Pier and Beam Floor Sound Reduction for Live Music Room

Good evening esteemed studiophiles. This is my first post and am new to this forum. My location is Houston, TX. Overview: I am in the planning phase to build a new construction home with a dedicated 19’ X 14’ X 9’ or 10’ live practice room/recording space built for sound isolation of a 3 piece rock cover band with guitar, bass, keyboards and drums. It will be a first floor room with parallel walls and floors (the room ratio does fall within Bolt area or favorable bass mode distribution). My questions are concerning building a robust sound reducing floor. How Loud/Reduction Goals: I haven’t measured my band specifically with an SPL meter, at least not recently. Several years ago in small room using a professional SPL meter from work, I think we hit 90-95 dBA on a typical up-tempo number. I would say at our max, somewhere between 95 and 105 dBA would be our absolute loudest live practice level. Sound reduction goals would be to reduce live playing to sub-50 dBA levels at the nearest neighbor’s structure approximately 12-14 feet from my practice room. I realize it’s a bit of a tall order but I am designing the room to be as well isolated as I can. Budget: I consider my sound isolation budget to be the incremental cost to be what I’d above spend building a normal stucco clad, wood framed room on the first floor. That said, I plan to spring for room-within-room construction, purpose-built exterior communicating sound doors, and pretty robust interior communicating doors. For the floor, the extra cost above a normal floor would be for the additional, plywood, damping compound, resilient mat, acoustic sealant, fiberglass batts, and if built this way, extra sheet rock, damping compound, furring channel and sound clips. I costed that out using online pricing of each and calculated quantities, and it’s about $1,000 in materials for the floor’s incremental cost. I realize labor for putting this together will be the major cost, but I figure the bulk of labor is already in building the normal room, and adding labor for these items will be a percentage rather than a multiple of constructing the normal room. So I’ll say if it’s in the $5,000-$10,000 + materials extra over the regular floor, I’ll be happy. Basic Room Design: Walls would be double stud, double drywall Green-glued leafs on each side with at least a 1” air gap between stud rows (9” between interior and exterior drywall leaves). So a pretty robust, decoupled wall. All of this would be acoustically sealed with staggered seams, sound sealed outlet boxes, the works. The ceiling would also be built as a floating joist decoupled system. I planning to make the floor surface wood or engineered wood, and use area rugs, wall diffusers and traps to adjust acoustics. For city floodplain code reasons, I have to elevate 3 feet off grade and the foundation for practicality and cost reasons would be pier and beam. I can’t do floating slab on 3 feet of fill due to cost and floodplain conveyance compliance reasons. The pier and beam would be implemented with a closed crawlspace using ground poly vapor barrier, rigid foam insulated crawlspace walls, code-required mechanical ventilation, and sealed, insulated breakaway flood vents. For most of the house, I wouldn’t put insulation in the first floor joists for building science reasons that in a hot humid climate it’s better energy wise to let the house living space thermally couple to the cool ground for the predominant summer condition vs insulating to keep in warmth during short winters. But I would consider it for the music room for sound isolation reasons. Concerns and Questions: From reading all the forum pieces here on pier and beam floor sound isolation, I realize pier and beam is not ideal sound-isolation wise due to the drumhead effect reverberating into the crawlspace area and out the sides of open, unsealed foundation walls. I also realize that I want to avoid single and triple leaf arrangements, and aim to do a well-designed double leaf system for resonance reasons. However, I’ve also seen some contradictory views on building a floating floor, or at least different ways the term is used. I’ve seen the term used to refer to top-level floor layers not attached to sub-layer decking and with neoprene or other resilient layer separating them, and similarly separated from the wall with acoustic sealing or resilient perimeter. I think most folks are on board with this approach. I think I’ve also seen “floating floor” used for a separate jacked-up concrete floor sitting on isolator pucks over a ground concrete slab, and plywood/cement board variants similarly isolated over a ground concrete slab. I think most folks think it’s unnecessary for ground floor sound isolation where airborne sound transmission is the bigger problem rather than direct impact sound isolation, and if a slab floor could be used. I totally get this (earth being a great impact and sound wave absorber). I don’t think this is an option for me, needing the elevation above the floodplain that I do. • Am I digesting these perceptions right? • Top floor layers separated from sub-layers and walls with resilient material, good? • Floating a slab on isolator pucks over another slab not necessary if airborne sound (i.e. via the “drum head”) is the real worry? That said, I need to build a floor that will reduce the “drum head” effect out of the crawl space sides to the neighbors and match the sound reduction I’m trying to achieve with the walls. I’ve seen a few configurations from the previous forum threads by frequent contributors. One was knightfly’s recommendations for someone building a jam room shed on piers, shown below. Since I’m building a double stud wall of different design, everything to the right of the red line and boxed in red is what I’m focusing on. For my situation, the joist space of course wouldn’t be open as shown here, but enclosed within a crawlspace perimeter wall which I would think would provide more sound reduction. As for the Celotex perimeter isolation of floor from wall shown, I’m not super familiar with celotex other than it’s polyisocyanurate. So two questions on this approach: • Would this approach be robust enough to reduce and contain the “drumhead” effect, especially if the crawlspace is sealed by a perimeter wall and not open as shown? The perimeter wall may be a concrete stem wall or a timber-based wall with only exterior façade material – I have not decided yet. With either type of foundation wall, there would be a rigid XPS insulation layer over it on the interior side, but that’s it. • Any reason I couldn’t use XPS (extruded poly styrene) like Foamular in lieu of the Celotex, since I’ll be using that in my walls? Another approach I found on a soundproofing site (Ted White might recognize this), that seems geared towards soundproofing a second floor, but I’m guessing would serve the purpose of reducing sound transmission into the crawlspace below the first floor too. I assume that since I-joists are intermittent items along the width of the floor and not continuous surfaces, they don’t count as a leaf, and this arrangement would be 2-leaf system with the drywall being the 2nd leaf with an air gap the size of the joist heights. One concern for detailing this to me would be how the air gap above the furring channel gets sealed from the sides of the foundation wall – shown by the red dashed circle. The furring channel and soundproofing clip would add about 1 ⅛” of a gap above the drywall. The walls shown are not part of the soundproofing site design – I’ve illustrated them in a simplified manner for purposes of discussion. • Would this small 1 ⅛” gap leading to a foundation wall that won’t be built as the double stud, double leaf decoupled really mean much? • If I have a concrete stem wall, maybe it’s not too big a deal. If it’s a timber-based wall with only exterior façade material, then I might be concerned more. With either type of foundation wall, there would be a rigid XPS insulation layer over it, but that’s it. • Am I sweating this bit of airborne transmission too much, or would whatever perimeter isolation I use (whether it’s the XPS itself or acoustic sealant) provide meaningful containment?

Hi there "spiv", and Welcome! :)

I think we hit 90-95 dBA on a typical up-tempo number.

Unfortunately, you measured on the wrong scale! "A" weighting is used for quiet sounds, or nature-type sounds (not so much man-made) since it roughly emulates the human hearing response to soft sounds and typical environmental sounds, but a full rock band is not exactly quiet, nor "nature", nor environmental! :) For loud sounds you need to measure with "C" weighting. Here's why: Red is "A", green is "C". As you can see, "A" weighting simply does not see any low frequencies: Starting at 1 kHz. on downwards, it rolls off more and more steeply. It is pretty much deaf to rock music: no drums, bass, growling electric guitars, low end of keyboards, even vocals are attenuated. When measuring typical contemporary music, you can see difference of 10 dB easily between A and C, 20 dB is fairly common, 25 occasionally, and even more for specific circumstances. If you were measuring only a six-string bass all by itself, played open (no fretwork), you could see differences of 30 to 35 dB. So, in reality, your band was probably pushing typical rock band numbers, of around 110 to 120 dBC. Call it 115, give or take.

Sound reduction goals would be to reduce live playing to sub-50 dBA levels at the nearest neighbor’s structure approximately 12-14 feet from my practice room.

You do have a little distance there, which is in your favor, as in the open sound levels fall at a rate of about 3 to 6 dB per distance doubling. So starting at 50 dB 14 feet away, you could be 55 at 7 feet, and 60 at 3.5 feet, which is close enough to standard measuring distance of 3 feet. So you could allow things to be at 60 dB outside your wall, and likely reach your goal of 50 dB at the neighbor's house. Doing the math: 115 - 60 = 55 dB. That's a reasonable goal. Achievable, with a good budget.

I consider my sound isolation budget to be the incremental cost to be what I’d above spend building a normal stucco clad, wood framed room on the first floor.

It's probably better to approach it based on typical studio construction costs, and work backwards from there. You live in the USA, in Texas, so you'd probably have roughly the same costs as many of mys customers in the USA have reported: Around US$ 100 per square foot, for a ground-up build, ranging from maybe 80 to maybe 120, depending on location and complexity. Since yours is not entirely ground up, from what I see on your diagrams, and since you did say it is on the second floor, I'd estimate total cost towards the lower end_ maybe US$ 80-90 per ft2.

Walls would be double stud, double drywall Green-glued leafs on each side with at least a 1” air gap between stud rows (9” between interior and exterior drywall leaves).

So you are planning on 2x6 framing for both the outer leaf and inner-leaf? And just checking here: But you DID mean "double drywall on only ONE side of each frame", right? Only two leaves, total? Because it sort of sounded like you were considering putting drywall on BOTH sides of EACH frame (total of four leaves) which would be pretty bad for isolation.

The ceiling would also be built as a floating joist decoupled system.

I guess you mean on isolation hangers? You could do that, but then it becomes rather complicated to tie in the floating ceiling to the new inner-leaf walls, and you'd also need sway braces on your wall tops, since they would have no structural bracing. It makes more sense (and cheaper) to just build your inner-leaf ceiling directly on top of teh inner-leaf walls.

For city floodplain code reasons, I have to elevate 3 feet off grade and the foundation for practicality and cost reasons would be pier and beam. I can’t do floating slab on 3 feet of fill due to cost and floodplain conveyance compliance reasons.

You don't need fill under your slab. You could just do a slab at 3 feet, then a floating slab on top of that, if you really do need that much isolation. I replied to a similar case a couple of days ago: viewtopic.php?f=1&t=20779

The pier and beam would be implemented with a closed crawlspace using ground poly vapor barrier, rigid foam insulated crawlspace walls, code-required mechanical ventilation, and sealed, insulated breakaway flood vents.

No problem with doing that for a concrete slab sub-floor either.

I realize pier and beam is not ideal sound-isolation wise due to the drumhead effect reverberating into the crawlspace area and out the sides of open,

There are ways of dealing with that...

However, I’ve also seen some contradictory views on building a floating floor, or at least different ways the term is used. I’ve seen the term used to refer to top-level floor layers not attached to sub-layer decking and with neoprene or other resilient layer separating them, and similarly separated from the wall with acoustic sealing or resilient perimeter. I think most folks are on board with this approach.

Actually, not so much! Count me among the "not on board" folks... :) At least as far as the "rubber pucks and 2x4 with plywood" crowd. That just does not cut it. No way. Uhh uh. The math doesn't add up. I'¿m not sure if you have read this thread, but it explains a lot of good facts about floating floors: viewtopic.php?f=2&t=8173 Even if you already read it before, it's worth reading again.

I think I’ve also seen “floating floor” used for a separate jacked-up concrete floor sitting on isolator pucks over a ground concrete slab, and plywood/cement board variants similarly isolated over a ground concrete slab.

That is, indeed, the correct way to float a studio floor.

I think most folks think it’s unnecessary for ground floor sound

Yes, but yours is not a ground floor slab! You already said that you cannot build slab-on-grade due to your flooding restrictions. So that is not applicable to your case. Yours is much more like a typical upper-floor build.

I don’t think this is an option for me, needing the elevation above the floodplain that I do.

Slab-on-grade is not an option for you, yes, but that does not rule out floating slab.

• Top floor layers separated from sub-layers and walls with resilient material, good?

Provided that the deck ("top layers") has substantial mass, yes. "Substantial" as in hundreds of kg per m2. (= "many dozens of pounds per square foot). You CANNOT float a studio floor on a low-mass deck of just a few PSF. Anything less than about 40 PSF makes zero sense, for reasons that I'll explain below.

• Floating a slab on isolator pucks over another slab not necessary if airborne sound (i.e. via the “drum head”) is the real worry?

Ummmm.... why not? I don't follow your logic.... If you think that two layers of substantial mass separated by a spring is not necessary for isolation, then why are you building two-leaf walls and a two-leaf ceiling? :) Also, you are NOT just isolating airborne sound! You said this is for a rock band, and I imagine that the rock band includes things like drums, bass guitar, people, amp cabs, and such like. All of those are major sources of impact noise... You should really take a look at IR-802, so you can get a good understanding of the physics behind floated floors, and high levels of isolation.

Another approach I found on a soundproofing site (Ted White might recognize this), that seems geared towards...

Your diagram seems to be missing a key element! It was in the original, clearly, and for some reason the test label was wiped out, but I'm pretty sure that the label said either "resilient channel" or "hat channel on sound clips"... I very much doubt that Ted would have left out such an important item.

• Am I sweating this bit of airborne transmission too much...

You are not sweating it enough, actually! To start with, it's not just airborne sound we are talking about here. Your big issue is impact noise. A typical rock band produces a lot of impact noise. But either way, even if it is just airborne, you still need to create a fully-decoupled MSM system. And since it is a floor, with highly variable live load (unlike the walls and ceiling), you need very substantial mass in the floor. Here's the issue: If you float your floor on rubber, then you need to do some rather complex calculations to figure out how to ensure that the rubber really does "float" the top deck of your floor. It is all related to mass. If you put too much on the rubber, then you squash it flat, it bottoms-out, does not act like a spring, and it does not float: it just becomes a bridge or "flanking path", so you get no isolation. The same happens if you don't put enough mass on it: it "tops-out", does not act like a spring, does not float, and etc. The only time it works is when you have just the right amount of mass to make it float. It only floats when it has enough mass to be "springy". So let's say, for arguments sake, that you try to go with the plywood deck approach. Let's say you go overboard, and decide to have 3 layers of 3/4" plywood. The density of plywood is roughly 500 kg/m3, so 2-1/4" will weight about 6 PSF. So every square foot of your floor will weigh 6 pounds: So you figure out the type of rubber, and the thickness, and the durometer, and the deflection, and the tan-delta, and all that fun stuff, But there's also frequency to consider! Your floor must isolate across the full audible spectrum, down to 20 Hz, so you need to ensure that it floats down to 10 Hz. Let's say that you manage to do all of that, and you come up with a solution that floats a 6 PSF load. And you even figure out that your deflection is 20% with 6 PSF, but it will still float at anywhere from 15% to 25%, which you further figure out to be as much as 5 to 8 PSF. "Great!" you think. "My floor floats!". Wellllll it does... provided that nobody walks on it! Let's say that an average 170 pound musician walks in and stands on the floor. Let's assume that his weight is spread over ten square feet of your floor. So you just added 17 PSF to that part of the floor, and now it no longer floats. Right where he is standing, he is causing the rubber to squash flat, it bottoms-out, does not act like a spring, and it does not float: it just becomes a bridge or "flanking path", so you get no isolation. Since isolation is only as good as the weakest link, and since that part of the floor is no longer isolating, your entire building is no longer isolating... "Hmmmm...." you say. "OK, so I'll recalculate all my rubber for a higher load! I'll do it for 17 PSF on average, just in case there are people walking around in there, and that gives me floating from 14 PSF to 21 PSF. Done!".... And that would be fine ... as long as you don't want any furniture in there! Same as above: You move a heavy sofa in, three people sit on it, all that weight is now concentrated on four tiny little legs with a very small surface area, at maybe several hundred PSI... it's spread a bit over a wider area by the floor itself, of course, but you still have the same issue, and maybe 26 PSF under those legs. Those four spots do not isolate, so the entire building does not isolate. "DARN!..." you think. "OK, so I'll re-calculate for an even higher load. Let's call it 28 PSF, for a range of 22 to 35 PSF. That has GOT to work". Well, not really.... Your sofa is only one place on the floor, not the entire floor. Now you have most of the floor that does not float because there's not ENOUGH load on it! Just the basic 6 PSF of the floor itself, but your floor only floats from 22 to 35... See the problem? See why I'm not on board with the "float a light weight deck on rubber pucks" crowd? It does not work for real-world studios, where the load is uneven. And we didn't even talk about what happens as people walk in and out, carrying heavy amps, drum kits, instruments, kit bags, WAGs, etc. You can easily have a load that changes from 6 PSF to maybe 35 PSF as things change. A floor built as a light-weight deck will never float successfully. So what's the solution? Obviously, the deck needs much more mass. A huge amount of mass: The deck itself needs to weigh at least 50 or 60 PSF, and 70 would be better. Where do you get that kind of weight? Well, you COULD do it with thirty layers of plywood... but that would be nearly two feet thick! Or you could do it with concrete. The density of plywood is about 500 kg/m3. Reinforced concrete weighs about 2500. A 6" concrete slab weighs about 75 PSF. Concrete also spreads the load a whole lot better than wood, and since the entire load of a properly floated floor is spread across just a few very small springs, the loading is already very high and having people walk around, or sofas, or gear, or whatever, makes no difference at all. You have a 260 ft" floor. At 75 PSF, it will weigh about 20,000 pounds Even if you have ten people standing on it, with all their gear and a couple of sofas thrown in for good measure, you are not changing the load by more than about 10%, worst case. Depending on the rubber, a 10% change in load might cause a difference in deflection of just a couple of percentage points. Not a problem. The floor will still float, even if you park an SUV on it! There's another major plus here: With a properly floated slab, you can build your entire room on top of that floor, and float the room! Now you might have a load of 40,000 or 50,000 pounds, and if correctly floated, no conceivable amount of loading will cause it to stop floating. So if you are serious about floating your floor, the only way to do it successfully for the typical variable load of a studio, and for high isolation, is with a concrete slab floated over a concrete slab, on proper isolation mounts, suitably calculated. Do take a close look at IR-802: some of those graphs are scary. You will notice that for all frequencies below about 500 Hz, you cannot expect any isolation at all, and for some constructions not only do you not get isolation, in fact you get amplification! Several of those tested configurations show an increase of several dB in levels... IR-766 is another one that might be interesting. IRC-RR-169 is even better. A few years ago, Kinetics put out a very interesting paper on floated floors, and came up the equations that accurately describe how well they isolate. There's a fascinating graph on page ten of that report, but it needs a little explanation to understand properly: On the vertical axis is the resonant frequency. The horizontal axis shows the size of the air gap. The four lines show four different floor loads. At first glance, it looks like there isn't much difference between them for larger air gaps. But look again: With a 3 inch air gap, your 5 PSF floor will get you a resonant frequency of about 47 Hz. For the 60 PSF floor, it would be about 12 Hz. Since a floor does not even start isolating until 1.414 times its resonant frequency, only starts isolating reasonably at twice resonance, and isolates well at about 3 times resonance, you can see that your 5 PSF floor does not isolate well until 141 Hz, whereas your 60 PSF floor isolates just fine at 36 Hz. 36 Hz is around the lowest frequency on a six-string bass guitar, so even that is isolated by the 60 PSF floor. 141 Hz is already in the vocal range! Below that is all of the bass guitar, kick, toms, low end of the electric, low end of the keyboard.... NONE of that is isolated well by the 5 PSF floor... even assuming you can get it to float at all with the musician standing on it! In fact, that graph is rather optimistic, since it considers only the air spring, not the actual isolation spring (rubber, for example). And since the two springs work in parallel, the resonant frequency is actually higher than shown in this graph. So that's the simple truth about low-mass floated floors: they don't work so well in the real world, since the load is too unpredictable, and too variable. Far better is to properly float a high-mass floor deck, such as a concrete slab. - Stuart -

Stuart, thank you so much for the very thorough and well-considered response. I will thoroughly read through it and digest it more before peppering this forum with more questions. Just a few bits of feedback on what you replied so far:

Unfortunately, you measured on the wrong scale!

I sure did. I knew about C-weighting, but that was unfortunately my bias as a former industrial hygienist using A-weighting and not putting my musician's hat on, and thinking that because I'm focusing on human ear response that dBA was more relevant. But I've got to learn and get used to C-weighting in the music world for more meaningful measures in sound reduction across the spectrum. My bad! But thanks for being flexible and reaching into your experience knowing what typical C-weighted levels run given the type of music and the dBA I quoted.

You do have a little distance there....Doing the math: 115 - 60 = 55 dB. That's a reasonable goal. Achievable, with a good budget.

I did almost the exact same inverse square law attenuation calculating to come up with similar achievable attenuation, and I thank you for confirming that I wasn't too crazy or wishful.

It's probably better to approach it based on typical studio construction costs, and work backwards from there.......Since yours is not entirely ground up, from what I see on your diagrams, and since you did say it is on the second floor, I'd estimate total cost towards the lower end_ maybe US$ 80-90 per ft2.

Thanks for the very useful rule of thumbs in this reply. I did want to clarify that this will be a first floor music room, just elevated 3 feet above grade with a crawlspace below. I pointed that out up front briefly, but it's real easy to miss, and the 2nd option I discussed with a ceiling layer can easily mislead someone to thinking it's 2nd floor - so my apologies.

So you are planning on 2x6 framing for both the outer leaf and inner-leaf?

I was actually aiming for 2x4 on both since this room will be a 1 story, but my structural engineer will ultimately weigh in, and the adoption of the stricter 2015 IECC may force me to use 2X6 for deeper insulation if the exterior rigid insulation I'm planning in the wall assembly doesn't do the trick to meet it in this warm Climate zone 2

And just checking here: But you DID mean "double drywall on only ONE side of each frame", right? Only two leaves, total? Because it sort of sounded like you were considering putting drywall on BOTH sides of EACH frame (total of four leaves) which would be pretty bad for isolation

Yes I did mean double dry wall on only one side of each frame, only 2 leaves total, which I've shown in simplified form below just to be clear. So only mass-air-mass.

"The ceiling would also be built as a floating joist decoupled system." I guess you mean on isolation hangers? You could do that, but then it becomes rather complicated to tie in the floating ceiling to the new inner-leaf walls, and you'd also need sway braces on your wall tops, since they would have no structural bracing. It makes more sense (and cheaper) to just build your inner-leaf ceiling directly on top of teh inner-leaf walls.

I will be doing the ceiling just as you suggested - inner-leaf ceiling directly on top of inner leaf walls, and not on isolation hangers. Thanks for watching out for me pretty thoroughly.

You don't need fill under your slab. You could just do a slab at 3 feet, then a floating slab on top of that, if you really do need that much isolation. I replied to a similar case a couple of days ago:

So you mean a slab elevated on piers to 3' like the below figure with another slab on some isolating element (pucks, springs etc.)? For simplicity I haven't shown beams and pay no attention to the isolator spacing - just for illustration. My only concern would be mating this slightly different foundation to the rest of the house on piers with wood beam and deck, but I guess that's what expansion joints are for.

I'¿m not sure if you have read this thread, but it explains a lot of good facts about floating floors: viewtopic.php?f=2&t=8173 Even if you already read it before, it's worth reading again.

I did read through this one, but will again. I believe it was the Rod Gervais quote "It's the airborne sound that transmits through the deck - deck assembly, windows, doors, ducts, pipes, holes, etc., etc., etc. that cause 99% of your problems" in this one that led me to believe the problem of transmission to a neighboring disconnected structure at some distance (i.e. a neighbor's detached single family unit home) was airborne rather than impact in nature, and I got why one should leave a first floor slab situation alone. But I'm still learning. But just to confirm, if the neighbor's structure is disconnected and separated by 12 feet of ground as shown below, should I still worry about impact transmission? I do realize vibration and impact would be an issue to consider within the house, hence the location on the first floor, and acknowledging I'd have to do something to decouple the floor from adjacent rooms. But I don't have a feel for impact/vibration transmitting through earth from drums and bass coming through floor components and to the neighbor's.

Ummmm.... why not? I don't follow your logic.... If you think that two layers of substantial mass separated by a spring is not necessary for isolation, then why are you building two-leaf walls and a two-leaf ceiling?

My bad. I thought the 2 options I presented were 2-leaf jobs with multiple layers of subflooring for mass and the joist spaces being the air gap. But I guess your point is mass of the leaves have to be more substantial to have any hope of lowering resonance low enough for drums and bass not to carry or amplify through i.e. bigger mass in the mass-air-mass system. I misread the applicability or utility of the floor arrangements I borrowed from knightfly and Ted White's version for my situation to reduce transmission to my neighbor's structure and need to consider impact and efficacy against this type of sound source better. I will read through IRC IR-802 as you recommend and hopefully develop a better feel for how resonance changes between options and consider the problem low frequencies I need to target.

Your diagram seems to be missing a key element!

...but I'm pretty sure that the label said either "resilient channel" or "hat channel on sound clips"...

That's correct, that's what that was. The corrected figure is below.

You are not sweating it enough, actually!.....

This whole explanation on why the lightweight deck floated on a few deformable pucks doesn't work is great and why the greater mass slab is better. I will read through the other papers you cite, but for the time being, do you have an example of the layer arrangement for the elevated slab you envision? Would it be as simple as slab-isolator-slab-flooring (properly calculated of course)? Stuart I thank you very much for the time you took to respond. Regards, Carl

thank you so much for the very thorough and well-considered response.

:thu: That's what we are here for!

I did almost the exact same inverse square law attenuation calculating to come up with similar achievable attenuation,

I figured you probably had done that! Theoretically, it is 6dB per distance doubling, but that's for free space. I real life, it's less than 6, due to buildings, trees, the ground, etc. I normally estimate about 4 to 5 dB per distance doubling. So you should be fine.

So you are planning on 2x6 framing for both the outer leaf and inner-leaf?

I was actually aiming for 2x4 on both

That's what I would have thought, but your numbers don't add up for 2x4s! You said: "double stud, double drywall Green-glued leafs on each side with at least a 1” air gap between stud rows (9” between interior and exterior drywall". 2x4 studs are 3.5" wide, so two of those plus an inch gap adds up to 8", not 9". And if you are doing 2x6 on both sides plus an inch, that would be 12", so that doesn't add up either! If you did 2x4 on one side and 2x6 on the other, that would be 9" without the gap, but adding an inch for the gap makes it 10".... so that's what was confusing me ... Anyway, 2x4's should be fine for your walls. Code normally only insists on 2x6 once you get to wall heights above about 12" or so.

sound sealed outlet boxes

I wouldn't risk that: Don't cut holes in your isolation shell! Instead, do all your electrical work using surface-mount systems, such as these: http://www.calcentron.com/Pages/fram-tr ... aceway.htm http://www.export.legrand.com/EN/dlp-wa ... ng_95.html Any hole in your wall is a potential point of failure, even if it is well massed-up and well sealed. I try to minimize those, especially when you are aiming for high isolation.

only 2 leaves total, which I've shown in simplified form below just to be clear. nly 2 leaves total, which I've shown in simplified form below just to be clear.

:thu: Perfect!

So you mean a slab elevated on piers to 3' like the below figure with another slab on some isolating element (pucks, springs etc.)?

Correct. But not pucks. Go with proper solutions form the people who really know: Mason Industries and also Kinetics have the right stuff. Like this: With both of those, you place them on the sub-floor, pour the concrete around them up to flush with the top, then when the concrete has cured enough, you turn the internal screws to jack up the entire slab to the height that you want. Here's what it looks like, when done (but with a different system, not from Mason Industries):

But just to confirm, if the neighbor's structure is disconnected and separated by 12 feet of ground as shown below, should I still worry about impact transmission?

Definitely! Here's why: If you don't float your floor properly, then the impact noise getting into the inner leaf (drum kit, bass amp, foot-stomping musicians, etc.) will also get into the outer leaf. If there is a flanking path between inner and outer, then impact noise is a huge problem. Arguably even bigger than air-borne sound. Any vibration in your outer-leaf causes it to act like a giant loud-speaker cone, transmitting the vibration in to the air. Interesting illustration: Close the doors and windows of your house, get a buddy to go stand inside and talk loudly while you stand outside ten feet away. Listen to how loud the sound of his voice is. Then get him to bang on the wall instead, with something solid like a wooden block. And see how loud that is.... Case closed!!! :) The point is that impact noise is a big deal if you allow it to get into the outer leaf. Rod was talking about something else: slab-on-grade. That's not a problem, since the entire slab is damped across the complete surface area, by the ground below. But you don't have that: your slab will be a drum head, elevated 3 feet off the ground...

But I don't have a feel for impact/vibration transmitting through earth from drums and bass coming through floor components and to the neighbor's.

That isn't your case at all. You won't have a slab-on-grade, so there won't be any damping on your slab. It's a giant drum head, or speaker cone if you prefer, and any impact noise that gets into that will be transmitted loud and clear. With a slab on grade, that does not happen, since the slab is damped.

I thought the 2 options I presented were 2-leaf jobs with multiple layers of subflooring for mass and the joist spaces being the air gap.

... except that your joists resting on the foundations! Your inner-leaf floor is directly coupled to the outer leaf like that regardless of what you hang below the joists.

Would it be as simple as slab-isolator-slab-flooring (properly calculated of course)?

Yep. That's basically it. You have the outer-leaf slab, which is your sub-floor, and that has the outer leaf walls attached to it. Then you float the inner-leaf slab on top of that, using suitable isolation mounts. Normally, you'd do the inner slab by first putting down a layer of semi-rigid insulation on the sub-floor and thin removable shims around the walls, then covering that with 6 mil plastic, taped up tight to seal it, then wire mesh as required, then pour the concrete and wait for it to cure, then pull out the shims around the edges, jack up the floor the to the final height, and seal the gap around the edge with suitable flexible caulk. You could then build the inner leaf walls on top of your floated slab, if you wanted maximum isolation, and if the floor is designed for that. - Stuart -

Thanks again Stuart for the feedback and ideas. I'll definitely consider using a floated concrete slab. I'll just have to work out the details with my structural engineer on what kind of pier and beam support is needed and figure out proper float gaps to aim for for my frequencies of interest. Also, thanks for the idea of surface mounted outlet boxes and raceways. I never really saw that in soundproofing forums or sites and don't know why. I also did get lazy on calculating a 9" gap assuming 2X4 as actuals, forgetting it's really 3.5". I guess the two approaches I was looking at were really meant for theater isolation or quieting footfall and not so much containing kick drums and such. Many regards, Carl