Hey Y’all,
I’m a contractor bidding a 600 square foot(250SF control room,350SF live room) separate studio building in Nashville TN that will be placed in someone’s back yard. This studio will be recording full bands but more than likely rock and acoustic bands and not heavy metal. It is in a residential neighborhood and because of that, I am more concerned for the noise coming out of the building rather than the noise coming in. Unfortunately this building will have to be built with a crawl space due to the slope of the lot. The width of the floor span will be around 30’ and I plan on dividing it into 3 sections with 10’ 2x10 joists and two girders running the length of the building which should be around 33’ long. My piers will be spaced every 8’ under the girders. The exterior foundation will be block. Ok, here are my questions.
1-I’m finding quite a good bit of information on sound isolation for walls and ceilings and with the budget I’m dealing with, I think a single 2x4 exterior wall with two layers of 5/8 drywall with green glue between on the inside and 7/16” OSB with Hardi board siding(I may switch to vinyl if codes will allow) on the outside and R-13 fiberglass insulation in the walls is the best I can do. I am reading a lot about adding RC to the interior side of the wall as well. RC claims a STC rating of 7. Will this be an automatic increase?
2-I’m having quite a bit of trouble finding good information on floating a floor over a wood framed subfloor. I would love to go with a sand filled floor but again the budget I’m dealing with will not permit this. So I’m looking at the best alternative for the money to separate the low frequency vibrations from the live room to the control room. Also, if I float the floor in the live room, do I need to float the floor in the control room as well? I do plan on building double walls between the live room and the control room with the double layer of drywall, both walls insulated and a 2” air gap but It would seem to me that vibrations in the control room coming through the floor would only be an issue if there is a subwoofer placed on the floor which is a lot of studios don’t use.
Thanks,
Richard
Help needed for walls and floor.
Originally posted at johnlsayers.com, topic 18381.
Hi Richard. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)
It's refreshing to get the actual contractor come to the forum for advice! It's normally the homeowner who comes here, asking about some things that his contractor is doing.... so this is great! Not many contractors bother, as they don't seem to care much about acoustics. So welcome to you! I wish there were more contractors like you.
That would get you fairly decent isolation, provided that you are very careful to keep the inner leaf totally isolate from the outer leaf. The concept you are aiming for is often referred to as "room-in-a-room", which means just what it says: you are building one room inside another, and they cannot touch each other. The outer "room" is the building shell, and the inner room is fully framed within the outer. The only place where the two meet, is the floor. So the inner room has its own four walls, and it's own ceiling that rests ONLY on those walls, not touching the outer shell anywhere. Not eve a single nail.I think a single 2x4 exterior wall with two layers of 5/8 drywall with green glue between on the inside and 7/16” OSB with Hardi board siding(I may switch to vinyl if codes will allow) on the outside and R-13 fiberglass insulation in the walls is the best I can do.
Keep the Hardi board! Don't switch! That Hardi stuff is fiber-cement, which is much more massive (heavy) and rigid (stiff) than vinyl. It will give you much better isolation. Also, make the OSB 5/8", or even 3/4" if budget permits. The key concept for isolation is mass: lots of it. LOTS of it. Mass is what stops sound, and nothing else. So put the greatest amount of mass in each layer that you use. There's another issue here: flexibility (or "stiffness", in acoustic terms). Thin flexible materials do not isolate as well as thicker more rigid materials, so go for the stiffest, thickest, heaviest materials you can get. There's one other key concept to isolation that most contractors are not aware of: sealing. Sound travels through air, so any place air can get through, so can sound. This sounds so damn logical when you see it in such simple terms, but is not so obvious in real life. Even a tiny crack between a bottom plate and the sub floor can cause massive degradation of the isolation. You'd hardly notice a 1/16" air gap a couple of feet long under a wall some place, but that "insignificant" crack can cost you 10 decibels of isolation, easily. That's huge. So make sure your guys pay very, very close attention to sealing everything. Caulk all possible cracks with good acoustic sealant, or even with common kitchen/bathroom caulk, but ONLY the type that stays flexible and rubbery forever, even after it is fully set. Do NOT use the type that hardens. Some materials that you can totally forget in your build: Expanding polyurethane foam, MLV (Mass Loaded Vinyl), styrofoam (polystyrene), any other type of closed-cell insulation. None of those are useful, acoustically (with the possible exception of MLV, for some very specific things).Hardi board siding(I may switch to vinyl if codes will allow)
No, not automatic, and in your case the number would be more like "0". RC is a great product, and works well when used correctly, in the correct application. What it does is to decouple the drywall from the studs on one side of a normal wall, such that any vibration (=sound) picked up by the drywall will not be transmitted into the studs, and thus to the drywall on the other side. But that is for a NORMAL house wall, with 2x4 studs having drywall on both sides. That's not what you are doing. You are going one step further, with an entirely separate from for the inner-leaf, so it is totally decoupled form the outer leaf. In other words, your wall is already "fully decoupled". So adding RC to that will not decouple it any more: it is already as fully decoupled as it possibly can be, so RC won't do anything additional. So skip the RC, in this case. You would only use it if you had a single framed wall, but not necessary on double-framed walls. One other comment: forget STC ratings. STC is not applicable to studios, since the method for calculating STC does not take into account low frequency sound. It only considers frequencies above 125 Hz, which is fine for speech, but music has a LOT of energy present below that: drums, bass guitars, keyboards, percussion, and a lot of other things put out huge amounts of energy down low. So it is entirely possible to have a wall rated at STC-50 that is really lousy at isolating music, while another wall, designed differently, might be rated at only STC-40 but isolate music much better. Beware of STC for acoustics: it does not tell the truth!I am reading a lot about adding RC to the interior side of the wall as well. RC claims a STC rating of 7. Will this be an automatic increase?
That's because it is really hard to do! This is the part that you are not going to want to hear, so I'll just give it to you straight anyway, in three steps: 1) A wood framed subfloor over an air cavity is about the worst possible nightmare for a studio. 2) Floating a floor properly is way harder than most people ever imagine (despite the silly claims and garbage videos you see on YouTube.) 3) There is no such thing as a cheap, light-weight floated floor. That is a mythical creature that does not and cannot exist in this universe, since it would have to defy all the known laws of physics. That's not what you wanted to hear, I'm sure, but it is the straight truth. You CANNOT get high levels of isolation from a light-weight floor (floated or not), no matter how hard you try. It is impossible, because the laws of physics are against you. To put this in perspective, here is the equation that describes the way walls and floor isolate: TL = 20 log (F * M) - 47 dB (where F is the frequency (Hz), and M is the mass per unit area (kg/m²) ) It is that simple. That tells you exactly how much isolation you get, for any given frequency, given ONLY the mass of the surface (surface density). As a contractor, you are very familiar with building materials, so you know more or less what the surface density of most things is. 3/4" plywood is about 10 kg/m2, very roughly, so take that as a basis. A 4'x8' sheet of 3/4" plywood weights about 70 pounds, which means about 2.1 pounds per square foot surface density, or about 10.5 kg/m2. Plug that into the equation, and for the middle frequency in the spectrum (1000 Hz), that will give you: TL = 20 log (1000 * 10.5) - 47 dB = 33 dB Well, that ain't too good! So you figure you'll add another layer, and get twice as good, right? Wrong. Do the math. Two layers of 3/4" plywood is twice the surface density, so: TL = 20 log (1000 * 21) - 47 dB = 39 dB What??? :shock: :?: You mean that DOUBLING the mass only increases isolation by 6 db? Yup. And that is in theory, assuming "perfect" mass. In the real world, you get more like 4 or 5 dB each time you double the mass... That's the sad truth about mass law. You need a HUGE amount of mass to get good isolation from a single leaf. The walls you describe are much better, because they are not single-leaf, and therefore are not subject to mass law. They are resonant MSM systems, which isolate much better than mass law allows, provided they are tuned correctly. You can do the same for the floor, but there's a catch: the walls isolate well because you are using air as the resonant spring. You CANNOT do that for the floor! There's no way you can support a floor on air alone! So you have to use physical springs instead, and that complicates things. If you could float your floor on air, you could do it just like the walls, and it would isolate to the same degree, but "floating on air" is not possible for floors, for obvious reasons. So "floating on springs" is the answer. And to do that, you need lots of mass on the floated part, usually a concrete slab (or a sand-filled deck), and enough structural support under it to hold it up safely. Here's how to do it right: How to float a floor CORRECTLY(Click on that, to open the thread). These are also useful threads about the same subject: viewtopic.php?f=2&t=8134 viewtopic.php?t=8135 If you want to understand a bit more depth of the science behind floating floors, and also to see the results of real-world laboratory testing on various types of floated floors, and how they perform in reality, then this is the document you need: http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir802.pdf That's a really good one, as it analyses a whole bunch of typical flooring methods, and shows the exact lab-tested results of how much isolation you get from each type. It is sobering... The best floor, by far, is a simple slab-on-grade. It solves all of these issues. So I would strongly suggest that if your customer wants to be able to have rock bands playing in his room, and NOT have the cops knocking on the door all the time, he needs to bite the bullet and excavate far enough that you can pour a proper concrete slab. Either that, or save him a stack of money, and tell him not to bother isolating the walls, since the floor is the weak link. It does not matter how well you isolate the walls, if the floor and ceiling are not done to the same level. Sound is like water: it takes the easy way out, ignoring the hard way. If the walls are great but the floor is "easy", then that's where the sound will go. And ounce the sound is out, it is out everywhere, all over the neighborhood.2-I’m having quite a bit of trouble finding good information on floating a floor over a wood framed subfloor.
The best alternative for this is simply to pour a concrete slab-on-grade. Trying to do this on a wood-framed subfloor is not going to work. Or rather, it might work somewhat, but not to the level your client needs. He wont be happy with the results, and as always happens in these cases, he will blame you for the failure....So I’m looking at the best alternative for the money to separate the low frequency vibrations from the live room to the control room.
If you try to do this on a raised wood-framed subfloor, then yes, most definitely: you need to float each room separately. If you do it as a slab-on-grade, then no, there's no need to do that. One slab for both is fine.Also, if I float the floor in the live room, do I need to float the floor in the control room as well?
It's not just that you need to have a two-leaf wall between them: the entire studio has to be built as a proper two-leaf system. You also haven't mentioned the ceiling and roof yet, but they too need to be done as two-leaf systems.I do plan on building double walls between the live room and the control room with the double layer of drywall,
Do you mean "gap" or do you mean "air gap"? that's two different things, acoustically. If you have your two stud frames with a 2" gap between them, then you have a 9" air gap: There 3-1/2" in each stud bay (assuming 2x4 studs), giving a total of 7", plus the 2" gap between them, for a total of 9". Acoustically, that's a 9" air gap. And it still stays as a 9" air gap even when you put insulation in it: insulation is mostly air anyway....both walls insulated and a 2” air gap
That's impact noise, which is different from air-borne noise, and can be dealt with easily buy putting bass amps and drum kits on isolated risers, but that will not stop the airborne sound from getting out through the floor. Airborne and impact are two different aspects of studios, yes, but airborne still gets through the floor in exactly the same manner as it gets through the ceiling and the walls. In fact, very low frequencies (below the critical frequency for the room) actually make the entire room "pump" slightly, with the walls, floor and ceiling flexing in and out, sort of like a balloon inflating and deflating, due to the overpressure of the sound waves acting on the entire room volume, rather than just one surface. The floor responds to that in exactly the same way as the walls and ceiling: it lets it through. That's why thicker, rigid materials are better at stopping low frequency sound. Such as concrete, for example... So, if I were in your shoes, I would suggest having a serious chat with your client, and explain to him the simple facts of life. Unless he is prepared to go to a slab-on-grade floor for his studio, there's no way you can give him the level of acoustic isolation that he will need to be able to have a rock band rehearsing in a residential area. Unfortunately, wishing and hoping and budget restrictions will not change the laws of physics. This is the hard reality of studio design: there are certain things you can accomplish in certain situations, and there are no magical materials or techniques that can change that. One of the things that cannot be accomplished, is to attain high levels of isolation form a light-weight wood-framed floor, on a low budget. You can not have all three: Light weight. Low cost. High isolation. - Stuart -It would seem to me that vibrations in the control room coming through the floor would only be an issue if there is a subwoofer placed on the floor which is a lot of studios don’t use.
I think you misunderstood my exterior wall construction. I was planning on having a single 2x4 wall with OSB on the outside covered by fiber cement lap siding and two layers of 5/8 drywall with green glue between each layer and R-13 insulation in the wall. According to you it sounds like the resilient channel will be necessary to separate the inner wall from the outer. Will this be anywhere close to as good as the double wall configuration you thought I was describing?
As near as I can tell, according to IR-761 this would be the situation (very roughly) for the first case (single stud plus RC):
And this would be the situation for the second case, as I described previously (double-stud):
Those are not exact, of course: just the nearest I could find at first glance in IR-761, for situations approximating each case.
As you can see, there's a substantial difference, even just considering the STC rating, and the full TL graph makes it even more clear. The double-stud wall is blocking about ten times more energy, and subjectively will sound about twice as good, in terms of isolation. The coincidence dip is very much less pronounced on the double-stud wall, and the low frequency resonances are totally gone. It's just a much better wall, all around.
As a further point of reference, without RC, it would look more like this:
Notice the huge resonant dip at 125 Hz...
- Stuart -
Ok, so obviously the double walls are the way to go. Here's another idea I want to run by you. If I were to build the live room on a concrete slab and the control room on a crawl, it may limit the amount of excavating I would be required to do. Would placing the control room on a crawl space be a big issue and would the double walls really only be a necessity for the live room?
also just a quick comment on the R-13 fiberglass insulation for use in the exterior wall. Wouldn't something like rockwool be better for him here without being too horribly different price wise? As I read through the forums, I'll often see fiberglass used in between control rooms and live rooms, but something beefier for the exterior walls/ceiling.
If you have to compromise, then that would be the best way to do it, yes. Of course, it would be even better to have them both on slabs. But please check the rules one more time: you are still missing something! - Stuart -If I were to build the live room on a concrete slab and the control room on a crawl, it may limit the amount of excavating I would be required to do. Would placing the control room on a crawl space be a big issue and would the double walls really only be a necessity for the live room?
It depends on the density (or rather, on the "gas flow resistivity"). Both fiberglass and mineral wool are good for damping inside an MSM wall system, but with different optimal densities. For mineral wool, the best density is around 50 kg/m3, while for fiberglass it is around 30 kg/m3. - Stuart -comment on the R-13 fiberglass insulation for use in the exterior wall. Wouldn't something like rockwool be better for him here without being too horribly different price wise? As I read through the forums, I'll often see fiberglass used in between control rooms and live rooms, but something beefier for the exterior walls/ceiling.