yep, was planing to do a floating floor with u-boots.
That's a common mistake, actually, so don't feel bad about it! YouTube is chock full of exuberant "studio" builders, showing this exact thing: 2x4 joists on rubber pucks with a light-weight deck on top... those misguided video makers wax eloquent about what a wonderful thing it is to "float" a floor like that, and how gorgeously fantastic it will be to "soundproof" their studio ... not realizing that, in reality, they actually trashed their isolation for low frequencies, and also trashed their room acoustics, since they now have a boomingly resonant floor system... It's sad, actually.
And it's interesting that even the very manufacturers of those rubber pucks don't make any real claims about what they do, and don't publish any acoustic data on how they perform.
Here's how it actually works, in real life, with real data from independent acoustic researchers:
First, a graph that explains the problem in simple terms:
resonant-frequency-of-floating-floor-by-mass-and-gap-Graph---GOOD!!!.-S02.jpg
That shows how much mass you need on your floor, and how much air gap you need under it, to get the right resonant frequency. What I mean by "right resonant frequency" is simply the one that will allow your floor to actually isolate! Your floor is a resonant system. It will resonate naturally at a certain frequency that is governed by the mass (weight) of the final floor, and the depth of the air cavity under it. At that frequency, and for one octave above it, the floor will NOT isolate. In fact, not only does it not isolate, it can potentially
amplify sounds at that frequency. And because this problem extends to one octave higher, obviously you want your floor's resonant frequency to be at least one octave lower than the lowest frequency you need to isolate. So if you need to isolate kick drums, which are often tuned around 80 Hz, then your floor should be tuned no higher than 40 Hz, which is one octave lower. If you want to isolate bass guitar, which easily goes down to 36 Hz (5 string bass), then you'd need to tune your floor no higher than 18 Hz. Let's assume this is the case, and now we can look at the graph.
The graph shows the frequency up the left hand side. You need something at 18 Hz, so draw an imaginary line across the graph a bit less than 20 Hz. You can now see that no matter how deep your air cavity is, the top two dashed lines are no use: you can never get a low enough frequency if your floor only weighs 5 PSF (pound per square foot) or 10 PSF. Not possible. However, at 30 PSF it is possible (the dotted line, third from the top): it looks like you would need to have an air cavity that is at least 4.5 inches deep, so you can't do it with 2x4's, as they are only 3.5" deep. You'll need to use 2x6's (which are 5.5" deep). Your other option is to go with an even heavier floor: the bottom curve on the graph, labeled 60 psf (solid line, not dashed). With that option, you
can get a frequency of 18 Hz. with a cavity about 2" deep, so you could use 2x4s there.
So those are your options: you can build up your floating floor on 2x4s with a 60 PSF floor, or 2x6s with a 30 PSF floor.
So that brings up the question: What would you need to do, to get a 60 PSF floor? Well, let's consider OSB: the density of OSB is roughly 610 kg/m3, which works out to about 3.2 PSF for every inch of thickness. So to get 60 PSF using OSB board, you'd need to make it about 19 inches thick!
In other words, you'd need to have 31 layers of 5/8" OSB on your floor, to get enough mass.
But if you wanted to go with the 30 PSF option, you'd "only" need 16 layers of OSB to get there....
As you can see, it is physically impossible to float a light-weight deck consisting of just a couple of sheets of OSB or plywood on 2x4 studs. If you did that, the resonant frequency would be around 42 Hz, so the floor would amplify kicks, toms, bass guitar, electric guitar, and keyboards! It would only isolate from about 84 Hz upwards.
So how do you get such a high mass? If you can't do it with OSB, then what do you need? Simple: Concrete. The density of concrete is around 2400 kg/m3, which is roughly 12 PSF for each inch of thickness. So a concrete slab just 3 inches thick (36 PSF) would let you do it with a 3.5" cavity, and if you went up to 5" thick concrete slab, you could do it on a 1.5" air cavity.
That's the plain, hard, cold facts. You cannot float a light-weight deck and expect to get good isolation for low frequencies. The laws of physics prevent it.
Now, all of the above assumes that the "deck" is fully isolated from the underlying subfloor, and that the only "spring" in there, is the air in the cavity. In real life, that is not possible: you need some type of resilient mounting to decouple the deck: it might be rubber pads, or metal springs, or something else, but there has to be something that disconnects the deck from the subfloor, mechanically. Which makes things
worse! That rubber or metal spring works in parallel with the air spring, and that REDUCES the total "springiness". So you actually need a deeper cavity to get the same frequency...
Now for the kicker that really dooms this whole light-weight deck concept: Whatever it is that you use as the spring to decouple the deck (rubber, metal springs, snake oil), you have to ensure that it will will float! If you put too much weight on a spring, then you flatten it out completely, and it is not "springy" any more: it bottoms out, and does not float. On the other hand, if you don't put enough weight on it, it is also not "springy"! It "tops out" and does not float. So you have to ensure that you put the right amount of weight on each spring, such that it has the optimal amount of compression, and really does float. For each type of spring, there are tables and equations that allow you to do that, but for most springs, you need to compress it about 10 to 25% to make it "float". Less that 10% "tops out" and more than 25% "bottoms out" (the actual numbers vary widely, per product).
Great! So let's go back to the light-weight deck (pretending that the above graph does not exist, and imagining that it might be possible to magically get the right frequency with just two layers of OSB). We already know that two layers of OSB weighs about 6 pounds per square foot, so let's say we do some calculations for magical rubber pads, made of purest snake oil mixed with pixie dust, and arrive at the conclusion that we need four pads of two square inches each for every square foot of floor, and with a load of 6 PSF, that will float just fine, with exactly 15% compression. Great! Amazing! The floor floats! ... Until you stand on it....
Assuming you weigh about 180 pounds, and that your weight will be spread across four square feet of floor, just by stepping on that floor you increase the loading from 6 PSF to 51 PSF
Gulp! I think you see where this is going.... You just flattened your rubber pads into oblivion! They are now squashed flat, and don't float.
So you think creatively, and decide that you don't need the floor to float when you are
not in the room, it only has to float when you ARE in there, so you re-design it to float when the load is 51 PSF. Fantastic! Wonderful! It floats! .... until you bring in your guitar, amp, a couple of pizzas and a crate of beer... now the load is 65 PSF, and the floor doesn't float....
So you wrack your brains, and re-design the rubber pads yet again, so they float at 65 PSF.... But then you invite your buddy over to join you for a jamming session, and he brings his girlfriend, another amp, more pizza, and a suitcase, since he's going to stay the night.... and now you have a load of 90 PSF....
OK, so I'm exaggerating a bit, but I can keep on adding scenarios here, such as the desk, a chair, a couch, your DAW, other gear, etc. etc., ... however, you can see the problem: The load on a light-weight deck varies so enormously that it just is not practical. But with a concrete deck, that has a much, much higher density, this is not a problem. Putting all that extra load on the floor, or taking it off, only changes the total mass by a few percent, and the floor still floats: the springs are still inside their optimal range.
So that's the issue. Floating a light-weight floor is not a viable solution. You need huge mass to float a floor successfully. It is certainly possible to float a floor, and companies like Mason Industries make devices to do that, but it only works with very high mass for the floor deck, such as 3 or 4 inches of solid concrete.
Excuse the rant, but it does annoy me that folks get fooled into buying stuff they don't need and wont work anyway, and build rooms in ways that are doomed to failure, just because some manufacturer wants o make a few bucks from his next-to-useless products...
I wish I would have found this forum a few months back before I ordered materials... oh well
You can probably return the materials you don't need. Most reputable hardware stores will take back unused materials that are in good condition and give you a refund. They might charge you a re-stocking fee, or give you less money than you paid, but something is better than nothing!
build an actual lighter frame for the ceiling, put roxul inside and cover it inside the room with Vinyl loaded mass
MLV (Mass Loaded Vinyl) is actually more dense than drywall! The density of drywall is about 670 kg/m3, MLV is about 1500 kg/m3. So a thin sheet of MLV weighs just as much as a thick sheet of drywall...
And since sound waves don't really care very much about how much you paid for your mass, they won't be impressed by the huge price tag of the MLV... they'll be attenuated by roughly the same amount, either way. It's the mass that matters, not the thickness or the price tag. The equations for calculating isolation have no variables for adjusting for cost, nor for the thickness of the materials. They only have two basic variables: the "mass" (surface density) of each leaf, and the "spring" (depth of the air cavity between the leaves). That's it. The wall or ceiling is a resonant system, just like a floated floor would be, and the equations are the same. The only two numbers you can plug into those equations are the weight-per-square-foot of the materials on each leaf, and the distance between the leaves.
Here's the actual set of equations, in case you are interested:
First, for a single-leaf barrier you need the Mass Law equation:
TL = 14.5 log (M * 0.205) + 23 dB
Where: M = Surface density in kg/m2
In this case, there is no air gap, so the ONLY factor that matters is the mass (surface density).
For a two-leaf wall, you need to calculate the above for EACH leaf separately (call those results "R1" and "R2"), then you need to know the resonant frequency of the system, using the MSM resonance equation:
f0 = C [ (m1 + m2) / (m1 x m2 x d)]^0.5
Where:
C=constant (60 if the cavity is empty, 43 if you fill it with suitable insulation)
m1=mass of first leaf (kg/m^2)
m2 mass of second leaf (kg/m^2)
d=depth of cavity (m)
Then you use the following three equations to determine the isolation that your wall will provide for each of the three frequency ranges:
R = 20log(f (m1 + m2)) - 47 ...[for the region where f < f0]
R = R1 + R2 + 20log(f x d) - 29 ...[for the region where f0 < f < f1]
R = R1 + R2 + 6 ...[for the region where f > f1]
Where:
f0 is the resonant frequency from the MSM resonant equation,
f1 is 55/d Hz
R1 and R2 are the transmission loss numbers you calculated first, using the mass law equation
And that's it! Nothing complex. Any high school student can do that. It's just simple addition, subtraction, multiplication, division, square roots, and logarithms.
Those are all for Metric units, not imperial, but it's simple to convert.
So, getting back to the point: you would gain nothing by using MLV instead of drywall. It's still the same principle, and the mass is the same, so the result would be the same.
Even worse, since MLV is very flexible, there's a chance that it would also like a diaphragmatic absorber (also called a "membrane trap"), which is a resonant acoustic treatment device used inside rooms, often in the form of a bass trap. That might or might not be a good thing for your room acoustics, depending on how it works out (what frequency it is tuned to), but it certainly would not be good for isolation!
OK, so you have a potential three-leaf wall problem, and a potential three-leaf ceiling problem. The reason why a three-leaf system is worse than a two-leaf system goes back to the same issue I've mentioned several times: resonance. All walls are resonant systems, and you need to get the fundamental resonant frequency as low as possible, at least an octave below the lowest tone that you want to isolate. A two-leaf wall is the best way of doing that, as it allows for the lowest frequency in the least total wall thickness, with the least amount of mass. In other words, it the cheapest way of getting good isolation, and also the one that uses the least materials, and the least space. If you have a three-leaf system, then you can compensate for the lost isolation by using more mass, and increasing the overall wall thickness. It's more expensive, but you can get the same result by doubling-up your mass, or your air gaps inside the wall, or both. So it's not the end of the world: It just means that it will cost you more money, it will cost you more space, and it will be heavier.
Even worse would be a FOUR leaf system, such as a pair of stud walls next to each other, where each wall has sheathing on both sides (eg. drywall, OSB, siding, MDF, plywood, MLV, etc.). A four-leaf wall has even worse low-frequency isolation than a three-leaf wall.
Your options right now are:
1) Remove the "middle" leaf, in order to make it back into a two-leaf system.
2) Add more mass (more layers of drywall) to the leaves.
3) Make the air gaps between leaves bigger.
4) Do nothing, and live with the problem of reduced isolation.
Number 1 above might actually be an option, depending on how your existing walls and ceiling are built. For example, if the walls around you and ceiling above you are ordinary stud framed house walls with drywall on the studs, then just take off that drywall, and leave bare studs. That removes one of the leaves. In fact, if you really want a good improvement in isolation, then use the drywall that you take off to "beef up" the sheathing on the other side of those same studs: cut the drywall into strips that hit between the studs, press it up tightly against the sheathing on the far side, caulk around the edges to get an airtight seal, then nail some small cleats sideways into the studs, to hold the drywall in place. That way, you don't even have to throw away your old drywall, and you get greatly improved isolation. The same applies to the ceiling: take off the current drywall, cut it into strips that just fit between the joists, press it up tightly against the surface above, caulk, cleats. Done!
But the basic question here is: how much isolation do you need, in decibels? Those equations that predict the performance of your walls / ceiling, all give answers in decibels, so you need to know how many decibels you NEED, in order to see if the result will be enough!
So your first order of business is to determine that number: how many dB of isolation do you need?
That way I have nothing too heavy above my head.
If you have nothing heavy up there, then you have no isolation!
As you can see in the above equations, the key to it all is mass. Mass is what stops sound. If you have no mass, you have no isolation...
Also is there a non destructive way I could fasten the outer drywall to the actual house walls of the room? As mentioned I am renting I can't do damage to the house walls...one of the reasons I liked the idea of a non-touching room in room.
If your existing walls are normal house walls (stud frames with some type of sheathing on both sides), then that's already a two-leaf wall, so adding anything at all in front of it makes it into at least a 3-leaf, and possibly a 4-leaf! Actually, the existing walls are really "sort-of" two-leaf: considering that the sheathing layers on either side are mechanically connected by the studs, that acts something like a single-leaf wall, and something like a two-leaf wall: Technically, its a "coupled two leaf system", which means that it does not isolate anywhere near as well as a true two-leaf system, but it still has detrimental characteristics if you add another leaf (or two) in front of it.
If you absolutely cannot touch the walls around you, then your only real option is to build a three-leaf system in such a way that it compensates for the lost isolation, and to be very careful about avoiding a four-leaf system!
So, what I would do is to build a stud walls a few inches away from the existing walls, and put drywall on only ONE side of those studs. In fact, I would put a layer of thick OSB on the studs first, then at least one layer of thick drywall, perhaps two layers. I would also consider using Green Glue in between the layers. Green Glue is not actually glue (despite the name): it's an acoustic damping compound that greatly increases isolation for low frequencies, which is where your problems will be, so it's worthwhile in your case. It's expensive, but really good. I would do the same for your ceiling: put suitably dimensioned joists across the tops of your new walls, with a layer of OSB on the joists, then one or two layers of drywall, the same as the walls, possibly with Green Glue. And of course, the air gaps would all have to be filled with suitable insulation (either fiberglass or mineral wool).
I realize that you already built some things, but to be honest, I'd suggest that you take that down and start again. It's not going to do what you are hoping it will do, and you can re-use the same materials in the correct configuration to get far greater isolation, probably ten to one hundred times better (10 to 20 decibels more isolation).
- Stuart -
