Existing wall is already MASS/Air/MASS so the new wall....?

Hello. This is my first post. I have probably spent 20 hours reading all the great information on this site in the past week. I'm going to be building a room within a room inside a living room + dining room of a house that I just bought. I'm hoping to achieve around 56 STC. ( Loud drums, neighboors about 25 ft. ) My 1st question: The existing wall I'm assuming is the exterior wallboard, then the stud/insulation and then the drywall inside. I have read that ONLY 1 air gap is important ( MASS/Air/MASS). So How do I build my new floating wall, and still maintain a MASS/Air/MASS system? The existing wall already counts as 1 MASS/Air/MASS, right? Will I need to remove the existing drywall inside the living room in order the make it the first MASS (leaf)? Thanks a bunch guys.

Well it may in fact be mass air mass, but it's a small amount of mass not decoupled from the structure. When you put up drywall hopefully you'll be mounting it on resilient channel. I'll leave the rest of your question up to someone who knows more than me.

I assume the picture are the wall(s) you are speaking about. If that's the case, your present walls are a M-A-M structure. Take into consideration though, that those walls are "standard home construction walls". Most likely (because of cost) your present walls are: 1/2" drywall, 2x4 frame with insulation, and another sheet of 1/2" drywall. This type wall will have a LOW STC rating. Also, most of the charts for STC have the drywall thickness at 5/8". As I said, most likely your present walls may have 1/2" drywall which is a slightly smaller density than the 5/8". You may already have this, but here are some links for wall structures and their STC ratings: http://www.stcratings.com/assemblies.html#01 http://www.saecollege.de/reference_mate ... 0Chart.htm In other words, for a recording studio, a wall like this will leak "A-LOTTA" sound. You need to be sure to have something constructed that will definately reduce low frequencies (which = walls having MASS) To achieve better sound isolation, you will have to build another "room within a room" (as you stated) and decouple the walls/floor along with RC on your walls. (as SonicClang talked about) By doing this, I would think you would then have a "double wall construction". Only thing is, your "outer" walls (the walls already constructed) will not give you significant sound isolation. (That is unless you play your speaker volume REAL low) If you build another "room within a room" the walls that you build will have their own M-A-M rating depending on how they're constructed. (Maybe a "staggard wall" with 2 sheets of drywall on one side and 2 sheets of drywall on RC on the other side is appropriate???) You are right to say that there should only be 1 air gap per a M-A-M wall, but remember that's M-A-M "PER wall". Hopefully I'm correct in my thoughts stated here. If I'm not, I'm sure the moderators or other more experienced people will step in and correct me. Hope all goes well in your project! You've come to the right place to get the info to make that dream come true! :)

Will I need to remove the existing drywall inside the living room in order the make it the first MASS (leaf)?

YES. Hopefully you are on a ground floor... is there a concrete slab under that carpet? If so GREAT, if not and your on a 2nd floor sound isolation, floating floor etc becomes difficult beacuse of weight and decoupling inner structure/room. Serious thought needs to go into floating a floor... a lot of internet reading out there suggests to float a floor BUT an incorrectly floated floor will be worse then just using existing slab. Search for "To Float or not to Float" on this forum. The walls and ceiling... yup tearing down the existing drywall is the best solution for sound isolation... either add mass to the other sides of existing walls or add drywall "beef up layers" inbetween studs of existing walls... then insulation. Then build new walls atleast 1" away from existing walls, insulate and add layers of drywall. Other lesser solutions: tear down drywall & mount new drywall on RC strips. Add layers of drywall to existing and confirm some insulation is in walls. Staggered studs will not be an option for you... you already have existing 2x4 walls w 2x4 top and bottom plates. Staggered stud is 2x6 bottom and top plate with 2x4 studs staggered on either side to mount drywall to. Pay close attention to fire stopping inbetween walls over 8 feet high. AND there is a lot to learn besides above. Rods book in the sticky section is great: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5670 Hear you'll find some good threads, beef up dryall, floating floor and much more has been covered: Build Diary and Completed Studios Thread I know Sharward, Andy's and my thread (Marc) has info and pics which will help you out. All are long reads... mine is just in the pre stage. Also Dan's thread shows some good beef up: Dan Fitzpatrick's One-Room Garage Studio Marc

Guitardad72... Just curious to know... Why would having a staggard frame not be an option as long as he can handle the space it will use? I'm not understanding what a 2x6 plate has to do with that. If he constructs another frame inside the room he's in (even if it's a 2x4 frame), something will have to be attatched to the ceiling joist/frame and floor to support the new frame. Also, doesn't the staggard frame offer the best STC for a single (2-sided) frame construction? (especially with 4 layers of drywall and RC) Obviously there are considerations, such as is what he wants to do within code? The weight of the construction, etc etc.

camistan wrote:

To achieve better sound isolation, you will have to build another "room within a room" (as you stated) and decouple the walls/floor along with RC on your walls. (as SonicClang talked about) By doing this, I would think you would then have a "double wall construction". Only thing is, your "outer" walls (the walls already constructed) will not give you significant sound isolation. (That is unless you play your speaker volume REAL low) If you build another "room within a room" the walls that you build will have their own M-A-M rating depending on how they're constructed. (Maybe a "staggard wall" with 2 sheets of drywall on one side and 2 sheets of drywall on RC on the other side is appropriate???) You are right to say that there should only be 1 air gap per a M-A-M wall, but remember that's M-A-M "PER wall". Hopefully I'm correct in my thoughts stated here. If I'm not, I'm sure the moderators or other more experienced people will step in and correct me.

Consider yourself corrected........ WRONG - WRONG - WRONG. In construction built with 2 wall frames seperated by an air space - that is considered one wall. You never EVER put anything on the layer between the 2 wall faces - other wise you create triple or (in your case) quad leaf wall assemblies. So even if it's 2x4 8" air 2x4 - (so 15 1/2" outside face to outside face of framing) you would only sheath the 2 outer faces to maintain a 2 leaf system. And you do not waste your money using RC if you build double walls or even with staggered studs. Rod

Why would having a staggard frame not be an option as long as he can handle the space it will use? I'm not understanding what a 2x6 plate has to do with that.

camistan, Well it could be an option where a new wall would go, not where existing wall is. In searching for a pic please see: Home Toys Article - April 2005 - About half way down the page there are 3D pic of both a 2x4 common (regular) and staggered stud walls. I have no idea what the article says, it's just the pic. In trying to give more than a simple answer :evil: > 2x4 wall = 2x4 top & bottom plate, 2x4 studs, finished on both sides. Staggered stud wall = 2x6 top and bottom plate (horizontal) then 2x4 staggered studs (vertical), 24" centered on each side, 12" apart measuring with the stagger... half of the 2x4 studs are on one side (edge) of the 2x6's, the other half on the other side, each side has drywall, sheathing or whatever finish. This decouple's the two finished sides somewhat but they are still coupled at the plates. Double wall = 2, 2x4 walls. finished on only the outer sides. Air inbetween walls and they do not touch (unless over 8 feet the a fire stop should by used such as a peice of drywall) Increasing Mass on either leaf will increase Isolation. Increasing Air between leafs will also increase Isolation. The Double wall with 1" air = 8" wide (with no drywall) Staggered Stud = 5 1/2" wide (with no drywall) The increased decoupling from no common top and bottom plates, increase in stud centers (hopefully 24" if not 16") and increase in air makes a double wall more sound proof (no wall is completely sound proof) then staggered stud. The 2 1/2" difference is not a lot but it's up to the individual to decide the real estate loss factor VS isolation. If adding beef up drywall inbetween studs on outer leaf with a double wall you do lose AIR. BUT when dealing with existing walls, most desirably you would not want to take a 2x4 wall down to rebuild it staggered stud with 2x6 plates. In some places such as load bearing walls, this would be either impossible or very expencive. You can add RC to existing to decouple an inner leaf. New walls can be staggered stud, but if doing double walls already, why not be consitent, plus the inner 2x4 walls can be constructed "splayed" to create a RFZ (reflection free (listening) zone... the sweet spot) in the room.

I'm hoping to achieve around 56 STC. ( Loud drums, neighboors about 25 ft. )

apexer, 56 STC in general is a low number for drums, you should be using STC only as a guide, STC was designed for voice (centered low at 500kH up to 5K) not music or especially a bass drum. You are more looking for LF TL (Low Frequenct Transmision Loss) for my one room studio my goal is STC of 65 with LF @ 50kH, a Transmission Loss of 30dB. I'm only planning on having drums in my room once every few months. BUT that sound isolatioin level is my personal quest. :twisted: Do a search on this forum for LF TL, and if you see it's Knightfly that wrote it, it's good info :D Marc :evil:

It doesn't seem like this is all a simple matter, but I think it's very important. What I have noticed about the references to 'third' leaves and such, is that the only direct comparisons between 2 and 3 leaves are when sheetrock layers are added to the between-leaf space and directly on the studs of one of the leaves. (This causes 2 things: reduction in air space, and direct conduction through the studs.) I have not (yet anyway) seen STC comparisons where an extra 'isolated' leaf was added between double walls, OR where an extra leaf was added to the outside of the outer leaf (or to the inside of the inner leaf). Plus, I have not read anything that addresses 'partial' or 'quasi-' leaves. What I mean by this is: Does a an extra 'barrier' REALLY act like a leaf if it does NOT form a seal around or between a 2 leaf system, or decrease the total air space, or touch either leaf? For example: Say that you build a small studio-room in the middle of another HUGE room (the HUGE room is NOT sound isolated from the outside world). You want to isolate sound coming from the studio-room and going into the HUGE room. You build this studio-room itself as a room within a room (that is, it has 2 leaves itself -- i.e., that doesn't include the walls of the HUGE room). The outside leaf of the studio-room is far from the walls of the HUGE room. Would this studio-room be considered to have 3 leaves? (And/or what effect would that have on the STC value of the room?) Now, say that you move the same studio-room to the corner of the HUGE room, BUT leave an air gap of a couple inches that freely flows around it ('communicates') and with the rest of the air of the HUGE room. What effect would that have on STC? Would there be a (serious) compromise with sound isolation? Does the studio-room now have a 3 leaf wall? The point (what I'm trying to say): There HAS to be limits to the 3 leaf effect(s). Some of these limits would seem to be based on: 1.) Whether the third leaf forms a 'seal' within, inside of, or around the original 2 leaf system (or room), or if air can freely flow around the third leaf. 2.) How close the third leaf is to the original 2 leaf system; in other words how big the air gap is between the third leaf and the rest of the 2 leaf system. I think this is a very important issue with many proposed studio constructions (including mine!). I wish someone could provide proven answers to this question (based on evidence and science, not speculation). thanx, K

Let's put it this way... Suppose you have a near perfect decoupled two beefy leaf wall system. It performs "X." Now suppose you add a third leaf on the outside of that wall system. Now it performs "Y." I'm pretty sure Y is worse than X at certain frequencies and yet it is better than X at other frequencies. Forget STC. Just forget it. It's irrelevant in your situation. You're just looking for "better" vs. "worse" and knowing what things tend to improve the results. Well, imagine adjusting the rabbit ears on that TV, and just when you get the image quality to look good, the audio drops out... :lol: Sometimes it's like that............ Third leaves are sometimes unavoidable, or practically unavoidable. I will have a three leaf wall in my project that I realistically can't do anything about. I intend to make up for the inferiority of that wall with extra mass and extra air gap between the two heavy leaves. Just don't underestimate the ill effects of the third leaf. Yes, it is true that the examples you often see demonstrate adding a layer of drywall (or whatever) in the "wrong place" (between the outer leaves), with another version showing the middle mass added to one of the outside masses and showing how much better it performs. That's mostly just to illustrate that, when building new, placement does count and it counts a lot. In your case, you could leave your existing walls intact and just build a new single leaf inside the space... But doing that is going to cost you in your isolation outcome. One of the advantages of removing the drywall on the inside of your existing space is that you expose the opposite leaf from the inside, so you'll have an opportunity to beef it up between the studs. So not only do you eliminate the third leaf, you improve one of the existing leaves. If that is not possible, you could in theory make up for some or much of the performance deficit by increasing the amount of mass and increasing the distance between the outer leaves, which will cost you some square footage. That's what I'm doing on my south wall.

guitardad72 wrote:

Double wall = 2, 2x4 walls. finished on only the outer sides. Air inbetween walls and they do not touch (unless over 8 feet the a fire stop should by used such as a peice of drywall) The Double wall with 1" air = 8" wide (with no drywall) Staggered Stud = 5 1/2" wide (with no drywall)

One CAN make a double wall using two parallel 2 x 3 base plates (and top plates) spaced apart, and using 2 x 4 studs (notched so that they don't touch any opposing base or top plate). If the base plates are spaced 1 inch apart from each other, then using 2 x 3's instead of 2 x 4's will save 2 inches in wall thickness (although the wall would lose 2 inches in air space in comparison to using two 2 x 4 base plates, it would have a gain of about 1/2 inch in airspace over a staggered stud wall using a single 2 x 6 base plate, and would also gain isolation in the base and top plate regions). Of course, the studs (which WOULD be 2 x 4's) will have to be staggered so that they don't touch any opposing stud. Most of the strength in a wall appears to come from the vertical studs, and not so much the base plates, so using 2 x 3's as base plates may not compromise the load strength of walls very appreciably; this vertical strength would seem to be mostly left intact since the studs are only notched where they would meet an opposing base or top plate. (Please correct me if I am wrong about the strength issue; if there is a problem with strength, it would likely be in a shear along the grain; the code issue is well noted.) thanx, K

Please reference the code section(s) that allow(s) for using 2x4 studs on 2x3 sole plates and top plates, and notching the studs where they are attached to the sole plates and top plates... :shock: (I really seriously doubt that's legal... But I've been wrong before......... :roll:)

Luftweg wrote:

(please correct me if I am wrong)

I can't, but sure wish some one who knows code could comment. ...but my guess is 2x3 plates in wall construction is not to code. Then if the inner 2x4/2x3 wall is used to bear the weight of joists for inner ceiling I wouldn' trust it. Losing that 2" of air (which is a spring) will effect sound isolation negatively. I've not seen any post with someone doing this, maybe with 2x3 steel studs you could. I think RC would win over this method, but I'm not an expert... just a musician who has obsessed for a few months on building a studio. Marc

Please reference the code section(s) that allow(s) for using 2x4 studs on 2x3 sole plates and top plates, and notching the studs where they are attached to the sole plates and top plates... (I really seriously doubt that's legal... But I've been wrong before......... )

Sharward, you beat me to the "Submit" button. :oops: Guess I spend to much time typing out long repsonces. :twisted: Marc

guitardad72 wrote:

Guess I spend to much time typing out long repsonces. :twisted:

Dear Kettle: Please quit spending so much time typing out long responses. Sincerely, The Pot ;-)

Hi: I’m not sure if your response was meant for me, but parts of it seem to be: .......

sharward wrote:

....I'm pretty sure Y is worse than X at certain frequencies and yet it is better than X at other frequencies.....

But without knowing the differences, then how could you know which would be the optimum for a given situation?

sharward wrote:

Third leaves are sometimes unavoidable, or practically unavoidable. I will have a three leaf wall in my project that I realistically can't do anything about. I intend to make up for the inferiority of that wall with extra mass and extra air gap between the two heavy leaves. Just don't underestimate the ill effects of the third leaf.

But what exactly constitutes a third leaf: Does it have to always create a seal either between, or inside or outside of the 2 leaf system? If it doesn’t create a seal of fully surround anything, or touch anything, wouldn’t it not be a ‘true’ third leaf?

sharward wrote:

I intend to make up for the inferiority of that wall with extra mass and extra air gap between the two heavy leaves. Just don't underestimate the ill effects of the third leaf.

Since any changes could either improve or worsen sound transmission – and often in a counterintuitive manner – how can you know that you are in fact making up for a bad situation and not – say for example – increasing the transmission of certain resonance frequencies?

sharward wrote:

Yes, it is true that the examples you often see demonstrate adding a layer of drywall (or whatever) in the "wrong place" .... That's mostly just to illustrate that, when building new, placement does count and it counts a lot.

Where can I find info (especially ‘trial’ studies, etc.) that take into account other situations which may or may not be related to a ‘full’ third leaf ?

sharward wrote:

In your case, you could leave your existing walls intact and just build a new single leaf inside the space... But doing that is going to cost you in your isolation outcome....

[not sure if you meant me] In my situation, since a potential part of an outer leaf COULD be a poured concrete wall, with nothing but deep earth behind it (and the fact that I can’t remove it), I don’t see how that could be improved upon (except of course if only an inner leaf is added, but that’s not really the question; the question is whether to add both the inner and outer leafs in front of the concrete wall). But for practicality it might be better to have contiguous walls of the same material. However, to do that would mean ‘ignoring’ the concrete wall as a leaf .... and again, the question is still: would the outer concrete wall be considered a third leaf IF it were NOT sealing any airspace in? After all, if the answer to that question is ‘yes’, then why wouldn’t any concrete wall in the whole basement be a third leaf – even the ones that are 15 or 20 feet away! THAT’S where I was thinking about the ‘limits’ of the third leaf effect. Is the ‘sealing-in’ of the third leaf more or less important than how far away the leaf is, and to what degree. Certainly, it would seem, if there is no seal, then the third leaf effect would be somewhat mitigated in relation to a sealed third leaf (we know how bass cabinets can be affected by opening the backs and such). thanx, K .

Thanx for the correction Rod! Thanx for the info Guitardad72! Rod... If I have it correct now, you're saying if he were to build a wall inside his pre-existing walls he would be better off with simply a frame with drywall on the inside (drywall facing the inside of his studio) possibly with insulation in the stud cavities and a reasonable size gap between his existing wall and the new one? If this is right, then that would be the 3-leaf system you're speaking of correct? Also tell me this... In my studio http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5951 I'm beefing up my walls where I'm putting 2 sheets of drywall in between my existing "outer" frame cavities (Control room West wall picture). Would all those different sheets of material (MDF, OSB etc) that touch from the outside of the house to the beefed up drywall count as "1" leaf (in which "ALL" materials from the outside to the beefed up drywall be considered as my "outside" wall)? Thanx

guitardad72 wrote:

Luftweg wrote:

(please correct me if I am wrong)

I think RC would win over this method, but I'm not an expert... just a musician who has obsessed for a few months on building a studio. Marc

Hi Marc: Why do you think this? The air gap most certainly would be greater than simply using resilient channel, and of course the wall could appear to support more sheetrock than any resilient channel. A double wall is already resilient, so no real loss there. The edge which has the tiny notching (and it IS a relatively small amount of material removed for notching compared to the entire 2 x 4 -- like 1 square inch per each 2 x 4) is not on the edge where the sheet-rock is attached. The most buckling stress of a vertical support member is in the middle of the member, not at the ends (if my engineering school days are remembered; I don't know wood that well at all... ah, but I'm a pharmacist now, go figure). The main thing that appear could keep it off code, would seem to be a slight potential for vertical shear (which seems very unlikely). I wouldn't think that compression across the grain would be a real big issue for the 2 x 3 base plate because it is essentially sandwiched between the floor and the stud. hmmm. I wouldn't be really afraid that it would be weak. But who knows? and code is code. thanx, K

camistan wrote:

Thanx for the correction Rod! Thanx for the info Guitardad72! Rod... If I have it correct now, you're saying if he were to build a wall inside his pre-existing walls he would be better off with simply a frame with drywall on the inside (drywall facing the inside of his studio) possibly with insulation in the stud cavities and a reasonable size gap between his existing wall and the new one? If this is right, then that would be the 3-leaf system you're speaking of correct?

Not if he removes the existing drywall from the inside face of the existing wall - then the outer wall face and the new innner wall face create a 2 leaf system. Also tell me this... In my studio http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5951 I'm beefing up my walls where I'm putting 2 sheets of drywall in between my existing "outer" frame cavities (Control room West wall picture). Would all those different sheets of material (MDF, OSB etc) that touch from the outside of the house to the beefed up drywall count as "1" leaf (in which "ALL" materials from the outside to the beefed up drywall be considered as my "outside" wall)? [/quote] Absolutely - when you add materials to the back of the existing sheathing on a wall - as long as they are tightly fitting - they create one leaf. Rod

apexer wrote:

Hello. This is my first post. I have probably spent 20 hours reading all the great information on this site in the past week. I'm going to be building a room within a room inside a living room + dining room of a house that I just bought. I'm hoping to achieve around 56 STC. ( Loud drums, neighboors about 25 ft. ) My 1st question: The existing wall I'm assuming is the exterior wallboard, then the stud/insulation and then the drywall inside. I have read that ONLY 1 air gap is important ( MASS/Air/MASS). So How do I build my new floating wall, and still maintain a MASS/Air/MASS system? The existing wall already counts as 1 MASS/Air/MASS, right? Will I need to remove the existing drywall inside the living room in order the make it the first MASS (leaf)? Thanks a bunch guys.

Yes - you will have to remove that drywall - and your best bet would be to add some mass to the outside wall as well as the new iunner wall. Rod

Luftweg

Why do you think this? The air gap most certainly would be greater than simply using resilient channel, and of course the wall could appear to support more sheetrock than any resilient channel. A double wall is already resilient, so no real loss there.

Presuming 2x3 plate is not to code, primary reason would be code. Secondary to that RC is within code and if the real estate is that important to builder then that would be the choice. Sure though your method should have more sound isolation but I've become a firm believer in: Do not try and use any sound isolation technique that has not been proven before. There are plenty examples of unsafe iso studios and iso studios that were built that could have been better with correct technique. SO, why bother with unproven technique (no offence). RC, staggered stud or true double wall would win in my mind. apexer, sorry we "took over" thread. :oops: Hopefully you'll be back soon to comment on our collective posts & discussion AND provide us with more details of your room, what construction techniques you are planning on using and most important bring the topic of the thread back to your room :!: Marc

guitardad72 wrote:

[b] ... Do not try and use any sound isolation technique that has not been proven before. There are plenty examples of unsafe iso studios and iso studios that were built that could have been better with correct technique. SO, why bother with unproven technique (no offence). RC, staggered stud or true double wall would win in my mind.... Marc

Hi: I have seen this method in diagrams of sound construction before (currently searching for the reference); whether it's 'unproven' or not shouldn't refer to it's ability to isolate -- since it's virtually the same thing as the double wall using 2 x 4 sole and top plates (but gives 2 inch thinner walls). If the walls are not supporting anything but the sheet-rock, i.e., they are only partitions and not load-bearing walls, I believe 2 x 3's in all members would be code -- so using 2 x 4's for only the studs shouldn't make much a difference to code, except that it would be STRONGER than needed, not weaker. But, as always, IF the code says it's no good, than it's no good by virtue of that alone. K

Leftweg, At one point I was considering using 2x2's for my own inner walls, but could not find code info for it. Plus I'm resting my inner ceiling on inner walls so anthing less then a 2x4 for a wall has been thrown out of my mind but... Sure why not use 2x3 plates, I just know I'm not going to. I'm just not a fan of that idea BUT I knew some structure used 2x2's for walls but couldn't remember what. Older Mobile Homes used 2x2's for interior walls as well as 1x2, 1x3 & 1x4. For exterior walls some mobile homes used 2x3's. Even in roof rafters & truss they used lumber less than 2x4's. I did a search, see this document: http://www.fpl.fs.fed.us/documnts/fplrn/fplrn237.pdf But most mobile homes no longer use lumber less then 2x4's and remember the Hurricanes of 2004 here in Florida. Many of these 1970's built mobiles homes were shreaded to toothpicks. The 2x3 walls were just holding up wood paneling, little bit of insulation and steel sheathing. Alot of Code has changed hear in Florida every good hurricance year. I grew up in a early 1970's built mobile home in Canada. It was dang cold at the far ends of the mobile home. Anyways, I'd love to see the reference to the 2x3 plate, double/staggered wall when you find it, regardless of whether it's code or not. Marc

WOW! impressive amount of response! Unfortunately i'm still not clear on the best solution. I'm coming to grips on the idea of removing the inner drywall, but also am thinking that removing it would not be worth the effort. Here are 2 ideas. Why would another layer of drywall decrease the STC even if the air gap is the same? And if I should in fact remove the existing drywall....are we talking a sledge hammer and some redbull? Thanks guys.

Aloha, Here's a chart that helps illustrate the differences between construction techniques. Hope this helps, Aloha 8)

option 2, at least. forget option 1 (read this forum again and you know why)