The manufacturers website is not in english, so likely you won't understand it but the insulation in the floor is a high density hard compressed insulation plate 50mm.
I tried Google Translate on that, and while it is understandable, there's not enough technical data there to be able to say if that is useful (or not) for that application. I suspect it might be too rigid and the density might be too high.
You say my floor is not floating. Why not? The fibreboard is resting on top of the insulation, nothing is nailed down.
In order for it to float, there must be resilient "spring" of some type which provides the ONLY connection between your floor and whatever is below it. You show a wooden frame under your floor, which is a solid connection. Even if that were not the case, that insulation is also an unknown factor: We would need to know the "spring constant" (K) for that stuff, and the load that is on it (the weight of the floor, furniture, people, equipment, etc.). The spring constant is a measure of the resilience ("springiness") of the material. If that is not correct for the load you placed on it, then it is not floating.
Think of it this way: Your car suspension has springs in it, which work exactly the same way as your insulation is supposed to. Those springs in your car are designed specifically to be slightly compressed from the normal weight of your car. If you were to take out those springs an replace them with the springs from a motorbike, those springs would be totally flattened by the weight of the car, way over-compressed, "bottomed out", so they would not keep the car "floating". On the other hand, if you were to replace your springs with springs from a large truck, the tiny weight of your car would not even compress them at all: they would be "topped out", acting like solid connections, and the car would not float. It is only when the correct springs are used for the weight of YOUR car, that the suspension floats.
The same with your floor: If the weight of your floor is too much, and it over-compresses your insulation, then it does not float: it acts like the "car on top of motorbike springs". If it is under-compressed, then it does not float: it acts like the "car on top of truck springs". It only floats if the insulation is compressed within the optimum range.
Since the manufacturer of that insulation does not seem to have measured or published the resilience numbers for that product, we don't even know what it should be! But let's assume that you got VERY lucky, and purely by chance you managed to make your floor just the right weight to float. You didn't mention how the floor is built up, but lets assume it was two layers of 16mm MDF. The density of MDF is about 750 kg/m3. The surface density of that would be about 24kg/m2. In other words, assuming you did it like that, then each square meter of your floor weighs about 24 kg. Great! But what happens when you stand on it... Assuming you are an average adult male, you weigh probably 85 kg, fully clothed. Your weight is spread across a small area of floor (just the soles of your feet, really) but to make the math easy, let's say that your weight is actually spread across an entire square meter of floor. You can see where this is going: that square meter where you are standing now weighs 110 kg! So there is nearly FIVE TIMES the correct mass on that spot. I think you can understand that the isolation "spring" will not be floating under such a huge load change. We are back to the situation of a car resting on motorbike springs...
You might assume that "Well, its only that one place that isn't floating: the
rest of the floor is floating fine!" No it isn't. In any isolation system, the total isolation is only as good as the isolation at the weakest point. If there is even one tiny area of your floor that is over-loaded or under-loaded, then that's the point that defines the isolation for the entire floor.
Think of it this way: If you have a bath tub in your house that is perfectly built in every place, except for one tiny hole, how well do you think it will hold water?
That's why I said that your floor it not floating. It cannot be floating under all circumstances, unless you specifically did the math to make sure that it is compressed exactly the right amount at each point. And if you had done that math, then we would not be having this conversation!
That's why I said that your floor is not floating.
Just like the "floating floor" thread points out, to do it correctly you need a massive floor, one that is very heavy, so that the weight of a person walking over it, or furniture sitting on it, is only a tiny change in point loading. For example, if you would have done your floor with 15cm of concrete, the surface density would have been different. Concrete weighs about 2200 kg/m3, so a 15cm thickness weighs 330 kg/m2. Your weight spread over 1m2 only adds 24% to that, instead of 500%. In fact, concrete is far more rigid than MDF; so your weight would actually be spread over a much larger area anyway: more like 6 or 8 m2, so the actual change in loading is just a couple of % points.
Floating floors need high rigidity, high mass, and properly calculated springs. The chances of it floating purely by luck, are zero.
* Regarding the drum aspect: why on earth would this building technique be a standard in households in Norway?
It might work fine for airborne noise, but not for impact noise. Two different things. I'm also not convinced that the way they told you to do it, is the way it is normally done... It doesn't make sense, acoustically, and you can see the results yourself: I predicted the outcome based on simple equations, which any acoustician knows, and my predictions were accurate. So I'm wondering if the person who suggested you should do it this way, really knows much about acoustics....
Proponents brag that it eliminates impact sounds, at least to the people underneath.
Impact noise is not airborne noise. Two different things. Plus, impact noise on a
decoupled and properly damped floor or properly floated floor will be greatly reduced, but impact noise on a
coupled floor (like yours is) will not be reduced much at all. The framing around your floor couples it to the sub floor, and you don't have enough mass on there to make it float anyway, so basically the entire floor is coupled.
* Regarding the wall: so the appropriate action I should have taken would be to put a double layer of sheetrock directly onto the concrete, without making a insulated cavity at all?
No. That would make no difference at all. It's all about mass. Assuming that your concrete wall is 20cm thick, the surface density is about 440kg/m2. The density of drywall is about 680kg/m3, so the surface density of two layers of 15mm drywall, is about 20.4 kg/m2. In other words, your drywall would increase the mass by about 4.6%. That does nothing at all.
What you would need to do is to build a wood frame about 2cm away from the wall, not touching it at all, and put your drywall on that, with insulation in the cavity. That is a fully decouple 2-leaf MSM system. The two "leaves" of the wall cannot touch, at all. Not even a single nail can join them.
* What I was trying to accomplish with all of this was to reduce neighbours airborne sounds coming into my apartment, both from my downstairs and "sideways" neighbours.
It is possible to do what you want, but not the way you did it (OK, you already found that out...). It can be done, but what you'd need to do is probably not what you'd want to do, and might be more expensive than you are willing to pay, and you might not even be able to do it, structurally. In order to make your floor float on that mineral wool, you would probably need to load it to somewhere around 200 - 500 kg/m2... There might be other ways, though...
I did a sound test where I played different HZ and it was the loudest at 48hz, 58hz and 88hz....
It looks like my predictions were pretty accurate! I said "
...the resonant frequency is likely somewhere in the region of 40 - 60 Hz." and also "
Probably around 80 to 100 Hz."The math for acoustic calculations is fairly simple, and it works.
- Stuart -