rooms by a generously sized soundlock. The soundlock has three doors that are supposed to have a TL of 48dB each, (though I'm not sure what standard was used by the manufacturer to reach this number), so in theory, there should be around 96dB TL between either sensitive room and the general area, as well as between each other (if I got the theory on this right, that is). My plan is to install a superchunk or two in the soundlock, as well as carpet flooring, to deaden the sound, contributing to a greater TL between the rooms (again, I hope I got the theory of this right).

At this point, we have successfully constructed a rather solid double window to the outside with two differently massive/thick panes of glass, allowing for a pretty view of the mountains, and letting in a fair amount of daylight. We dug out part of the backyard to allow for a back entry/smoking area. One part of one wall of the live room is constituted of 25cm thick concrete and this double window with the smoking area outside it and an open field beyond that. So far we've only done a lawnmower test, with my dad mowing the lawn just outside the window and me listening inside, and it was practically inaudible. I haven't done any solid measurements just yet as we've only just put in the interior doors. One thing I noticed, though, by closing the soundlock and playing a radio loudly in the LR, listening in the CR is how much sound still makes it through the ducting system via the machine room. I suppose once it's all hooked up, including the mufflers and all, this should not be a problem, but it certainly surprised me.

We then made the control room window in the same fashion, but adding a third window to the construction (meaning two windows fixed to the concrete "leaf" of the wall and another window mounted to the cinder block "leaf"). This might have been a little overambitious and potentially redundant in hindsight. Alas. That said, how loud do I want to be, and how loud may I be?
The purpose of this studio is pretty broad as I'll be using it for Sound-for-Film (Foley, ADR/VO, Sound Design, Scoring/Composition, Mixing), simple music production, as well as recording and mixing of primarily independent artists from time to time. I'll mostly be working by myself, with the occasional co-producers or studio artists, and sometimes full bands.

That makes the spectrum of loudness pretty wide too. Drums will certainly be played in there, as well as loud amps, full bands, horn sections. So that would put the ceiling somewhere at 115dB I suppose. The surrounding area is typically lively but not noisy, with a little bit of traffic, the occasional farmer with his tractor, cowbells in the field behind the house might be an occurrence, but all of that was already practically inaudible in both rooms with still no doors installed. We even placed rubber mats around the insulated basement walls before filling in the dig site again, so that if a large tractor or truck barrelled past at some point, that the LF wave travelling through the soil doesn't necessarily make it through to the studio, which seems to be working great. There is so much more I'd love to get into, but I feel like I'm already straining your patience with details.

The Current Plan

I've since moved into the house just days before Christmas and had a little time to reflect on how to move forward. My father and I discussed this the other day and we came to the conclusion that we'd still build an inner shell for both rooms, using 5x8cm scantlings set on Sylomer pads (1.2mm). We'll be fixing the ceiling construction , and the inner leaf to the concrete ceiling/walls using resilient hangers and are currently contemplating whether one layer of gypsum board (15mm) would be sufficient, or if 2 layers (2x12.5mm) would be preferable. That would actually be my first question to y'all.

For the Control Room, we're planning to construct a rectangular inner shell in the same fashion, fixing the speaker wall and geometric features to the stud construction before mounting the needed materials (drywall, OSB for the speaker baffles). The speaker wall will hold a pair of ATC SCM45 pro's, using John's rigid soffit variant.

In terms of the actual treatment of the room, I'm frankly quite clueless. I have worked out a geometry that should work well in terms of my mixing position and sweet spot and by creating a pretty wide Reflection Free Zone. The far left and far right flanks of the speaker wall, in this design, would be angled slat absorbers (12°) extending slightly behind the sweet spot mark.
I initially wanted to build skyline diffusers or QRD boxes for the rear of the studio, but I read on a thread around here that they don't really work very well in ranges under 3m. So I split the rear wall and pulled in the edges, forming two more 12° splays. The two rear corners might be good spots to build additional traps, but I'm by no means experienced enough to know if those will harm the acoustics more than they'll do good. These are all things I'm hoping to get some insight on from you.


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So here, my specific questions to you:

• Would the use of two layers of gypsum board for the inner leaf of my Live and Control Room have any major benefits over using just one layer, given the already rather solid isolation from and to the outside, as well as between the rooms? What would be the effects on RT60 and frequency balance in the room if I only mount one layer of 15mm drywall?
  
  Given the raw dimensions of my rooms (7,86m x 5,15m x 3,31m (LR) and 5,04m x 5,23m x 3,31m (CR)), which treatment options would you recommend I (re-)consider? I do not think I actually want either room to sound as impressively flat as Studio Three Productions, but adequately flat to be comfortable for long sessions and suitable for critical mixing sessions.
  
  When soffit-mounting the speakers (preferrably by John's rigid method), are the speakers firmly clamped by the massive box or would it make sense to separate them with some resilient material like Sylomer? How does the box deal with heat coming from active speakers?
  
  What are the rules for a good soffit/baffle construction, aside from rigidity and mass? I've seen vent-holes above the speakers and read to use mesh or ducting to keep airflow going. Where is that airflow coming from? Is this opening there for purely acoustic reasons (i.e. to avoid resonance in the cavity behind the baffle) or for heat dissipation from active speakers?
  
  When we set the inner leaf construction in the LR onto Sylomer pads (12mm thick), does the construction need to be sealed from the air gap between the inner and the outer leaf? If yes, is it enough to mount the gypsum boards with, say, a 2mm space at the bottom, and then sealing that with resilient caulk?
  
  Which modes should I treat specifically, and how? This point, in particular, makes me go numb in the old comprehension compartment. Problematic areas in the CR seem to be 32 and 34Hz, then at 52, 65, 68 and around the 100 mark. In the LR, I'd see 33, 44, 52, 66, 87, and again around the 100Hz mark as potentially problematic. Is this about right?
  
  What kind of diffusion would be practical/reasonable for the Live Room, if I want to be able to have a broad range of recording applications, from Foley, over dialogue to full-band productions? I'm considering splayed side wall slot-absorbers again, in the back left and right of the studio, where the drums are in my sketches (I reached the attachment limit, so I'll post my other images in another comment).
  Any alternative recommendations are welcome.

Budget:
My budget is probably bigger than usual, but my costs thus far are probably also significantly lower than one might expect. Because I had so much support from friends, tradesmen in my family, this forum, and most importantly my dad's incredible capacity to save money in construction by doing nearly everything himself, I was able to set myself up very professionally without overstretching my financial reserves. For the rest of construction, I alotted €6k for materials (drywall, studs, etc.) and a bit of time from my carpenter. I will adjust my budget for the actual studio equipment according to the actual costs of this stage.

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I suppose I've repeated a few questions and details and forgot to mention at least as many. But this is already a pretty big post, and any more would be overstretching your patience.

If I can provide any more detail, I'll do so as swiftly as I can, and other than that, thanks for even reading this far! I'm excited about moving forward and hearing all of your thoughts.

Warm regards and much love to you all,
Thom Osl

I couldn't add any more images to the original post, so I'll list a few more here.

If there's anything else you'd like me to provide, I'll get it done as soon as I can.

Thank you all so much,
Thom

Hi there Thom, an WELCOME to the forum!

Wow! What a great first post. That's a pretty amazing story, and clearly a huge investment. I won't rain on your parade about some of the things that were done and didn't really need to be, but that's water under the bridge, and won't really do much harm.

OK, first here's a series of comments in general (and some questions), then I'll get into your specific questions.

Firstly I noted that you built the studio on three separate partially decoupled slabs. Therefore I'm assuming that you have a need for extremely high isolation? I'm not sure I see WHY you have that need, living out in the country, but I assume your original acoustic consultant informed you of the cost/benefit for several scenarios, and this is the one you chose due to needing extreme isolation. Maybe you can elaborate on why you need such high isolation?

which unfortunately led to less than ideal proportions in the Control Room. ... 5,04m x 5,23m x 3,31m

Correct. It is practically square. It's a problem Fortunately the size is not too small: you have around 26m2 floor area there (20 is the minimum recommended). And the ceiling is nice and high, so you have very decent air volume at 85m3 (47 is the minimum recommended). I think it is usable, and can be quite good, but it's going to need some careful treatment.

However, you seem to have mixed up your measurements. You said "5,04m x 5,23m x 3,31m (LxWxH)", but that isn't correct: the Length here is 5.23m, not 5.04m. You should always set up the room so that the speakers are firing down the longest possible axis, not along a short axis. In your case, there's not a big difference, but every cm helps. More about this later....

At the time I thought (for some reason) that modes are less of a problem in the control room because it would have more treatment applied than the live room anyway, which was obviously a misconception.

Right! Your ratio is not so good: it fails two out of three "critical" tests for control rooms. Here's one analysis of what you would have with those dimensions: As you can see, your modes would be "bunched up" in pairs and triplets across the low end, creating rather intense response in certain areas. Not smooth at all.

However, the good news is that it can be fixed: more on that later.

Once I had a good enough idea of what I wanted to build, I went to a professional (and renowned) acoustic consultant

I'm surprised that he didn't mention the problem with the CR dimensions... Was he aware of what the room was going to be used for? Maybe he didn't realize that was going to be your CR?

We split the foundation of the basement into three segments, one for the live room, one for the control room, and one for the general area.

This ties in to my question above: Why do you need such extreme isolation? Is it for the Foley work? I did notice that you mentioned Foley as one of your areas, but I don't see any Foley pits in the live room, so that's confusing. Are you going to add those later, on an additional slab? Also, there's the issue of the mess associate with Foley work: Is it really a good idea to mix that with drum kits and grand pianos? How are you going to deal with that, and keep the sand and water out of the drum kit and grand piano?

We used iron rods wrapped in sylomer to lock them into one another akin to decoupled dowels.

Why? Do you live in a seismic area, with frequent tremors and earthquakes? Is that the reason for the "decoupled dowels"? Or was there another reason?

I'm not going to question what another studio designer did, but frankly, I would probably have done this as a single slab for the entire building, with three floated rooms inside it. It would probably have been cheaper...

The three segments are entirely separated by a 20mm thick cork mat.

It's unusual to see cork still being used in this application. Most engineers use more modern materials that can decouple and isolate better than cork. Is cork very cheap where you live? Maybe that's the reason why cork was used here?

using cork and thick rubber ribbons (I'm not sure what they'd be referred to in English. It's "Dehnfugenband" in German).

According to Google, that translates as "expansion joint strip", and that's what I would have expected in the expansion joints, rather than cork. I'm curious.... Why use that between the walls, instead of where it is designed to go, between the slabs? Very curious... And are you sure that it really is decoupling them? Did you do the calculations to ensure that the rubber is compressed correctly, and not flanking?

The ceiling slabs contain a bunch of AC-Ducts, all leading directly to the "boiler room", where they will pass through mufflers and all that. And when they cross from one slab into the next, we used a kind of rubber flange to break the path of any vibration that may be present.

This is very confusing for me. Not a common way of doing HVAC for studios. Are those going to carry water, for heating/cooling the studio? They look too small to be carrying air.... Please can you clarify this. You did mention a boiler room, so I'm guessing that these are water lines for circulating hot water through the rooms, for heating via radiators of some type. Is that correct?

Was the HVAC system designed by the acoustic consultant as well? Or by someone else?

(I have since realized that the embedded ducting tubes in the ceiling slab reduce the slab thickness along the ducts by about half, which likely leads to a bit of otherwise avoidable Sound Transmission.)

More than just a bit! I would expect a large reduction from that. In addition, y.You have HVAC ducts/pipes running directly IN the slab, where they will pick up 100% of the structure-born noise, and transmit it very well to the other slab, as well as into the air in both rooms. This is a very unusual way of doing HVAC: I'm really surprised it that was designed by your acoustic consultant.

The rest of the house was then entirely put on top of cork mats (10mm) so that no wall-knocking or foot-stepping from the ground level could flank down into the studio walls.

I can't agree with that. I have never heard of cork being used in this way, and a quick Google search did not turn up ANY examples of cork being used as a structural member. So my big question here is: was that approved by your local structural authorities? Did a qualified and certified structural engineer sign off on this, giving it his approval? Did the building inspector see this, and certify that it was permitted? Does your local building code allow this?

I just can't see that actually accomplishing what you think it is doing. The compressive strength of cork isn't that high, so I would think that the cellular structure of the cork is squashed completely flat by the huge load on it, therefore eliminating any isolation benefit. I may be wrong about that, but I can't see the resilience of cork being able to handle that load. What is the design isolation frequency for the wall? In other words, at what frequency does that combination of cork and the mass resting on it, resonate? I just can't imagine that the frequency is low enough to be useful, even assuming that the cork really is floating the wall.

And the even BIGGER question: If the wall is resting on cork, then how did you anchor it to the slab? Was that anchoring method approved by a structural engineer?

The live room and the control room are effectively separated by a 30cm concrete wall, an 8cm airspace and another 25cm of a cinderblock wall filled with concrete.

I might not be understanding that correctly: Are you saying that the live room wall consists of 30cm of concrete, and the control room wall consists of 25cm cinderblock? Or are you saying that each of those rooms has its own wall, an IN ADDITION to those walls, there are also these two other walls in between?

In simple terms, the question is: Do you have two-leaf walls, or four-leaf walls?

The soundlock has three doors that are supposed to have a TL of 48dB each, so in theory, there should be around 96dB TL between either sensitive room and the general area

No. You can't add decibels like that: the decibel scale is logarithmic, not linear, so if you ADD decibel values, what you are actually doing is MULTIPLYING the underlying linear values. Using two doors does not multiply the isolation.

In fact, to calculate the real isolation provided by those doors, you'd have to know the mass of each door (or rather, the surface density), and the distance between them. They form a resonant system, so the isolation is defined by the resonant frequency for the low part of the spectrum, and by the coincidence dip for the higher part of the spectrum. I would expect that the combination should probably give you isolation in the region of 60-something dB. Perhaps 70, or even a little more, if there are multiple independent seals around the perimeter of each door.

My plan is to install a superchunk or two in the soundlock, as well as carpet flooring, to deaden the sound, contributing to a greater TL between the rooms

Actually, that won't make any difference. The sound moves between those doors through the air in the room, so putting treatment on the walls will not stop that, nor affect it in any way. Putting treatment inside the room will make it sound better yes, but it will do noting to increase isolation.

This is a common misconception, but in reality isolation and treatment are two entirely separate and totally unrelated aspects of acoustics. They are based on completely different principles, and use completely different materials. Isolation is achieved with massive, hard, solid, rigid, thick dense materials, while treatment is achieve with light weight, soft, fluffy, porous, flexible, low density materials.

Putting treatment in the room can help to make it SOUND quieter inside, but does nothing at all to improve isolation.

At this point, we have successfully constructed a rather solid double window to the outside with two differently massive/thick panes of glass,

I don't see any desiccant in there: is it hidden under the foam? What type did you use?

So far we've only done a lawnmower test, with my dad mowing the lawn just outside the window and me listening inside, and it was practically inaudible.

That makes sense, to a certain extent: A lawnmower puts out around 90 dB, and your single concrete wall is providing about 50 dB of isolation, so you should be getting around 40 dB inside. Therefore, when you are playing drums inside at around 115 dB, you should be getting around 65 dB outside. Is that what you were wanting? But then the question arises: if you only want average isolation, then why go to all the trouble of building separate slabs? There's something here that I'm not understanding...

One thing I noticed, though, by closing the soundlock and playing a radio loudly in the LR, listening in the CR is how much sound still makes it through the ducting system

That's a problem! I'm very curious about your entire HVAC design, since I'm not getting the concept at all: it's very strange. Why so many thin, small diameter pipes? Once again, I'm not sure if those are meant for water or air?

I suppose once it's all hooked up, including the mufflers and all, this should not be a problem,

I don't agree: I did not see any mufflers in the pipes where they cross from one slab to the next, and there's no way of installing them now, so I don't see how you will be able to "include mufflers". Thus, I think it will still be a problem. What you hear now will not be a lot different when "it is all hooked up".

Also, if those are air pipes (they are too small for me to call them "ducts"), then there's the problem of the very high speed air flow that you will have to have inside them, and that will be creating a lot of noise all by itself. Small diameter requires high speed air flow in order to get the correct volume of air. That's why HVAC ducts in studios are usually very large: to keep the velocity low enough that it cannot create any noise. But small pipes like that are going to need a very high speed, which implies hiss, rumble, and turbulence. That's a lot of noise. What are your plans for dealing with that noise, and how will you slow down the air flow enough?

Also, what type of AHU are you planning to use and can it even produce those high airflow speeds? Or are you planning to add in-line fans to increase the speed enough? Have you checked the static pressure of such a system? I would imagine that it is going to be rather high: how do you plan to deal with that?

but it certainly surprised me.

It is surprising, isn't it? Most people don't realize how much sound can travel down an open pipe. It's quite impressive.

We then made the control room window in the same fashion, but adding a third window to the construction (meaning two windows fixed to the concrete "leaf" of the wall and another window mounted to the cinder block "leaf"). This might have been a little overambitious and potentially redundant in hindsight. Alas.

I'm REALLY surprised that your acoustic consultant did not warn you about that! That's a THREE LEAF WINDOW!!!! He should have warned you that three-leaf systems ALWAYS give worse performance than two-leaf systems, all other factors being equal. So there's a real probability here that adding the third window has REDUCED your isolation: it is now lower than it would have been if you would have had the same total mass of glass in only TWO windows.

This is not intuitive at all, but is true. The issue once again is resonance. With two windows, you have one single resonant cavity between them, and because the air volume is large, you have a very low resonant frequency, and therefore good isolation. By adding another window in the middle, you divide that space into TWO resonant cavities, each of which now has a much lower air volume, and therefore a much higher resonant frequency. Thus, the total isolation is lower, not higher.

Here's a simple illustration (This shows walls, but the exact same principle applies to windows): The example on the left has a four-leaf wall. It is made from two stud frames with a single layer of drywall on each side. The total isolation (measured as STC in this case) is STC-44.

The middle example shows what happens if you take out one of those layers of drywall from the middle of the wall, leaving only three leaves. Even though there is LESS total mass now, the isolation has improved massively, by nine points! This wall is now giving STC-53.

The final example on the right shows what happens if you take out the other layer of drywall from the middle of the wall, and then put both that one and the other one that you removed in step 2, on the outside of the frames. So you now have a two-leaf wall that has the SAME total mass as the original version, and the SAME total thickness... but the isolation has taken another massive jump, and is measured at STC-63.

In simple terms, the wall on the right isolates about one hundred times better than the wall on the left, and about ten times better than the wall in the middle.

You have the same situation as the middle example here. It would have been about ten times better by leaving out the window in the middle of your wall. It is making things, worse, not better.

However, depending on the mass of each glass pane, and the distance between them across the cavity, you still might be getting enough isolation.... or maybe not. I'd have to do the calculation for that, and I don't have the time right now as I'm working on a number of projects for paying customers, plus you didn't provide enough information for me to do that.

The purpose of this studio is pretty broad as I'll be using it for Sound-for-Film (Foley, ADR/VO, Sound Design, Scoring/Composition, Mixing), simple music production, as well as recording and mixing of primarily independent artists from time to time. I'll mostly be working by myself, with the occasional co-producers or studio artists, and sometimes full bands.

You mentioned Foley, so I'm assuming that's the reason for the extreme isolation attempt?

That makes the spectrum of loudness pretty wide too. Drums will certainly be played normally can indeed produce around 115 dB.

Played hard along with a full band where everyone has their amp turned up to eleven... well, that could be closer to 120 dB.

The surrounding area is typically lively but not noisy, with a little bit of traffic, the occasional farmer with his tractor, cowbells in the field behind the house might be an occurrence, but all of that was already practically inaudible in both rooms with still no doors installed.

That's all subjective, but not a real number. You'd need to actually measure that with a meter, to be sure.

Also, that's only about isolation to the outside world: you also need to define how much isolation you need between the CR and LR. For Foley, it needs to be high. And for Foley, your HVAC needs to be absolutely silent: no hiss, rumble or turbulent air flow....

For Foley work, you need lower than NC-15.

We even placed rubber mats around the insulated basement walls before filling in the dig site again, so that if a large tractor or truck barrelled past at some point, that the LF wave travelling through the soil doesn't necessarily make it through to the studio,

Sorry, but the rubber mat won't be doing anything there. It is helping to keep ground water from getting to the concrete, and it is also helping with thermal isolation of the slab, but it is not doing anything to isolate the slab from the soil acoustically. Did your acoustic consultant recommend this?

My father and I discussed this the other day and we came to the conclusion that we'd still build an inner shell for both rooms,

Yes! At least for the control room: That will allow you to fix the poor modal problems that you would have if you just left it like it is.

using 5x8cm scantlings

I'm not sure what "scantlings" are: Studs?

set on Sylomer pads

Why? There's no need for that. It's a myth that you need to isolate inner-leaf walls from a concrete slab. The slab itself is already providing good isolation. If you want more isolation, then you would need to float another concrete slab over the first, and build your walls on that.

We'll be fixing the ceiling construction , and the inner leaf to the concrete ceiling/walls using resilient hangers

So you DON'T need high isolation then? I'm really not understanding a lot of what has been done here, and what is being planned. Some of it indicates a need for extreme isolation, but other things only indicate a need for moderate isolation...

The correct way to build your inner-leaf is to just bolt the new inner-leaf wall framing to the floor, and build the inner-leaf ceiling framing on top of that. Done! Nothing more. The slab is isolated and well damped, so that's not a problem. The inner-leaf room should simply sit on top of the slab, all by itself, with out touching anything else except the slab. The entire room (walls, ceiling, windows, doors, HVAC, electrical) should be built as a single isolated structure that rests on the slab. That's how you get maximum isolation.

currently contemplating whether one layer of gypsum board (15mm) would be sufficient,

"Enough" for what purpose? You didn't say how much total isolation you need, so it is not possible to say if one layer will be "enough". One layer might already be too much, or you might actually need four layers! There's no way of knowing that, until you define how much isolation you need, and what frequency range you need it for.

For the Control Room, we're planning to construct a rectangular inner shell in the same fashion,

Correct! Once again as a single structure, of walls AND ceiling, all built together, and all fully decoupled for the rest of the building, except for the slab.

fixing the speaker wall and geometric features to the stud construction before mounting the needed materials (drywall, OSB for the speaker baffles).

No. You seem to be missing the concept of how speaker soffits are built (OK, "soffit" isn't really the technically correct term here, but everyone in the studio industry calls them soffits, so I guess we are stuck with the name....).

First you build your room, complete with the drywall on all sides (including the ceiling). THEN you build the soffits within that.

The speaker wall will hold a pair of ATC SCM45

Nice! What subwoofers do you plan to use with those?

Also, are you going to use the remote mount option? If so, be sure to specify the correct distance when you order them.

using John's rigid soffit variant.

Any reason for going with that option? Or maybe a reason for rejecting resilient mounting?

I have worked out a geometry that should work well in terms of my mixing position and sweet spot and by creating a pretty wide Reflection Free Zone.

It would be good if you could show the details of that: I can see something in the images from the SketchUp model, but nowhere near enough to check if it is correct.

Did you ray-trace both ways to determine that there are no reflections in there? What is the radius of the RFZ sphere?

The far left and far right flanks of the speaker wall, in this design, would be angled slat absorbers

Those are tuned resonators! In general I try to NOT have anything at the front of the room that could "color" the direct sound from the speaker. And since they are tuned, they will reflect only some frequencies while absorbing others, and diffusing yet others... did you take that into account when you calculated the reflection free zone?

angled slat absorbers (12°)

Sorry, but 12° is not enough to create a reflection free zone. Are you SURE you ray-traced this correctly?

I initially wanted to build skyline diffusers or QRD boxes for the rear of the studio, but I read on a thread around here that they don't really work very well in ranges under 3m.

The problem is not that they don't work well for less than 3m: The problem is that htey work far TOO well! There's so much uneven lobing in all aspects below 3m that it's not a good idea to have your ears in that area, if you are doing critical listening. For distances beyond that, it's fine.

So I split the rear wall and pulled in the edges, forming two more 12° splays.

Why? For what purpose? And why 12°? I'm not understanding what you are trying to achieve here. The rear wall in an RFZ room must be highly absorptive for low frequencies, somewhat diffusive in the mid range, and somewhat reflective in the highs.

The two rear corners might be good spots to build additional traps, but I'm by no means experienced enough to know if those will harm the acoustics more than they'll do good.

Yes! You will need deep bass trapping across the entire rear wall, with additional precautions to help prevent over-treatment of the mids and highs. The corners are a big part of this.

Would the use of two layers of gypsum board for the inner leaf of my Live and Control Room have any major benefits over using just one layer,

Yes it would. It would lower the MSM resonant frequency of the wall, and considering that you will be creating 4-leaf walls here (count them... ), you WILL need to keep the frequencies very low. You will need large air gaps (for the same reason) and might even need three layers of sheathing.

given the already rather solid isolation from and to the outside

If you can clearly hear a lawnmower through the walls, then the isolation isn't "solid"! Drums are about five hundred times louder than a lawnmower (around 115 dBC vs only 90 dBC). Therefore you do need additional isolation, and it has to be designed very carefully because you already have a two leaf system that has three-leaf windows in it, which will end up being 5 leaf windows in a 4 leaf wall, so this is going to be VERY complex! You are going to be doing some rather complicated math to figure this out, and get it right. If not, you'll end up with even LESS isolation that you have right now.

What would be the effects on RT60 and frequency balance in the room if I only mount one layer of 15mm drywall?

Zero. Nothing

There would be no difference to the room acoustics from using one, two, three, or more layers of drywall on the walls. Once again, isolation and treatment are different things. Adding more mass to the walls WILL increase the isolation, yes. It will lower the MSM resonance frequency of the wall. But it won't change anything about the acoustic response of the room itself. Or rather, it would only have a very small effect, due to things like the slight reduction in room dimensions, and possibly a slight increase in the low end due to the improve bass isolation, etc. But overall, there won't be any real change to the room acoustics: just a big change in the room isolation.

Given the raw dimensions of my rooms (7,86m x 5,15m x 3,31m (LR) and 5,04m x 5,23m x 3,31m (CR)), which treatment options would you recommend I (re-)consider

For the live room, based on what you said you need, I would certainly do that with variable acoustic panels on the walls and ceiling, such that you can modify the acoustic response of the room as needed for each of the senarios you mentioned. They are all very different, and need very different response (ADR vs grand piano, for example, or Foley vs. rock band: MAJOR differences). That's the only realistic way to treat a room that has to cover such a broad range of scenarios.

For the control room, I would suggest a major change: Rotate the orientation of the room so that it is facing the live room! That will produce two major benefits right away: 1) Much better sight lines and visibility in both directions, and 2) The speakers will be firing down the long axis of the room, instead of the short axis. I would then design the inner-leaf with a better ratio, even though that would necessarily decrease the room size a bit. However, you are starting with a room that is large enough to permit this: Good floor area and good volume. So it would be possible to narrow it down a bit, maybe lower the ceiling a bit, and get a better ratio, without reducing the area and volume too much.

I would then definitely have soffits for the speakers, but I would use resilient mounts (in fact, I'd use my own proprietary floating system for that... ). Then I'd have the rear wall as a deep bass trap, with some non-numeric diffusion on it, plus side wal absorbers (probably), and a ceiling cloud. I would test the room response at each stage of the build and treatment, and adjust the design for the next stage appropriately.

I do not think I actually want either room to sound as impressively flat as Studio Three Productions,

Why not? If you can get it perfect, then why not do that? Why settle for less?

but adequately flat to be comfortable for long sessions and suitable for critical mixing sessions

If you want your room to be suitable for critical mixing, then it pretty much has to be as good as Studio Three! That was tuned to meet the most accepted spec for critical listening rooms: ITU BS.1116-3 . That's the spec that defines the term! OK, so your room is probably not big enough to fully get to that situation, but you should still be aiming to get as close as possible.

When soffit-mounting the speakers (preferrably by John's rigid method), are the speakers firmly clamped by the massive box or would it make sense to separate them with some resilient material like Sylomer?

Well make up your mind! Do you want John's rigid mount system, or do you want my fully floated resilient system! ? They are two different things. With John's method, yes, you clamp the speaker cabinet very tightly inside a massive box that fully surrounds it, and clamp that box rigidly and massively to the frame, which is also clamped rigidly and massive to the baffles, and the rest of the front wall. My system also has a massive rigid baffle and massive rigid frame firmly attached to the floor and wall, but the speaker itself is fully floated in carefully calculated resilient system...

How does the box deal with heat coming from active speakers?

In my soffits (John's too) there is a very unobstructed large air path up the rear of the speaker, large enough to provide the required cooling. But I would have imagined that with the ATC SCM45's, you would go for the remote kit. Is there a reason why you don't want to use that? It's expensive, yes, but then again the speakers themselves are expensive! On the other hand, you still need the cooling path up through the soffit, even with the remote kit, since the drivers do emit a fair amount of heat when drive at high levels, so you still need cooling.

What are the rules for a good soffit/baffle construction, aside from rigidity and mass?

A while back I wrote a set of "rules" for this, so I'll just repeat that here:

---

A few "rules" and guidelines for speakers in general and soffits in particular, in no specific order:

1) The speakers should not go in the corner, nor on the line that divides the corner. In other words, if your walls intersect at 90°, then draw a line out from each corner at 45°, and stay away from that: don't put your speaker exactly on that line, since it implies that you'll be getting the same artifacts from the side walls as from the front wall. Put your speakers either outside or inside of those lines. More commonly you'll want your speakers "inside" those lines (more towards the center line of the room).

2) The "38% of room depth rule" is not a rule, but it is a useful guideline for a starting point. You'll generally want to have your listening position a bit closer to the front wall than that location, but do be aware that you might be getting into problematic SBIR territory there. (You can treat that, to a certain extent).

3) Keep the mix position away from 25% and 50% of room depth, and try to stay between about 32% and 44%

4) You can angle your speakers differently than the "textbook" 30° angle: Anything in the range 25° to about 35° will work well under most circumstances.

5) Keep the speakers as far apart as possible, wile not violating rules 1 and 4.

6) Keep the mix position at a good distance from the speakers, within the range of about 1m to about 5m. Further away is usually better.

7) Don't put the speakers at 25% of the room width: that's a modal null for some frequencies, and a peak for others. Try something more like 28% to 34%.

8 ) Make the front baffle of your soffit as wide and tall as you can, within reason. The width should be at least three times the diameter of your low frequency driver. In other words, if you have a speaker with an 8" woofer, then you want the soffit baffle to be at least 24" (60cm) wide. Wider is better. If you have a three-way speaker where the tweeter is on the middle, between the woofers, then the "diameter" is the distance from center to center of the woofers.

9) Do not put your speaker in the middle of the soffit baffle: Offset in both directions. In other words, the distances from the acoustic center of the speaker to each edge of the baffle should be very different, by at least 20%. So for example if your speaker axis is 30cm from one side of the baffle, it should be more than 36cm from the other side, less than 24cm from the bottom edge, and more than 44cm from the top edge. (Rough distances, for illustration only...). Larger differences are generally better. Try to get it at the 2/5th location side-to-side

10) Make the baffle as massively heavy as you can, and as rigid as you can.

11) Make the structure inside the soffit (the framing that holds the baffle and speaker in place) as rigid and massive as you can.

12) Mount the speaker inside an enclosure box that is either a very tight fit, in order to keep the speaker rigidly fixed in place, or mount it on suitable resilient mountings, to completely decouple it from the the box. Carefully choose the properties and dimensions of that resilient material, to make sure the speaker is still decoupled down to at least one octave below the speaker's low cut-off frequency.

13) Take into account that speakers need a lot of space behind them for cooling, and a path through the soffit for cooling air to flow.

14) Rear-ported speakers need special attention: Do not overload the rear port, acoustically, with an enclosure box that is too small, or un-ventilated, or un-damped.

15) Damp the hell out of the soffit interior! Fill it entirely with suitable damping if you want, except for the cooling path.

There's more to it than that, but it's a start!

----

Where is that airflow coming from?

From below. Up through the hanger section, below the shelf.

Is this opening there for purely acoustic reasons (i.e. to avoid resonance in the cavity behind the baffle) or for heat dissipation from active speakers?

Mostly for cooling, but if the speaker is rear-ported then it could also be part of the system for dealing with that. Contrary to popular belief, it IS possible to soffit-mount rear-ported speakers. The ones in Studio Three, for example, are Eve Audio SC-407's, which have huge reflex ports on the back. But they are soffit mounted and working just fine.

When we set the inner leaf construction in the LR onto Sylomer pads (12mm thick),

DON'T! What you are proposing is illegal and unsafe. The entire sole plate of the wall must be completely resting on the slab. You CANNOT just have a few thin pads at some locations. If you do that, the wall will not be sound, structurally, and it will fail eventually. The loads will not be distributed correctly, the wall will sag, the sheer forces will not be counteracted, neither will the stresses and strains, and something will eventually give.

Instead, build your walls correctly: sole plates bolted to the slab, nothing in between.

does the construction need to be sealed from the air gap between the inner and the outer leaf?

Yes, absolutely! That's part of how the MSM system works. It's also part of how isolation works: there can be NO cracks, gaps, holes, or penetrations. As you already discovered with your non-isolated HVAC "pipes", sound can get through very small holes, very loudly. Think of it this way: if air can get through, then so can sound. If you have even a tiny gap under your wall, sound WILL get through. Each leaf must be fully sealed, as a completely air-tight envelope.

If yes, is it enough to mount the gypsum boards with, say, a 2mm space at the bottom, and then sealing that with resilient caulk?

You must do that anyway, but in addition the sole plate must be flat on the floor and that must also have seals under it. THe easiest way is to run three beads of caulk along the sole plate before you put it in position to bolt it down: one bead down the center line of the plate, and another bead each side, about 2cm away from that.

Which modes should I treat specifically,

ALL of them! With your current dimensions, you have 17 modes below the Schroeder frequency, and a total of 143 nodes below 180 Hz. They ALL need treating, to damp them enough that the decay times meet the specs for a critical listening room.

and how?

General broad-band bass-trapping. With 143 modes to worry about, 17 of which are serious, that's way too many to be able to treat individually. Your only hope is broad, deep bass trapping, and perhaps one or two devices aimed specifically at indivudal modes that turn our to be stubborn.

Problematic areas in the CR seem to be 32 and 34Hz, then at 52, 65, 68 and around the 100 mark.

It's far more than that: see the image I posted above: those are just the AXIAL modes, without considering the tangentials and obliques.

What kind of diffusion would be practical/reasonable for the Live Room,

Who knows! Or rather: none. What I mean by that, is you mention a huge range of tracking scenarios, so there is no such thing as one diffuser that will fit all of those needs. Foley, for example, needs a very dry, dead sound usually, perhaps with some distant low level ambience, but vocals need more air, and drums need a ton of air and a much brighter response. Grand piano needs a slightly warmer sound than drums, and acoustic guitar is similar to vocals, but not the same: more air, more ambiance. Bass cabs need a deader acoustic, electric guitars need more life. ADR is similar to vocals. etc. So there's a hug range of acoustic response that you neeed in your room, and since you only have one room, you need variable acoustic panels that can be opened, closed, slid, flipped, rotated, retracted, extended, or whatever to change the acoustic response of the room to match each situation. There is no "one size fits all" for what you want to do. If you only ever wanted to record grand piano in there, then it would be possible to come up with a fixed treatment plan, but you want to do EVERYTHING in there, so you need variable.

I alotted €6k for materials (drywall, studs, etc.) and a bit of time from my carpenter. I will adjust my budget for the actual studio equipment according to the actual costs of this stage.

Ummm... you assigned 15,000 Euros for speakers, but only 6,000 for building the rooms, treating them?, testing them, and tuning them? Something doesn't sound right about that. You need high isolation (apparently); that's expensive. You need acoustic response for critical listening: that's expensive. You need variable acoustics to cover every possible scenario from Foley to a full rock band, and ADR to grand piano... that's expensive. I would suggest that you lower your sights on the speakers, and increase your budget for building, isolating, treating, testing, and tuning the rooms. Or, if you have more budget available, then increase the assignment for building, isolating, treating, testing, and tuning.

File comment: The empty CR one week ago, with audio conduits visible in the corner.

Why in the corner? How will you get it from there to where it needs to go?

File comment: First stud construction, set on 12mm sylomer pads, with added pads to keep it from ever touching the concrete wall.

NO NO NO NO NO!!!! Take that down and re-build it properly, before someone gets hurt. And don't build it again until you have the COMPLETE design for the control room: So far, you are guessing, and building things before you even finish guessing! That's not the smart way to build a studio. FIRST design it, then confirm the design, and only then, when the design is completely done and approved, then you can start building.

File comment: Sylomer pads screwed into studs (far enough to not touch solid ground, even under tons of pressure (hopefully)).

NO NO NO NO NO! Danger! Bad problem! Unsafe! Probably illegal too... That is NOT the way to isolate a wall, your framing is undersized or the job, and this is doomed to fail at some point.... I would not want to be inside that room when it collapses...

File comment: The entire inner shell construction will be separated from the outer shell using these Sylomer pads

How do you now that your pads will isolate? What is the resonant frequency of that system? What is the resilience of the pads? How much mass is going to be on them? What is the areas of the pads? What is the load factor? What will the refection be? What deflection do you need with that material to ensure that it floats? Do you understand what this equation means? : T=2*pi*sqrt[m/k] If you do not fully understand that, and did not use it when calculating the the loading and deflection, then you have a MAJOR problem: you guessed. You CANNOT guess with studio design! For any give wall, ceiling, floor, or speaker, there's only two or three ways to float it correctly, and about a million ways to float it incorrectly. So what are the chances that you hit one of the good ones and avoided all of the bade ones, just by luck? What is the probability that you got all the dozens of parameters exactly right to ensure that your wall floats, just be chance?

Please, please, please, take that down and do it right. Don't guess: Calculate! The equations are not that hard to do.

But this is already a pretty big post, and any more would be overstretching your patience.

No problem! That's what we are here for.

I'm excited about moving forward and hearing all of your thoughts.

[/quote]I hope I didn't step on that excitement too much, with some of my comments above! You have the potential for a great studio here: World-class. Several mistakes have been made, yes, but some of them can be fixed, and the ones that can't be fixed... well, you'll have to live with those, and they aren't too serious in any case.

I'm looking forward to following your thread! I'm fascinated to see where this goes, and how good it gets!


- Stuart -

I'm floored, Stuart, but in a good way... I think! I'm a lot of things since your reply, primarily humbled.

I highly appreciate your incredibly swift, comprehensive, constructive, very much honest, and yet encouraging reply. I have a lot to (re-)think and educate myself on these coming days and weeks.

First off, your warnings about the rigidity and usefulness of the inner wall construction are well taken and I will think this over and rectify this before moving forward with anything else.

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I have written a point by point reply first, but it quickly became very long and repetitive, so I'm trying to sum up the key points and furthering questions in this top section. I obviously had a lot to process, and I obviously still do.

• You're certainly right in noting that there is a clear discrepancy between the effectiveness of some measures VS others. Some measures are seemingly overkill, while others are barely thought through.
  The reason for this as I see it is, that I have a tendency of taking on projects that are well beyond my capabilities at the time of starting. I don't think that's necessarily a bad thing, but it certainly comes with a range of risks, difficulties, and compromises.
  
  When I first met with my acoustic consultant, I gave him the same broad range of applications for the studio as I gave to you. Him being a professional, and me being a paying customer, he took my wishes 1:1 and advised me accordingly. He was aiming for NC-20, if I remember correctly, which came with a whole host of increasingly complex and expensive measures he advised me to take. I tried to find a more reasonable compromise between versatility, high standards, affordability, and ease of construction with him many times, but he was rather unwilling to lower his requirements, and I found myself unable to properly communicate what I was actually aiming for. Most of this was obviously a matter of poor communication, and hence mostly my fault.
  
  What I should have done from the start was to outline a clear prioritization of what I wanna do in this studio.
  The primary purpose of this studio is mixed-source music production for video productions. This means, that I'll partly work with virtual instruments, electronic instruments (synths), and occasionally with session musicians for drums, horns, strings, and vocals in overdub.
  
  Aside from that, I want to offer my services and space to small-mid-sized artists (primarily independent), on a project-by-project basis. I don't intend to have the best studio far and wide, but I do want to offer a great space to work in, offered at a relatively affordable rate.
  
  Foley is a tertiary application, meaning that I'm willing to make some compromises for this one. NC-15, at this point, is simply not a realistic target, in my assessment. I want to be able to wheel in my wooden boxes filled with material, and my props from the storage room, whenever I do have a foley project. I expect, maybe 1 or 2 video projects a year that require dedicated Foley work.
  
  In terms of variable acoustics, I'll try to come up with some good solutions for that, as I think it's an important point. I intend to build movable baffles of different types, some highly absorptive, some highly reflective, some highly diffuse, and then set up areas in the studio accordingly for foley or ADR/VO work.
  
  The environmental noise level outside the studio window sits at around 50dbA (60dbC) on average, and hardly ever reaches or exceeds 65dbA (75-80dBC) even during especially noise times. (both A and C weighting measured with slow impulse response)
  
  The current noise level in the studio with all doors firmly closed sits at around 32dBA (42dBC) in both rooms (without AC/ventilation installed). I used an AZ8922 SPL meter, and I was in the room during measurement, for what it's worth.
  
  My father has some serious reservations about drilling into the screed slab, because it contains the heating circuits. Drilling into those by accident would lead to serious problems. We're certainly going to remove the Sylomer pads from the construction and seal it with caulk, The ceiling studs will sit on top of the inner shell construction as planned, but we would still prefer to use the resilient hangers I posted to secure the ceiling studs to the concrete ceiling, and several of the wall studs to the concrete walls for security, before filling in the spaces with rockwool and mounting a first layer of 15mm drywall. Once that is complete, we'd evaluate if a second layer of drywall is needed to increase the wall's mass and to hence lower the MSM resonant frequency. Does this sound like a workable approach, or do you still think this does more harm than good?
  
  Considering the placement of my control room window, I don't think that changing the orientation of the CR will do me much good. Would my current orientation be significantly worse than having the speakers firing down the longer dimension, considering that the room is already nearly square in footprint?
  
  You'll find more questions and comments further down, but these are some points that I'm hoping to get another response on from you, so I can reconsider my planning with a little more clarity.

Once again, thank you so much for this exchange, it's given me so, so much to think about .

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Firstly I noted that you built the studio on three separate partially decoupled slabs. Therefore I'm assuming that you have a need for extremely high isolation? I'm not sure I see WHY you have that need, living out in the country, but I assume your original acoustic consultant informed you of the cost/benefit for several scenarios, and this is the one you chose due to needing extreme isolation. Maybe you can elaborate on why you need such high isolation?

The acoustician was of the opinion that it would ultimately be cheaper to build it that way, rather than trying to isolate the rooms after the fact. He was also nervous about the occasional tractor driving past. They can make a bit of a ruckus.

To be honest, I don't think he was very happy with me as a customer and I wasn't very happy with him as a consultant. I'm normally not a bad communicator, but the two of us seemed to be talking past one another, and I ended up trying to determine things on my own whenever I thought I could, with mixed results as it's becoming apparent. But to be clear, I don't wanna speak badly of the man at all, as he's clearly very good and experienced at what he does, but we seemed to be pulling in different directions. That's probably the reason why some measures are overkill, and some are barely thought through...

Water under the bridge, as you say.

However, you seem to have mixed up your measurements. You said "5,04m x 5,23m x 3,31m (LxWxH)", but that isn't correct: the Length here is 5.23m, not 5.04m. You should always set up the room so that the speakers are firing down the longest possible axis, not along a short axis. In your case, there's not a big difference, but every cm helps.

I didn't realize it made such a difference. I chose this orientation, primarily for convenience, as I could fix a screen to the wall in front of me for video reference while still seeing everything going on in the live room when I need to, and while having all instruments and outboard gear always within reach.
I'll see if I can figure out a room design that works so that the speakers fire in the long directions and so that the inner shell comes closer to a favourable ratio, but I do have trouble seeing how I could mount the speakers on that left wall with the window off-center. Any ideas for this? Would it be conceivable to keep the orientation this way, and to increase the rear wall absorption substantially?

I'm surprised that he didn't mention the problem with the CR dimensions... Was he aware of what the room was going to be used for? Maybe he didn't realize that was going to be your CR?

To be honest, I am surprised too. I showed him the plans before I handed them in for approval, and he didn't note any significant problems with it.

Why do you need such extreme isolation? Is it for the Foley work? I did notice that you mentioned Foley as one of your areas, but I don't see any Foley pits in the live room, so that's confusing. Are you going to add those later, on an additional slab? Also, there's the issue of the mess associated with Foley work: Is it really a good idea to mix that with drum kits and grand pianos? How are you going to deal with that, and keep the sand and water out of the drum kit and grand piano?

I'm not really sure that the extreme isolation was entirely necessary for this purpose. I followed the advice that I paid for, I suppose, if I may be so cynical.

I intend to build a stack of sandboxes with different materials that I can wheel into the room when I do have a project that requires Foley work.

Why? Do you live in a seismic area, with frequent tremors and earthquakes? Is that the reason for the "decoupled dowels"? Or was there another reason?

It's actually an incredibly stable area, with great undergrounds for building . There was some disagreement between the building contractor and the acoustic consultant. Ultimately, those dowels were the acoustician's idea, though, oddly enough.

I'm not going to question what another studio designer did, but frankly, I would probably have done this as a single slab for the entire building, with three floated rooms inside it. It would probably have been cheaper...

I guess I should have asked you sooner!

It's unusual to see cork still being used in this application. Most engineers use more modern materials that can decouple and isolate better than cork. Is cork very cheap where you live? Maybe that's the reason why cork was used here?

That stuff was by no means cheap, actually. It's called Pronouvo-Cork Type 1073 and costs an arm and a leg. The acoustic consultant said that the cork we put in between the foundation slabs may rot away in time as it gets wet from the groundwater, but that that would be nothing to worry about. I should also mention that he's probably overdue for retirement, so some of his measures may well be on the dated side too.

Why use that between the walls, instead of where it is designed to go, between the slabs? Very curious... And are you sure that it really is decoupling them? Did you do the calculations to ensure that the rubber is compressed correctly, and not flanking?

The expansion joint strip runs along the gap in the slab as well as up between the walls because the basement is partly sitting in groundwater during the warmer months. I did not consider the flanking potential of those strips, and neither did the acoustic consultant, as far as I'm aware. It was put in as a necessity, without really considering any alternative solutions...

This is very confusing for me. Not a common way of doing HVAC for studios. Are those going to carry water, for heating/cooling the studio? They look too small to be carrying air.... Please can you clarify this. You did mention a boiler room, so I'm guessing that these are water lines for circulating hot water through the rooms, for heating via radiators of some type. Is that correct?

Was the HVAC system designed by the acoustic consultant as well? Or by someone else?

This part, I'm most bummed about. I feel like I could have found a significantly better solution for this with a little more preparation. The ventilation and heating design was decided on by myself and the contractor who will install it. The acoustic consultant didn't offer much insight on this, and at this point, we'd kinda given up on finding common ground.

The tubes carry only air from and to the rooms. The heating circuits are embedded in the screed slab in the floor. The technician who thought up the solution for the air supply with me ensured me that it'd be moving slow enough for it to be practically inaudible. I feel like a fool now for pretty much taking him by his word for it. I'll see that I can determine these factors and improve on them before I move forward with anything else.

What is the design isolation frequency for the wall? In other words, at what frequency does that combination of cork and the mass resting on it, resonate?

I'm afraid I have no idea. And I'm afraid I have no idea how to find out either . It seems to be doing its job, so I guess it wasn't all for nothing, but... yeah.

And the even BIGGER question: If the wall is resting on cork, then how did you anchor it to the slab? Was that anchoring method approved by a structural engineer?

Mortar and gravity, basically . The building contractor signed off on it, so he can't be too worried.

I might not be understanding that correctly: Are you saying that the live room wall consists of 30cm of concrete, and the control room wall consists of 25cm cinderblock? Or are you saying that each of those rooms has its own wall, an IN ADDITION to those walls, there are also these two other walls in between?

In simple terms, the question is: Do you have two-leaf walls, or four-leaf walls?

It's the former. a 30cm concrete wall on the LR slab, and a 25cm cinderblock wall on the CR slab.

No. You can't add decibels like that: the decibel scale is logarithmic, not linear, so if you ADD decibel values, what you are actually doing is MULTIPLYING the underlying linear values. Using two doors does not multiply the isolation.

I feel dumb for not recognizing this as I wrote it. It's very obvious now.

I would expect that the combination should probably give you isolation in the region of 60-something dB. Perhaps 70, or even a little more, if there are multiple independent seals around the perimeter of each door.

How would I reasonably test for this? Pink noise generator at 80dB in the LR, and SPL meter in the CR?

Actually, that won't make any difference. The sound moves between those doors through the air in the room, so putting treatment on the walls will not stop that, nor affect it in any way. Putting treatment inside the room will make it sound better yes, but it will do noting to increase isolation.

This is a common misconception, but in reality isolation and treatment are two entirely separate and totally unrelated aspects of acoustics. They are based on completely different principles, and use completely different materials. Isolation is achieved with massive, hard, solid, rigid, thick dense materials, while treatment is achieve with light weight, soft, fluffy, porous, flexible, low density materials.

Putting treatment in the room can help to make it SOUND quieter inside, but does nothing at all to improve isolation.

Your advice is well taken. I've come across this idea in Alton Everest's Handbook of Sound Studio Construction, I think.

Speaking of the soundlock, though. I do have this airgap between the concrete and cinderblock wall, and I haven't yet sealed it. Should I seal it, or would the walls and the control room window benefit from an opening into the soundlock area to increase the volume of movable air?

I don't see any desiccant in there: is it hidden under the foam? What type did you use?

Yes, there is a generous amount of a hemp-clay mixture underneath the foam. So far, I didn't have any moisture problems with either window, but that may be different in the long term. Of course, it was kind of a guess if it'll work or not...

A lawnmower puts out around 90 dB, and your single concrete wall is providing about 50 dB of isolation, so you should be getting around 40 dB inside. Therefore, when you are playing drums inside at around 115 dB, you should be getting around 65 dB outside. Is that what you were wanting? But then the question arises: if you only want average isolation, then why go to all the trouble of building separate slabs? There's something here that I'm not understanding...

If I can bring it down to 55db or so, I'll be more than happy. It won't be a problem as it is either, I don't think.

I did not see any mufflers in the pipes where they cross from one slab to the next, and there's no way of installing them now, so I don't see how you will be able to "include mufflers". Thus, I think it will still be a problem. What you hear now will not be a lot different when "it is all hooked up".

The plan is to place a kind of aluminium muffler plug in each of the pipes where they come into the studio rooms, as well as a central HVAC noise attenuator box placed before the air distribution box to reduce the noise transmission from the AHU.
The Wernig Q600 is the unit we plan to install.
I hope it won't be as much of a problem as I now fear, but I'll certainly keep an eye and an ear out for any problems with this.

I'm REALLY surprised that your acoustic consultant did not warn you about that! That's a THREE LEAF WINDOW!!!! He should have warned you that three-leaf systems ALWAYS give worse performance than two-leaf systems, all other factors being equal. So there's a real probability here that adding the third window has REDUCED your isolation: it is now lower than it would have been if you would have had the same total mass of glass in only TWO windows.

I guess it's more accurate to say that I should have actually asked him about it. At this point I knew that he charges for a phone call close to what I paid for the glass, so I decided to save on the phone call. Not exactly clever, I know. But what you're saying makes perfect sense. I read (after building it, of course) that a third window doesn't really improve the isolation beyond a two window construction, but I wasn't really conscious of the fact that it can make it worse. Thank you for the schematic, too. It illustrates this point quite well. Should I find that the solution is insufficient as it is, I'll remove the middle glass from the window frame. Perhaps someone else can use it, or I'll store it for a future construction.

You mentioned Foley, so I'm assuming that's the reason for the extreme isolation attempt?

I suppose that was the primary reason for why the acoustic consultant proposed such drastic measures. I am casting a pretty wide net because I'm very interested in a broad range of projects and because it's difficult to tell, as of yet, to gauge what kinds of projects will form the bulk of my work.

I should probably have prioritised my requirements more clearly from the start. Foley is probably secondary, or tertiary even. Primary focus will be composition and music production for film, secondary application is recording and mixing of bands, tertiary application is Foley and ADR/Dialogue recording.

Sorry, but the rubber mat won't be doing anything there. It is helping to keep ground water from getting to the concrete, and it is also helping with thermal isolation of the slab, but it is not doing anything to isolate the slab from the soil acoustically. Did your acoustic consultant recommend this?

He practically insisted on it. He proposed I use two layers of 4cm thick mats of compound rubber, which would have been insanely expensive. I opted instead for 1.5cm thick compound rubber mats which cost a fraction. They only wrap around the outer walls of the control room and the live room, not the entire basement either, but you can faintly hear a tractor driving by from the general area, but you can't hear it in the studio rooms at all, so the mats seem to be doing something at least.

I'm not sure what "scantlings" are: Studs?

Haha, yes, sorry. I had to look up the word and only remembered the usual term later on.

So you DON'T need high isolation then? I'm really not understanding a lot of what has been done here, and what is being planned. Some of it indicates a need for extreme isolation, but other things only indicate a need for moderate isolation...

I suppose I don't need as much as my consultant recommended, but maybe more than I'm currently aiming at...

The correct way to build your inner-leaf is to just bolt the new inner-leaf wall framing to the floor, and build the inner-leaf ceiling framing on top of that. Done! Nothing more.

I will see to it! I'm not clear on the ceiling construction, though. 5m seems like quite a distance if I won't be suspending the ceiling studs at all from the concrete ceiling. Are the resilient hangers such a bad idea?
My father also has strong reservations about drilling into the floor slab, as it contains the underfloor heating circuits. There should be about 5cm of only concrete before hitting the heating circuits, but it's still risky drilling down there in case one of the tubes managed to float up enough to be accidentally punctured.

We're obviously going to remove the sylomer pads from the underside of the structure, so that the studwall sits directly on the slab, but we would still prefer to hold it all in place using the mentioned resilient hangers. Would that make a bad situation worse or would it simply be less effective than it could be?

"Enough" for what purpose? You didn't say how much total isolation you need, so it is not possible to say if one layer will be "enough". One layer might already be too much, or you might actually need four layers! There's no way of knowing that, until you define how much isolation you need, and what frequency range you need it for.

Let's assume general music production as my main purpose. In terms of isolation: What I have seems to be almost good enough. You already have to be pretty close to the outside window to hear someone playing drums in the LR, and virtually no sound from the outside or the living room above makes it down into the studio, unless someone physically hammers into the walls above.

I'm getting an average of about dB (C-weighted, slow response) outside in the back area, with peaks of about dB (C-weighted, fast response) when cars drive past or a rooster crows. This is measured in the afternoon. in the Live Room, with all the doors closed, I'm measuring about dB (C-weighted, slow response)

No. You seem to be missing the concept of how speaker soffits are built

It seems I've been missing a lot of things, actually. But your explanations help a tremendous amount.

Nice! What subwoofers do you plan to use with those?

Also, are you going to use the remote mount option? If so, be sure to specify the correct distance when you order them.

Well, after your advice, I am indeed considering going for a more affordable option than the ATCs. The original plan was to pair it all with a Genelec 5.1 system, including a 7050 BPM sub. Everything is back on the table right now, as I wanna make the most of your advice.

If I decide to go ahead with the SCM45s, I'll certainly inquire about the remote amp option. I hadn't been aware that this was a possibility. But to be sure, what distance are you referring to? The distance from the remote amps to the speakers?

Any reason for going with that option (John's soffit version)? Or maybe a reason for rejecting resilient mounting?

Primarily for simplicity's sake. Perhaps I shouldn't be so timid, but I currently feel like I'm in over my head, so I'm trying to keep things simple.

It would be good if you could show the details of that: I can see something in the images from the SketchUp model, but nowhere near enough to check if it is correct.

Did you ray-trace both ways to determine that there are no reflections in there? What is the radius of the RFZ sphere?

I'll work out more detailed plans in the coming days and post them in this thread as soon as I can. It's possible that I have neglected the vertical plane, so I should probably spend some more time on that too, to be sure.

Those are tuned resonators! In general I try to NOT have anything at the front of the room that could "color" the direct sound from the speaker. And since they are tuned, they will reflect only some frequencies while absorbing others, and diffusing yet others... did you take that into account when you calculated the reflection free zone?

That is good to know. So I suppose the general idea is to deflect early reflections to the rear of the room, where the LFs and some of the MFs can be absorbed by some generous trappings, would that be correct? What would you propose I use that can achieve that? Slat wall absorbers here instead of at the front would seem plausible to me (which isn't saying much)

Sorry, but 12° is not enough to create a reflection free zone. Are you SURE you ray-traced this correctly?

I'll read up again on how to do it properly and come back to you with a better model if that's alright with you. I'll see how others here have created their RFZs too, to get some ideas.

So I split the rear wall and pulled in the edges, forming two more 12° splays.

Why? For what purpose? And why 12°? I'm not understanding what you are trying to achieve here. The rear wall in an RFZ room must be highly absorptive for low frequencies, somewhat diffusive in the mid range, and somewhat reflective in the highs.

I suppose my method of ray-tracing was flawed, but that's how I reached that number. Again, I'll read up on it again and rethink my whole strategy.

Do you understand what this equation means? : T=2*pi*sqrt[m/k]

I do in principle, but haven't yet applied it. It describes a harmonic period as a function of mass and a spring coefficient. So I would need to know the spring coefficient of the sylomer pads (or rather he combined spring coefficient of the system), as well as its combined mass, to figure out at what frequency it resonates, if I understand it correctly. It's becoming painfully obvious how much work I still have to do

I hope I didn't step on that excitement too much, with some of my comments above! You have the potential for a great studio here: World-class. Several mistakes have been made, yes, but some of them can be fixed, and the ones that can't be fixed... well, you'll have to live with those, and they aren't too serious in any case.

I'm looking forward to following your thread! I'm fascinated to see where this goes, and how good it gets!

Not at all, Stuart. I'm very good at making mistakes, but I'm usually not too bad at learning from them either. My brain hurts and I do need a drink, but I'm sure I'll get where I want to be, eventually, and your comments have already been a huge help.

I didn't comment on all of your remarks because I still need to process a whole range of them, and I do hope I'll be able to continue to pester you with any queries and misconceptions that may still arise along the way.

If you could briefly comment on my opening questions, and perhaps check this thread from time to time, I'd be very grateful.

Thank you so much in the meantime,
Thom

Hey Thom, I'm so glad that I didn't discourage you too much yesterday! I was sort of concerned that you might take it badly... Glad to see you took it constructively!

your warnings about the rigidity and usefulness of the inner wall construction are well taken and I will think this over and rectify this before moving forward with anything else.

If I might make a suggestion here: Don't build anything else yet! Hold off on building until you have a solid, sound, verified,cost-effective plan, completed. I know it's very disappointing to hold off for a couple of months when you seem to be so close to completing the place and being able to use it, but that's really what I would recommend. As I mentioned yesterday, I think your place CAN be great: it has the potential. But considering the mistakes so far, it will need careful design and careful construction to compensate, and to get things good. You were about to do some bad things, and I'm concerned you could be planning to do more bad things, so I really hope you take this suggestion to heart, and make sure that the design is done completely, in full detail, taking into account all of the aspects, verified for acoustics, verified for structure, verified for HVAC, verified for usability, verified for everything... and then, when it is completely designed, only then start building.

I've been through this process with several people over the years, some paying customers, some forum members, and it's always a tough call to stop when you have momentum and you think the end is in sight.... but you are actually not as far along as you think! There's still a lot to be done....

The reason for this as I see it is, that I have a tendency of taking on projects that are well beyond my capabilities at the time of starting.

So aren't you glad you found the forum!? It's a good place to hang out your ideas, concepts, and thoughts, to see of they are feasible, and ask for advice. We'll try to keep you on track!

I don't think that's necessarily a bad thing, but it certainly comes with a range of risks, difficulties, and compromises.

It's not a bad thing at all! But when you run into things that are "well beyond my capabilities" as you put it, it's a good idea to ask!

He was aiming for NC-20, if I remember correctly, which came with a whole host of increasingly complex and expensive measures he advised me to take.

NC-20 is a typical goal for a good studio. Getting NC-20 is actually more about the HVAC system than the isolation system. Or perhaps "both in equal measures" would be a better way of putting it. To get NC-20, you need to design the HVAC system for that, along with the room. You might well be able to get NC-20 with the HVAC turned off, but there's not much point to that! You need to be able to use the room with the HVAC turned ON! HVAC design is an integral part of studio design: When I'm designing a studio, I often spend as much time on the HVAC as I do on the rest of the studio all together: HVAC is a big issue.

I tried to find a more reasonable compromise between versatility, high standards, affordability, and ease of construction with him many times, but he was rather unwilling to lower his requirements, and I found myself unable to properly communicate what I was actually aiming for. Most of this was obviously a matter of poor communication, and hence mostly my fault.

Communication is a two-way street: It's a pity that more effort didn't go into it from the other side, ... As a studio designer myself, I do appreciate that some clients can be ... ummm... "difficult" (!), but you don't sound like that type to me....

The primary purpose of this studio is mixed-source music production for video productions. This means, that I'll partly work with virtual instruments, electronic instruments (synths), and occasionally with session musicians for drums, horns, strings, and vocals in overdub.

Great! But that prompts a question; mixing for video and cine these days is often 5.1, 7.1 or even something more exotic. Do you plan to do that? Maybe not now, but at some point later? If you plan on ever doing multi-channel mixing, then the control room acoustics and overall design need to be done for that NOW! It's really tough to upgrade a dedicated 2.0 or 2.1 studio to 5.1. It basically involves ripping out all the treatment and starting over. Perhaps even needing to move the mix position and gear... It's perfectly fine to run a 2.0 or 2.1 system in a room designed for 5.1: no problem at all. But going the other way is a problem. So if there's any possibility at all that you might want 5.1 in the future, design the room for that now, even if you only use it for 2.1.

I don't intend to have the best studio far and wide,

Ahhh, but it COULD be! The only real difference between a good studio and a great studio, is attention to detail in the design and tuning... You have seen what we achieved with Studio Three: But there's a back story there. Rod (the owner of Studio Three) first came to the forum wanting a little advice on how to soffit mount his speakers. Here on the forum, we pointed out several other things that were wrong with his initial design, and he decided to hire me to fix it. In fact, he just wanted me to design the soffits: that was the original brief. I named the project on my computer "front 2 meters", because that's all he wanted from me; a design for the two meters (six feet) at the front of the room, including the soffits and cloud. That's all. But as we got into it, that expanded to eventually include the entire control room, and then some other rooms too. At one point in our e-mail discussions, he commented to me that he didn't think his room could ever be useful "for A-listers" (top artists). I asked him: "why not?". I basically said something like: "If you don't think it can be great, then why are you investing all this money, and also hiring me? Do you really only want me to do just a mediocre job? Or do you want it to be really great, a place where A-listers would be happy to work?". That got him thinking, and he challenged me to give it my best shot, make it the best room I possibly could, put it "among the top 1% in the world". I have no way of proving that it really is among the top 1%, but it sure as hell is as good as I can get it! You can see that on the graphs: the response is flat, and can still be molded to fit any need.

Yours can be great too. I can see that. Not just good, but great.

The only thing in the way of making it word-class, is how much detail you put into the design, how carefully you build it, and how well you tune it. It probably won't get as flat as Studio Three, since that room is a lot bigger than yours, but it can still be well beyond a typical home studio.

Here's another thread you might be interested in (link below). It is in progress right now. A studio built buy one guy, from the ground up. I designed it a couple of years back, and it has been built quite. The live room is finished, and we are now just starting the process of tuning the control room. Today I posted the first results of the initial tuning, and you can see the "before" and "after" graphs there, from the acoustic devices that I designed last week, and that he has now built and installed. This is an on-going thing, and there will be more updates as we move forward with the build. I wanted you to see that, since his room is about the same size as yours, but based on a very different concept. However, due to the size similarities, you should be able to get similar results. Ir might be interesting for you to watch this thread, and get ideas for your own room design and treatment: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368 .

What I'm trying to say, is that you should not under-estimate the capabilities of that room: it can be really good. As good as most pro studios, for sure. Since this is a major investment for you, and obviously is your passion, and your future, to me it makes no sense to just say that "It will be sort of OK, but not fantastic". It CAN be fantastic, if you want it to be.

In terms of variable acoustics, I'll try to come up with some good solutions for that, as I think it's an important point. I intend to build movable baffles of different types, some highly absorptive, some highly reflective, some highly diffuse,

One of the rooms at Studio Three is what Rod and I call the "Varicustic room". It was originally intended to be a vocal booth / iso booth, but I suggested making it variable. Here's what we did:
Those are variable panels that you simply open or close, like a door. They swing over the central slotted wedge, modifying the decay times of the room in a controlled manner.

Here's the results, acoustically:
That was measured in a setup that would typically used for tracking an acoustic instrument, about a meter or so in front of the panels, so it's the overall room response that you are seeing. As you can see, as you swing the panels from fully opened to fully closed, the decay times in the LOW end go down, while in the high end they go up, with not much change in the mid range. In other words, it skews the response from being bass heavy and slightly "boomy" to being "bright" and "airy". You might want to consider doing something like that.

The environmental noise level outside the studio window sits at around 50dbA (60dbC) on average, and hardly ever reaches or exceeds 65dbA (75-80dBC) even during especially noise times. (both A and C weighting measured with slow impulse response) ... The current noise level in the studio with all doors firmly closed sits at around 32dBA (42dBC) in both rooms

Hmmmm.... so you have around 75 dBC outside, and around 40 dBC inside. That implies isolation of around 30 dB, which isn't much. And with 32 dBA / 42 dBC inside, you definitely are not getting NC-20! Probably more like NC-30. And you don't even have the HVAC turned on yet.... NC-30 is not going to be any use for Foley work.

Not trying to scare you! Just pointing out that there's a problem here: you are not getting what you should be getting. You should probably concentrate on investigating WHY you aren't getting the results you should be seeing.

My father has some serious reservations about drilling into the screed slab, because it contains the heating circuits.

There's a simple solution: thermal camera! Turn on the heating system, then take a thermal picture of the floor, and you'll see exactly where the heating pipes are, so you can avoid them:
Simple! Fast, accurate, no problems. No drilled pipes!

You DO need to anchor the studs to the floor: Check your building code and local regulations: I'm pretty sure you'll find that it is a legal requirement. But even if it is NOT a legal requirement, you STILL need to do it, for a very simple reason: Your inner-leaf doors will be heavy, and as you open and close them there will be a large amount of stress and strain on the framing. Plus, there will be air pressure changes in the cavity as the doors open and close: You do NOT want the walls "walking" over the floor from that! Not to mention the vibrations from sound played at high levels, or instruments played at high levels... Your walls cannot just sit there without being anchored. If you don't anchor them, your doors will end up not closing properly, not sealing, not isolating....

The ceiling studs will sit on top of the inner shell construction as planned, but we would still prefer to use the resilient hangers I posted to secure the ceiling studs to the concrete ceiling, and several of the wall studs to the concrete walls for security,

There is absolutely no need for that, and it will trash your isolation. You CANNOT have any mechanical connections between the leaves of your rooms. Even on single nail or screw that connects them is enough to destroy the isolation.

Have you ever used a tuning fork? How instruments were tuned before electronic tuners appeared... Tap it on the table, hold it up in the air, and you can faintly hear the tone. Tap it on the table, and hold the base of the fork on the table, and it is MUCH louder... because the solid connection transmits the vibration into the table, which then acts as a speaker. The size of the base stem is about the same size as a nail or screw....

That's illustrates perfect why there can be ZERO connections between the inner-leaf room and the outer-leaf.

Once that is complete, we'd evaluate if a second layer of drywall is needed to increase ...

Bad idea! That is called "building with no design", and is doomed to fail. It is also called "guessing", and you cannot successfully build a studio by guessing.... Instead, just CALCULATE! There are equations for predicting how an MSM wall will isolate. Just do the math, and design the studio to perform the way it needs to perform.

before filling in the spaces with rockwool and mounting a first layer of 15mm drywall.

Don't use drywall for the first layer: use either OSB or plywood. That gives the wall MUCH greater structural integrity, especially in sheer. Put one layer of OSB (or ply; whichever is cheaper where you live), then put a layer of drywall on top of that, optionally with Green Glue in between. But first design the wall so that the combined mass of those two, along with the depth of the air cavity, and the damping of the insulation, will be correct for your needs.

Does this sound like a workable approach, or do you still think this does more harm than good?

More harm than good.

One very well respected forum member, a renowned acoustician, used to have a signature that said; "Building a studio is 90% design, 10% construction". He is absolutely right! If you spend most of your time designing it, then the construction will be smooth, fast, and cheap, with a successful outcome. If you DON'T design it properly, construction will be problematic, slow, and expensive, with a very poor outcome. If you don't believe me, take a look at some of the build threads on the forum: Those that were designed carefully ALWAYS work out very, very well. Those that were "designed" by guesswork or built with no real design at all, always turn out badly. Or they never turn out at all...

Considering the placement of my control room window, I don't think that changing the orientation of the CR will do me much good.

You might be right. I'd need some time studying the actual SKP model to see if there are any possibilities, but from the photo, it looks like you are out of luck.

Would my current orientation be significantly worse than having the speakers firing down the longer dimension, considering that the room is already nearly square in footprint?

There would be a difference (20cm is 20cm!), but probably not life-or-death.

To be honest, I don't think he was very happy with me as a customer and I wasn't very happy with him as a consultant. I'm normally not a bad communicator, but the two of us seemed to be talking past one another, and I ended up trying to determine things on my own whenever I thought I could, with mixed results as it's becoming apparent.

Understood. Sometimes there's just no "connection" or "chemistry", and f that happens, it's better to pass on the project to someone else. I'm just completing the design for a mastering studio where that happened. The customer hired a very big name designed initially, but the design he delivered was nothing like what the customer needed. Communications issues: the designer wanted to do it one way, but the owner did NOT want it that way, for practical reasons: There was no way to actually build it on his property! There's nothing at all wrong with the design: it would have worked out well. Except that it could not be built in the space available. That's when the owner contacted me to take over, and re-do it completely, the way HE wants it, not the way the designer wanted it. So I fully understand! That one is currently under construction: I'll see if I can get permission from the owner to post some images.

Anyway, you made it to the forum, so you can now get the right advice, to do it the way you want it to be... but doe right! Not by guesswork, but by design...

But to be clear, I don't wanna speak badly of the man at all, as he's clearly very good and experienced at what he does, but we seemed to be pulling in different directions.

Completely understood! That's very similar to the issue with the mastering studio I mentioned above: Big name designer, good reputation, many successful studios... but a lack of connection with the customer in this specific case. It happens.

Would it be conceivable to keep the orientation this way, and to increase the rear wall absorption substantially?

Possibly, but there's a lot of calculations that would need to be done to make sure. I would need to see the full layout and design intention, then spend some time working through it. But I'm rally tight on time right now! Several projects under way, and my paying customers get first priority. I'm sure you understand!

To be honest, I am surprised too. I showed him the plans before I handed them in for approval, and he didn't note any significant problems with it.

Curious...

I intend to build a stack of sandboxes with different materials that I can wheel into the room when I do have a project that requires Foley work.

You will need filters on your HVAC return registers! Foley work tends to put a lot of particulate stuff into the air, as you thump, beat, batter, clip, tear, shred, and mangle things. It's a good idea to filter that out, before it gets in to the HVAC ducts. Also, you will need to oversize your AHU, as there will be higher humidity in the room when you are playing with water, and you need to get that under control.

All of these things should have gone into the original design...

I guess I should have asked you sooner!

But you did find us in the end, and it's not too late: things can be fixed, and improved...

That stuff was by no means cheap, actually. It's called Pronouvo-Cork Type 1073 and costs an arm and a leg.

Interesting! You live and you learn.... I have never seen cork being used in that application before. It would not be allowed where I live: Chile is the earthquake capital of the world. If you have every been in a magnitude 7, or 8, or even 6 earthquake, you realize WHY things have to be anchored firmly. Things MOVE in a quake. But anyway, if you don't live in a seismic area, and that stuff is approved by your building code, then I guess it is OK....

The acoustic consultant said that the cork we put in between the foundation slabs may rot away in time as it gets wet from the groundwater, but that that would be nothing to worry about.

Ummm... So WHY did he put in there? Very strange.... Why not use an inert synthetic water-proof compound, that won't rot? Curious....

I did not consider the flanking potential of those strips, and neither did the acoustic consultant, as far as I'm aware. It was put in as a necessity, without really considering any alternative solutions...

There are several very good expansion joint compounds that are good both acoustically and also with water.

This part, I'm most bummed about. I feel like I could have found a significantly better solution for this with a little more preparation. ... The tubes carry only air from and to the rooms.

That's a problem. I would say that your HVAC is going to need a complete re-design. Sorry to tell you that in such blunt terms, but that's the way I see it.

What I'm seeing in the photos is ribbed 2 inch (50mm) pipe. Maybe a bit bigger, but I don't think so. The cross sectional area is small: therefore the air must move FAST (meters per second) in order to provide the correct flow rate (cubic meters per minute). Air that moves fast creates noise. Even worse, those are RIBBED pipes, meaning that the interior is a very rough surface, with bumps an valleys all over: That will create high turbulence, and high resistance to the flow of air. So you will fans that can move air at high speed, against high resistance, and they will also be noisy. The AHU will probably not be able to deal with that by itself: Even high static units usually don't go beyond about 0.8 in.water (about 200 Pa). So my guess is that you will need high static booster fans, in line.

The normal way of doing studio HVAC is with very large diameter ducts that move a large volume of air slowly, with low static pressure (low resistance). I normally use 6" ducts (150mm), or 8" ducts (200mm). The cross sectional area of a 50mm pipe is 1900mm2. Not very much. The cross sectional area of a 200mm duct is 31400 mm2, or nearly SEVENTEEN TIMES as much as one of your pipes. Therefore, air will have to travel seventeen time faster than normal through your pipes. And because air noise and turbulence rise with the SQUARE of the velocity (V^^2), there will be a LOT of noise. Air drag also rises with the square of the velocity, so there will be huge resistance to the flow of air.

To put all of this in perspective, current HVAC standards say that you should be circulating the room air through the HVAC system at the rate of about 6 "room changes per hour". In other words, you need to move the entire volume of air in the room, through those pipes, every ten minutes. For your live room, that is 7,86m x 5,15m x 3,31m x 6 = 803 cubic meters per hour, or 13.4 cubic meters per MINUTE. Every single minute you need to pump 13 cubic meters of air through those tiny little pipes. It's hard to be sure from the photos, but it looks like you have four pipes feeding the live room (and another four return pipes). So, assuming that those are 2" / 50mm pipes, the cross sectional area is 4 x 1900 = 7600 mm2 = 0.0076 m2. With a flow rate of 800 m3/hr, that implies a flow speed of 105,263 meters per hour (105 km/hr !!!), which is 1,754 meters per minute. The MAXIMUM flow velocity you want in a studio is about 90 meters per minute. o your flow speed will be twenty times the maximum allowed. This is not viable. Your silencer boxes will have to expand out to twenty times the cross sectional area, and keep that right up to the registers, and even then you would be running at the maximum rate: I like to aim for something more like 40 or 50 meters per minute, which is half of the maximum... so you'd need silencer boxes that expand to 40 times the cross section of your pipes...

To be very honest, I do not see this as being a viable, usable, valid approach. The flow speeds are just way too high. Unrealistically high. Unreasonably high. Even if you only go with half the recommended flow volume, it is still going ten times too fast. There is no way you are going to get NC-20 like this! There will just be too much air noise in the HVAC system.

I would strongly urge you to completely re-design the HVAC. You can use those pipes for running cables between the rooms, so they won't be wasted.

The technician who thought up the solution for the air supply with me ensured me that it'd be moving slow enough for it to be practically inaudible.

Air running through pipes at a hundred kilometers per hour is not slow! I'm wondering if he made a mistake in his calculations?

I'll see that I can determine these factors and improve on them before I move forward with anything else

I can't see how you can do that, to be honest. You would have to sloe the air down by 20 times, meaning that there would be way, way to little air circulation through the rooms. It will be stuff and unpleasant in there. The entire system needs a re-design. It is not feasible with those little pipes.

To give you an idea, here's a view of just ONE of the HVAC silencer boxes for Studio Three: You can see the size of those things: That unit is fed by an 8" duct (31,000 mm2), and it then splits out into two separate paths, exiting though two registers, each measuring 8" by 12" (62,000 mm2 each side, total of 124,000 mm2). In other words, it slows the speed down by a factor of four, from 400 fpm to 100 fpm (121 meters per minute, to 30 meters per minute). It is dead silent! (That unit also incorporates an acoustic device in between the registers, for another purpose: ignore that).

That's what you need for your studio.

The building contractor signed off on it, so he can't be too worried.

Ummm... the CONTRACTOR signed off on it???? Nope. Just nope. It is the building INSPECTOR who has to sign off on it. When you got your building permit with the local authorities, they must have assigned an inspector to visit your construction site at various points in the build, inspector it to check that the contractor is doing it correctly, complying with the law, etc. He signs off, not the contractor! If the contractor is allowed to sign off on his own work, that's like allowing the bank teller to keep his own money, and count it himself, and sign off that it is all there, without anyone else checking!

Also, the contractor is not a structural engineer. They way things SHOULD work on a build like this, is that the architect hands the design to a structural engineer, who confirms that it can be built safely, and he signs off on that. The design the goes to the municipality, and if it it is all in order, they give you your permit. You then give the plans to the contractor, who builds it, but the architect and structural engineer still come in to check that things really are being done according to the plans, and the building inspector also checks at several stages, signing off the paperwork to show that the stage was approved... The contractor does not get to sign off ANYTHING! He just does the work, and it is signed off by someone else. If not, it's like putting the town drunk in charge of the beer factory....

How would I reasonably test for this? Pink noise generator at 80dB in the LR, and SPL meter in the CR?

Use REW. Set up full-range speakers in one room, and put the measurement mic first in the same room, then in the other room. Useh full spectrum sine sweeps.

A simpler way is to get together a loud rock band, with a good bunch of musicians, tell them to play like crazy in the LR. Measure in the same room, then measure in the other room, using your hand-held sound level meter.

Speaking of the soundlock, though. I do have this airgap between the concrete and cinderblock wall, and I haven't yet sealed it.

Where? Photos please. There should be no visible gaps.... there should be one door in the CR wall and another door in the LR wall. The gap between them can be covered in any of several ways, but the easiest is with OC-703 wrapped in black fabric, and press fitted into the gap.

Yes, there is a generous amount of a hemp-clay mixture underneath the foam. So far, I didn't have any moisture problems with either window, but that may be different in the long term. Of course, it was kind of a guess if it'll work or not...

That should be OK; but I prefer to use Silica gel: it is inert, and can adsorb a lot of moisture. If you ever replace those windows, I'd suggest switching to silica gel.

Did you calculate the amount correctly, according to the volume of air in the gap?

The plan is to place a kind of aluminium muffler plug in each of the pipes where they come into the studio rooms,

Sorry, but that won't work. Those little mufflers are for light machinery, not loud music in studios. Studio silencer boxes are HUGE. Here's an example:
That's a very small silencer box, for a tiny vocal booth: It is being fed by a 6" duct (150mm). The box just fits between the outer-leaf joists, that are spaced 400mm OC. That's a studio for one of my customers in Australia. That's the type of silencer you need, except yours will need to be MUCH bigger. Here's the one for the Control Room in the same studio, under construction. This one is fed by TWO 6" ducts:
Here's another, from the same studio (the thread I linked you to above, that we are busy tuning right now):
That's what you will need. LARGE silencer boxes, properly designed for the job.

as well as a central HVAC noise attenuator box placed before the air distribution box to reduce the noise transmission from the AHU.

Nowhere near enough! You need one silencer box on each duct, at each point where it penetrates a leaf. I ave developed a proprietary design that allows combining some boxes into one unit, but they are still very large. The tiny little in-line mufflers just do not have anywhere near enough insertion loss to be useful.

I hope it won't be as much of a problem as I now fear,

It will! And more.... Sorry to be blunt, but that's reality...

The Wernig Q600 is the unit we plan to install.

The link seems to be dead. All I get is a message saying "Link Expired. Access denied!"

I knew that he charges for a phone call close to what I paid for the glass,

Wow! He must be one of the most expensive guys around! Most studio designers do not charge anywhere near that much!

He practically insisted on it. He proposed I use two layers of 4cm thick mats of compound rubber,

There's a problem here then. That's not how vibrations get into structures, and that's not how to stop them getting into your studio. Soil vibration is typically vertical, coming up from below. Not so much horizontal, coming on from the sides. Unless you also put those 4cm pads UNDER the complete foundation, there's not much point doing the sides alone.

Also, rubber is only good down to a certain frequency )depends on type and thickness: thin pads are only for very high frequencies, thick pads for lower). It is far more effective to use springs. What I would have done in your case, is to pour a normal foundation in the usual way for your area, build a concrete shell walls and roof, then float the rooms on properly floated isolation system, like this:
Much simpler, works down to to very low frequencies, and probably less expensive than what you did.

I opted instead for 1.5cm thick compound rubber mats

There's a reason he specified 8cm of rubber... That is relate to the frequency of the vibration and therefore the isolation. By going with something that is only 19% of what he specified, the isolation frequency is now much, much higher, and the isolation is lower. Once again, since this is a tuned system, it is probably that you made things worse than having no rubber at all, since you are now likely on the amplification part of the curve for low frequency vibrations, such as tractors....

I suppose I don't need as much as my consultant recommended, but maybe more than I'm currently aiming at...

I will see to it! I'm not clear on the ceiling construction, though. 5m seems like quite a distance if I won't be suspending the ceiling studs at all from the concrete ceiling. Are the resilient hangers such a bad idea?

There's a limit to the amount of isolation you can get with hangers like those.

5m is not a large span. You an easily span that distance with typical studio ceiling loads, using normal sized joists. 2x8's, or maximum 2x10's would be all you need.

My father also has strong reservations about drilling into the floor slab, as it contains the underfloor heating circuits. There should be about 5cm of only concrete before hitting the heating circuits, but it's still risky drilling down there in case one of the tubes managed to float up enough to be accidentally punctured.

See above: rent or borrow a thermal camera, and you can locate the pipes very simply, and very accurately.

We're obviously going to remove the sylomer pads from the underside of the structure, so that the studwall sits directly on the slab

Yes, but your framing itself is too small to be usable for this. You need 2x4 or 2x6 studs. In metric, that's commonly 38mm x 89mm (2x4) or 38mm x 140mm (2x6). What you are using there is not able to structurally support the loads you will need to put on it.

but we would still prefer to hold it all in place using the mentioned resilient hangers. Would that make a bad situation worse or would it simply be less effective than it could be?

If you build it properly with the correct sized lumber (2x4 at least, = 38mm x 89mm), with OBS or plywood as the first layer of sheathing, then it is structurally very sound, perfectly capable of being self-supporting, and able to handle the loads a typical studio will place on it. There is no need to add vibration mounts or seismic snubbers. Studios around the world are built like this.

I'm getting an average of about dB (C-weighted, slow response) outside in the back area, with peaks of about dB (C-weighted, fast response) when cars drive past or a rooster crows. This is measured in the afternoon. in the Live Room, with all the doors closed, I'm measuring about dB (C-weighted, slow response)

??? The numbers are missing!

Well, after your advice, I am indeed considering going for a more affordable option than the ATCs. The original plan was to pair it all with a Genelec 5.1 system, including a 7050 BPM sub. Everything is back on the table right now, as I wanna make the most of your advice

Ahhh! So you are thinking 5.1 at some point! So, the studio control room needs to be completely re-designed to deal with that. 5.1 is a very different acoustic concept than 2.1.

OK, if you are doing music scoring for the big screen, then you will need a system that is capable of producing the same effect that you'd hear in a movie house, watching the movie. That's a little more complicated to set up than a typical studio!

One question: if you are doing audio for movies, are you required to comply with dolby, DTS THX, or some other standard? Do you need to have your studio certified? Some companies insist that all outsourced work must be done in certified studios. Is that the case with you? IF so, that's EXPENSIVE! Certification is not easy.... This is a big deal.... You have to buy only the speakers and equipment for that specific certification, and it's a complex, expensive process. Hopefully this is not the case with you! Hopefully, all you need is a normal 5.1 setup. Still complicated, but much, less so than a fully THX system...

If I decide to go ahead with the SCM45s, I'll certainly inquire about the remote amp option. I hadn't been aware that this was a possibility. But to be sure, what distance are you referring to? The distance from the remote amps to the speakers?

Right. You have to specify the cable length when you order, as they amp and cable kit come together. You can't make up the cables yourself: you have to use their cables, or your guarantee is void. So you have to measure the distance and order the correct cable kit.

Primarily for simplicity's sake. Perhaps I shouldn't be so timid, but I currently feel like I'm in over my head, so I'm trying to keep things simple.

Follow the thread above! We'll be soffit-mounting his speakers using my proprietary design. Similar to what I did in Studio Three. The same basic concept. You won't see all the "magic" that goes into the mount, as that's something that has taken me yers to develop, but you'll see the general overview, and the results...

That is good to know. So I suppose the general idea is to deflect early reflections to the rear of the room, where the LFs and some of the MFs can be absorbed by some generous trappings, would that be correct? What would you propose I use that can achieve that? Slat wall absorbers here instead of at the front would seem plausible to me (which isn't saying much)

Your entire control room should be based around one of the accepted design concepts: LEDE, RFZ, NER, CID, MR, etc. LEDE is dead, so forget that. CID is complicated, so forget that: I'd suggest RFZ, as in my opinion, that's the hands-down no-questions-asked best method. But it IS a method. With RFZ, the concept is to direct all first-order reflections away from the mix position, leaving a sphere of large radius around the engineer's head where there are no reflections at all: only direct sound. All of the reflections go to the back of the room, where they are absorbed, and diffused, then eventually return to the mix engineer as a low level reverberant field that dies away slowly and evenly at the correct rate for the room. The basic design criteria is that no reflections arrive within the first 20ms (the Haas time) of the direct sound, after which the diffuse field arrives at a level that is -20dB below the direct sound, and decays at the rate that is correct for the room dimensions.

Your design does not seem to be accomplishing that.

So I would need to know the spring coefficient of the sylomer pads (or rather he combined spring coefficient of the system), as well as its combined mass, to figure out at what frequency it resonates, if I understand it correctly. It's becoming painfully obvious how much work I still have to do

Yep! You would also need to know what the correct deflection is for that product: how much it needs to be compressed to actually "float", and what the useful range is. Then you'd need to calculate the load and surface area that you need in order to get that amount of deflection... If you over-compress the pad outside of its "floating" range then it "bottoms out", and flanks: no isolation. And if you under-compress the pad outside of its "floating" range (not enough weight to make it float) then it "tops out", and flanks: no isolation. SO you have to get it right! The load must be within the range at all times...

I didn't comment on all of your remarks because I still need to process a whole range of them, and I do hope I'll be able to continue to pester you with any queries and misconceptions that may still arise along the way.

No problem at all! But I'd repeat my number one suggestion here: Stop building! Don't do anything more until the complete plan is in place, with every last detail worked out.

Thank you so much in the meantime,

- Stuart -

It's been indeed quite a bit to digest, Stuart, so my replies are taking a little longer than I would like. I want to make sure I understand your comments as well as I can before I reply, so I don't take up any more of your time than I need to.

Getting NC-20 is actually more about the HVAC system than the isolation system. Or perhaps "both in equal measures" would be a better way of putting it. To get NC-20, you need to design the HVAC system for that, along with the room. You might well be able to get NC-20 with the HVAC turned off, but there's not much point to that! You need to be able to use the room with the HVAC turned ON! HVAC design is an integral part of studio design: When I'm designing a studio, I often spend as much time on the HVAC as I do on the rest of the studio all together: HVAC is a big issue.

I've done some calculations on this to see where I really stand. It's certainly not ideal, but I would think it's also not as bad as your observations lead you to conclude. The ducts/pipes are actually slightly bigger than you assumed from the photos (62mm internal diameter) and are ribbed for her pleasure – I mean, on the outside only. The inside of the pipe is practically smooth (only minimal waving, no deeper than half a mm).

With 4 pipes feeding the live room 6 times per hour, the air would have to move at 276m/min. To bring it down to speeds of, say, 70m/min, I would have to build muffler boxes that expand the cross-sectional area by 4 times that of the feeding tubes, meaning about 120 cm2. Does that sound about right? That's roughly what you built for Studio Three if I'm not mistaken, only that your initial airspeeds were already much lower.

What would you say is the minimum amount of air exchange per hour that I could reasonably work with, considering that long full-band productions will be a relatively rare occurrence? If I aimed at 4 volumes per hour, then what I have would seem to be workable, unless I've miscalculated.

I just ordered Rod's book, as I've been told that it goes into a fair amount of detail on this, so I expect I'll be able to work out the specifics with some time and careful consideration. If you could warn me of any potential misconceptions or link me to other resources/guidelines, I'd very much appreciate it. We'd obviously rebuild the inner shell sturdy enough to be able to comfortably hold 8 such boxes in the LR, and 4 of them in the CR.

mixing for video and cine these days is often 5.1, 7.1 or even something more exotic. Do you plan to do that? Maybe not now, but at some point later? If you plan on ever doing multi-channel mixing, then the control room acoustics and overall design need to be done for that NOW!

I do plan on being able to handle 5.1 projects down the line. Nothing more exotic than that, and I also don't intend to aim for a certified setup. Most of my projects require sound for web video, so it's all been stereo thus far, but I'd love to work on documentaries and potentially feature films eventually.

I've also caught up with Frank's build and it's been very insightful. Particularly the corner trap in the back is a work of art in itself. It actually prompted the idea of going with a similar layout for my control room, meaning diagonal in its orientation. I know you'd need to spend some time calculating some of the finer details, time which you can't spare at the moment. But I'll outline my thinking, and perhaps you can make an early judgment based on that. If it doesn't seem reasonable to you, I'll simply try to improve upon my initial design.

For the diagonal option, I would make the inner shell actually square, but make the two rear walls highly absorbent across the spectrum, and the rear corner would strike me as a suitable spot for targeted treatments. The speakers could only be spaced about 1,5m apart this way, perhaps slightly more, but that seems to be the most limiting factor. Any thoughts?

Hmmmm.... so you have around 75 dBC outside, and around 40 dBC inside. That implies isolation of around 30 dB, which isn't much. And with 32 dBA / 42 dBC inside, you definitely are not getting NC-20! Probably more like NC-30. And you don't even have the HVAC turned on yet... NC-30 is not going to be any use for Foley work.

I turned up my stereo last night so that it sat at about 100dBC in my living room just above the LR, where I measured 56-60dBC. I suspect that my exterior window is my main weak point (aside from the HVAC problems), leading to the still relatively high background levels of 42dBC without music pumping upstairs. I'll get a full-range speaker into the room, which should paint a clearer picture about potential flaws, weak points, and potential solutions. Removing the inner window from my exterior double window construction and re-mounting it on the inner shell would probably improve the TL quite a bit.

As to the NC ratings, I think NC20 is probably too ambitious, considering my budget, my abilities, and the flaws already present in the build. NC-30 would be slightly disappointing considering the same aspects, but a worst-case scenario I could live with. NC-25 or thereabouts seems to be a reasonable goal to aim at, would you agree?

Your inner-leaf doors will be heavy, and as you open and close them there will be a large amount of stress and strain on the framing.

Regardless of the anchoring problem (which we'll surely be able to solve the way you outlined), I was hoping not to require any additional doors. I'll make some measurements once I set up my full-range speakers in there, which should paint a clearer picture, but I was hoping that it would be sufficient to seal the inner shell around the existing door frames. Do you expect me to have problems doing it this way?

Ummm... the CONTRACTOR signed off on it???? Nope. Just nope. It is the building INSPECTOR who has to sign off on it. When you got your building permit with the local authorities, they must have assigned an inspector to visit your construction site at various points in the build, inspector it to check that the contractor is doing it correctly, complying with the law, etc. He signs off, not the contractor! If the contractor is allowed to sign off on his own work, that's like allowing the bank teller to keep his own money, and count it himself, and sign off that it is all there, without anyone else checking!

The way it works here (unless we somehow accidentally circumvented the law), is that the building company/contractor is financially liable in case any measures don't comply with the regulations, deviate from the approved plans, or are otherwise unsound, so they have a financial and legal stake in doing it right. The company's structural engineer came to visit the site several times during critical building stages and found all measures to have been adequately executed. Anything going wrong with the interior build is on me, however, so I'm taking your words-of-warning very seriously!

??? The numbers are missing!

Sorry about that, I wrote the post late at night but thought daytime measurements would be more representative, so I just typed a placeholder. You did find the numbers at the top of my last post, I just forgot to place them in the placeholder...

I suppose that's a good a cue as any to take a break for a few hours doing something else. I'll probably put on some Floyd to try and remember why I'm even doing all of this.

I know I've skipped over many of your comments, but rest assured that they're all duly noted. I'll likely come back to them as I go along.

I also can't say it often enough, Stuart, but I'm very humbled by your honest advice, your kind words and kind warnings, and the generosity with which you share your time and expertise. I can't help but think that we would have this world singing and dancing again in no time if helpful, friendly guidance like this were more commonplace. Should I never get to return the favor directly, I'll at least make sure to pass it on.

Many thanks and warm regards in the meantime,
Thom