Temporary "FAQ"- (was "Complete Section")

How thick should my walls be, should I float my floors (and if so, how), why is two leaf mass-air-mass design important, etc.

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Post by wildplum »

Yup, still around. I just don't have as much time as I'd like to participate in forum discussions. However, I have just bought (couple days ago) a CAD package (Turbocad) to help me through the process of designing the new studio. Just haven't had the time to install it.

In the not too distant future, I expect to seek a lot of help from this forum in designing the new space. My situation will be a little different than I've seen here for the most part, though I believe the principles and general approach will be the same. Instead of doing a basement or garage convertion, I'll be renting space in a warehouse building. Most likely a multi unit building, single story, concrete tilt wall construction. It'll be fun working out the details on this site.

I am still confused about the walls construction. Not so much the walls per se, but rather the enclosing of the space between the walls (or, more properly, the air space "spring" between the two mass leaves). What does the top and bottom of the wall section look like? From a few private emails I got, I take it others have similar questions. Here's the essence of my problem (and i stress that it is my problem, one of understanding; I am not claiming anything that you've said is wrong). My understanding of the physics involved is that in order for the air mass to act as a spring, it must be in a sealed space. That is, all six "sides" of the wall (two leaves, top and bottom "plates" and the end studs) must form a closed space. Without the drawing program up I don't think I am getting across what my problem is, but I'll give it a shot.

Let's say I have the following:
outer building shell/mass-air-mass/control room/mass-air-mass/live room/ mass-air-mass/iso room/mass-air-mass/outer building shell

If the ceiling of the control room rested on the inner wall (asuming separate studs for the inner and outer masses)- ie, the wall closest to the control room, and the ceilings of the other rooms where similar- and all independant of the outer shell ceiling, as would be the case when builidng the walls on a floated floor and the ceilings on the walls- then the space between masses would all be common and would not operate efficiently as a spring, especially given the "leaky" nature of the typical warehouse shell/ceiling contruction (not only would the air space between masses be common, but the air space would also be common with the other space in the building outside the enclosed studio rooms, for example, between the studio rooms' ceilings and the shell ceilings) . So, what are the details of closing the space between the wall's two masses?

If all this isn't very clear, my apologies. I am just not explainging it very well. Once I have the CAD program up, I'll be able to illustrate my difficulty better.

Thanks for the concern and the help.
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Post by knightfly »

First of all, Turbocad is a really powerful proggie for the bux, but one thing it WON'T do without help is output a bitmap file, such as tif or jpg - I have it, but haven't used it much partially because of that but mostly because of "inertia" - I'm used to my old DOS cad program, which will export DXF files, which I import into Autodesk's Quick Cad (also cheap, and WILL export JPG's ) As John pointed out it's a roundabout way, but it's still quicker than learning all the in's and outs of a new proggie when I've got one that works -

Anyway, to the meat - leakage between air spaces "inside the envelope" works FOR you - the inverse square law works close enough here to weaken any sound that makes it into the envelope between inner and outer masses, so that by the time it gets to the second mass in any direction it's not as able to affect that mass. Stuffing fluffy fiberglas in cracks also helps cut down on convection, etc, as well as damping the panels it touches (damping also helps isolation) - even using rigid fiberglas slightly bowed in cavities so that it touches the inner panels is a GOOD thing.

Just a comment - if you guys are "PM-ing each other" and discussing possible confusing issues, it means I've not been clear enough on that subject. That means it's time to post a question (as you just did) - just don't hold back, I hardly ever bite (and almost NEVER swallow) but I can't answer questions that aren't asked, nor does anyone lurking get the benefit from private conversations - BE BOLD - a question isn't "dumb" if you don't know the answer, and I've mentioned before that I won't tolerate rude behavior against members here because this forum is NOT here for "cat-fights", it's here to learn and share.

So please, LEARN if you don't know (by asking questions) and SHARE if you do know (I'll comment if I disagree, it's called discussion)

Thanks for bringing this up, I don't remember covering it anywhere else... Steve
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Post by TerrorFiend »

Call me a moron, stupid, ignorant or a newbie. Thats fine, but can someone PLEASE tell me what the hell "RC" is??? It's mentioned all the way through this thread and i can't picture in my head what people are talking about because I don't know what this forsaken abbreviation stands for!!! Same goes for "TL".

Is there a glossary around here somewhere that someone can direct me to?

Also, in spite of everyone contradicting each other on every point to do with studio walls, which of these cross-section diagrams is correct? I know you're supposed to have different wall coverings, for different frequency sounds, plasterboard, wood, etc. but i cant envision where each is supposed to go.

Can someone who knows their stuff please take a look at the diagrams, and tell me straight out what the best way to build the wall is.

And how would it be attached to a concrete floor?, would the concrete floor need a second floor on top of it?, and how wide an airspace between the two walls is the airspace supposed to be?
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Post by knightfly »

Hi, welcome to the board - first, this is a friendly place and no name-calling is allowed - anyone who starts that will be completely ignored, as I feel there is already enough "kid stuff" available on other sites - I feel that everyone learns at their own pace in their own way, and if I can't explain something well enough it's MY shortcoming, not yours.

As to the various acronyms, you're right - there are posts where I've spelled it out, but no one place with all of them defined. Until I get the chance to add one, here's a partial list of terms -

RC stands for Resilient Channel - here is one example, the RC-deluxe is their best product -

http://www.dietrichindustries.com/bigdp ... sories.htm

TL stands for Transmission Loss, which is separately calculated for each 1/3 octave frequency band. When you see TL used in a sentence, it needs to be specified at what frequency or it's meaningless.

STC stands for Sound Transmission Class - this is an "all-in-one" number, which is arrived at with a formula I've yet to find - generally, the TL at 500 hZ corresponds to the STC value for that wall.

703 refers to an Owens Corning insulation product that is compressed fiberglas with a density of 3 pounds per cubic foot - the compression is great enough that the stuff is also referred to as "semi-rigid", rigid fiberglas, etc - this is overall the best acoustic treatment for the most applications.

Rockwool, mineral wool, slag wool all refer to similar products, except they are made with either rock byproducts or leftover slag from metal manufacturing plants. They have similar grain structure as the fiberglas, but not exactly. Acoustically they are very similar.

Here is a short glossary of some acoustic terms I probably left out -

http://www.acousticalsolutions.com/educ ... ossary.asp

As to your drawings, the top one is correct. If you read through the "stickies" at the top of the forum, there is a LOT of info that should help clarify your questions. I'm out of time for now, but generally if you're in doubt remember I'm the moderator - If I don't know the answer, I'll say so. Then, as time permits, I'll find the answer and post it.

My philosophy on questions - stupid people don't bother to ask questions. Smart ones do... Steve
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Post by Aaronw »


I agree on the acronyms. Need to make a sticky on top of the forum w/ all the acronym definitions. I almost posted one a couple months ago, but didn't. Got too busy.

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Post by TerrorFiend »

Haha, thanks. It's good to come across a forum where everyone isn't abusing each other over some tiny little detail that has no relevence to anything.

Thanks for the acronyms, that was very helpful, and I also have a clear picture in my head of the makeup of the walls, now.

Just wish I had more space :-(
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Post by knightfly »

You're welcome - and yeah, NASA is probably the only outfit that has more space than they know what to do with... :lol:
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Post by knightfly »

Just updated my comments on page one of this thread, changes are in dark red. Please ignore any OTHER references to Type G laminating screws, turns out they are neither practical nor easily available, and may cause the wall to fail if not applied exactly right... Steve
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Post by BradJacob »

knightfly wrote:Carl, believe me I feel your pain, and have felt it for the last 20 years as I've studied everything I could find after building a room while thinking I knew what to do - that room is inside a barn about 100 feet from my house, and I was amazed when my wife could tell from inside the house which song I was playing on the piano in the "studio" -

I've been trying to find the time between answering posts and the interminable daily crap we all put up with to do just what you ask - so far, I've got a long ways still to go.

In looking back, there are a few posts where I've delineated quite a few of the "rules" of sound proofing as I believe them to be - Here is a rough gathering of those comments, totally un-edited as yet. If there are any conflicting comments they will be gone when I'm finished with the FAQ - meantime, as usual I'm further behind than I'd like to be so this is all there is for now -

First of all, here are some definitions, then some rules of wall construction as I see them, with reasons if I'm lucky enough to remember them - afterward, I'll tell you what I think you should do where, and why -

The most effectuve use of materials can be had using a mass-spring-mass type of wall. The mass is whatever layers of paneling are attached to either side of the frame.

A leaf is all the layers of mass on ONE side of the frame, whether it's one layer or four.

An Air space is any non-solid, including insulation. The wider the studs in the frame, the deeper the air space.

Air is considered a "spring", because it is relatively stiff and will transmit sound from one leaf to the other.

1. Never put RC(Resilient Channel) on both leaves of a wall - it allows too much movement on the part of one of the leaves, decreasing TL through the wall.

2. Two different thicknesses of wallboard beats two of the same size for mid/upper frequencies, two thicker panels does better at low frequencies.

3. Low frequency attenuation is improved by NOT having RC, by increasing mass, increasing air gap between leaves, and increasing stiffness.

4. Fastening a second layer of wallboard to a first layer, when the first is mounted on RC or STEEL studs, should be done with screws through the first layer and into the RC or (steel)stud ONLY - if these screws touch WOOD studs the isolation of the wall will be reduced by as much as 9-10 dB. The STEEL studs are flexible enough not to cause a loss in performance.

I'm updating the following paragraph with the one marked 5A, below it - newer more complete information and practicality are the main reasons - I've left the old one in, so differences are obvious.

5. Fastening a second layer of wallboard to a first layer, when the first is mounted on WOOD studs, should only be done using 4" wide stripes of slightly thinned joint compound over the stud area, then fastening with Type G laminatings screws approximately 2-3" away from the studs and parallel to them, on approximately 12" centers. This allows the two layers to act as separate panels, which maintains each panel's coincidence dip separate from the other. It also keeps any fasteners from penetrating BOTH layers of wallboard AND entering the WOOD studs. NOT doing this will lose about 9-10 dB of isolation due to flanking through the fasteners and into the studs.

5A - replaces 5, above -

Fastening a second layer of wallboard to a first layer, when the first layer is mounted on WOOD studs: First, if building a SINGLE frame with wallboard on both sides, it's STRONGLY recommended to use Resilient Channel on ONE of the sides of the frame – otherwise, you lose several dB of isolation at mid and higher frequencies (above 100 hZ typically) – follow the rules for mounting wallboard to RC on this side – no screws in line with studs so you don't accidentally "short out" the RC.

Fastening a second layer when there is NOT RC under, the most practical way is to mount the first layer using half as many screws as normal, same with any following layers EXCEPT the outer layer – this one should have full fastening schedule used, and with long enough screws to penetrate all layers and solidly fasten to the studs.

In the case of double frame walls with wallboard only on the outside of each frame, use half schedule fastening on all but final layers on each side.

Full schedule screws for wallboard, according to USG – 8" on center around the edges of panels – 12" on center in the field (middle of panels) – half-schedule screws would be twice as far apart for all but the final layer.

In all cases, ¼" spacers should be used under panels until fastened, then pull the spacers and caulk before repeating for the next layer.

For a standard single stud frame with no RC using 2x4 wood studs, two layers of 5/8 sheet rock on each side will give an STC rating of around 48 dB – the same wall using ½" will also rate about 48 dB, but will actually perform worse in lower frequencies by 2-3 dB because of the extra mass of the 5/8" panels.

A double framed wall with 2 layers of 5/8 sheet rock on only the outer sides of each frame, with a total air/insulation gap of 8" (1" between frames) will test out at about STC 66 – the same wall using ½" sheet rock will be about 2 dB worse STC (64) and 3 dB worse at the low end as compared to the wall using 5/8 panels.

6. Insulation should be placed against inside wall panels to increase damping of the panel - This helps TL at low mid/high bass regions, as well as decreasing the effect of the Coincidence Dip which occurs in drywall at between 2 kHz and 4 kHz. Optimum density for in-wall, rigid insulation is around 2.5 to 3 PCF.

7. RC should never extend far enough for its end to contact the intersecting wall - cutting it about 1" short works well. Wallboards should also not directly touch the intersecting wall, but should have a gap of approximately 1/8" between them. This gap must be caulked with enough acoustic sealant to ensure complete seal.

I don't think I would personally feel too comfortable in a room with 3 layers of drywall overhead mounted on ANYBODY's RC - I would personally tend more toward the heavier leaf of a 2-leaf wall or ceiling being mounted solid to the studs, and just putting two layers of 5/8 firecode sheet rock on the RC. It kind of depends on how much isolation you really need, and whether you can MATCH it with your glass, doors, HVAC, flanking noise, etc - if not, it's a moot point at best.

In any sound barrier, the primary task is getting two leaves of mass separated by one air space, with ZERO hard coupling between the two leaves. It helps if each leaf has different characteristics, since any frequency that excites BOTH leaves will pass thru with the least attenuation.

As always with RC, if you goof EVEN ONCE and put a screw thru the wallboard and into a wood stud, you will lower isolation by enough to almost totally NEGATE the use of RC at all. I've read of walls being tested and dis-assembled, only to find that as many as TWENTY screws were "shorting out" the RC - a good argument for marking stud/joist locations before putting up wallboard.

For insulation, knowing what I know now I'd use 2-3" 703 in between the frames, and fiberglas batts (possibly the newer "high density") slightly compressed against the panels, between the studs just like standard house construction, but with some compression (use next size thicker batts than stud cavity depth) - Alternately, if you can't find or afford 703 the standard house fiberglas batts are almost indistinguishable inside a wall, and may actually improve low frequency performance slightly.

With ANY sound wall construction, you want ZERO penetrations if possible, and definitely NO BACK TO BACK ones. Best electrical is surface mount, second best is offset boxes (by at least one cavity, preferably two) and total caulking of boxes.

If using surface mount wiremold, I'd put it just below any wall treatment so it almost disappears. I don't recall what the minimum height for outlets is to meet code, but you should conform to that whatever it is.

On the subject of glass between rooms, John will probably dis-agree strongly with this, but from 3-4 different sources I've seen, maintaining a wide air gap is at least as important as minimising flutter. If you could widen the gap between your walls at the window area, you could do both, but I wouldn't set up less than a minimum air gap in the window I described above that was less than 8 inches. If you figure that a slant of 1 inch in 10 will get you a 6 degree splay, that means that the width of a 2x4 (3.5") would be just right for a 36" glass. If you maintain a minimum 8" distance between glasses at the narrowest point, your wall (including wallboard and channel) would be a total of about 18" thick. (8" space, two 3.5" frames, 2.5" total wallboard, + at least 1/2" channel = 18" - more if you were to use the RSIC-1 clips and "hat" channel instead of RC.

First, for some background (lazy typist here) go to this thread

http://www.johnlsayers.com/phpBB2/viewt ... 86&start=0

and scroll down to the STC chart John posted on Mar 01 - look at the various wall constructions closely, then check the comments I made on Mar 17 as to WHY this is so.

Here are some general guidelines for soundproofing -

1. NEVER waste time/money/materials on construction methods that aren't proven to work, unless you have no life and just like to hurt yourself...

2. The best performance in a sound wall for the money, unless you can afford 3 foot thick concrete, will ALWAYS be a double-leaf wall with only ONE air space. Adding extra walls will usually make things WORSE, not better. (A "leaf" is however many layers of solid material that are layered together on one side of the frame. A standard, interior house partition with drywall on each side of 2x4's is a "double-leaf" wall.

3. This double leaf wall should almost NEVER have exactly the same construction on both sides - a wall transmits sound (bad) more efficiently at its RESONANT frequency. If both leaves of your wall are identical, then so will their resonant frequencies be identical. If that frequency is, say, 44 hZ, then that frequency will pass right through the wall with MUCH less attenuation than other frequencies. Not good.

4. For best performance, there should be no point where the inner and outer leaves of a wall have direct, hard contact with each other. This will allow sounds that impinge on the one leaf to directly vibrate the second leaf, and pfpfpfttt!!! Right on through... The way around this is separate frames, whether wood or steel studs. Drywall on the inside of the inner frame, and on the outside of the outer frame.

5. Things that improve Transmission Loss are: Mass of leaves (more is better, but DIFFERENT is better yet) - Distance between leaves (more is better - at normal wall thicknesses, even an extra inch can help) - Insulation - so far, it appears that 2.5 to 3 Pounds per Cubic Foot is the best overall density for in-wall insulation. This is why USG settled on 2.5 PCF for their Sound Attenuating Fire Blankets - see this link

http://www.usg.com/Design_Solutions/2_3 ... onperf.asp

That’s it for now, I hope this helps condense things a bit… Steve

I think everbody who used/uses this site should document or write up a post-project-review of some sorts. List all the materials, the sizes, the studios requirements, any photos, steps taken, advise, problems/solutions encountered, etc... What do you think? I know I will when it'a all done.

- Brad

- Brad


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Post by z60611 »

In all cases, ¼" spacers should be used under panels until fastened, then pull the spacers and caulk before repeating for the next layer.

I presume this 1/4" spacer is to give room to apply acoustic caulk. But I wonder if it's to allow mud between the gypsum.

So, are these 1/4" spacers:
a) to go along the floor only ?
b) to go around the wall (over the top, along the floor, along each side)?
c) to go around each gypsum panel ?

(BTW, excellent summary knightfly!)
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Post by knightfly »

Bob, there are two schools of thought I'm aware of as far as where to use spacers and caulk - one says do this all around the perimeter of each wall (not wall panel) - the logic here is to decouple each wall leaf from intersecting ones, which theoretically can improve TL overall - The other is to space at tops and bottoms, and treat corners as standard drywall practice. If I were to do that, the LEAST I'd do is use some of the newer, flexible plastic inside corner mold and NOT mud clear into the corners, leaving the flexible fold.

You can also do this keeping the 1/4" gaps in the corners, caulking per layer, and THEN putting the flex mold and finishing; still, be careful NOT to bridge between intersecting walls with mud, or you've negated the "flex" part.

Any gaps between panels within the plane of the wall, need to be mudded solid - you want a continuous mass with no breaks, so the mud makes sure there are no voids in a layer of mass.

Also, since sheet rock is tapered along its long dimension, you need to mud and tape joints between layers or you'll have a void in the mass where the taper gets covered by the next OFFSET layer (meaning no joints should be coincident from layer to layer)

Spacers make it easier to maintain the proper gap - too wide, caulk sags, bad seal - too narrow, caulk doesn't penetrate totally, bad seal. For spacers at wall intersections, just tape with masking tape to keep them in place - for ceiling/wall gaps, trimming the panels to dimension before screwing them in place negates the need for spacers. Gets kinda tricky if framing isn't square, though...

For partition walls, it's important to calculate ceiling joist sag to keep the wall from becoming load-bearing - otherwise, flanking can result transferring sound up through the wall frame and into structure, and ultimately into the rest of the building... Steve
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Re: Complete Section - (Temporary "FAQ")

Post by practiceshef »

One question, on a wall, how many layers can i hang from RC?
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Post by NickMac10 »

For insulation, knowing what I know now I'd use 2-3" 703 in between the frames, and fiberglas batts (possibly the newer "high density") slightly compressed against the panels, between the studs just like standard house construction, but with some compression (use next size thicker batts than stud cavity depth)

Apologies if this has been answered elsewhere (I've searched the stickies, but couldn't find it)...

Is this suggesting that two types of insulation are used behind the plasterboard sheets, in the stud frames?

I'm just about to buy my insulation, and am looking at Rockwool RW3 (which I understand is the UK's answer the OC 703)
Should I also be using an additional layer of fiberglass as well?

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Re: Complete Section - (Temporary "FAQ")

Post by Soundman2020 »

Should I also be using an additional layer of fiberglass as well?
Filling the cavity as much as possible will improve isolation, yes, but it does not need to be two different types. You can if you want, but it won't improve things. Just fill the cavity as much as you can afford to with the optimum insulation.

- Stuart -
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