Air Cavity??

I'm building a double wall with an air gap in between. Does the size of the air gap matter? What's minimum? Do I have to put insulation in the gap or will putting it in the studs and leaving the air gap be fine? What would be an approximate STC rating for a wall like this? It's double 75mm stud walls with the air gap. 75mm insulation and one layer of 16mm plasterboard on either side. What's an ideal or realistic STC rating to keep most sound out and bearable for those in the rest of the house? Thanks James

Check this chart out James http://www.saecollege.de/reference_mate ... 0Chart.htm cheers John

Is the staggered stud wall as good as a double wall? What would the STC of a double wall be? Do I need to fill the air cavity with insulation even though i've got it in the studs? Thanks James

check this. cheers john

Here's another chart for you relative to your question

Ok thanks. That's really helpful. One last question, If I put two layers of plasterboard, is it better to put different thicknesses or two of the same? I say this because I remember reading that sound doesn't like going through different thicknesses or densities. Thanks again James

yes that's sorrta correct james, it really prefers a different medium more than a different thickness. i.e drywall - mdf - drywall. whaqt thickness of drywall were you intending? cheers john

To continue with your idea of using a different medium, e.g. drywall - MDF, how well does particle board work in place of MDF? I can get 4' x 8' sheets of 3/4" particle board easily here for something like $18 a sheet. Does particle board work well inside a wall? Is it anything like that "canite" product you show in your insulation hanger design?

particle board is more like mdf than soft fibreboard (canite) and yes you can use particle board as a wall treatment- make sure you seal the joins though. cheers john

Here are a couple more extremely informative links, both from US Gypsum - they don't talk about materials other than Gyp-rock, alias Sheet-rock, alias gypsum wallboard, etc, but they cover nearly every type of framing method known to man, with several versions STC rated and some even (gasp) MTC rated... http://www.usg.com/Design_Solutions/2_3 ... ontent.asp (Be prepared for this - as a Word document, it was about 125 pages - For this next link, you can either view online or download the pdf file - I had problems downloading, but if you start reading online, then click the "save" icon, it will download it to your drive for offline use. (At least it worked that way for me) http://www.usg.com/Expert_Advice/const_ ... .asp?menu= The first link had some insight on stairwell building, (such as how NOT to attach) for those of you who have upstairs studios - all in all, some serious reading... Steve

James, your original question about the width of air gap should be answered here - Think of the air between wall surfaces as a spring, having a fixed rate per length - the longer the length, the softer the spring, hence the more de-coupling between surfaces. The more decoupling, the less transmission... Just an observation, open to comments - Did anybody else notice that in the chart of wall construction vs. STC ratings, posted by John above, that the chart seems to support Eric DeSart's statement that multiple leaf walls (beyond two) actually WORSEN the STC rating? Note that the transition from one normal wall to two normal walls ONLY increases the STC from 36 to only 40. (Seems like a small gain for TWICE the materials) - Then, removing one inner layer (which changes the wall from quad-leaf to triple) increases STC to 50. Next, removing the other inner layer (changing the wall to a double leaf with only ONE air space) increases the STC by 7, to STC 57. Finally, replacing the mass that was removed in the earlier steps, but as a part of the only two leaves remaining, further increases the STC to 63. In my limited understanding of "Air as a spring" theory, this would make sense (decoupling-wise) when you look at one long spring, vs. 3 shorter springs of the same diameter, etc - the three short springs (in series) would have a higher spring rate since each is stiffer. Anyway, somebody wanna blow the smoke away here? Or is it all "Clear as Muddd"... Steve

Hi.. I´m buiding my recording studio... so I want to "see" this configuration with all of you... to accept agrees or comments (good or bad). Left to right (materials) Plasterboard (9.5mm) + Glasswool (50mm) + Concrete Block (200mm) + Air Space (100mm) + Glasswool (50mm - bTW concrete walls) + Concrete Block (200mm) + Glasswool (50mm) + Plasterboard (9.5mm)... How much STC can I get with this configuration... I think thay maybe It´ll be better to replace a Plasterboard for another with more thickness (15mm). Thanks a lot!Fernando Musarra AWS

Fernando, there are several problems I see with your proposed construction - First, unless concrete block construction is much cheaper in Argentina than it is here in the US, there are much less expensive ways to achieve the same or better sound isolation. Second, please re-read John's post of Mar. 2, and mine of Mar. 17, in this thread - the comment I referred to by Eric De Sart, addresses the physics of "getting the most for your money", so to speak - Mr. DeSart is one of the moderators of studiotips.com, and a degreed acoustician, which is only one of the reasons I have a hard time understanding some of his comments, but here goes - When building a wall for sound control, it (apparently) works best if you concentrate all the mass in only two leaves (layers) with only one air space between them. This can be seen in the diagram John posted about STC values of different wall construction, posted on Mar.2 (or Mar.3, depending on your time zone) - read my post of Mar.17 for clarification. Your proposed wall construction, if I understand correctly, would have a layer of thin wallboard, then an airspace filled with insulation (but still, an air space) then a concrete block wall (filled or hollow?) then another air space, then another concrete block wall, then another air space filled with insulation, then another thin sheet of wallboard. If concrete block construction is ridiculously cheap in Argentina, you could improve the STC of your wall by probably 15-20 points just by placing the wallboard directly on the outer sides of both concrete block walls and placing the insulation BETWEEN the block walls - The result would be even better if you filled the blocks with well-rodded concrete. Perhaps a better way, if you intend on having an exterior wall that is concrete block, would be to put up only one block wall, fill the holes with concrete (or at least, sand), maybe stucco the outside, then attach either wood or metal studs to the inside of the concrete vertically, 24" apart, then Resilient Channel horizontally per the USGypsum links I posted, and then two layers of 5/8 (15mm) wallboard on the RC, using real Acoustic sealant for caulk. Again, I don't have a clue what materials are going for in Argentina, but at the very least you should use a construction that has only ONE air space between TWO layers of mass. Another thing you didn't mention, is what is the ambient noise level where you're planning your studio? If you're not planning on using the studio for hire, and there are quiet times available for sensitive recordings, you could be wasting a lot of money that could go for equipment. Any professional studios I've been aware of, have always had a study done at the proposed location that covers at least a week, usually more like a month - the actual sound levels at the site are recorded by the person doing the study, then analyzed to see what kind of construction is necessary in order to achieve the desired Noise Criteria curves. I've talked to people who live out in the country far enough that they actually do some recordings using only a tent to keep the gear from getting wet - granted, this is rare - I only mention it to help make the previous point - On the other hand, if you have close neighbors and they are picky and you intend to record acoustic drumkits at two AM, you will need all the isolation you can get. Under those conditions, I'd shoot for an STC of at least 75, hoping it would be adequate. Keep in mind, that STC (Sound Transmission Class) only covers frequencies down to 125 hZ - what this means is that two walls, both rated for STC 60, may have quite different amounts of attenuation down at 30 hZ with a vigorously applied kick drum. For a better idea of what kind of isolation a recording studio needs, we refer to MTC, or Music(Machinery) Transmission Class - these numbers are universally less optimistic than STC, since it's harder to stop low frequencies. For exterior walls, if you want serious isolation, you need to follow the "two layers, one airspace" idea no matter what materials you use. And, if one of those layers can flex a little, it will make a big improvement in performance. Also, doors are the weak link in any partition, so plan for a double-door airlock. Finally, the rule of thumb I follow in any sound proofing plan is this - If it won't float, it won't stop sound. (Exceptions would be well-designed, baffled and absorbed air passages) If I mis-understood your proposed construction, feel free to start over - preferably with some kind of drawing to clarify... Steve

hello! Well... you really undertand me.. that was what I tried to explain... First, the Concret Block 20x20x40cm is about $1 (argentine pesos = u$s 0.35)... It´s very cheap compare with a gypsum board $10m2 (u$s 3.22)! So... in resume... It´s convening that my material aplication would be gypsum (9mm) + Concrete (200m) + Air filled with insulation + Concrete (200) + gypsum (9mm).. is this ok? In argentine the prefer materials for construction are concrete blocks, gypsum board (9/15/18mm), vynil rubber, wood, plasterboard, glass wool, glass fiber... etc. We already think about what kind of costumers and aplications will going to do, it´s a comercial studio... So, figure out... drum kit at 125/130 db... (heavy metal or new metal mostly), loud guitars, etc. I want to achive something like 29/30 NC (if it´s possible)... but that have to be tested once the studio is done. For the neighbors there´s no problem... all the walls are separated from the original wall and roof... I wanna try to get rid of the mechanical transmission... (if it´s posible too!). When you refer to "flex" a little a material... you mean that make it curve with a few degrees ? My wall is going to have 210mm of thickness... this is enought space to put a door frame for two doors? I imagine that this doors are going to be very thin... but with a lot of density/m3... or not? Well Steve... I really preciate your help in this project, for me it´s a honor to take your knowleadges and put in practice! Best Wishes! Fernando Musarra AWS

Fernando, If I'm following your prices right you can build a 4 foot by 8 foot section of block wall for about $12.60 US - where a single layer of sheet rock would be $3.22 US, since it is a 4 foot by 8 foot sheet, correct? This would mean that two layers of sheet rock would cost $6.44 US, unless that price was for the 9mm stuff - I'd not use any less than 15 mm personally though. In your case, if you're into headbanger volumes, you would be better off with a single concrete block wall, adding Resilient channel and two layers of 15 mm gyp-board - I'd make sure to fill the blocks with either sand or well-compacted (rodded) concrete, it will make several dB difference. Also, here are some other factors: bare, non-filled concrete block in 8", or 20 cm, typically has an STC rating of 45. Putting two coats of paint on each side raises it to STC 48. Plastering both sides raises the STC to 56, and although I don't have figures to back it up I would estimate that putting two layers of 15 mm gyp-board on just one side, over RC, would raise it to around STC 62 or thereabouts. Keep in mind that 32 square feet of block wall will cost about $12.60 US, where 32 square feet of double-layer 15mm gyp-board would cost the price of two sheets, or around $11 US. Add the cost of the RC-1, which here runs about $1.80 US per 12 foot length, and you're looking at about $27 US per 32 square feet of wall, with an STC of around 60+... Those costs do NOT include fasteners, tape and texture, caulking or labor obviously. Don't try to save costs with cheap caulk - even if you have to import it, get true Acoustic-rated, non-hardening caulk. Remember, a 1/16" crack 10 feet long in this particular wall will lower your STC by at least 15 points, maybe more. As to doors, I read recently of a test where a 60 dB wall (tested) was cut and two standard, solid-core, exterior doors were installed, and CAULKED SHUT so that they weren't doors at all - it still lowered the test results to STC 44 ! Reading that just finished convincing me that sound-lock doors are the only way to go. Don't try to put two doors that close together, you're better off with a vestibule with two doors, preferable NOT parallel to each other, and with some kind of absorption/trapping in the vestibule. My comment about flexing did NOT refer to INSTALLING a panel with a built-in flex, but to mount one half (say, the gyp-board side) of a wall on Resilient Channel, so that the wall will be allowed to flex when a sound wave hits it. This creates a natural bass-trap effect, and improves the STC of the wall by about 4-6 dB compared to solid mounting. The downside of making two RIGID walls, is that you will need lots more bass trapping inside the rooms to compensate for the lack of "natural" bass trapping afforded by flexible walls. This would probably make the "one block, one gyp-board" approach much less costly in the overall picture. I hope this helps... Steve

Hi Steve, Of course that it helps… I really appreciate your helpful tips… I´m a little confuse about the “sheet rock”… do you have a picture or some info about the characteristics of this material? Maybe here in Argentina have another name… My basic idea is to separate Control Room for Recording Room… so I don´t want to build only one wall for connect the two rooms. The tip of the well-compacted (rodded) concrete has been taken!!! Wow… 62 STC is a lot! But you´re talking about only one wall… right? Where can I get Acoustic-rated, non-hardening caulk over the internet? The door idea is really great, we (my brother & I) have think about it, talking about cost and performance, and we get the same conclusion… Sound-lock for our studio… about the separation between doors… 15 cm is ok? More, less? I really don´t know what resilent channel are? I have a little clue… but I don´t have the picture in my head… so… is ok if I install RC in two walls that joint together…(north wall & east wall)? I really get your point… but I´m between the sword and the wall… or I get good STC (a lot of mass) or I get good bass trapping... I can say that the sizes of the room maybe help me with this problem of low frequency control (room modals)… of course the room aren´t big enough to control them… but I think that we can deal with this… what do you think about it? Well Steve… I don´t have enough words to express my appreciation for your professional help!!! REALLY THANKS! At your service! Fernando Musarra AWS

Some other names I'm aware of for sheet rock - Gyp-rock, Gypsum Wallboard, (in some areas) Plasterboard - it is a compressed white (gypsum) powder, covered and contained by heavy paper on both sides, in the US the standard sizes are 4' x 8' and 4' x 12', in thicknesses from 3/8" up to at least 3/4", with 1/2" and 5/8" being the most common. US price for 5/8" 4 x 8 panels runs around $5 per sheet. It is heavy, and hard to beat for sound control at a reasonable cost. About the one wall between two rooms - read back through this thread to my comments of mar. 17 - more is sometimes less. check the STC chart above. The STC 62 was an estimate of one filled block wall with two layers of 5/8" (15mm) gypsum wallboard on resilient channel. If you were to build two of these walls between rooms, you would probably either not gain anything or at most maybe 2-3 dB. It would make more sense to build a wall such as the STC-63 example in the chart above, since it would be tons lighter and just as effective as the concrete block - it would also be easier to modify should you change your mind at a later date. At this time, I have no idea where on the Internet you can buy real Acoustic caulk - if anyone does, please post in the Building Materials section for all to see. Sound lock doors are better when farther apart, and all surfaces between the two doors should be absorbed. Also, the two doors should not be parallel to each other, which would require a deeper area between them. Ideally, if the sound lock was a 4-sided enclosure, the doors should NOT be across from each other. Parallel walls are best avoided too, so there is no single frequency that can excite a standing wave within the sound lock. So, 15 cm is kind of small for the best case since the lock would need to have all dimensions large enough to mount a door, which would mean more like a minimum of 100 cm if the doors are to be 36", or 915mm. Resilient Channel - read this short thread - http://www.johnlsayers.com/phpBB2/viewtopic.php?t=122 As to using RC in two adjoining walls, sure - One of the two links to US Gypsum I posted earlier in this thread has recommendations as to how to do this - basically, you stop the RC about an inch short of the adjoining wall, and run both layers of wallboard beyond the intersecting RC, then attach the layers of wallboard to the remaining wall leaving about 5-6 mm gap from the edge of the wallboard to the surface of the adjoining wallboard, making sure to thoroughly caulk EACH LAYER joint completely. Another school of thought on adjoining wall construction is to alternate layers of wallboard so that the corner joint is rabbeted, caulking as you go - the downside of this is that the two wall surfaces aren't as isolated from each other, but the joint itself is better performance. Your comment - "I get good STC (a lot of mass) or I get good bass trapping..." - isn't really true. The STC 63 wall in the previous illustration will give as good sound control as a concrete block wall, maybe even a double concrete block wall, but with MUCH better bass trapping due to the added flexibility. I personally would NOT use concrete block walls except on the exterior, and even then I'd probably use stuccoed and filled block outside, and maybe 3 layers of wallboard furred out 6" on Resilient Channel for the inner leaf. Otherwise you may not have enough room inside for enough bass trapping to compensate for those stiff walls... Steve

Right! Here we call it Durlock (brand). I will check the thread on Mar. 17 Ok… your tip is very good!!! It saves me a lot of bucks! I´ll try to find some caulk dealers. So… you´re saying that I´ll need 1 meter (deeply) to put both doors in the same frame, right? What happens If one door will open for the inside and the other for the outside? This would work? About the RC… as you say… I have to built until I arrive to the end of the wall, I left 6mm gap, and continue to built the perpendicular wall? Later I caulk the gap? Do I understand it right? I think that we´re going to use concrete on the exterior walls, filled with sand or caulk, inside RC, with two or three plasterboards. In the intersection wall between the control & the recording room, we´re going to put 2 Gyp 15mm + RC + Concrete filled + RC + 3 gyp 15mm. Do you think that this “system” will be a little “hard”? There´s something that I cannot figure out… the glass wool, where I´ve to put it? Between the concrete and the plasterboard (in the RC space)? Sorry for the delay... I had some net problems Thanks again! Fernando Musarra AWS

My recommendation for the 1 meter (or more) depth for a sound lock (vestibule) wasn't so that the door could swing into that space - it is so that the interior of the vestibule can be completely absorbed with thick 703/705 type board, covered with cloth, and still leave room for a person to enter thru one door, close that door, and exit thru the other door so that at no time are both doors open (assuming there is either noise inside or a recording happening, or both.) Ideally, the two door frames should NOT be rigidly connected to each other just the same as the two halves of a double wall between studio and control room should not be rigidly coupled to each other. Yes, I think your wall between control and recording room would be quite hard. Plus, you're not remembering my warning against triple leaf walls, which is what you just described. If I were building that wall, I'd put the (filled) concrete block wall up, then put a separate wood or steel stud frame up on the control room side, and either build the frame wall "inside out" (see the SAE site or John's site, I forget which) or fill between the studs and then put 2-3 layers of sheet rock over RC. Either way would soften the bass somewhat - the "inside out" wall would also give you some absorption behind the console to lessen early reflections. As to the gaps between adjoining walls - you want a break so there is no metal-to-metal contact between adjoining RC's - when mounting wallboard, I would alternate layers - put a layer on one wall, leave a small gap and put a layer on the adjoining wall, CAULK well, put the second layer on the first wall, CAULK, put the second layer on the second wall, etc - That way, the corner between the walls will have a zig-zag joint with multiple beads of acoustic caulk. That should make an excellent seal and still separate the two walls acoustically. You're right about where the glass wool or rock wool goes - except, as I said above, I'd NOT do that on both sides, instead do a separate frame on ONE side of the block wall ONLY, put the Glass wool between the studs (or tack it behind them if there's room), put the RC on that frame, then 2-3 layers of wallboard. Remember - put ALL the mass you're going to use in a wall, in only TWO layers with only ONE airspace between and you will get the most isolation for your money. Then, leave room for traps/absorbers, etc, as a separate system. Otherwise, you could space one of the wall leaves out even FURTHER, put some bass hangers in the space, and kill two birds with one stone. If you have the ceiling height, one good reason (forgot to mention previously, sorry) to float the floor would be to allow space for cable trays for power and signal, depending on how much of each you will need... Steve

Sorry to interrupt but does this:

Otherwise, you could space one of the wall leaves out even FURTHER, put some bass hangers in the space, and kill two birds with one stone.

mean that hangers can work behind drywall, even double drywall? If so, would bass passing through a normal wall of drywall to the room next door (say a kitchen that the control room doesn't need that much isolation from) get rid of bass buildup as well as, say, building hangers and a false wall in front of the drywall in the control room? Thanks, J.J. J.J. McLeod Different Drummer Studios www.differentdrummerstudios.com

Hey JJ - After re-reading that, I came to the conclusion that I was still in need of more rest after a recent bout with pneumonia - In reality, the answer to your question would be, "sorta"... By that, I mean that inside a wall that is panelled with drywall, there is still appreciable sound energy even though it would be LESS than if the front surface were made of more absorptive material, such as 703. So, yes, hangers inside a drywall, much as rockwool or 703, will add to the absorption and reduce the amount of sound going through. However, it would not be nearly as efficient for bass trapping in particular, as having a 3-4 foot deep bass trap, faced with 3-4" of 703, AND hangers spaced inside the trap. Under these conditions, the hangers would both broaden the range of absorption AND improve on the QUANTITY of absorption. Think of it this way: Air, by scientific definition, behaves very similar to water, and because of this, both are sometimes referred to as being fluids. If you hang some fine mesh netting on frames in a tank of water, then cause a disturbance in the water on one side of the meshed frames, if you look at the surface of the water behind the first frame, it is calmer than in front - as you progress thru more of these frames (assuming they are one behind the other) you see less and less disturbance in the water. This is pretty much how bass hangers work inside a trap - however, the less disturbance you START with, the less effect these "impedances" will have. Always keep in mind that absorpton of any kind works by converting a portion of the sound energy into HEAT energy - since you can't hear HEAT, the level of sound is reduced. Another major factor in absorption is the position of the absorbent away from a solid barrier, versus the 1/4 wavelength of the sound to be absorbed. This is why absorbent traps, in order to absorb low bass, would need to be several feet deep. And, this is why other methods of absorption are used for low bass unless there is an abundance of space available somewhere in the room design. Sorry for any false hopes I may have raised, I'm going to try to force myself to get more rest which will hopefully reduce the incidence of "brain farts"... Steve

No worries Steve :) Thanks for clearing that up, and for all your other great posts as well. J.J. J.J. McLeod Different Drummer Studios www.differentdrummerstudios.com

I'm feeling much better lately thanks - Damn, now I'll have to find a different excuse... :=)

you could have a relapse:D

Certainly tempting, under some conditions...:=)