John Sayers' Recording Studio Design Forum

Is it my imagination, or are you attaching your inner-leaf studs directly to the outer leaf? I see metal brackets all over the place that seem to be directly coupling the new studs to the existing wall. Or maybe I'm not understanding what you are trying to do.

Maybe you could clarify: Are you going to attach your inner-leaf MDF and drywall to the studs that are visible in your most recent set of pictures?

If the answer is "yes", then to me it looks like you have a serious problem: you are not decoupling your leaves at all! You will get very little isolation like that.

If the answer is "no", then maybe you could explain what the procedure is going to be.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Stuart……my Photoshop skills are not that great…… so yes, the metal brackets
are connected to the wall, they will be caulked properly.

My presumption is that the sound caulk will prevent any eventual sound leaks caused
by the brackets and the screws which are there in order to sustain the weight that the wall(s)
will be exposed to (I am pretty sure that I explained this before in one of my prior posts).

Even though decoupling with the use of resilient channel, GreenGlue etc might be the optimal
way to go to achieve the best isolation possible (give you a better STC rating etc) my assumption
is that the drywall, MDF drywall combination that I mentioned in my previous post will be effective
as long as I caulk properly (145 mm frame together with double layers of 15mm drywall sandwiched
in between a layer of 6mm MDF plus isolation, even if it was poorly caulked, has to be better
then not having nothing at all).

Stuart, if my assumptions or presumptions are wrong I would love to be in lighted by your knowledge.

Sincerely,

Useg Diaz-Granados

Unfortunately, it doesn't work like that. The bracket and screws themselves are creating a hard mechanical connection between the studs and the wall. No amount of caulk around the edges will stop the vibrations from being transmitted from the studs into the walls. The vibrations travel through the direct contacts, not around the edges of the brackets. Caulking will make no difference at all. The purpose of caulking is something entirely different: Caulking does not decouple things that are already coupled.

I hate to have to say this, and I'm sure you don't want to hear it, but what you are doing there is basically useless. It will not accomplish what you are hoping it will accomplish.

Fortunately, it is not too late to fix it. There are basically two options that I see for you right now. One is to remove all those brackets and move the framing away from the existing wall so that there is no physical contact at all (even 1 cm would be enough). That frame is supposed to be built so that it stands on its own, without being supported by anything else. If you don't know how to make it self-supporting, then you could use proper isolation brackets (also called sway braces), instead of those solid steal brackets, but either way you still have to move the frame a bit away from the wall.

If you want good isolation then you cannot allow any part of your inner leaf to touch the outer leaf. If you have any kind of solid connection between the leaves, even one single screw, then that destroys the entire MSM system. The principle of physics that this is based on is called "Mass-Spring-Mass", and the air is the "spring". If you connect something hard between the two layers of mass (the two leaves) then you are "short-circuiting" the spring, and you no longer have any MSM system, so you no longer have any isolation. It is a delicately balanced system, that MUST have the correct spring characteristics in order to work. Even a single nail or screw that accidentally connects across the air gap between the two leaves is enough to kill the spring effect. In your case, you don't just have a single screw, but dozens of solid steel brackets that are firmly screwed into the leaves.

The other option (if you can't or don't want to take off those brackets) is to use proper resilient channel across the front of those studs, to support your drywall. That would be easy: Just attach the resilient channel to those studs, then screw the drywall to the resilient channel but being very careful that no screws touch the studs. If you can't get resilient channel where you are (it is not the same as ordinary hat channel!) then you could by some proper acoustic isolation RSIC clips, put those on the studs, then use normal hat channel, and once again make sure that none of the drywall screws touch the studs.


The entire purpose of building an isolation wall is to decouple the two leaves, mechanically. Right now, you are not doing that, but both of the methods I outlined above can solve your problem. I would recommend that you do the first one (take off the brackets and move the frame to make it self-supporting). That would be the best option, but if you don't want to do that, then the resilient channel or the RSIC clips will accomplish the same thing.

Unfortunately, I've been way from the forum for a few months for personal reasons, so I haven't been following your thread until today.

Caulking is VERY important, absolutely, and you still have to be very careful with that when doing what I outline above, but the caulking does not decouple things that are already screwed together! The purpose of caulking is to get a totally air-tight seal on both of your leaves. But just putting some caulk around a bracket that is screwed to the wall does not stop vibrations from being transmitted. The ONLY way to stop vibrations, is to break all physical links. That's what the word "de-coupling" means: you remove whatever is "coupling" the leaves. Caulk cannot do that. Even after you put the caulk on, the bracket is still screwed to the wall, so it is still "coupled".

That sounds right, intuitively, but is not necessarily correct. Acoustics is not intuitive. Sound does not behave the way we think it will, just by reasoning. It does things that don't make a lot of sense at first sight, but when you understand the scientific principles of how sound behaves, then you start to see why it is not intuitive.

In reality, adding all that mass to your wall without decoupling it MIGHT increase the total isolation by 6 dB or so. No more than that. In other words, it would be like moving the fader on your console down by just 6 dB: it hardly makes any difference at all.

On the other hand, if you correctly decouple the wall, then adding that same mount of mass might improve things by 20 dB! That's a really big difference.

In fact, depending on the characteristics of the existing wall, adding all that extra mass that you mentioned might actually make things WORSE at some frequencies! So your new wall could, quite possibly, not even isolate as well as the existing wall, if you don't decouple it correctly. If you happen to re-tune the wall to a higher MSM resonance than where it is right now, then the result would be that the resonance dip could end up in the low end of the audible frequency spectrum, at the same place as drums and bass guitars put out a lot of energy. So it is possible that adding the mass you mentioned might make drums and bass guitars sound LOUDER on the other side of the wall than they do right now.

Yes, I know that sounds stupid, and is the absolute opposite of what yo would expect logically, but it is simple acoustic truth. Walls are resonant systems, and unless you take that resonance into account when you modify a wall, you can change the resonance in such a way that the wall LOOSES isolation at some frequencies, even though it got better at other frequencies.

So my suggestion would be to either take off the brackets and move the frame, or to use resilient channel / RSIC clips, but one way or another, it has to be decoupled in order to work.

If you do not decouple that structure, then it will not isolate well.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

I am extremely thankful for your guidance Stuart. I will decouple the wall according to one of the methods
you have illustrated and have been aware of this problem. You have proved, in a very understandable manner,
that there are no shortcuts when it comes to proper sound isolation.

Unfortunately many of the more price efficient decoupling systems (and even the expensive ones) are not
readily available in Sweden. This factor drives up the overall cost of the project. I had to pay as much money
in taxes and shipping for the epoxy that I bought in the States, compared to the price of the actual product itself.

One way to resolve this dilemma is to purchase the decoupling devices from Germany. I will have my German
( I don’t speak or read German) friend look into the possibilities of getting the decupling devices from there.

Sincerely,

Useg Diaz-Granados.

Have a question regarding a product.
The Auralex RC8 Resilient channel, any opinions/experiences regarding this product?

I have also a question regarding drywall
What is better in terms of sound isolation. 3 layers of drywall; 15mm x 13 mm x 13 mm compared to 2 layers of drywall 15mm x 15 mm (fire retardant)

if you have the room, using isolation clips and hat channel as it's less likely to short circuit and will provide more isolation than RC will but does take about 50mm (clip + hat) versus about 16-19mm for RC. Pacific International, Kinetics Noise, Mason Industries, http://www.soundproofingcompany.com/products/clips/ etc all have isolation clips which can do the job.

_________________
Glenn

I'm not familiar with the RC8, but if it is proper acoustic resilient channel then it should work fine. And if that's all you can get where you are, then go for it!

Hard to say! a lot depends on construction techniques and the actual characteristics of the specific drywall brand that you use.

However, in general it is not a good idea to use thin drywall, for several reasons: it is more flexible, has a higher resonant frequency, and less mass than the thicker stuff. Once again, there is the issue of the "tuning" of the wall, and how that changes with different materials. As a general rule, it is better to use thicker, more dense, heavier materials, and using two layers of 15mm drywall is known to work very well. It will give you decent isolation, so I'd go with that.

But if you are thinking of using three layers, then why not go with three layers of 15mm drywall? That would be REALLY good!

You don't need to mix different materials, or different thicknesses. Yes, it is true that mixing different types of materials or different thicknesses can reduce the effects of the coincidence dip, but the small benefit that you get isn't really worthwhile. It is a small effect, and occurs in a part of the spectrum that doesn't really matter anyway, so I really wouldn't bother with that. Just put up 2 (or 3) layers of ordinary 15 mm drywall, caulking it and sealing it very well, and that will work great.

One thing you should be very careful with when screwing the drywall to the resilient channel, is the placement and length of the screws. You need to carefully mark the position of the studs on the ceiling and the floor, and make sure that you do NOT put any screws in places where they might accidentally touch the studs. You also need to use progressively longer screws for the second and third layers of drywall, because they have to go all the way through the drywall underneath and into the resilient channel. so the screws you use on the second layer should be 15 mm longer than the first, and those for the third layers should be 30mm longer.

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Once again......Thank you Guys for guiding me in the right direction!

I have another question. I have a free bearing ceiling (attached to the wooden frame not touching the roof). Does this mean that I do not need Resilient channel on the ceiling?

(The reason I ask is because I am concerned that the ceiling will not be able to sustain the weight of my sound cloud)

Sincerely,

Useg Diaz-Granados

Putting the door together. Still need an answer on the last question I asked regarding the ceiling.

Sincerely,

Useg Diaz-Granados

That's correct. If the ceiling joists are already decoupled, meaning that they are not attached to the original wall or ceiling in any manner (not even indirectly, through those studs and steel brackets!!!) then you don't need resilient channel.

Post a picture of how your joists are set up so that we can check.

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

He has an apartment above him...a typical sheetrocked/joist/subfloored coupled assembly is what the ceiling is existing.


Options seem to be zero...

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

What a positive perspective Brien, you should have been a motivational speech writer. (Hopefully no one would commit suicide if you had chosen that profession)
If there is a will there is a way, can you translate your statement in plain English please? (Brien)

Here are the pic's Stuart requested, One shows the brackets attached to the studs and the drywall (not the ceiling
which is made out of solid concrete) and the other is on the rails that is going to hold the frame that is going to house
the drywall.

……
I am still curious (and anxious) to hear what you guys have to say about the ceiling. I know some of the studs touch the ceiling
(even though they are not attached or screwed on to it).


Sincerely,

Useg Diaz-Granados

I have a question that concerns resilient channel overlap. I was told by a supplier in the UK that the nesting of two resilient channels does not have to take
place over one of the studs. After googling it up I found a link that states that the nesting has to take place over a stud.

Could anyone with experience in these matters give me a clearer picture of which of the two alternatives I presented is the correct one
(I got an email from the supplier insuring me that it is possible to nest two resilient channels together without them being attached to a stud, but would like a
second oppinion......please......pretty please ) (Still waiting to get an response on the ceiling questions I asked )?

Sincerely,

Useg Diaz-Granados

Finished placing the last stud and caulked the corner making the room finally ready for drywall!!!!!!

Since Brien’s last statement have caused me to get little sleep I found a link that might be useful if I am forced to decouple the ceiling.

http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=9591&hilit=resilient+channel+ceiling+weight&start=15


The resilient channels would not sustain the weight of the sound cloud we are going to make. I believe that this sort of decoupling
system is what Glenn was recommending.

Not relying on common sense (because as I am learning, the characteristics of sound are as complex as they are) I still need a second
opinion on the ceiling matter. I do not see how the ceiling could be a problem. My presumption is that the Rubber that sustains the ceiling
rails would in fact decouple the ceiling.

Sincerely,

Useg Diaz-Granados

I think your only real option is isolation hangers. You can't use RC on the ceiling, because that would not leave enough air gap: you need at least 4 inches for good isolation, but I guess you could reduce that a bit if headroom becomes a problem. However, I would not go less than about 2 1/2", or your MSM resonant frequency will just be too high. Isolation hangers also come in different capacities, so you could use heavier duty hangers at the location where you need to hang your cloud. Of course, you will have to do the calculations beforehand, in order to know how heavy your cloud will be, so you can buy the correct hangers for that section of the ceiling.

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.