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:
Image not preserved: oslthom-CR-ratio-AMROC-S00.jpg
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.
:shock: 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):
Image not preserved: 2-leaf-3-leaf-4-leaf-STC-diagram--classic2-GOOD!!!.gif
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 ([b]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:
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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!
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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!
:thu:
- Stuart -