SOUND-DEADENING BOARD

SOUND-DEADENING BOARD ??? good or waste of time. Didn't find any prices either.

'pends on who's calling what a "sound deadening board" , and where you wanna put it - got any more details, maybe a link? Steve

it's said to be lightweight, which would be real easy to handle. I'm still searching for the cost per 4 x 8 sheet. STC looks about the same as adding a resillient channel??? Sound board is a material made from compressed wood fibers (Sometimes called "construction panel") another similar trade name is "Homasote" ( Somewhat better, but considerably more expensive) and it functions as a thick paper cushion. http://www.fiberboard.org/sound_pubs.html http://www.fiberboard.org/sources.html Rockwool vs Cellulose???? http://www.comfortech.biz/stc_info.html also something to pass on :

It is important to distinguish acoustically effective resilient channels from hat channels, z-channels, and other lightweight metal furring systems that drywall contractors are used to installing. These other systems may resemble resilient channels, but they allow no movement and are simply too rigid to be effective. Only true resilient channels have any acoustical benefit.

now I'm lost............

Sound Board (fiberboard): Sound deadening fiberboard manufactured specifically for use in sound rated wall partition and floor/ceiling construction. When product installed with two ½" drywall sheets, they shall have a minimum Sound Transmission Classification of STC-46 or greater. Drywall, 5/8" x 4' x 8' $6.88 Sound Board (Wood Fiber Board), 1/2" x 4' x 8' $7.68

What you have posted is similar to celotex. On a wall The it is recommended 2 - 5/8" Sheest of drywall and the fibreboard sandwiched between them. Cellulose is denser, yes, but rockwool is MUCH easier to handle and the few db in difference will be negligible compared to the amount of work required to install the materials. Bryan Giles

OK, J, what you were looking at really IS sound board, as it's referred to normally - you never know, we get some strange materials brought up once in a while. Now, what's confusing you - specifically, what are you trying to do (and where) with the sound board? As Bryan brought up, the normal construction would be two layers of 5/8 sheet rock with a layer of Celotex/Homosote/Sound board between them. This gives a SLIGHT decoupling effect, but the main reason it works is that the sound now has to change "mediums" from air to sheet rock to Homosote to sheet rock to insulation/air, then repeat on the other side of the frame, to get through. Since sound loses some energy every time it changes direction (diffraction) and speed (different material) the net result is more Transmission Loss. Yeah, I try to mention once in a while about the different kinds of channel but maybe you missed it - there are special isolators available for the hat type channels, but if you can find RC-1 it's usually more reasonable cost-wise than going that route. Here's a link to hat channel isolators - http://www.acousticalsolutions.com/prod ... /clips.asp But, at $5 a pop if you're using wood studs on 24" centers, a 12 foot wall section 8 feet high with 2/3 layers on channel would cost about $100, just for the isolators!!! Then you have the cost of the hat channel on top of that. BTW, their recommendation for spacing of the resilient clips is 24" centers on top and bottom rows, then staggered on 48" centers thru the rest of the wall. Otherwise, if you stuck to 24" centers, the clips for an 8' x 12' section of wall would run about $240 just for clips. Sorry, kinda digressed there - J, if you could state specifically what you're trying to do (and maybe how and why) it would be easier to tackle than random bits and pieces... Steve

Sorry....Just trying to finish the studio(20x20x10 garage) and please the wife at the same time. For her new house she "NEEDS :roll: " a new sofa set, patio set, curtains, fence, etc, etc. I'll never save enough for those $5001.03 speaker cables we talked about. But anyway......I was just looking at combining materials to beef up STC. I already have the interior walls up. They're 2x4 wood studs, 24"o.c., except the wall in front of the garage door which is 2x6,none are load-bearing. I used the existing outer walls(rear of live booth and right CR wall) and rear inner wall(rear of vocal booth and closet). Using a sound meter I tested the STC of the existing walls, standard contruction: brick>shreadboard>2x4 framing>5/8 drywall. I cranked up the speakers to 100db and on the other side of the wall the meter read 60db. I could just hear the kick and bass from the sidewalk(14ft away). My home is on the corner so I only have one close neighbor to "Not Disturb". 8) If you remember, I changed the design to the one below which should work better for me in using existing walls, meaning..... I'm trying to use the washroom and master closet as a sort of sound lock :wink: with seems to work pretty good. My main concern is for a little more isolation with the existing outer walls(rear of live booth and right CR wall)and the ceiling. The ceiling/attic should be easy, it's 2x12 framing :?: .

OK, so what is already there, as far as the outer walls? Can you do a basic drawing of them, layer by layer, from the outer siding clear through to what you see from inside the studio, along with whatever text it takes to clarify? From your tests, it sounds like you're already close. Also, check out the ceiling construction pix on the SAE site again, to see if any of those will help... Steve

ok..I'll see if I can explain. if you look at the 2 pics I have converted a standard 20x20 garage. The washroom and walkin closet will go untouched, which should work as a sort of sound lock between the studio and the rest of the house. I have only used the the 20 x 20 ' area inside of the garage. north, east, and west existing walls are(gray in color): Brick + 2" air gap + 7/16" shrandboard(plywood) + 2x4" wood framing(with standard insulation) + 1/2" drywall. Standard home contruction. The north wall has the large 2 car garage door. the south existing wall: 1/2" drywall + 2x4" wood framing(with standard insulation) + 1/2" drywall. one side is garage and the other side is the washroom and walkin closet, then another standard wall. all the new inner walls(black in color) are framed with 2x4" wood, and that's as far as my wife let me make it :lol: ***I have framed a 2x6 wood wall in front of the garage door (north wall)...... I wanted it to look like a garage from the outside of the house. the existing ceiling: 1/2" drywall + 2x12" wood framing + attic(no insulation in attic over garage) I mostly listenback with headphones in the control rm when recording vocals, so I was looking for a simple when to finish the inner walls. I may need to add something to the wall east wall in the live rm and the west wall in the Control rm to help with STC. My only close neighbor is to the right of the control rm

OK, I think I've got the drift now - First, the door(s) on the right are most likely going to be a weak spot unless you've already spend a few hundred on each one for custom seals and drop thresholds, something like this - http://www.acousticalsolutions.com/prod ... l_kits.asp The next weakness would be the standard construction - those brick walls need weep holes for moisture control, so the brick is almost not there acoustically. This means you have effectively a 2-leaf wall consisting of the Strandboard outside, the standard insulation, and the 1/2" sheet rock inside. If that wall were acoustically caulked, at least on the inside, you'd be lucky to have an STC of around 35. If you're losing 40 dB as is, count your blessings. Just adding more layers of sheet rock on the inside will probably frustrate you. With 5/8" rock, you might get 3-4 dB for the first additional layer, then 2-3 dB for the next - that amount of improvement might just be enough, but if it doesn't quite make it you're screwed. You can get about 9 dB improvement by doing the following: I know you don't want to hear this, but the only way you're going to get much of an improvement in wall isolation is to REMOVE that inner layer of sheet rock, get Resilient Channel onto those studs, or if you had the room, put a completely separate steel stud frame inside with more insulation and at least two layers of sheet rock on the inner side of that frame. With resilient channel on your existing frame (removing inner wallboard first) then adding two layers of 5/8" sheet rock, your walls should no longer be the weak link. As for the ceiling, again the only way for serious improvement is to remove the existing wallboard and put RC up, adding a couple layers of 5/8" sheet rock over that. You could just add a layer to what you've got, blow in cellulose insulation (10 inches if possible) and put sound board with plywood above it on the tops of the joists, but the problem here will be flanking noise. Each of those 2x12's is exposed to sound at the ends, tied into (probably) a fascia board which will transmit sound along the joists allowing it to radiate thru the solid connected sheet rock and into/out of your studio. You really need to break that path, and an inner leaf floated on RC is about the only practical way I know of. One way to find out just how much more isolation you REALLY need, is to have a helper in the room to adjust the volume while you talk to them from outside with a cell phone and your SPL meter - have them turn down the volume til you are happy with the level outside, then measure it there, measure it inside, see how much louder you want to be able to have it inside, and that's how much improvement you need to achieve minimum. If that difference is only 4-5 dB, I'd just put a couple layers of sheet rock on outer walls and ceilings, caulk well, and call it good... Steve

One way to find out just how much more isolation you REALLY need, is to have a helper in the room to adjust the volume while you talk to them from outside with a cell phone and your SPL meter - have them turn down the volume til you are happy with the level outside, then measure it there, measure it inside, see how much louder you want to be able to have it inside, and that's how much improvement you need

:D never thought about this, tried it! I need(want) about another 5db of noise redution. You're the man! one more question.....with adding a few sheets of drywall..... would a sandwich work better? meaning.... drywall + sound board + drywall (all glued together) or just different thicknesses of drywall? Thanks.....I'm off tto home depot and lowes 8) P.S. very strange idea :roll: ....I was in a small studio earlier today that used 5/8" drywall + 1 1/2" styrofoam sheets on each side of 2x4 framing(with insulation). It really works. weird right? They got the styrofoam from a company that makes real large refrigirators.

J, the sandwich would work better, any time you can "confuse" the sound it has a harder time getting through. Gypsum has a sound propagation speed of about 22,000 feet per second, solid fir is about 12,000, and air is 1130. Each time the sound has to change speeds, it also gets diffracted (bent) then bent back again to the original course but offset - going from air to gypsum to MDF or celotex to gypsum to insulated air, then thru the other half of the wall, takes a lot out of the sound (that's a GOOD thing) For your walls, adding sheet rock/sound board/sheet rock should give you the 5-6 dB you need. As for fastening, you shouldn't glue the new layers on because it will make them act as one panel. That can be ok in some ways, because it lowers the resonant frequency of the panel and makes it harder for lows to get through (as long as they aren't at the resonant frequency) - however, using screws to attach the separate panels lets each act at its own resonant frequency, which further blocks sound (it passes thru more easily at resonance) by making the wall have multiple resonant frequencies, so no ONE frequency finds an easy path through. On the styrofoam thing - refrigerators use closed cell foam, which has very little acoustic use other than a slight attenuation. I think the main thing helping those walls out is the extra effective 3" of distance between leaves caused by those layers of foam under the wallboard. I once did a (sloppy) test of a refrigerator to see if one could be used for a computer silencing box - I put a ghetto blaster in the frig, cranked it up to 90 dB on my SLM, then closed the door - it dropped by about 36 dB... The only thing that stopped me from following thru was that all the frig's I found were either too big or too small for my control room. It did tell me that magnetic seals work really well around doors, and then (just my luck) Stanley decided to discontinue their magnetic sealed prehung exterior doors in favor of a less effective one... (sigh) Anyway, glad you only needed about 5 dB, that's certainly doable without major re-construction... Steve

Thanks Steve, You should see the smile on my face! :D Now I can use the extra cash on those $5001.03 cables. I'll take some photos along the way. I know a friend of mine that used 3 layers of the black asphate sheating on metal studs(and no drywall) that worked. The stuff is like soft particle board, lightweight, and about $4 a sheet(4x8). But I think it's flamable. :roll:

Don't even THINK of doing that - the 5/8" firecode sheetrock is only about $6 a sheet, more mass, and NOT flammable. Insurance doesn't make kids not miss their dad, assuming they survive the fire. PLEASE READ MY ANNOUNCEMENT AT TOP OF THE FORUM... Steve

Just out of curiosity, I'm new to this forum: I didn't get how you shut the garage door, if it is just a wood frame partition it could be your weak spot, you should increase its mass as much as possible... masonry would be the best! Cheers, Lorenzo

Steve, Last night (July 30th) you quoted the USG manual to state that gluing sheets together is the way to go because, as you said

A wood-stud partition with 1/2-in. USG Sound Deadening Board base layer and 5/8-in. SHEETROCK Gypsum Panel face layer laminated to each side will provide STC 49. The same construction with SHEETROCK nail-applied will test only STC 36

You also said to ignore previous posts. Does that mean you no longer believe this is true, which you wrote July 28th:

As for fastening, you shouldn't glue the new layers on because it will make them act as one panel. That can be ok in some ways, because it lowers the resonant frequency of the panel and makes it harder for lows to get through (as long as they aren't at the resonant frequency) - however, using screws to attach the separate panels lets each act at its own resonant frequency, which further blocks sound (it passes thru more easily at resonance) by making the wall have multiple resonant frequencies, so no ONE frequency finds an easy path through.

This is an important issue, so I'd like to focus on it for a moment. Your quote from the USG manual, the way I read it, does not really say that gluing is always better than using screws. In this case it is, and it's clear to see why. The Sound Deadening Board is serving the same role in this specific type of construction as does resilient channel, breaking the path of conduction. But if you are already using resilient channel to do so, or if you are using a double stud-frame wall with separate sole plates, and those separate sole plates are resting on a couple layers of vinyl barrier or thicker closed cell foam or some other viscoelastic material, then you have already broken the path of conduction. So the question is, if you have already interrupted that direct path, what's the best way to mount additional gypsum panels? And we should probably be asking for what purpose, for that can make a huge difference as well. If we're shooting for a general increase in transmission loss as defined by STC value, that's one thing. But if we are most concerned about blocking more low frequencies, then the STC values may lead us off in the wrong direction. Here's a good explanation of exactly what STC is: http://www.sota.ca/stc_info.htm Any more light that you can shed on this tricky issue would be most helpful. (Heck, you're already extremely helpful...) Lee

Lee, I'm still working this out in my head as well - first, I know exactly what STC is, and that's part of what's confusing when picking wall designs for studios instead of "living space" - although any more, what with home entertainment centers and subwoofers, I would hope that eventually ALL building criteria would move to MTC ratings. Sure would make things simpler for us, huh? So far, my interpretation of the USG info is (subject to change, as I learn/think more) Solid fasteners thru a second/third layer of paneling (any kind) into WOOD studs are a big no-no. Solid fasteners thru a second/third layer of paneling into RC are (maybe) OK, since the decoupling takes place because of the RC. Just don't "short out" the RC with a mis-placed, too-long screw. Solid fasteners thru a second/third layer of paneling into STEEL studs are (again, MAYBE) OK, since the steel studs are the decoupling factor here. Need to study ALL these factors a lot more. There are three basic types of screws for wallboard construction - don't EVER use the wrong one. Type W for going into wood studs, Type S for going into Steel studs or RC, and Type G for laminating panels WITHOUT having to put screws thru multi-panels into WOOD studs. The easy way to remember these (probably the reason for the designation, duh) is W for wood, S for steel, and G for gypsum. Adhesives for laminating seem to be just the normal joint compounds, but they appear to assume you're using the Type G screws to keep the panels from slipping, and to make intimate contact between panels (layers, that is) The USG manual also state NOT to use less than 1/2" for a first layer if using the Type G screws, and NOT to get the panel wet with glue for any extended length of time prior to assembling, or they won't hold properly. Part of the confusion in my mind was caused by "learned" comments regarding the "causing all panels to act as one is a BAD thing" - Considering that other statements regarding good low frequency isolation stated that "lowering the resonant freq by adding mass" should be done for MTC improvements - guess what, this is EXACTLY what happens when you laminate multi-layers together - lowered resonant frequency... My goal here is to (at least) work out the ideal combinations of materials/construction to build a quality "music wall" - one that can handle ALL frequencies equally well, for the least amount of money. I know from other reading that it's important to BALANCE the TL, or what little sound DOES get thru will be MORE intrusive than it otherwise would, because it sounds "funny". This means to me that you can't get away with "brute force bass reduction" unless you apply other principles to get equal "brute force mid/high reduction" - in fact, brute force doesn't even seem to work AT ALL unless you go grossly over-budget with double 6 foot thick concrete walls separated by 32 foot air spaces filled with insulation/sand/lead, etc... Everybody, please don't jump on me with a thousand questions about this next statement, because I'm still looking for answers myself - but, one of the ideas I'm researching is whether the frequency balance of isolation values would be negatively impacted by putting all the layers of mass (except ONE) in a "mass-spring-mass) wall, in JUST THE OUTER LEAF. If this didn't cause problems with mids getting through, the wall would still have dissimilar resonances in the two leaves, good LF rejection due to the mass of the outer leaf, with the ADDED BONUS of keeping the inside leaf thin enough to add significant BASS TRAPPING thru panel absorber physics. If you built the wall so that there was intimate contact between insulation and the INNER panel, the damping would broaden the Q and improve the TL. This concept, if it would work, should lessen the need for gross amounts of bass trapping. Just a thought, I'm sure it's going to take some time to figure out (especially from a self-taught late-bloomer like myself) I'm probably forgetting a few dozen things along these lines, but am planning a more thorough attack on this ASAP. Everyone feel free to chip in with ideas, but please don't ask me for drawings of the "ultimate wall" just yet (if ever) - I'll share more when I actually HAVE more... Steve

Steve, this will definitely interest you. Here's a discussion amongs acousticians on this very subject: http://www.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=3D6062B3.3050803%40worldnet.att.net&rnum=7&prev=/groups%3Fas_epq%3Dscrew%26safe%3Dimages%26ie%3DUTF-8%26oe%3DUTF-8%26as_uauthors%3Dangelo%2520campanella%26lr%3D%26hl%3Den

Lee, thanks very much for that interesting link, some definite "heavies" in conflab there. I must be getting closer to the "holy grail" of understanding, nothing glaring jumped out at me on a brief scan - copied the whole thing to Word and will dig deeper as I can. Apparently I'm not the only one confused by the "glue/don't glue" smoke screen... BTW, does anyone YET know WTF a "Camden" really is???!?

knightfly wrote:

Don't even THINK of doing that - the 5/8" firecode sheetrock is only about $6 a sheet, more mass, and NOT flammable. Insurance doesn't make kids not miss their dad, assuming they survive the fire. PLEASE READ MY ANNOUNCEMENT AT TOP OF THE FORUM... Steve

Ya.. that's what I told my friend. Fire would not be a good thing..........looking where I work professionally http://www.nofd.com I also watched "Marvel Mysteries" on the HIstory Channel(Cox Cable TV) about "adhesives". Did u know that Duck Tape was designed for the military to be used a a waterproof tape for ammo boxes....."Quack - Quack" :lol: But the military personal learned that it worked for all types of things. Man. it's funny how things start off. First time seeing "Liquid Nails"(a glue the acts as a nail). They said that adhesives will replace nails and screws in the future. I'll try to watch that show again because I missed the first few minutes.

Just out of curiosity, I'm new to this forum: I didn't get how you shut the garage door, if it is just a wood frame partition it could be your weak spot, you should increase its mass as much as possible... masonry would be the best! Cheers, Lorenzo

Well Lo, the garage door is closed just like it would be normally, and can't be opened because I took the tracks and door-openner down from the ceiling and filled all leaks. I will build(framing done) the 6" wood frame wall 6 inches away from the door: drywall+soundboard+2x6 wood(insulated) + soundboard + drywall. I'm looking at using RC 's(instead of sound board) if it saves money. Hey......... :idea: wonder what a STC the wall 6" wall will have if a 4" wall is 49???????? :lol: maybe just a few db.

"adhesives will replace nails and screws in the future" - How 'bout right NOW? from what I've read (not much, really) if you've flown commercially in the last few years you were being held up by glue - at first, that seems really scary - but when you think about it, if a glue is the right kind for the materials, it's not all that different from welded metal - and that's perfectly fine with almost everybody... " I took the tracks and door-openner down from the ceiling and filled all leaks. I will build(framing done) the 6" wood frame wall 6 inches away from the door: drywall+soundboard+2x6 wood(insulated) + soundboard + drywall. I'm looking at using RC 's(instead of sound board) if it saves money. Hey......... wonder what a STC the wall 6" wall will have if a 4" wall is 49???????? maybe just a few db" - J, be sure and thoroughly read that thread Lee linked to - I can see at least 3 mistakes you're about to make that will cost you both money and performance. 1. You should never (in any reasonable cost wall) use more than ONE air space. Insulation is considered an air space in this case. Sooo, if you've SEALED your garage door, that is your first MASS in your mass-spring-mass wall. If it's not heavy enough, you should either add more mass, or ventilate it so it's not there acoustically. 2. The USG manual is very clear on this - you should NOT use through-fasteners into WOOD studs for any but the FIRST layer. Where the problem would come up in your proposed construction is that Soundboard (celotex/homosote) is NOT STRONG ENOUGH to allow Type G laminating screws to hold for fastening a layer of gypsum over sound board, and there should be ZERO hard fasteners going through both layers into WOOD studs. 3. The subject of Lee's link is Coincidence Dips - in plain english, this means that you should NEVER build a wall that has both leaves built the same way. Even if you put one leaf on RC, the Coincidence frequency will be nearly the same as the other, solidly mounted side. So, if you were to put gypsum over sound board (not a good idea, period) on ONE side of the frame, then the OTHER side of the frame should have a DIFFERENT construction - say, 3 different thicknesses of gypsum wallboard, or two different thicknesses of wallboard with a layer of sound board sandwiched between. For what you're doing, my recommendation would be to "un-seal" that garage door (because it will be a real bitch to add mass to it, unless it's already one piece and smooth) and then build a mass-spring-mass wall (your 2x6 frame) - From what I understand right now, you would get really good isolation by putting at least two different thicknesses of sheet rock on the outside (next to the garage door), solid onto the frame (I hope you haven't fastened the frame in place yet) with the second layer laminated (check out my stickys on the USG manual, the page #'s are there) - then, tip the wall up into a pre-laid double bead of acoustic sealant (use Sill Seal first if the floor is uneven) - once the wall is up, then comes insulation and the inner layer. If you can afford it, what I'd do for insulation is to use a layer of 3-1/2" fiberglas batt pushed into the cavity with the un-faced side away from you, toward the outer leaf, then 2" 703 or mineral wool semi-rigid, and finally another layer of standard 3-1/2" fiberglas batt (face out), all held in place by RC (read the USG manual, search on "resilient", it shows you exactly how to install RC) - The insulation will not want to fit the cavities very easily, because you're trying to put 9" of insulation into a 5.5" cavity - my reason for this is to provide damping for the two wall leaves, which is widely believed to broaden the "Coincidence Dip", thereby reducing sound transmission at or near those frequencies. Then, put a layer of 5/8" wallboard on the RC, and follow that with a layer of Soundboard and a layer of 1/2" wallboard. These, because they are on RC, can all be screwed to the RC (mark where the studs are, and AVOID that area like the PLAGUE when attaching to the RC.) This leaf of the wall should be NOT glued, only screwed to the RC - this retains the individual coincidence frequencies (supposedly) of each differing layer, so there is no ONE frequency that is resonant to all components of the wall. The flexing of the RC keeps through-fasteners from causing flanking loss. With the outer side of the wall LAMINATED, that will lower the coincidence frequency of that side to below ANY of the inner layers and should help a lot with low frequencies. Be sure to follow USG's recommendation of spacing the wallboard off the floor on the side with the RC, then caulking thoroughly with acoustic sealant - If you're using multi-layer on the intersecting walls, alternate the layers so you have a "Z" joint at the intersection - caulk each successive joint before putting the next layer up. Use 1/8" removable spacers at the floor, then once the layers are all up pull the spacers and caulk. BTW, you're right about 6" over 4" (really 5.5 vs 3.5", til you add RC on one side) it will (with proper insulation) probably add only about 2 dB, but that's as much as you'd get from a third layer of wallboard, so why not? Do yourself a big favor, and don't finish that wall without asking about any changes you plan - what tends to seem "right" for sound proofing, usually ISN'T... Steve

Apparently a Camden is just a stud wall, named after the first place it was built over there. Let's see if I've got this right: Whether you glue or whether you screw depends on what you want to do. To block more bass, glue. To block more evenly across the entire frequency spectrum, screw. Why? Mass law and coincidence dip. You can predict that a certain mass will block a certain amount of sound at various frequencies. Theoretically the mass law works on a straight line, blocking less in the bass range, more in the mids, and still more in the highs, EXCEPT at the panel's own resonant frequency, at which more sound is let through. The thinner the panel, the higher the resonant frequency. (The resonant frequency of 5/8" sheetrock is about 2500 Hz, and of 1/2" is something like 3200.) So you combine several panels of different density/resonant frequencies so that together somebody in the bunch is covering the acoustic holes. If you're stuck with using all panels of the same thickness, and you screw them together, you've got the same hole at the same range in the frequency spectrum. In that case you could glue the panels together, making them act as one larger panel. There will still be an acoustic hole at some frequency, but it will now be lower because larger masses resonate at a lower frequency. You have to decide whether that's good or not. Other complicating factors: stiffening the wall with added bracing will damp the wall's vibration but will also raise the resonant frequency - it's a trade-off. Again, when you glue several panels together, the glue tends to make the whole thing work as one, but the total performance becomes harder to predict, as it depends on the nature of each panel and the nature of the glue itself. I've also read that you HAVE to use at least a couple of screws per panel even with glue for stability and security, or else the damn thing is just going to fall off over time. Just looking at STC ratings of various walls obviously doesn't tell you enough to help you decide. That's why good studio builders like John Sayers and Rod Gervais with tried and true experience that goes way beyond the theory are so essential in leading us out of the darkness. Lee

put 9" of insulation into a 5.5" cavity - my reason for this is to provide damping for the two wall leaves,

Steve, you've been giving great advice - with the possible exception of this point. Angelo Campanella has a mantra of "fill but don't overstuff". I'd feel comfy with 6.5" of batt insulation in 5.5" space, though. I'm guessing that the reason for their admonition is that if you squeeze the batts too tight, they no longer absorb as well, i.e. they don't turn the wave energy into heat energy. Too stuffed and the energy may just transmit more than you want from one side to the other. It's a good intention to want the insulation to serve the purpose of damping as well, but it's just a question of degree to get it right. One thing I've learned from all this reading is that the air space itself is very very important. The more air you can get between your two leaves, the better. One of the reasons why the RSIC-1 clips give you 7 STC points more than standard 2x4 walls with resilient channel has little to do with the materials of the clip itself, but rather that they add over an inch to the air gap, and make room for R-19 instead of R-13. Lee

Lee, the things we both believe to be true are apparently the same right down the line - as for the squished insulation, if you subtract the 2" of basically "non-squishable" 703 from the stated wall, you have 4" of space left - cut that in half, and you have 2" into which to stuff 3-1/2" of fiberglas, which to me isn't a very tight fit. OC makes their 700 series panels in a version that's purposely too wide for a stud cavity, just so they will bow enough to stay firmly in contact with the wall panels - If they can do that with rigid, it wouldn't seem (to me, anyway) that 3-1/2" into 2" would be too tight. I agree completely that the air space is more important than generally thought - and maybe when I actually started trying to cram that much insulation into a wall I'd reconsider. Right now, it just doesn't seem like it would be tight enough to be detrimental... Steve

one of the ideas I'm researching is whether the frequency balance of isolation values would be negatively impacted by putting all the layers of mass (except ONE) in a "mass-spring-mass) wall, in JUST THE OUTER LEAF. If this didn't cause problems with mids getting through, the wall would still have dissimilar resonances in the two leaves, good LF rejection due to the mass of the outer leaf, with the ADDED BONUS of keeping the inside leaf thin enough to add significant BASS TRAPPING thru panel absorber physics.

Interesting idea, Steve. Let's consider: A standard gypsum wall built 16 OC absorbs .29 of 125 Hz, i.e. there's 29% less bass in the room at that point. Where does it go? Either it's turned completely into heat by the flexing of the gypsum panel, or some of it passes right into the wall cavity. (Common experience indicates the latter.) What happens to it then, and is that what you want? Lee