Double Walls: What to believe?

[DurtyMics]

I want to build a wall in my studio similar to the one in the first attached picture.

On two different sites, there are two vastly different STC ratings for this type of wall.

On USG Design studio, http://www.usgdesignstudio.com/walls...t=STC&dir=desc , it says this wall would have a rating of 59. on STC Ratings.com, STC Ratings , it says a similar wall (2nd picture, though it only has one layer of gypsum on the outer faces) would have an STC of ~45.

Which one should I believe?

[spm_gl]

The second layer of gypsum can make a huge difference, as well as the type of board, and the distance between the two walls. Construction details also count. So make sure they are exactly the same before comparing ratings.
On a side note, these ratings are always rather theoretical.

[nosebleedaudio]

One thing NEVER use sheetrock INSIDE the wall like both of those show..
And it's not uncommon for the same wall config. to show different numbers...
Why??? Good question..

The top one would be the best, but with out the inner layer of sheetrock..
Add more space, and pack it with pink stuff...

[xaMdaM]

The main differences between all these STC ratings for the same wall assembly is due to the testing facility and generally their methods of testing. Also, since no two wall assemblies are exactly the same, you get variations due to the physical differences in materials... screw patterns, stud densities, etc...

For practical purposes, you'll find that while these ratings may change value from one person's calculations to another, they generally all follow the same curves and delta among the same assemblies. e.g. One lab may have a wall rated at 45, while another has it at 50. Yet when looking as a lesser wall assembly, the 1st lab may show an STC of 36, while the 2nd shows an STC of 40. The point is that they will all generally show similar numbers for the same wall assembly. You have to realize that these are tested assemblies and numbers that are calculations, not hard numbers that you can just simply measure and be done with... but they are accurate indicators of how well a wall assembly will perform in a real world installation.

If you want to see both the theoretical and the practical STC rise even higher, take the layers of gypsum from the inner cavity and place them on the exterior surfaces.

To go even higher, place the studs at 24" OC and use a base layer of 3/4" plywood or OSB, then 2 layers of gypsum.

... then, to add even more LF TL loss value, use green glue between the layers of gypsum.

To drive them even further, you can switch to a 2x6 or 2x8 stud, and/or increase the cavity spacing.

The numbers for that wall assembly are somewhere between 69 and 72... depending on who has done the calculations.

You can really push the boundaries of STC by starting with known assemblies and drive those ratings way up. But they come at the expense of loss of square footage, increase in materials cost, or a combination of both.

Eric Desart generated a very interesting spreadsheet where you can enter the wall assembly and it will calculate the STC for that assembly.

I probably spent a good week digging through the calculations to find the point of diminishing returns on a combination of stud, stud cavity and surface materials. What I came up with, that I've used in my place, was a theoretical STC of 76 for a double 2x6 stud wall, 24" OC, with a 16" cavity, 1 layer of 3/4" plywood and 2 layers of 5/8" gypsum with 50% coverage of green glue between the gypsum layers.

To get to a 77 or higher, you would have to increase the stud cavity to 24", add 2 more layers of gypsum to the walls, or make both walls 2x8 studs and increase the cavity to 18".

I would directly link to Eric's file, but as it is copyrighted, I can only tell you to check out the StudioTips Forum, register and dig through the files section for submissions by Eric Desart. If you are not familiar with Eric's work, he was part of the acoustics team that designed and built Galaxy Studios in Belgium.

[David-Morpheus]

you need to drop the layer of plasterboard on the inside of the walls because this way you are doing a triple leaf system and you want to avoid that.

so you have 2xgypsum insulation and insulation + 2xgypsum on the other side. I would also recommend using green glue or similar between the two layers of gypsum to dampen the transfer of vibrations.

[DurtyMics]

Thanks for all your help, folks.


Trouble is, the space that I am building in is a warehouse, in which two walls are concrete and two are drywall. The drywall walls are the ones separating me from my neighbor. These gypsum-stud-gypsum walls will not suffice for the sound isolation I need for my studio. All I can see to solve this problem is to build another wall in front of it, as part of building my live room as a room-within-a-room, yet since the preexisting walls already are covered by gypsum, building a wall in front of them will create a three leaf system.

I would prefer to not rip the drywall off of the preexisting wall. Yet, do I have any other options?

[nosebleedaudio]

Originally Posted by DurtyMics

Thanks for all your help, folks.


Trouble is, the space that I am building in is a warehouse, in which two walls are concrete and two are drywall. The drywall walls are the ones separating me from my neighbor. These gypsum-stud-gypsum walls will not suffice for the sound isolation I need for my studio. All I can see to solve this problem is to build another wall in front of it, as part of building my live room as a room-within-a-room, yet since the preexisting walls already are covered by gypsum, building a wall in front of them will create a three leaf system.

I would prefer to not rip the drywall off of the preexisting wall. Yet, do I have any other options?

Leave that wall alone, build another one at least 6 inches from the existing wall,6 inch space from stud to wall, NOT total space, if you know what I mean..
Air space is you friend..

[Warren Beck]

Hi.

Huge project - good luck. Great advice here too. Be wary of parallel walls, etc.. do not fasten the dry-wall directly to the studs on the inner wall. Rather hang them to minimize vibrational transference of un-wanted noise. Green glue or any spreadable glue is terrific.

Give us pictures of you doing the construction, like a step-by-step sort of thing.

Regards,

[DurtyMics]

Nosebleedaudio --

Thanks for your response. Would you suggest that the new wall I build, 6" from the existing wall, be gypsum-stud&insulation-gypsum, or should I leave the backside of the new wall open so it would just be gypsum-stud&insulation-air cavity-preexisting wall ?

Warren Beck --

I appreciate the sentiment, this has been my dream for quite a while. I will surely post tons of pictures.

[nosebleedaudio]

Originally Posted by DurtyMics

Nosebleedaudio --

Thanks for your response. Would you suggest that the new wall I build, 6" from the existing wall, be gypsum-stud&insulation-gypsum, or should I leave the backside of the new wall open so it would just be gypsum-stud&insulation-air cavity-preexisting wall ?

Warren Beck --

I appreciate the sentiment, this has been my dream for quite a while. I will surely post tons of pictures.

leave the back of the new wall open, this creates the maximum air space between the two hard surfaces.
1/2" soundboard works very good IMHO, and it's not much cheeseola..

[xaMdaM]

Originally Posted by nosebleedaudio

leave the back of the new wall open, this creates the maximum air space between the two hard surfaces.
1/2" soundboard works very good IMHO, and it's not much cheeseola..

That's creating a 3rd leaf...

1. Neighbor's Space
2. Gypsum
3. Stud - empty cavity (probably fire rated )
4. Gypsum

5. 6" Air Gap

6. Stud (Filled with insulation)
7. Gypsum
8. Gypsum
9. Poster's Space

If I'm not mistaken, a 3 leaf wall has a much poorer TL curve than a four leaf wall...

1. Neighbor's Space
2. Gypsum
3. Stud - empty cavity (probably fire rated )
4. Gypsum

5. 6" Air Gap

........ (Potential additional Gypsum)
6. Gypsum
7. Stud (Filled with insulation)
8. Gypsum
9. Gypsum
10. Poster's Space

If I'm wrong, I apologize, but I've seen this discussed several times before, and in each case, I thought the outcome was that is is better to have a 4 leaf wall, as it has the secondary effect acting as a larger 2 leaf system.

[nosebleedaudio]

Originally Posted by xaMdaM

That's creating a 3rd leaf...

1. Neighbor's Space
2. Gypsum
3. Stud - empty cavity (probably fire rated )
4. Gypsum

5. 6" Air Gap

6. Stud (Filled with insulation)
7. Gypsum
8. Gypsum
9. Poster's Space

If I'm not mistaken, a 3 leaf wall has a much poorer TL curve than a four leaf wall...

1. Neighbor's Space
2. Gypsum
3. Stud - empty cavity (probably fire rated )
4. Gypsum
5. Gypsum

6. 6" Air Gap

7. Stud (Filled with insulation)
8. Gypsum
9. Gypsum
10. Poster's Space

If I'm wrong, I apologize, but I've seen this discussed several times before, and in each case, I thought the outcome was that is is better to have a 4 leaf wall, as it has the secondary effect acting as a larger 2 leaf system.

Have you looked at ALL the wall configs on the BBC's site???
It's up to the OP..
Done both and tested both after..
I would not tear out that single layer for it...
That's me...

[DurtyMics]

xaMdaM, the design you propose is precisely what I was thinking of doing. I think that one of the keys will be ensuring that there is enough air gap between the new wall and the preexisting wall.

I think the problem with the 3rd leaf is that I would get sympathetic resonance of the inner leaf. I think that a 4th leaf would hinder this sympathetic resonance, though I'm not sure.

[DurtyMics]

Upon second thought, it seems that I would gain a huge amount of TL if I were to take out that layer of drywall. Maybe it's worth it after all...

[jayfrigo]

In general, avoid any more than two leafs if possible, use insulation in cavities, and leave as much airspace as is practical. There's also some advantage to putting your extra mass on one side, in other words, if you have 4 layers of sheetrock, instead of 2 and 2, do 1 and 3. Having different densities for each leaf can lessen the mass-air-mass resonance.

There are a number of ways to add mass and/or decoupling for existing walls. It depends on numerous factors such as the makeup of your original wall, if you can alter that, your target STC, or necessary TL requirements in different octave bands, space, budget, structural load issues etc. It can be anywhere some 1" strips of wood with 703 and an extra layer of sheet rock, to hat channel with RSIC clips, to a second wall ranging from one or more layers of GWB (sheetrock, drywall, whatever), sandwich layers of other materials, masonry, or masonry with RC-1 and drywall etc.

Constrained damping layers, such as green glue, also improves STC in multi-layer sheetrock or sandwich constructions. There are also mass-loaded products like quiet rock, or vinyl curtains/sheets. Don't forget to consider flanking paths, such as penetrations for electrical, plumbing, or HVAC, and coupling at walls and floors. In critical applications, you'll want to decouple those as well.

[jwl]

Definitely go 2-leaf, Mass-Air-Mass.

This graphic is very enlightening:

[xaMdaM]

I agree, it would be best to go 2 leaf, hands down.

Here's the decision process I'd think through...

How long is your lease? If it's long term, 10 years or more, then it's a no brainer; rip the gypsum off your side, fill the cavities with mineral wool, make your airspace as large as you dare then put up your Room-in-Room structure, proceed with life.

If your lease is short term, or you have covenants that prohibit alteration of the party wall, then I'd probably ask to get out of it and move to another space. But that's just me and wanting to protect my capital investment so I could at least start to recover my money.

If the space is perfect, the rent is right, etc,.... and you STILL can't modify that wall as it's fire rated, then you either have to make the decision to live with a 4 leaf, or pay to have the 2 leaf re-certified.

Hope this helps a little bit.

Max

[nosebleedaudio]

There are several REAL world scenarios that NO ONE has mentioned YET..That I would ABSOLUTELY consider.

One; Not being in the room makes it VERY hard for ANYONE to consider all aspects...The floor, the ceiling, the HVAC ect...
Two: are their people in those rooms? A girl on the phone kind of thing???
IF you simply start ripping out that sheetrock will you be opening a HUGE can of worms, such as WHAT is in the walls??? See my point.
How about noise of ripping off that rock???
How about the thickness of that rock, is it 5/8", 1/2" that would make a difference to me for several GOOD reasons..

Number Two: HOW much isolaion do I really need??? In some situations over 60STC for sure...in the 70's for others..A set of drums in one room and a person on the phone in the next room REQUIRES a boat load of isolation.

Just something to consider...


If it was me I would float that NEW wall..

[DurtyMics]

What if I go for the best of both worlds and use the existing wall as one face of a new double leaf wall. So I would have...

Gypsum-stud&insul-air cavity-stud&insul-gypsum-stud-gypsum.


Is that still considered a three leaf wall? It seems to me that that would be a two leaf wall, just replacing one side of gypsum with an entire wall. It seems that I would actually benefit more from this design, since the preexisting wall has more mass than a single or double layer of gypsum.

Any thoughts?

[nosebleedaudio]

Did you look/compare the wall specs on the BBC's site, you will find some VERY interesting comparisons...

[DurtyMics]

I don't exactly know which site you are referring to. Do you have a link?

I've looked at all of these: http://www.toolbase.org/PDF/CaseStud...cc_ratings.pdf

[drpgleeson]

I agree particularly with the following points, which have already been made:

1) It's always a good idea to have different thicknesses of sheet-rock on different walls. For instance, instead of 2 layers on both sides of a single wall, put 1 layer on one side, 3 on another. Some slight benefit in reduced resonance is assumed and it costs nothing.

2)By all means mount the second layer of sheetrock to the wall assembly using hat channel. While mentioned in one previous post this point should be further emphasized. It makes a big difference.

3) One (and I think only one) earlier respondent mentioned the advantage of floating the new wall. This is a very useful technique. Many designers (I'm one) put down under the floor plate a stud-wide strip of 1/2" to 3/4" hard rubber. This helps, although a lot of the good of this method is diminished by the fact that building codes will require that the floor plate itself be mounted to the floor. Still, it helps. The more radical method, which I've seen used in several high-end installations here in LA and NYC, is to build the second (inner) wall on the floating floor. This will require an indulgent (or not particularly astute) building inspector, but it can be done this way. Note that this loads the floor with considerable additional weight, and you have to be cognizant of that in the general design.

[jayfrigo]

Originally Posted by drpgleeson

3) One (and I think only one) earlier respondent mentioned the advantage of floating the new wall.

Two I think:

...and coupling at walls and floors. In critical applications, you'll want to decouple those as well.

Which is worth a quick elaboration: don't isolate only at the floor. Remember that the ceiling counts too.

[DurtyMics]

I think I will just place a sheet of rubber under each wall, though I'm wondering how much I will benefit from that if I'm screwing the base boards into the concrete anyway.

In terms of my previous question... "[should I] use the existing wall as one face of a new double leaf wall. So I would have...

Gypsum-stud&insul-air cavity-stud&insul-gypsum-stud-gypsum."


What do you all think? I'm pretty sure I'm going to go ahead with this idea. Anybody see any flaws?


EDIT: A sketch of what this wall would look like (side view) is attached.

[drpgleeson]

I'm not aware of any tests that would provide a clear answer to your question about the benefit of rubber under floor plates (that's the bottom member of a stud wall) when, in fact, you're going to be nailing, screwing or otherwise connecting the plate to the original underlying floor. If another member knows of a test that would help here, please contribute.

Meanwhile, I'm going to give you my best guess and underlying reasoning. Even though you are coupling the "floating" wall to the floor by nailing or screwing down the floor plate, I see some benefit.

First, let's be clear that we are talking about at least 1/2" thick rubber, 3/4" or 1" being better, and that the rubber (or similar compound) needs to be relatively dense--it's holding up a heavy wall system and if you use light rubber you will simply compress it with the weight of the wall and will then have a much thinner dense rubber isolating member.

I can't quantify the benefit, but there definitely is some benefit. To see what this might be compare the transmission from wall to floor (although in general the problem is going to be going in the other direction, the situation is similar) by hammering on the top of a floor plate connected directly to an underlying floor in the normal way; now do the same thing (assuming you have a section of stud wall that's not fully enclosed with gyp) to a floor plate that's isolated by rubber. You will see a considerable attenuation of high-frequencies penetrating into the floor. And in general, although low-frequencies are harder to stop, the problem with floor transmission has a lot to do with impact noise--there's a lot of stuff in the range you hear when you hammer on a floor or take a high-heeled shoe and bang it on the floor. So rubber isolation between floor and walls helps.

The moderator's related point is well-taken: you do need to be thorough about this kind of decoupling and every little bit of decoupling helps and (even truer!) every little bit of coupling hurts. So, as he said, be sure your ceiling is similarly decoupled. In practice, this isn't difficult to achieve: you'll be building what amounts to a little roof on top of your inner and sound-isolated walls.

There's a lot of literature at this point that will give you good practical ways of isolating electrical conduit, so I won't go into that. Just be sure to decouple everything: air-conditioning conduits as well as electrical conduits . In some instances you'll have to fake-out the electrical inspector (flex conduit, for instance, is not now allowed without a variance), but it can be done, and once the inspector has approved the installation with the stud-walls open for inspection, you can remodify as needed and then close them up.

I will also say that if you're having a contractor do the work, you're going to have to watch out for the crew regarding consistent application of sound isolation practices. They will be well-intentioned, almost certainly, and, equally, they will screw it up. I could give you some amusing examples of this (well, not amusing at the time and particularly for the person who's paying for the job), but I'll refrain. Everyone who has had a contracting crew build a sound-room (unless they're specialized in this area, in which case you and I can't afford them) will tell you about amazing decisions in this regard. So be aware of the need to check all work daily as it's progressing.

[jayfrigo]

Originally Posted by DurtyMics

I think I will just place a sheet of rubber under each wall, though I'm wondering how much I will benefit from that if I'm screwing the base boards into the concrete anyway.

In terms of my previous question... "[should I] use the existing wall as one face of a new double leaf wall. So I would have...

Gypsum-stud&insul-air cavity-stud&insul-gypsum-stud-gypsum."


What do you all think? I'm pretty sure I'm going to go ahead with this idea. Anybody see any flaws?


EDIT: A sketch of what this wall would look like (side view) is attached.

Which part is the proposed construction? I'm not sure why there's an extra leaf in the middle there, between the studs on the right. Was this part of the original wall, and that's why you're leaving it? If that's the case, then you just use what you have and don't worry. However, if that's part of what you're building, that is indeed a triple leaf, and therefore not recommended.

If the left is what you're building, then great. You have an airspace, new studs, insulation, followed by double GWB with green glue between. That will certainly make a positive difference. You'll still have some structure-borne transmission due to the floor, and you'll need to pay attention to all the other details, but what you have is reasonable (3rd leaf excepted).

[DurtyMics]

I've attached a picture delineating what is there and what I am proposing to build. I know this is kind of crazy to ask -- but -- do you think this whole thing will have an STC above 58?

Shot in the dark.

[DurtyMics]

Ok -- so I've clearly been struggling with this 'three leaf' problem for a bit. This is my attempt at applying my mind to a solution:


It seems to me that, the issue with a three leaf design isn't that the number of leaves, three, is just inherently bad for acoustics. Rather, what I think is that, if all three leaves have the same mass to them, each leaf would have the same resonant frequency as the others. Thus, if one leaf was being resonated at a certain frequency, the pressure wave induced by its resonance would in turn cause the resonance of the next leaf, and the same would be true from the 2nd leaf to the third leaf. This phenomena is called sympathetic resonance (it's also what makes Sitars sound so cool).

If this is in fact true, then it would logically follow that -- to combat the three leaf plague -- I would simply have to ensure that all three leaves of my system were of a different mass.

Sound good so far? I hope so.


Here's my plan to combat this issue:


(5/8" gypsum + GG + 5/8" gypsum) (Stud + Insulation) (Air Cavity) (5/8" gypsum + GG + 1/2" gypsum) (Stud) (1/2" gypsum)

See attached picture.


Still sound good? I hope so.


Anyone have any supporting/contradictory thoughts on this? Please chime in.

[jayfrigo]

Originally Posted by DurtyMics

I've attached a picture delineating what is there and what I am proposing to build. I know this is kind of crazy to ask -- but -- do you think this whole thing will have an STC above 58?

Shot in the dark.

Here's an educated guess, and there's no way you could rely on this number, and I probably shouldn't even go out on this limb, but... top of my head I'd say somewhere in the STC 53-56 range, perhaps a bit better considering the green glue, but I don't think you'll get above 58.

Remember also that STC gives you a better idea about speech-range frequencies than wider-range music. An STC 53 wall will not give you TL 53 (Transmission Loss) at lower frequencies that may be created with drums, bass guitar, or even electric guitar amps.

[spm_gl]

Originally Posted by drpgleeson

So, as he said, be sure your ceiling is similarly decoupled. In practice, this isn't difficult to achieve: you'll be building what amounts to a little roof on top of your inner and sound-isolated walls.

That will only work if you have a rather small room, for structural reasons. You could also "simply" suspend the ceiling with a spring system, as we did: Elastically suspended ceiling – DIY | Spreemusik Blog
A lot easier than building a roof, too. We floated the entire shebang, i.e. a sturdy frame on sylomer pads, and hung the ceiling inside. Works great, but damn expensive to do.