Isolation Strategies for wall construction

Hello all. I'm about to start the construction of a studio that is going to be used as rehearsal room too. The location is near a very busy avenue with high SPL noise (I would like to measure it with a sonometer). So I have to prevent the contamination of any exterior noise inside the studio. As the studio room is going to be used as a rehearsal room for rock bands and the building has other activities like teaching audio lessons and office activities, perfect isolation is needed too, that means that internal loud (bass freq) noise has to be controlled to the maximun for other activities to continue with out being anoyed by drums and bass noise. I'm new to building walls. I already read the John articles about wall isolation and downloaded and printed the whole material about acoustics by SAE college. So I'm well informed about the basics. But I have my doubts that I want you to help me clear. The room is a space that has 4m x 4.25m. I'm planning to build first a floating floor (I'll ask you about it later) then I'll build the walls over the floated floor. The actual construction of the walls is made of bricks and concrete rendered in both sides they are at less 15cm wide. I'm aware of the 2 leaf rule Mass-air-mass so I understand that the actual brick/concrete walls are the first leaf and adding a second leaf of plasterboard with air inside will make it. The question is how should the plasterboard leaf be attached or mounted. I did 3 drawings that I call Isolation Strategies A, B and C. I'd like you to help me choose or re-design the best one for good isolation, yet with the less budget expenses. Isolation Strategie A: Here both leafs phisically connected by the timber stud. Isolation Strategie B: Here both leafs are separated since the studs that hold the plasterboard leaf is only attached to the floor and ceiling using metal plates. There are no phisical conection between the external brick wall and the plasterboard leaf. Isolation Strategie C: Here the timber stud is in direct contact to the brick wall and the plasterboard leaf is attached to the stud with a flexible channel, thus, reducing the transmission of vibration between the two leafs. What will happen if I change the timber studs with metal studs? how about the STC rating? Well that's it. If you need futher explanation just ask. And thanks again to all. Ed.

Assuming that your "really loud music" has strong bass in it, the best isolation will be achieved with "B", the worst with "C." Hope this helps! Andre

Thanks again Andre. I think the same. The only difference is that I'll change the timber studs and go fot the steel ones. It's much cheaper and easy to build and they weigth less too. According to the SAE acoustic manual steel studs have better STC rating than timber studs. I'll float the floor and over it the steel framing is going to be builded. So the winner strategie is B with 900mm steel studs instead. I'll post some photos of the progession of the construction. This week we will start with the floating floor: 7cm x 4cm wood joists over 2 cm rubberfoam, 3 1/2" fiberglass insulation and 18mm MDF cover. Thanks Ed.

hey AudioMedia, I'm busy on a simular plan. Done some extensive resource. Metal Studs is, indeed, easier and cheaper. Extra bonus is the not-to-stiff material which is good for STC. Beware that not every DIY store will sell it to ya. They are also e.z. to fill with (opencell/lightweight) insulation plates. When using 93,8mm studs you can fill'm with 100mm insulation so they compress a bit to the front gympsum boards. Any backpaper on the insulation must face the INSIDE of the room (pressed against the gympsum). Otherwise it act a bit like a third leave. Better use 2 or even 3 layers of 12mm gypsum for serious isolation. (you might wanna look vor 15mm boards, which rate a bit better) Also, unless you're floor supports these walls, don't forget to decouple the frame with the ground/ceiling using rubber/neoprene or alike. RC (resilient channel) will perform worse on lower FRQ. Don't forget about the ceiling too! Good luck. ro

I'll float the floor and over it the steel framing is going to be builded

WARNING! An improperly designed floating floor will be MUCH WORSE than a regular floor. A floating floor is also expensive to build properly.

The only difference is that I'll change the timber studs and go fot the steel ones.

It did not cause a problem this time, but be carful to ask one question and then take the answer and use it in a different situation. In this case the wood versus steel stud choice is not significant, but there are many things with acoustics that are not obvious to a new person that are important. Andre

AVare wrote:

WARNING! An improperly designed floating floor will be MUCH WORSE than a regular floor. A floating floor is also expensive to build properly.

Thanks for the warning Andre. This is what I plan to do with the floor: The studio is located in the second floor (in the first there is a car repair shop). The area is 17m2 being 4.25m x 4.0m. I will use the Floating Timber Floor design from the SAE manual. First I'll put 7cm x 4cm wood joists over 15mm rubberfoam pads, 60cm centers. That will made my framed floor structure. Then I'll put 3 1/2" fiberglass insulation in the spaces and finally I will cover all with 19mm particleboard and finish with carpet. Is this design any good? how can I improve it? I can draw a design if you think it's necesary. I can post pix and drawings but I really need your help. I've been reading a lot about acoustics but I've never done anything more complex than a drum riser. Now I have a whole big project and I'd like some advise from experienced people here. Unfortunately I can't afford a professional paid supervision, so I depend on my research and your expert advise that will be very welcome and appreciated. I plan to start with the floating floor construction and go one step at a time. Thanks and any warning, comment and advise are very welcome. Ed.

i think there was a mistake andre ... the worst is A, since it directly connects inner and outer leaf. at least C has resilient channel. of course you are right B is best. or if i am wrong, can you clarify this because i thought that and RC wall would be better than a single stud wall, is there an exception for bass i'm forgetting? floating floor is very complex ... but a couple of basic rules are, use a thick elastomer, 15mm is pretty thin, you should double it or get thicker still. second, make sure the weight upon it will compress it at least 10 to 15 percent, or even a bit more ... third, make the airgap as big as possible and make the top skin of the floor as heavy as possible, with mutltiple layers. and of course fill cavity with insulation. even this does not guarantee that floating will be better than not floating ... but if you are determined to float keep these tips in mind

You want to definitely decouple the outside wall from your inside walls. If you can, you should try to get at least one layer of gypsum on the back side of your interior wall. Even better yet would be to put up some insulation against the exterior wall, then build your interior wall. Remember to caulk! Caulk is very important at keeping things sealed up. I've done enough caulking over the last 6 years constructing my studio to caulk a thousand bathtubs for a life time. :) Also remember the ceiling is just as important when it comes to keeping sound from getting in or out. You could build the beefiest wall ever, but if your ceiling is thin, you'll be wasting your time. I'm by no means an expert at studio design though, I'll let the smarter guys give you more advice on this.

SonicClang wrote:

You want to definitely decouple the outside wall from your inside walls. If you can, you should try to get at least one layer of gypsum on the back side of your interior wall.

As I understand what you suggest adding one layer of gypsum at the back of the interior wall will let me with 3 walls and I've read that the 3 leaf situation should be avoided. Because first leave is the brick/concrete original wall, then the ouside wall of the interior wall you say and last is the inner wall of that interior wall. Correct me if I'm wrong but I understand that 3 leafs is a NO, NO.

Dan Fitzpatrick wrote:

even this does not guarantee that floating will be better than not floating ...

I'm a bit confused here, so what guaranties that a floating floor will be better than a non floating floor? Hey this is science, I suppose that it is possible to be absolutely certain if a soundproofing is going to work or not. According to the room in a room principle, floating the floor and building the inner walls over it is the best way of acheiving sound isolation. Explain me please because I don't want to build and expensive floated floor just to find that it doesn't work the way I need it. Thanks. Ed.

Dan Fitzpatrick wrote:

i think there was a mistake andre ... the worst is A, since it directly connects inner and outer leaf. at least C has resilient channel. of course you are right B is best. or if i am wrong, can you clarify this because i thought that and RC wall would be better than a single stud wall, is there an exception for bass i'm forgetting?

Resilient channel increases the TL on higher frequencies by 10 to 12 dB. It also reduces the TL at the MAM resonance by 6 to 10 dB. Because the MAM resonance is below 125 Hz, this does not have a negative effect on STC. If you have loud music with high bass content, RC makes the isolation worse. Something that scared me when reading the thread, if C was chosen and the studs changed to steel, the isolation would have been worse than A, because the only effect of the channel would have been to float the second layer even more! RC was designed to help wood stud walls achieve steel stud wall performance. Andre

AudioMedios wrote:

Correct me if I'm wrong but I understand that 3 leafs is a NO, NO.

Actually I think you are correct. I forgot about that whole leaf thing. It's been a looooong time since I constructed my walls. :) Sorry, carry on.

AVare wrote:

Something that scared me when reading the thread, if C was chosen and the studs changed to steel, the isolation would have been worse than A, because the only effect of the channel would have been to float the second layer even more! RC was designed to help wood stud walls achieve steel stud wall performance. Andre

So, according to this the best option for better isolation would be B with steel studs? What about the floor issues? do you want me to do some drawing? Thanks Ed.

What are your plans for the ceiling? Even if you do float the floor and secure the new walls to it, you'll still have a flanking problem if your new walls have hard contact with the existing ceiling. If you end up floating a floor (correctly of course), then the best option would be to rest your new ceiling on top of your new walls which would give you the best decoupling all around.

Hello. I've worked on some simple drawings in order to let you know how I plan to build the floating floor and the walls. First draw is the floating floor. And second is the same floor with the wall made with steel studs over it. I know I should have a second layer of Gypsum but here in my country it's so expensive because we have to import it. Let me know what do you think about the whole design. Thank you Ed.

Hey guys... Sorry to call you but I really need to decide wich way to go. Do you think I should start a new thread about the whole project I'm about to start? Thanks. Ed.

1. The wall design that I originally indicated with stell studs is the best of what have suggested. 2. A new thead with what you want would be good. 3. Floating floors cannot be built to work. They have to be designed as system. Read Paul Woodlock's and Sharward's theads for a good feeling for what is involved. Andre

AVare wrote:

Resilient channel increases the TL on higher frequencies by 10 to 12 dB. It also reduces the TL at the MAM resonance by 6 to 10 dB. Because the MAM resonance is below 125 Hz, this does not have a negative effect on STC. If you have loud music with high bass content, RC makes the isolation worse.

Andre, this is good info. i just checked IR-761, looking only at single stud wood walls with 16mm gypsum on both sides. you are right that the RC wall performs worse at some frequencies, by over 4 db at 80hz. when i have time i'll have to compare this effect on more robust walls. it's a difficult call since the single stud wall performs really badly at 160hz, over 16db worse in fact. but if you really are focused on the lows then RC might be questionable.

AudioMedios wrote:

I'm a bit confused here, so what guaranties that a floating floor will be better than a non floating floor? Hey this is science, I suppose that it is possible to be absolutely certain if a soundproofing is going to work or not. According to the room in a room principle, floating the floor and building the inner walls over it is the best way of acheiving sound isolation. Explain me please because I don't want to build and expensive floated floor just to find that it doesn't work the way I need it.

when you float a floor that creates an air cavity which will have a resonant frequency. so your floor can amplify sound at that frequency. usually this frequency is in the low range. so floating a floor can be bad, unless it is designed so that the frequency in question is extremely low (well below human hearing range). to do this you need a VERY heavy floor (think concrete or brick) and/or a large airspace. This is science in that construction methods can be tested. however each particular construction is unique and so the tested wall will not always work the same way in the field as it did in the laboratory. usually only walls are tested, without doors for example. so as soon as you add the door you make it less like the test, so the test will predict performance less well.

Dan Fitzpatrick wrote:

when you float a floor that creates an air cavity which will have a resonant frequency. so your floor can amplify sound at that frequency. usually this frequency is in the low range. so floating a floor can be bad, unless it is designed so that the frequency in question is extremely low (well below human hearing range). to do this you need a VERY heavy floor (think concrete or brick) and/or a large airspace.

Great and clear answer. Thank you Dan. I can build a floor made of wood. I plan to build it with 7cm x 4cm wood joists spaced (centers) at 70cm, wich makes a wide cavity that will be filled with fiberglass insulation. Over it 25mm Particle board. Of course the joists will be over 20mm rubberfoam pads. I'm gonna star a new thread describing the whole project with pictures of the place. It will be called AudioMedios Studio thread. Thanks and see you there. :wink: