Mason Industries' FSN Floating Floor Concrete Slab Test Data

Check out this 1974 civil engineering testing report of Mason Industries' FSN Floating Floor system. For those not familiar with Mason's FSN mountings, they're very similar to Kinetics' Lift Slab Floating Floor Isolator. I found the test data fascinating. :cool: It's a "must read" for anyone considering floating a concrete floor. I think it's also useful for folks like me who wondered if their existing concrete slab can take the weight of a heavy soundproofed room: if a floated slab can take on so much weight, why wouldn't my slab on grade do better? (Meaning, I don't think I have to worry about crumbling my existing garage floor! :) ) I also find it interesting that on the brochure, it shows three purposes of a floating slab:

1. Vibration Isolation
External image, not preserved — original: http://www.mason-ind.com/html/images/jackup_floor/a102c1.gif
2. Sound Isolation
External image, not preserved — original: http://www.mason-ind.com/html/images/jackup_floor/a102c2.gif
3. Impact Isolation
External image, not preserved — original: http://www.mason-ind.com/html/images/jackup_floor/a102c3.gif

I can't help but notice that in all of these examples, the illustrations are of isolating the upstairs from the downstairs. Admittedly, the brochure does state:

The best approach is resting these walls on the perimeter of the floating floor so the floor isolation system serves the walls as well. If this is not possible, the second choice is supporting the isolated wall on the structural slab with continuous neoprene pads, and providing a caulked fiberglas seal between the floating floor and the wall as described for the perimeter in the previous specifications.

However, it goes on to say:

Isolated walls are often used without floating floors to reduce sound transmission between adjacent spaces (emphasis added). Here the floor provides a possible flanking path, but if results in the STC 60 range are satisfactory this is certainly a valid technique.

This is all good food for thought in the "to float or not to float" debate... But what exactly am I eating here? ;-)

I've had a hard time getting as worried about this as Rod, for one thing he's at a corporate level where they absolutely MUST be over cautious or they will be sued for millions, even if no one is hurt at all - I'm not saying anyone should "throw caution to the winds" here, but here are some real facts - I had a slab poured in 2/3 of a pole barn a few years ago - 24' x 48' slab in a 36 x 48 barn. From the bottom up, the floor consists of clay soil :cry: 4-5 inches of compacted 3/4" minus crushed rock 5 inch, 5-sack mix concrete slab, ZERO re-bar other than a "bobby pin" of #4 rebar thru each 6x6 creosote-treated pole, to anchor the slab to structure (the mix included fiber-mesh but no steel other than the previously mentioned "keys" - the "haunches" around the perimeter of the slab are about 10" wide and 12 inches high total - again, no rebar other than the keys thru the poles. I had the contractor go heavy on the gravel to help avoid wicking from the clay (poor drainage) and have yet to see ANY signs of moisture thru the slab (no plastic ANYWHERE) once the cure was complete (did the thin sheet metal test a few times) Kicker #1 - my backhoe (Case 580) weighs 12,500 pounds, of which about 10,000 pounds rest on the back tires - total "footprint" in both tires would be about 3 square feet. I've had the hoe parked inside the barn on several occasions - no sign of any cracks whatever. This equates to localized loading of over 3000 pounds per square foot. Kicker #2 - I bought 2 full units of T1-11 5/8" siding about a year after the slab was poured, to be used to finish the rest of the barn once my old studio is removed and the other 1/3 of the slab is poured (and to re-side my house), and I wanted it stored out of the weather; so I set each full, banded unit (55 sheets each unit, IIRC) one on top of the other, on the rails of a "shop crane", otherwise known as a "cherry picker" or engine hoist; these have steel wheels, about 3-1/2" diameter (4 of them) - I "winched" this entire load across the concrete floor with chains and a "come-along", til it was out of my way near the rear of the slab - so there is approximately 5000 pounds of "plywood" (a stack about 6-1/2 feet tall) sitting on steel wheels with a total contact surface of roughly 3 square inches for ALL FOUR WHEELS against this same concrete slab - this translates to point loading of around 1600 pounds per square INCH - STILL no cracks. That stack has been sitting there for 3-4 YEARS. Granted, I've not put one of these 1600 PSI "pucks" every 3 feet over the entire slab, but if I had this would equate to a total room weight of 36 such "stacks", or about 180 thousand pounds. Granted, I didn't use the sleaziest "schmuck CON tractor" for the concrete work (sorry Keith) but I'm STILL wondering if there could be a real problem here - I'm too lazy to check back on ALL your posts, Keith - did you mention any actual DAMAGE to your slab (like cracking, upheavals, crumbling, etc)? If so, then I WOULD tend to worry... Steve

Thanks for posting your "real facts," Steve. Very interesting indeed! :cool: I'll try to keep most of the talk about my own project in my project thread so that this one can be focused on the strength of concrete and the merits of floating a concrete floor when isolating from adjacent space (the latter being the most curious and pressing question I personally have right now).

. . . did you mention any actual DAMAGE to your slab (like cracking, upheavals, crumbling, etc)? If so, then I WOULD tend to worry...

Negative, other than a couple of hairline cracks, and some not-so-hairline cracks in "all the right places (i.e., the scored expansion joints where the cracks are supposed to go). The floor is straight and level (except for the intended slope of about 1/8" per foot over most of the entire surface). Bottom line: I'm no longer very concerned about my existing floor taking the load of a floating concrete floor. I'm simply back to "prove it to me" on the issue of whether or not it is necessary, given that my project is about horizontal containment, not upstairs/downstairs containment: I'm not trying to keep the area below the sound room quiet, since there's no living space in the clay muck under my slab. ;)

Could be you're right; only REAL concern is if your room were going to be sitting on the SAME slab as your neighbor; then, I'd be floatin' fer sure. You WILL get quite a bit of flanking thru your concrete, so your "horizontal" iso won't be super between garage and house unless there's a break in the concrete that completely separates house structure from garage structure... Steve

Thanks, Steve. :) Are there any published reports, or even published specs by the floating concrete isolator makers, that demonstrate the effectiveness of floating a concrete floor for TL in adjacent spaces? I'm trying to apply everything that I have learned about what soundproofing is and what soundproofing isn't to this concept as well, and it's been challenging. We know that three- and four-leaf walls are inferior to two leaf walls, even when the same aggregate amount of mass. We know this because there are test results that prove it. We also know how severe the inferiority is from the test data. From that, we conclude that two leaves are good and three leaves are bad and four leaves are worse. Lord knows we've seen this enough times! ;-) However, I'm not finding any of the same types of data cited here about the benefits of floating a concrete floor for TL in adjacent spaces. I agree that it stands to reason that floating a concrete floor is "better" as it would address flanking along the outer floor. However, again, I'm not seeing the test results that demonstrate "how much better," what factors come into play (e.g., thickness of the original concrete floor), etc. I would think that if floated concrete floors were so superior to "not," the makers of the isolators would be "front and center" with test results to prove it. The same makers are not shy about other types of test results -- why the apparent silence on this issue? :roll: I took the Auralex U-boats off my list because of their lack of published specs and their subsequent deafening silence on the subject when pressed for more information. As a result, I've taken EPDM off my list as well: no specs, no proof: no use.

EDIT: I just found this document, which does provide more information. Unfortunately, it is not linked from the product main page or the U-Boat Spacing FAQ or the U-Boat Weight Support FAQ. In fact, the latter link illustrates my "no specs, no proof" point the best. :?

I don't want to make the same mistake in floating a concrete floor if it isn't necessary -- and if it is necessary, I'd like to know how necessary. I know that I am not the only person here contemplating the "to float or not to float" dilemma. It sure would be nice to have something concrete (no pun intended! ;) ) to demonstrate its effectiveness... And if there is no such thing, then maybe we're just making a lot of well-educated expensive assumptions....... In closing, I'll share something I exclaimed when Mike and Dan and I got together weekend before last:

"Where are all the people who didn't float a floor and regret it?" :?

I should also reference Dan Fitzpatrick's "Estimating Flanking thru Concrete" thread on studiotips.com. I referenced it in my own project thread, but it's very relevant to the discussion here as well.

Could be you're right; only REAL concern is if your room were going to be sitting on the SAME slab as your neighbor; then, I'd be floatin' fer sure. You WILL get quite a bit of flanking thru your concrete, so your "horizontal" iso won't be super between garage and house unless there's a break in the concrete that completely separates house structure from garage structure... Steve

Does this mean since I have a control room I should float no matter what happens with Keith. Dans post on studio tips have alot of points against the floor. But its even more confusing than my posts( to me). How cutting the slab. There was alot of talk of that, but I think one person said if your slab is connected to the outer walls and continuous through the structure you cant. Was that just a theory or a definite "nono" for me.

to briefly summarize the thread sharward mentions above ... TL for a 4" slab at 63hz is 37db (see thread for references). The folks on studiotips assure me that flanking TL will be AT LEAST 37db perhaps 41db or so at that freq the rule of thumb provided by IR-754 (pg 3/pdf pg8) says that as long as the floor performs 5db better than the wall, the wall performance will not suffer from flanking so, the wall has to provide at least 36db TL at 63 hz, preferably more. above 36db for the wall flanking will start to have its effect, until they are equal at 41db, when the apparent TL will be 3db less. i've just realized i've had this backwards until now, i've thought that the wall had to be better than the floor. if the wall is "better" the flanking through the floor will dominate. only once you exceed that wall performance wil the flanking prevent your room system from getting better. of course, this assumes 63hz data is similar for other frequencies, but 63hz is the lowest freq there is data on. hope that helps dan EDIT: my focus on the low frequencies here assumes that this is all that matters. however that might not be right ... see June 8 post here.

Im looking like you in your new picture right now from reading your last post, Dan. Are you saying I want my walls to be 5db better or worse than the floor? If the walls exceed the floor, than all you will have is the flanking,right?. than that kinetics underlayment and a cool floor on top could maybe hide that. If the walls are less than the floor you wont hear the flanking because your walls are suckin, right? thats seems worse,right?

yeah that's one of those areas where my brain starts to stall out. :cry: it's like this. you can make the wall "better" than your floor, but you will waste your time because of the flanking. the system will not exceed its weak link, the floor. you can make the wall "equal" to the floor, the performance of the system will be 3db less than what you'd expect from the wall -- or the floor -- by itself. because the poor performance of each combine together. you can make the wall "worse" than the floor (~5db), in which case the performance of the wall will be about what is expected of the wall. so you're better off making them equal, but the return on investment between a 5db worse wall and an equal wall is not very good. you're building a wall 5db better but getting a 2db improvement. make sense? dan :lol:

ya, but did you read this

I'm thinking at this time (you too, Keith) that the best approach here is to build WITHOUT floating a floor FIRST: but do it in such a way that an "inside the walls" floated floor could be added later if necessary.

its here http://www.johnlsayers.com/phpBB2/viewt ... 7147#27147 If that ends up being it would you make walls better with that in mind? Also, if I make "equal" walls and say an underlayment product and flooring helps some with the floor. Would I possibly shift into the floors into being better and not lose that 3bd so id get the 5db from (instead of 2db) back from the walls.

Huh??!?

Simple. If I think Im gonna float a floor within my walls. Do I have to build the walls to be equal to the floated floor ? The second part is if I build my walls equal to the slab foundation as dan suggested and then add a simple floor like an iso foam underlayment and flooring on top. That should make my floor a little better then the wall. If the floor is better than the wall I will no longer lose 3db from them being equal. My theory is this makes his walls less than floor approach and brings it up 5db, or you can look at it as a way to not build an equal wall(5bd better than less "wall") and only get 2db better performance.

sharward wrote:

I think it's also useful for folks like me who wondered if their existing concrete slab can take the weight of a heavy soundproofed room: if a floated slab can take on so much weight, why wouldn't my slab on grade do better? (Meaning, I don't think I have to worry about crumbling my existing garage floor! :) )

Sorry, It doesn't logically lead to your conclusion. Your slab on grade could very well be placed over poorly compacted soil in areas......... with a slab itself that was never made to carry that load. The analysis by a structural engineer on the slab of the studio determined that it could take the loading with a 2' square grid. In other words - a structural engineer examined the existing construction - I promise you that they did non-destructive testing to determine the size and spacing of the reinforcing within the slab, and - after a careful analysis determined what the slab could safely carry. And from this you have enough information to determine that your slab on grade won't have a problem? Just to give you a picture of what a 5 1/2" composite slab can be capable of - I headed the design team for an expansion of a national museum at a military base in CT. We decided that we wanted to maximize the space within the library - so we designed the slab with the intent of installing movable compact storage (we did the same within the archive storage area). The slab was designed for a total long term loading of 400 psf. Let's see now - the typical residence is designed for 40psf of loading in family rooms, living rooms, dining rooms......... and 30 psf in bedrooms. No loading is even considered for slab on grade in either garages or basements for residential construction. They just pour a 4 or 5 inch slab - maybe with a little reinforcing (typically a roll of 6x6 light gauge wire). Even slab on grade for commercial construction is based on 100 psf for assembly use group - 125 psf for storage - 50 psf for business - etc. Please don't jump to conclusions that you have no data to support. I've said before - it would be a pain to get an entire room finished - and all of a sudden have one section of an elevated slab crack and drop because the slab beneath it dropped a 1/2" or so. That would be one heck of an expensive fix. BTW - Steve, You can't consider your situation - 1st off - the construction technique was above average - 2nd you oversaw the operation. Most people never see anything having to do with their slabs except the tops. Not quite the same thing. Hey peeps - you can draw your own conclusions - in all honesty - there probably would not be a problem with one in a thousand slabs - the problem is I can't tell which one is the problem slab from here............... :wink: Sincerely, Rod

Rod, thanks as always. Your words of wisdom are not always what we want to hear, but they are surely what we need to hear.

Rod, You can't consider your situation - 1st off - the construction technique was above average - 2nd you oversaw the operation. Most people never see anything having to do with their slabs except the tops. Not quite the same thing. True, I do tend to "overkill" when I have the choice - I've seen several garage slabs that were measured with a 2x4 frame (so only 3-1/2" deep), no rebar, in some cases not even 6x6 mesh, definitely no fibermesh, and not poured in cool damp weather like I insisted on (forgot to mention that part :=) Still, if my slab can handle point loads of 1600 pounds per square INCH, I would think that even a poorly laid 2" thinner one could handle ONE pound per square inch, wouldn't you? That's 144 pounds per square foot, and a 4" slab only weighs about 50 PSF. I know you're 'way deeper into this than I am; do any of your NDT guys have ways of using ultrasound to find out more than just the slab thickness and where the steel is? Like, how solid the soil is compacted below the slab, for example? (I deal with ultrasonic testing at work quite a bit, but we're looking for pinhole sized inclusions or voids in the metal that keeps you in the air when you fly, kinda a different scenario...) I know that kind of testing can get really expensive quickly, but maybe not AS expensive as ripping out a slab without knowing it's necessary - whaddaya tink?? Steve

knightfly wrote:

Still, if my slab can handle point loads of 1600 pounds per square INCH, I would think that even a poorly laid 2" thinner one could handle ONE pound per square inch, wouldn't you? That's 144 pounds per square foot, and a 4" slab only weighs about 50 PSF.

Steve - 1st - the issue isn't the concrete - the issue is the material it's sitting on. Suppose for a moment - that a contractor did a lousy job compacting before placement. You could have areas of the slab that had literally no earth in contact with it....... picture a void 1/2 to 1" in depth (I've seen much MUCH deeper) that's 2 or 3 feet across. If this occurs in a basement or in a garage where the tires never load - the concrete itself could stay in place without ever developing a crack. I had a house once that we built back in the 70's that the site contractor over-excavated the back right hand corner of the foundation. We were building a 2 story contemporary - and the settlement never even started until we had the building completely framed and roofed - doors and windows in. I had begun the siding on the building and was working my way around to the back when I discovered it............ there was this weird kink in the back of the building (vertically). It had settled (at that point) 2"...... and I had one hell of a time getting it fixed. Very expensive error that one.

I know you're 'way deeper into this than I am; do any of your NDT guys have ways of using ultrasound to find out more than just the slab thickness and where the steel is? Like, how solid the soil is compacted below the slab, for example? (I deal with ultrasonic testing at work quite a bit, but we're looking for pinhole sized inclusions or voids in the metal that keeps you in the air when you fly, kinda a different scenario...)

No - I don't know any way to non-destructively test for density - problem being that in order to perform a density test on earth - you have to 1st analyze the earth and determine it's properties. (this is called a proctor analysis). You could open up an area - take a sample for proctor analysis. There are only 2 ways that soil density is tested that I am aware of. The 1st is done using silica sand (because it weighs exactly 100pcf). A sample is carefully dug out of the earth to a perfect cone shape- the edges shaped by hand and cut as close to perfectly as humanly possible to fit a metal cone. The cuts are with a small spoon so as to not disturb the material around it. a SS plate is then placed over the hole - and a measured amount of sand is placed within and tamped to fill the hole. The remaining sand is then weighed to determine exactly how much sand (by volume) is within the hole. Now that we know the exact area of the material we removed we weight it - and then douse it with alcohol........ which we then burn off. This removes any moisture from the material. We weigh the material again to determine the actual dry weight. This also gives us the moisture content of the material as a percentage of volume. Once we have all of this data we can compare it to the proctor analysis to determine the actual density of the material in place - and thus determine the percentage of compaction and the true bearing capacity in place. The only other method is done with radiation testing - in which a rod is driven about 1 1/2 feet into the earth - the equipment releases a radiation charge into the earth and the rate of dissapation is used to calculate density - but again - the proctor has to be known.......... Obviously the slower the rate of decay of the radiation the denser the material. No other ways of doing it that I am aware of. The problem with either of these means is this - a sample test - say in a 4' or 6' grid - could miss problem areas in their entirety. This is why onsite testing is done with 100% visual observation by the labs - and then spot checking of actual density. Once they establish that 25 passes (for example) of a 250 pound plate compactor on an 8 inch lift tests between 94 and 95% compaction by density - and the requirement is 93% (this would be standard with road work for example) then the visual serves for the majority of a lift. When a contractor screws up and works a weekend without letting anyone know - 99% of the time after we make him open up sample areas - the work they did has to be completely removed due to lower compaction rates than required by the design.

I know that kind of testing can get really expensive quickly, but maybe not AS expensive as ripping out a slab without knowing it's necessary - whaddaya tink?? Steve

Personally - I think that the need for an elevated slab is much less than people think - and that more and more people are interested in it because it's the "trendy" thing to do. "Everybody else is doing it - so we should too".............. regardless of the actual need. I have never seen any one come into any of our rooms and make the statement: "I did extensive testing on my existing environment - and the data from the testing indicates that my needs are 79dB weighted reduction and I cannot acheive this with my slab. This was determined through the use of an accelerometor and tapper. Apparently my slab is sitting on a bed of fairly liquid (i.e.: movable) earth which allows it to move more than we would like". Nope - people just come in and say: I'm building an isolated slab in my studio and want to know how far apart the pucks should be". This knowing nothing about how to design an elevated slab - what the center frequency is of the slab - or (before we teach them anything) even how it can cause problems rather than solve them if done wrong. So then I must needs ask myself - knowing as little as they did - how did they know they needed this at all? Sincerely, Rod

Fantastic, Rod. I'm glued to this thread, lapping up every syllable. Thank you for your generous contribution of time on this subject. I would like to remind everyone that just two houses away from me, a few years ago (before we moved in), a large portion of the garage floor had to be excavated and repoured. This was due to some significant settlement of one (or more?) of the sections. The house is identical to mine -- same floorplan, even the same orientation (i.e., not reversed) and on the same side of the street. If a Toyota Camry could do that in their garage, then surely 7 Toyota Camrys stacked on top of each other could do the same in mine. :!:

I thought I remembered SOMETHING about your area being a problem, musta missed that when I looked (or else we talked about it on the phone) Thanks again Rod, and I do understand about CON-tractors - my entire place was built by one, and every 15-minute job I do to repair something takes about 2 weeks :evil: ever wanted to fasten a guy down to extra flaky particle board with a nail gun through the scrotum, then set fire to the board? (Prob'ly a really good thing I don't know where this guy lives, might be more of a test of self-control than I could muster) Steve

thinking back to the idea of metal plate from keith's thread, (and back on the idea of floating) what about the idea of putting down wood to spread the load under pucks ... there is no reason the puck has to be directly against the slab for example you could put down a square cut-off from a 2x8 (7.5 in x 7.5 in) under a puck to spread the load out. or, if that doesn't address pressure well enough, use full lenghts of 2x8 if that didn't do enough perhaps 2x6 on edge, or double 2x6, anyway you get the idea or perhaps a couple of layers of plywood on the slab first, and then 2x6 joists on top you might then be able to "bridge" hypothetical weak areas in the slab depending on the load of your room you might be able to distribute the psf load enough to be reasonable in this way. is this a reasonable train of thought? or is any possible room just too heavy even with a fully distributed (100% of floor area) load if your room is 10,000 pounds and your area is 200 sq ft that is 50 lbs/sq ft. of course it would be more around the perimeter ... dan

Dan Fitzpatrick wrote:

if your room is 10,000 pounds and your area is 200 sq ft that is 50 lbs/sq ft. of course it would be more around the perimeter ...

As a matter of fact it would be more - Period. if the slab was only 4" think lightweight concrete - without reinforcement - at 115 pcf for lightweight concrete it would weigh almost 7,700 pounds - JUST FOR THE CONCRETE.......... Now seeing as one is throwing their money away building an elevated slab if they don't follow through on the remaining construction sas far as isolation value goes - the room (including slab) is going to weight quite a bit more than 10,000 pounds. The 7 layers of drywall in Pauls studio weigh in at roughly 17.5 psf - with a 10 x 20 room with an 8' ceiling that's 8,400 pound of drywall plus framing - then you need to add in the ceiling............... - Point is - i don't see this happening anywhere that weight - so now we are more around 100 psf - and that's just dead load........... even if the spacing (to maintain a 10hz center frequency) was 2' centers - that's still 400 psf plus 4 times the live load............ (calclulated with a 12" square plate to distribute the load........... As I work my way through what it takes to get this done - it begins to look easier and easier to just remove 200 sf of slab and repour it. I am confused why this looks so daunting to everyone? Oh - another thing - if we remove the blab - we may as well pour an isolated slab on grade and save the extra bucks for the floating slab (which will now not gain us anything). Pulling up that old slab is looking better and better all the time............ Rod

Keith, I jackhammered AND removed the peices of a small driveway slab last fall, just about the size of your garage, in one day. Of course, in your case, the slab would have to be cut first. But not as bad a deal as I thought it would be. But at least you don't have to do what I did either. Try digging out an old steel SEPTIC TANK afterwards.... Steve..you think your contractor was an idiot...the previous owner poured a slab OVER the access to the tank. I had to dig the whole slab up to find the access. Nailgun torture would not good enough. Burying him up to the neck in concrete might satisfy me though. :lol: fitZ BTW Keith, how was the WeekendWarrior fest? :P

Rod, thanks once again for your thoughtful and detailed responses on this important topic. I actually have been strongly considering removal of a portion of my garage floor and having a new isolated 6" reinforced slab poured in its place. Another advantage of this approach is that I could have the slab poured level with stronger perimeters to support the weight of the walls. In fact, I'm contemplating contracting to have walls built of cinder blocks filled with dry sand for my inner leaf. Edit: Scratch this part! After reading Sound Transmission Through Concrete Block Walls by our Canadian Friends at the Institute for Research in Construction, I think I'm better off sticking with good ol' gypsum wallboard on frame! This is all very preliminary (as usual), and I'll post more on my project thread once I have more of the details worked out.

Interesting thread for sure but the question begs why have I been in countless recording studios over the years that do not have floating floors, or double leaf walls and the isolation, for the purpose, is fine . I think the first question that never seems to get asked in any of these forums is "what level expressed, in db, do you require from your project?" It would be a nice sticky to roughly know what db output different instruments make - just as a guide - as a starting point and perhaps there rough frequency ranges. As an example I am a fairly heavy hitting drummer - what rough db will I be producing?, what about if I record a marshall stack wound up 3/4?. I know with my own project I too have been going mad trying to work out what to do with the floor. Everytime I think I have an anwer some one else posts, telling me I am doing it wrong, or wasting my time- I think if I could say that I will be playing drums at about 100db and I can live with 30db leakage to the outside world - as an example - then it will be easier for you guys to help me make educated decisions on the floor (and walls) rather than overspecking and overkilling every part of my design because you think I want a bomb shelter!! just a few thoughts from another totally confused floor builder!! JG

Johnrg wrote:

Interesting thread for sure but the question begs why have I been in countless recording studios over the years that do not have floating floors, or double leaf walls and the isolation, for the purpose, is fine .

Well, as far as the point on the floating slab - I have to agree - in fact I made the same point above when I posted: Personally - I think that the need for an elevated slab is much less than people think - and that more and more people are interested in it because it's the "trendy" thing to do. etc., etc., etc. But the walls are a different issue - I've built professional world class studios - have constructed isolated slabs for them - and have always used double wall construction and been concerned with room to room isolation. Floating slabs is one thing - room isolation is another. What pro studios have you been in where isolation betweem rooms isn't an issue? Bleed through of instruments on a vocal taking place could be an issue - as could too much bleed through into the control room (there's always a certain amount - after all - walls are not sound proof). What are say - 20 or 30 of the countless studios you refer to - I'd be interested in finding our how they deal with this and why it works for them when it doesn't for the vast majority of the studios I've been involved in. Sincerely, Rod