New studio design need help with soundproofing | John Sayers’ Recording Studio Design Forum archive

Hi "Jackinthebox", and welcome!

it's amazing how many variables there are and differences of opinion on the subjects of acoustics and soundproofing!

Well, to start with there is no such thing as "soundproofing", since any sufficiently loud sound will get through any conceivable barrier, so that sure can be the source of differing opinions! :) trying to do something that is technically impossible, can indeed lead to differing opinions regarding how to accomplish the impossible... : So you can't sound"proof" a room, but you sure can isolate it, very effectively, and there are tried and true methods, thoroughly tested both in laboratories and the real world: There aren't many "differences of opinion" about that, since science doesn't care about opinions, and neither do sound waves. Science works despite what you believe, not because of it, and sound waves follow the laws of physics exactly the same, everywhere: So the trick is to use scientifically proven principals, about which there is no doubt, for your isolation, rather than trying to figure out which is the best opinion about the impossibility of "soundproofing". :)

I have decided against a floating floor as there is nothing below and i beleive the concrete floor is in contact with the earth below and therefore massive and damped enough to not resonate.

You should try to confirm that this really is the case, as there could indeed be a large difference between have a slab on grade and a slab over an air gap.

I will be decoupling the live room floor a certain amount but it won't be a fully floated slab or anything. I have a load of 1m square recycled granulated rubber slabs and a layer of profiled neoprene sheet to essentially float the live room floor but i am still unsure of the best possible way to approach the whole thing yet.

If the live room floor really is slab on grade, then why do you need to decouple it from anything? And on what scientific research are you basing your concept of using granulated rubber and neoprene sheets? If there is no published research on this approach, then do you really want to be the first guinea pig to try it? Do you really want to build an acoustic laboratory that tests an unknown concept, or would you rather prefer to just build a studio that works, based on existing research?

I will also retain as much ceiling height as possible.

Then don't float your floor! :) Floating your floor will subtract a large amount of room height. Rather, use a drum riser or isolation pads where they are specifically needed, and leave the floor alone.

The outer walls of the empty room are currently plasterboard on at least two sides.

So you already have two leaves? One of those will have to come off.

i guess i will have to drill some investigatory holes to make sure of the construction. I am hoping there is some brick, block or concrete between me and the neighbours.

You might as well take off a large chunk, rather than just drilling holes, since it will have to come off anyway if that is two leaf. Hopefully the other leaf really is brick or block (that would be good), but regardless of what is on the other side, the side facing you still has to come off.

Now if the wall is a plasterboard stud construction and i am building a double walled metal stud construction in front of it would this constitute a triple leaf?

That would be four leaf! :shock: There are already two leaves in your existing wall. If you add a "double walled metal stud construction" in front of it, that adds another two leaves. Total=4 leaves. Isolation=Bad.

Would i need to insulate between the outer wall and my inner room within a room structure with rockwool or would it be best to leave a simple air gap with no absorption?

Yes, you ALWAYS need to put insulation in the cavity. That is part of the "S" in MSM. Without it, you have no damping and no means of removing energy from the cavity. Leaving it out could cost you up to 16 dB of isolation, and at least 10 dB.

I may use this kind of construction (|from the lafarge white book) for the inner walls mainly because it involves a fairly large cavity in between the studs which will hopefully give me good low frequency response: http://s669.photobucket.com/albums/v...sic/gearslutz/

The link does not work. Gets a 404 error. But anyway, "hoping" that it will get you anything is not going to actually get you anything! :) You have to calculate and design accordingly, not "hope". Also, I'm not sure what you mean by "good low frequency response" with regard to an isolation wall! You don't want it to have any "response" at all! You want it to be dead at all audible frequencies, and for at least one octave below that. Did you mean that you want to get your MSM resonant frequency as low as possible?

with a layer of bitumen impregnated softboard on the studs, then 19mm plasterboard plank with a 12.5mm soundboard layer on top of that.

Bad idea. Apart from anything else, that would be a fire hazard, and in any event 12.5mm boards are too thin, too flexible, have too low mass, and too high resonant frequency to be good for MSM walls.

i'm hoping to get about 70db reduction plus whatever reduction the existing walls might give me.

Actually, you would have to SUBTRACT the existing walls, not ADD them. Since you would be building a 4 leaf system, your isolation would be WORSE in the low end than if you just built a two leaf structure of the same overall mass and thickness. Simple physics.

One worry is that the existing plasterboard walls of the building might cause problems. I have heard that a triple leaf design is worse than a double leaf. This is an area i still don't quite understand.

Correct, except that you are describing a 4-leaf system, not a 3-leaf system. 4 leaf is even worse than 3 leaf, all other factors being equal. The basic concept of MSM construction is that the wall acts like a bandpass filter. It is tuned to a specific frequency, at which it is transparent to sound, and even amplifies sound. So you want that resonant frequency to be well below the range of human hearing. The wall passes sound perfectly at that one specific frequency, but blocks sound at all higher frequencies, to a greater or lesser extent. The resonant frequency depends on basically two factors: The mass in the two leaves, and the depth of the air gap between them. Increase either of those, and you increase isolation. However, if you add ANOTHER leaf, then you change everything: Now you use a different equation, and you have TWO resonant frequencies for the wall, BOTH OF WHICH are higher than for the equivalent two-leaf wall. If you add yet another leaf (total of 4), you change things yet again, and once again your overall resonant frequency increases. Of course, as the resonant frequency goes up, the isolation of the wall goes DOWN for the low end of the spectrum. In other words, 2-leaf is optimal, 3-leaf is poor, and 4-leaf is even worse.

Should i be making use of the existing outer plasterboard wall and uprate it with extra layers of board or insulation as part of one of the leaves or leave an air gap between my internal structure and the outside wall?

No, you should be taking off one of the leaves on that existing two-leaf wall, then building your single second leaf, all by itself, on a separate frame. Anything else is NOT 2-leaf MSM.

guess this i because the mass is provided by the the layers of sheet material and the lower density quilt is more effective at lower frequencies.

The insulation in the air cavity is not there to add mass. It is there to damp the resonance of the spring. The amount of damping is not given by the density, but rather by the gas flow resistivity of the specific type of insulation used. For mineral wool, the density needs to be about 48 kg/m3 for optimum gas flow resistivity. For fiberglass it needs to be about 32 kg/m3. Etc. Each material is different. And yes, you are right: in a MSM wall, the mass is always provided by the leaves themselves, while the spring is provided by the air, and the damping is provided by the insulation.

Can anyone help point me in the right direction to achieve the greatest isolation with the minimum of building required.

I'd suggest that you read two books, to start with: Master Handbook of Acoustics, by F. Alton Everest (that's generally regarded as "the bible" of acoustics), and "Home Recording Studio: Build it Like The Pros" by Rog Gervais. Between them, they explain both the theory and practice of how to do it right.

I am quite prepared to use a number of layers of different materials,

The question is not "How many layers to use" but rather "How do I get the right amount of mass and the right air gap for my isolation requirements". In other words, you have to start out by defining how much isolation you need. You mention a figure of 70 dB (I'm assuming you are talking TL, not STC?) which is pretty high, and not too common for a home studio. Do you really need that? How did you arrive at that figure? What were the actual levels that you measured when you did your tests with your sound level meter?

use resiient bars if necessary

No use if you want that kind of isolation that you are talking about. RC won't get you there.

and seal and damp every possible problem spot with acoustic sealant

Acoustic sealant doesn't damp: it seals! :) Two different concepts.

i don't want to go ahead and order materials if i am missing some important point or i'm uncertain as to what the outcome might be

Smart move! :) Way too many folks come in here with photos of their partly-done construction, only to be told what they already did wrong, and why it wont work: Most of those stop posting here, and we never hear from them again (so we never find out how badly it turned out for them), but a few do bite the bullet, so to speak, tear down what they did wrong, then re-build it right. And they end up with great places, because they base their builds on solid science, tested and proven techniques. So yes, you are certainly doing the right thing by stopping to learn now, before even buying a single nail. There are just so many ways to build it wrong, and only a very few of building it right. Even worse is the mountain of myth about acoustics, all over the internet! That's hard to fight. But at least you are in the right place now, and all the information you need is right here on this forum.

I know there is always the option of adding more layers to the inside of the studio and adding sufficient treatment and absorption to the inside of the live room to control the leakage but i'd like to get maximum isolation initially.

Wrong. Adding "sufficient treatment and absorption to the inside of the live room" will do nothing at all to "control leakage". Isolation and treatment are two totally different concepts. Isolation keeps sound in the room preventing it from getting out. When you do that, it makes the room sound BAD! Obvious, when you think about it! If the sound cannot get out, then it must be staying inside, bouncing around all over until it eventually dies away. That is called "resonance" and is what makes a room sound bad. So that's why you treat the room: to make it sound good again. The better you isolate, the worse the room sounds, so the more treatment it will need. Materials that isolate are mostly pretty lousy at treating, and materials that treat are mostly pretty lousy at isolating. Two different concepts, two different methods, two different sets of materials. Many people do assume that because fiberglass absorbs sound, that means that it will also isolate a room, but it just isn't so. Think of it this way: You can use a sponge to mop up water that you spilled on the kitchen counter, and it does that really well, but you cannot put the sponge in front of the tap and expect that it will stop the water flowing! Same with sound: insulation is really good at "mopping up" unwanted sound that "spilled" into the wrong places, but is useless for trying to stop the sound from getting out of the room...

This is a sketchup file of the proposed design.

I'm looking at that design, and seeing many issues with it: the rooms are not decoupled from each other, and are not decoupled from the existing structure, there are strange angled hard walls where they should not be, and there is wasted space all over.

I've borrowed quite a lot for one of john's excellent designs.

Yes, but you have borrowed things that are not applicable to your design, and changed other things that are applicable, but will now no longer work because of the way you changed them! - Stuart -