John Sayers' Recording Studio Design Forum Archive

Hello! This is my first post. I'm pretty sure I followed all the rules before posting

Our NYC studio (Flatiron neighborhood) will be relocating soon. We do tons of VO recording, as well as audio post. We’re looking to build a two-room facility that uses modular VO booths. The facility will have a client lounge & offices. We want to have control rooms with windows for natural light (similar to the Sound Lounge 5th Avenue style of build - see attached picture for reference). The idea is to get an advantageous location that does not require floating the control rooms: the full top floor of a building (in which case the only neighbor would be below us); a high floor away from a subway line (very little street noise/no subway noise). Since the cost of floating control rooms is very high compared to what isolation it achieves (at least in this type of situation) we want to avoid this. We’ll make sure we put up proper control room walls, and use air space between rooms to help isolation.

Let’s figure that the building has concrete floors, a hardwood flooring, and 12 foot ceilings. The control rooms will use near-field monitoring at moderate listening levels, with some sub-woofer use for 5.1 mixing.

So if we don’t float the control rooms, this brings up two questions about isolating the rooms from our own usage that I’m hoping to get some advice on. Are there any special techniques used in non-floating situations we can learn about?

1. Sound from one control room will get into the other control room through the shared floor and ceiling. If the two control rooms are separated by 8 to 10 feet, with the VO booths in between, will this distance prevent most of the vibrations from getting through? How can I help to prevent this room-to-room issue?

2. Sound (voices, footsteps etc.) from the hallways and lounge will get in to the control rooms. I imagine using throw rugs will help with footsteps. And locating the lounge away from the doors will be good. What else can I consider?

Any help is greatly appreciated!

Hi Bob, and welcome to the forum!

I'm pretty sure I followed all the rules before posting

Yup, you nailed it!

The idea is to get an advantageous location that does not require floating the control rooms

You'll find that most studio designers share your opinion of not wanting to float your room, or your floor! It's a common misconception that floating is even needed for most studios: in reality, it very seldom is needed. Here's a link to a thread on exactly that subject, that might interest you:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

Floating is really hard to do right, really expensive, and seldom needed anyway. It can get great results, though, when done right.

OK, so with that out of the way, your basic concern seems to be getting enough isolation between your control rooms and VO booths so that there is no bleed between them. That can be done, without too much trouble, by using the simple isolation technique know by the long-winded name "fully-decoupled two-leaf MSM isolation". That's a mouthful of syllables that basically means you build each control room and each VO booth as a separate "box" that does not touch any other "box" mechanically, and all of them together are surrounded by an isolation wall. It's a bit more complex than that, but that's the basic idea. This is sometimes also called "room-within-a-room" construction. It's a lot easier to build it than to describe it! You can get upwards of 50 dB of isolation between rooms with this technique, which should be more than sufficient for typical VO and mixing work at typical monitoring levels.

The limiting factor for how much isolation you can get in a building, is something called "flanking noise", which basically means sound that gets into the structure of the building itself, bypassing your isolation. If you have a really massive and well-damped concrete slab for your floor, then the flanking limit will probably be up around 70 dB , and for a less excellent floor, the limit is probably around 60 dB, give or take. (The flanking limit means you won't be able to get more isolation than that, no matter what you do, unless you float your floor and/or walls).

So the question is this: Is 50 dB of isolation enough for you? For voice work, I'm guessing that 50 dB is fine. For mixing too, at typical levels. 80 dB coming out the monitors will be knocked down to 30 dB outside the room, which is practically inaudible, and well below the ambient sound level in a typical office building anyway.

However, if you want to track live drums or full rock bands, then 50 dB is very likely not enough! Live drums can easily hit 115 dB or more, so 50 dB of isolation will only get that down to around 65 dB outside. Not quiet.

So it would be good if you can put a number to how much isolation you actually need, in terms of decibels. That's the basic design parameter you need to know in order to design your isolation system.

Are there any special techniques used in non-floating situations we can learn about?

Yes! There are several things you need to keep in mind to maximize isolation.

First is sealing. As in hermetic sealing. Air-tight. Each of your rooms must be very carefully sealed all around, without no air gaps at all. Not even a tiny crack under the door. If air can get through, then so can sound, so sealing is critical.

Next is decoupling. That just means that the rooms can have no mechanical connections between them at all, which implies that each room is built with it's own separate, independent stud frame, and with drywall on only ONE side of those studs (not both sides). Not even a single nail can connect the framing of one room to the framing of another room. Each is an independent, stand-alone unit.

Third is mass. Stopping sound requires mass, unfortunately. There's no way around the laws of physics here, and they say that the most effective way of stopping sound is with a very heavy materials that are very rigid (stiff). A couple of layers of 5/8" drywall is usually enough to meet that.

Forth is damping. Meaning materials that absorb vibration and absorb sound. Usually that can be plain old fiberglass or mineral wool insulation. It needs to be the right type and density, of course, but nothing exotic. Easily found at Home Depot or Lowe's.

There's a few others, but those four are the key to good isolation at low cost.

1. Sound from one control room will get into the other control room through the shared floor and ceiling.

Only the floor is shared: each room has it's own separate ceiling: that's part of the "room-in-a-room" concept. You build 2x4 framing for the walls around each room, but they don't go up all the way to the existing ceiling: they stop a few inches short, and you then frame across the top of those new walls with ceiling joists, and hang your new separate independent ceiling drywall from that. So the only thing in common between the rooms is the floor. If you connect your walls to the existing ceiling, then all bets are off, and you won't get good isolation.

If the two control rooms are separated by 8 to 10 feet, with the VO booths in between, will this distance prevent most of the vibrations from getting through?

Not if the ceilings are connect. The ceiling is a major flanking path, and since flanking implies that the sound is running in the building structure itself, it can cover very long distances without much attenuation. Tap on a concrete pillar in the basement of a building, and you can hear that all the way up, many floors above. Sound can flank over very long distances, once it gets into the building structure.

How can I help to prevent this room-to-room issue?

By totally isolating the rooms from each other, except for the floor. As above: build each room as a simple 2x4 frame with drywall on one side. Four walls and the ceiling, for each room. Sealed air-tight. That gets you big-time good isolation.

2. Sound (voices, footsteps etc.) from the hallways and lounge will get in to the control rooms.

Voices are airborne noise, and will easily be stopped by the system I described above. Footsteps are impact noise, and therefore are flanking noise. The only way to deal with that is to prevent the impact from ever getting into the building structure: thick carpet on thick underlay does the trick. So carpet all your hallways and the lounge, and other service areas (lobby, offices, kitchen, storage rooms, etc.). The studios themselves cannot have carpet on the floor, obviously, but all those service areas sure can, and that's the best way of dealing with all impact noise: Stop it at the source. Ones the vibration is in the floor, it's too late: there's nothing you can do about that, realistically.

The control rooms will use near-field monitoring at moderate listening levels, with some sub-woofer use for 5.1 mixing.

Great, but keep that sub off the floor! For the same reason as above. Set it on an isolation pad or small isolation riser if it is big. A sub directly on the floor is going to do some major flanking. Low frequency sound is the hardest of all to isolate, so it's really important to stop that sub and the speakers from touching and thing structurally. For the main speakers, the best idea is to properly flush-mount them ("soffit mount") with good isolation techniques and a massive, rigid soffit: Or if your budget won't stretch that far, then mount them on massive stands (sand-filled hollow steel, or concrete, or brick, etc.) and with isolation pads on top. Same for the surrounds: do not put them on wall mounts, since those are also potential flanking paths.

5.1 is an entirely different ball-park from 2.0 or 2.1, so more careful design is needed with better attention to layout, geometry and treatment. 5.1 done right can knock your socks off, but done poorly sounds terrible.

If you are planning to design and build this studio yourself, then I'd suggest two books: "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics), and "Home Recording Studio: Build it Like the Pros", by Rod Gervais. There's also John Sayers own work @ http://johnlsayers.com/Recmanual/index.htm . Between them, those three will give you the theoretical background and practical guidelines on how to go about all of this, using the methods I mentioned above.

Hope that helps!


- Stuart -

Hi Stuart, thanks so much for the nice welcome and the extensive reply! I really appreciate the time you've taken to contribute.

FYI I had already read through the topic you posted about floating rooms - this was extremely helpful.

I do have some questions I'd like to run by you. Actually many questions but for now I'll address the two things that are first on my mind. I'll likely follow up with some other thoughts and questions later on - I hope you don't mind coming back a few times.

First in regard to the ceiling. Our idea was to build control room walls up to the existing ceiling, and not have to build a new ceiling on the walls. Honestly, I'm basing this idea mostly on pictures of audio post rooms in NYC. (If they can do it, why can't we?) For example in the attached picture, the ceiling really looks like it is the original ceiling - you can see the sprinklers, ducts, lighting. You write that a good slab will prevent flanking of up to 60 or 70 dB. So why won't the ceiling act in the same way as the floor? Maybe I'm assuming something incorrect here - but would the roof of the building be the same concrete slab as the floors? Or perhaps the roof is different - and that's why one needs a new ceiling?

Second, regarding natural light in the control room. How do you keep the light, but retain isolation? In the attached image, the windows appear to be double windows, which makes sense for isolation from the street & from other studios in the facility. Can you tell me - Is the inside window wall part of the room-within-a-room? From looking at the picture it's hard to tell if that wall is just built off the original wall a bit, rather than being one wall of the room-within-a-room.

So basically, is it possible to get about 60 dB isolation by building four solid walls that go from existing floor to existing ceiling? That is what we'd like to achieve.

Thanks!

First in regard to the ceiling. Our idea was to build control room walls up to the existing ceiling, and not have to build a new ceiling on the walls. Honestly, I'm basing this idea mostly on pictures of audio post rooms in NYC. (If they can do it, why can't we?)

The basic answer there is another question: "Do they need as much isolation as you do?" Or "do they already have it from some other factor?" All studios are different: it is seldom possible to look at what was done in one place and copy it exactly to a different place. Some things can be copied, but at best most things need to be adapted or modified, to work in other places.

You write that a good slab will prevent flanking of up to 60 or 70 dB. So why won't the ceiling act in the same way as the floor?

It most likely will act the same way, but that's part of the problem, not part of the solution!

OK, think of it this way: the basic concept of a room in a room is that the inner-room is as independent, separate, etc. as possible. You want it to be free to move, shake, rattle, roll and vibrate as much as it feels lie WITHOUT transmitting that to the building itself: that's the final goal.

But in reality, the room has to sit on something (unless you know some magic spells to make it levitate! ). You have no choice there. And since floating is out of the question, you sit it on the concrete slab floor, which all of a sudden imposes a flanking limit. Call it 60 db, to be reasonable. If you could levitate, then there would be no flanking limit at all: your isolation would be limited only by air transmission. But the simple fact of having to put it down, imposes that limit. Now it is firmly anchored on one of its six sides, but all the others can still move, shake, rattle, roll, etc. freely, without transmitting any of that to the rest of the building. A bit goes into the floor, which is why you now have a limit, but not much.

Now consider what happens if you attach the top end of everything to the ceiling: You just jammed the entire room solidly in place! NONE of the sides can now shake, rattle etc. freely, since ALL sides are firmly anchored at both ends! Sure, the wall panels themselves can still flex a bit in the middle, but even that is transmitted to both ends, since both ends are firmly anchored.

Not sure if that helps to understand the concept here: It's not exactly like that, of course (nothing is ever simple or intuitive in acoustics!), but it gives you an idea of what is going in if you anchor both ends of your walls to the structure.

Second, regarding natural light in the control room. How do you keep the light, but retain isolation?

That's a bit easier to explain: You have one pane of glass in the outer leaf probably the existing windows in the existing walls, then you put a second pane of glass in the right place in the inner leaf.

In the attached image, the windows appear to be double windows, which makes sense for isolation from the street & from other studios in the facility. Can you tell me - Is the inside window wall part of the room-within-a-room? From looking at the picture it's hard to tell if that wall is just built off the original wall a bit, rather than being one wall of the room-within-a-room.

It's really hard to say from those photos, since much of what goes in in acoustic isolation and acoustic treatment is frequently hidden from view (it is pretty ugly to look at!). So it could be that you are seeing acoustic fabric covering the gap between the inner and outer leaves, assuming that the room actually is built like that. Or you might just be seeing he surface of a very thick brick or concrete wall, if that's what it is made of. And if that is a 12" concrete wall, then that would explain why they didn't need a room-in-a-room: 12" of high density reinforced concrete will get you upwards of 50 dB of isolation all by itself, so if that room is built like that, and the don't have flanking issues in the building (elevators, HVAC equipment, footsteps, water pipes, traffic, subway, etc.), then they are fine like that, except for the windows. Since glass 6" thick is really expensive (to match 12" walls), it just makes much more sense to put two panes of 3/4" glass on opposite sides of the wall, with a big air gap between them, to still get good isolation like that.

But like I said: it's impossible to tell from a photo what the situation of that room is. You'd have to directly ask the designer that built it, to see what he did and why he did it. And even if you did know that, you'd still get back to the same original issue I mentioned: all rooms are different, so what they did in their room to get it the way they need it, is most likely not applicable to you doing in your room to get it the way you need it. There are just too many variables involved in studio design to be able to take the "cookie cutter" approach. If you scan the forum for some of the threads where people tried to do that "Because my buddy saw that in a studio where he went once", you'll notice that 9 times out of 10, copying "what the buddy saw" leads to disaster, and the tenth time it did nothing useful, but at least didn't do anything bad either! Maybe that's a bit of exaggeration, but you get the point: What works for me in my studio is most likely not going to work the same for you in yours.

So basically, is it possible to get about 60 dB isolation by building four solid walls that go from existing floor to existing ceiling? That is what we'd like to achieve.

Physics to the rescue! Acoustics is a science, based on physics. There are equations that describe how it all works. The most basic is called "mass law", and this is what it says:

TL(dB)= 20log(W) + 20log(f) -47.2

"W" is the surface density of the wall, and "f" is the frequency. In real-world terms, that describes how much isolation you get at each frequency for a wall that has a given mass. So if you do that equation 20,000 times, for each of the 20,000 possible frequencies in the audio spectrum, you can draw a graph of how well a wall isolates!

Or for lazy folks like me, you can use the empirical version of the equation, which approximates all those 20,000 others, into one:

TL = 14.5 log (Ms * 0.205) + 23 dB

Where: Ms = Surface Mass in kg/m2. So all you need to know is the surface mass of your single wall! Let's talk about that really massive 12" thick concrete wall. Concrete density is roughly 2300 kg/m3, so a wall 12" thick has a surface density of about 782 kg per square meter. Plug that into the "mass law" equation, and you get 54.97 decibels. So if you find a building with 12" reinforced concrete walls, floor and ceiling, you can use it-as, since you are already getting pretty darn good isolation. Not the 60 dB you wanted (you'd need 30" of concrete for that...), but not far short.

That's the absolute truth: The laws of physics do not lie. to get high levels of isolation from a single leaf wall, you need amazing amounts of mass. Which is why studios are not usually built that way, and why I'm assuming that if the photo does show a studio with 8" or 10" concrete walls, then all they needed was 40-soemthing dB of isolation, not the 60 that you need. It is quite literally one hundred times harder to isolate to 60 dB than it is to 40 dB, simply because the dB scale is based on log10. So stepping up from 40 dB to 50 dB is ten TIMES the energy, and ten TIMES harder, but then going from 50 to 60 is ANOTHER ten times the energy, and ten times harder. So 10 x 10 = 100. Log math is a bitch! You think "I just need a few more dB, that's all!". But the logs catch you, as they apply to bank balances too...

OK, so what to do then, if there are no handy buildings with 30" thick concrete walls? That's when you resort to TWO-leaf walls. A 2-leaf wall uses a totally different principle of physics. Not mass, but resonance. That's why it can isolate to much higher levels with much less mass. In essence, it uses sound to kill sound. It uses the power of resonance to fight back. A two-leaf wall is a tuned resonant system, so all you need to do is tune it accordingly, and you get the isolation you need. You "tune" your wall by varying either the mass per unit area of the wall (surface density), or the size of the gap between the two leaves (or both). There are equations for figuring all this out too, but the they are a bit more complex than mass law. So in order to determine what you need to do with your SECOND leaf (the inner one that you plan to build, to create the "room", you first need to know what you already have with the outer leaf. The equation needs to know the surface density of BOTH leaves. So until you know what that is for your outer leaf, there's no real way of knowing what you need for the inner leaf or the air gap. If your outer leaf is paper-thin and has very little useful mass (eg, sheet metal), then you need a major big air gap and stacks of mass on your inner leaf. On the other hand, if the outer leaf is already pretty substantial (say 4" brick), then you can get by with a smaller air gap and less mass on the inner leaf. However, if your outer leaf turns out to already be two leaves, then you have yet another problem: Your inner leaf will make that into a three-leaf system, which very counter-intuitively REDUCES your isolation in low frequencies, so you need even MORE mass and/or even larger air gaps than you would have for a two-leaf...

I'm not trying to be evasive and skirt around answering your question: it's just that, without knowing some more details about what your outer leaf might be, I simply can't give you a valid answer! You are basically asking me "how long does my piece of string have to be", but neither of us knows yet what the string will be tied to, so it simply isn't possible to say.

So getting back to the actual question: "is it possible to get about 60 dB isolation by building four solid walls that go from existing floor to existing ceiling?", I would have to say "Yes", it is possible, but it might not be feasible in YOUR building, depending on how it is built. And seeing that tying the walls at both ends greatly reduces isolation due to the multiplied flanking paths (the walls are not decoupled), I would have to add that I wouldn't like to be the one trying to do that. Or rather, I'd love the challenge as a designer, but I sure wouldn't want to be the guy paying the bills for the materials and labor!

On the other hand, achieving 60 dB with a fully-decoupled MSM "room-in-a-room" that ONLY sits on the floor, and is not attached to anything else, sure is possible, and also feasible, at reasonable cost.

Not sure if that was much help! But really, without knowing the basic parameters of the actual physical building that we are dealing with, that's the best I can do. Sorry!


- Stuart -

Thanks so much Stuart! your detailed explanations are extremely helpful, both for my specific situation, and in the general understanding of room construction. I particularly like the way you describe how a room should be able to shake and rattle that totally makes sense once you explain it like that.
And pointing out the difference between a possible amount of isolation vs. a feasible amount is also great.
And also, now I can see how much of what I'm asking does depend on lots of specific factors.

With your help I do feel better about making a decision on what's necessary to get the isolation needed. We'll be seeing some spaces over the next few weeks, and I'll probably come back to this thread before too long.

Again, much appreciated!!

When visiting locations I recommend bring a Sound Level Meter and save some readings. Inside and out. When you are getting serious about one of them, do a fuller noise survey.
It's hard to keep out the sound of an airplane or ship's horn, or even loud street cleaning machines.
A Smart phone app would be fine. Faber SoundMeter is good but so is the NIOSH free one.

DD