John Sayers' Recording Studio Design Forum Archive

Good morning everyone. This is Magí writing from São Paulo, Brazil.

I moved to Brazil (from Spain) about 6 months ago and I've finally found a room I'm going to convert into my working space. I was looking for a smaller place (around 20 square meters) just to do pre-production, editing, mixing, mastering, and light recording work. I found a bigger rental space for a very good price and pulled the trigger. It's a single space of 80 square meters (4x20, weird geometry for a studio, I know). The owner doesn't allow me to build anything permanent, so I have to be creative. I don't intend to build a full-fledged studio, just a nice over-sized home studio. Luckily, isolation is not a concern so I will be using the space as is, just treating the sound inside the room using broadband absortion, superchunks in corners, clouds in the ceiling and some difusion. The idea is being able to pull everything apart the day I leave the space. Besides the imposed restrictions, my wife and I plan to move to a quieter city in 2-3 years (São Paulo is great for business, but we don't think it's the best place to rise our children once we have them), so it doesn't make much sense throwing too much money in this conversion.

For now I'm going to settle with a single-room approach. Buuuuuut... a room 20 meters long is too much and obviously wrong to be used as a mixing space, so I thought of dividing the space in two, just using the half of it and offering the rest of the space to a partner (not necessarily an audio-related professional, in fact I would rather share the space with a visual-artist, a video-maker, a graphic designer...). I'm writing here to ask for some advice on building the partition wall which would divide the space, as I'd like to isolate one half from the other in order not to bother too much whoever is working on the other half of the room.

I've had Rod Gervais' book for years and I'm somehow familiar with the construction methods explained there. I have also lurked around here a lot (for years, just for pleasure) and did some intensive research on the subject. I have never built construction structures, but I'm a hobbist furniture-builder and I'm pretty handy with tools and wood. I have a pretty good idea of how I would build this wall, but because of the limitations of what I can do in the space, many questions are coming up. I'll try to do my best to explain what's in my mind, but please understand that I'm not a native english speaker and I'm lacking a lot of technical vocabulary (add that to the fact that I'm living in a country where I can't use my native language either... I mean, I can speak portuguese quite fluently, but in regards of construction vocabulary I'm screwed, so finding every little thing I'm gonna be needing will be quite an adventure... anyway, this is going to be a greate learning experience for me). Let's get to it.

I've attached some pictures of the room. You can see its length (image "Inteiro") is divided in 5m runs by those arches. I plan on using the two 5 meter sections in the end of the room (image "Fundo2" shows the last 5m) as a single space for me to work (probably using large 2x1,20m movable broadband absorbers to create a fake back wall, placed where necessary). Then I want to build a double wall where the middle arch is (the first one you can see on image "Entrada2"). That is - two walls, one each side of the arch. Very schematically, it would be 2 separate wooden frames (using 4,5x10cm beams) holding a sandwich of 15mm OSB - 100mm rockwool - 150mm air gap - 100mm rockwool - 15mm OSB. Of course, I need an entrance way, so I plan to build a double door too. Here's a list of my initial concerns:

1) I'm forced to leave the concrete floor intact, so I can attach the frames to the side walls only (and to the arch). Would this mean any safety issue? I mean, will the structure hold in place in a safe manner? I'm mostly concerned about the moving doors (I'm assuming they're going to be pretty heavy). What about where the wall meets the ceiling? Will that joint be sealed enough if I can't screw the frame to the ceiling? I've thought of splitting each frame in two (one part from the floor to the arch, then an independent frame from there to the ceilng) in order to make the ceiling joint easier to adjust.

2) Do I have to worry about gaps in the assembly? I know gaps mean huge isolation losses, but do I have to worry about where the wood meets the wall/floor/ceiling? What about between each OSB panel? I'm supposed to leave a couple of mm between them so they can expand... And between OSB panels and the frame? Should I use some kind of caulk in those places? Maybe adding a layer of mass loaded vinyl in all those places? Some kind of sealing tape? Nothing at all should be fine?

3) I plan to use screws everywhere (instead of nails) so I can pull the walls apart and recycle the materials the day I leave the space. Apart from the extra work, should it be a concern in terms of safety and/or performance?

4) If I get this all to work properly, will it benefit from adding a second OSB layer per side? I assume it would improve the isolation because of the mass increase, but is it worth the extra cost, work (not that I'm lazy at all) and weight? I mean, I guess I will get to a point where improving the wall will be of poor benefit as sound will be leaking structurally through the floor and ceiling, right?

I'm sure many other concerns will pop up under your evaluation. Thanx in advance for your time and help.

Hi there "magibatalla", and Welcome!

São Paulo is great for business, but we don't think it's the best place to rise our children once we have them

Absolutely! It's a massive concrete jungle, for sure. Nice people (most of them...), great food, great for shopping and business, but I wouldn't want to live there. Having been there many times, I fully get what you are saying, and why you'd want your studio do be temporary.

I would rather share the space with a visual-artist, a video-maker, a graphic designer...

Since you don't want to do any isolation, I'd suggest NOT going with a video maker... probably better to go with the graphic designer. The reason I traveled to Sao Paulo so much is because I used to design and install high-end video post production studios, so I'm pretty familiar with how loud video makers get, when doing their work. Even if all they are doing is voice-overs! Since you can't isolate your place, I'd look for a sub-renter who is very quiet, and does not mind your noise.

some advice on building the partition wall which would divide the space, as I'd like to isolate one half from the other

There's the problem. A single wall will not provide much isolation. In order to isolate well, at least one of the "halves" would have to be built as a proper "room in a room" system. With a single-leaf partition but shared walls, floor, and ceiling, there is a limit on how much isolation you can get. There's also the issue of those windows. I would suspect that you won't be able to get much better than 40 dB of isolation, best case. Is that enough? Only you can say...

probably using large 2x1,20m movable broadband absorbers to create a fake back wall, placed where necessary

They won't create a wall. They will provide some acoustic benefit, yes, but they will not act as a wall, and will do noting to isolate your area from the other area.

Then I want to build a double wall where the middle arch is

... Hang on a sec! You said: "The owner doesn't allow me to build anything permanent"... Building a double wall would be rather permanent!

it would be 2 separate wooden frames (using 4,5x10cm beams) holding a sandwich of 15mm OSB - 100mm rockwool - 150mm air gap - 100mm rockwool - 15mm OSB.

That would provide a reasonable level of isolation... provided that you also isolate the rest of the rooms! That partition would have to go all the way up to the vaulted ceiling to be of any use at all, but the ceiling itself will transmit sound between the two rooms, as will the walls and possibly the floor. You will also have sound flanking though the windows, and through the HVAC system. So it doesn't matter how good your partition wall is, the sound that flanks around it will always be louder than the sound it blocks.

1) I'm forced to leave the concrete floor intact,

That's a problem! How would you prevent the wall from moving slightly, as you open and close the doors, or from pressure differences, or from vibration, or from building movement, or from earthquakes? Check your local building code: I know that the code isn't very strict in Brazil, and isn't enforced very much, but I'd still check to see what it says. I'm pretty sure you'll find that walls must be anchored to floors.

I mean, will the structure hold in place in a safe manner?

Probably not. I would certainly not want to be in a building where the walls are not anchored. Look at where I live, and you'll understand why I'm very much aware of how buildings can move, bend, twist, shake, distort and come apart in an earthquake. You get lots of magnitude 4 tremors in SP, and quite a few 5's. Plenty enough to trash your un-anchored wall.

2) Do I have to worry about gaps in the assembly? I know gaps mean huge isolation losses, but do I have to worry about where the wood meets the wall/floor/ceiling?

Yes. The rule is simple: if air can get through, then so can sound. Here's the simple truth:
Look at the scale along the bottom: That is "decimal fractions of a percent"! The vertical line marks the point showing what a gap of 0.001% will do to your wall: for a wall that would have got over 60, the result will be less than 50. A loss of roughly 10 dB, which is huge. And that comes from a gap that is one-one thousandth of one percent, which is 0.00001. In other words, if your wall was 5 meters long and 2 meters high, it would have a surface area of 10,000,000 mm2. A tiny crack along one edge of that wall, just 10cm long and 1mm high, would be 100 mm2. Do the math: 100mm2 over 10,000,000 mm2 is 0.00001: So that tiny little crack would cost you 10 dB of isolation. If the crack was 1 m long (instead of just 19cm), then you would lose 20 dB of isolation. That tiny crack would allow one hundred times more sound to pass, than is blocked by the entire rest of the wall...

Take another look at the graph: it shows that for larger air gaps, there is an effective limit on how much isolation you can get, regardless of the wall design: it is around 40 dB. It does not matter how good the wall is, if it has a total open area that is greater than about 0.01%, then you can never, ever get better than 40 dB of isolation.

This is why you'll often hear us repeat, over and over again, that "sealing everything air-tight is critical". The truth is in that graph!! even very tiny air gaps will totally trash your isolation.

In other words, build everything to be absolutely air-tight. No gaps, no cracks. Seal all possible cracks with abundant caulk.

3) I plan to use screws everywhere (instead of nails) so I can pull the walls apart and recycle the materials the day I leave the space. Apart from the extra work, should it be a concern in terms of safety and/or performance?

Screws are fine. No problem. Provided that code allows you to do that!

4) If I get this all to work properly, will it benefit from adding a second OSB layer per side? I assume it would improve the isolation because of the mass increase, but is it worth the extra cost,

Normally, for a proper 2-leaf fully-decoupled MSM "room-in-a-room" situation, yes, that would be important. But in your case, not really as you will probably already have reached the flanking limit for the rest of the building. The wall you describe will get you about 40-something dB of isolation, which is about as good as you can hope for.

Bottom line: If you build that partition wall, and you seal it carefully to the existing walls, floor and ceiling, and you put excellent seals on the doors and windows, and you isolate the HVAC system for your area, then you could realistically expect a maximum of about 40 to 45 dB of isolation, best case, but probably not even that high. The only way to get more than that is to build a proper "room in a room".

So here's the million dollar question: "Is 40 dB of isolation enough for your needs?" Only you can answer that question. If you are mixing at the typical level of 80 - 90 dBC, that would audible outside your room at a level of about 40 to 50 dBC. Is that enough?

- Stuart -