I've seen many people raving here on GG and the likes so I was hesitant to dismiss it entirely .
GG is great, no doubt about it.... but it sure ain't rubber! It's a gooey polymer that never hardens, not like rubber at all. And when used as directed by the manufacturer, it does work.... but I sure wouldn't waste any of it between a concrete wall and a sheet of drywall...
I'm considering to build room within a room thus making a floating floor on neoprene pads and osb3 sheets to be on the safe side,
Actually, that really would be a mistake! Not on the safe side at all.... Here's why:
http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173
Read the above first, then carry on reading below:
This is the part that the purveyors of "plywood deck floated on our magic rubber pucks" don't tell you. Here's 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 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.
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 actually 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 and 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 here, but I can keep on adding scenarios here, such as the desk, chair, 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.
There's another option here, which is even better: build your inner-leaf walls on top of the floor! In that case, the entire room is floated. The calculations for the springs are a bit more complicated like that, but the total floated mass is even greater, so variations from people standing on the floor and moving gear in and out are even lower, as a percentage of the total floated mass. That's a lot more expensive, of course, and more complex, but if you really do have a need for extra high isolation, that's as good as it gets.
i wouldn't risk any transmission on the building structure causing me any troubles with the neighbors. Using risers on drums and amps may prove a very effective solution but Im still a bit reluctant. I'm not sure i would get away with just the concrete floor!
Why not?
If you really do need to float your floor, then it certainly can be done. As I outlined above. But it is expensive, and not easy to do.
On the other hand, what is under your floor? It's a basement, so I assume that under your floor is good old Mother Earth. And she's pretty big! In other words, your slab is being damped by the entire Planet Earth.... it's hard to beat that! I'm having trouble imaging how a few tiny bits of rubber and some thin insulation could do a better job than the entire planet...
(You would be amazed by the amount of unnecessary materials i had to cut down)
And you can probably cut down on even more.... Post your design, and we can help you with that, for sure...
- Stuart -
Maybe they could explain to you the purpose of doing that? There's certainly no acoustic reason for it. It would make absolutely zero difference in terms of isolation.
It's easy to write numbers on paper... not so easy to produce that performance in real life. Claiming that a substrate gets 30 dB of sound reduction is pure hype: Since it is a "substrate", it has to be used along with something else, and without saying what that "something else" is, that's a meaningless claim! Totally useless. The results would be VERY different if you used it with a sheet of cardboard on top, or a sheet of MDF 25mm thick, or a sheet of concrete 300mm thick!