Apartment sound construction failure

[soundbanana]

Hello, I've just renovated my apartment and I was trying to reduce noise from my neighbours, however I fear I might have shat the bed.

It is a concrete building, so in the living room to reduce noise from downstairs neighbours I put "pressure resistant" insulation with fibreboard on top, as a floating floor. On top of the fibreboard I also have one layer of sheetrock and then the wooden floor.

Sadly I am experiencing a "booming" sound when walking on this floor now, like a drum. It's surprising to me as I thought the insulation would be dense enough to absorb any sound. I was recommended this procedure when talking to professionals about sound-insulating a floor.

I was wondering if someone could explain to me what is going on with this floor? Triple-leafing effect should not occur as to my knowledge there would be only one airspace in this floor. Concrete + airspace/insulation + fibreboard + sheetrock.
Have this floor actually made it worse? Making the noise from my neighbours resonate?

***
I also insulated the wall. 2x4 on the wall with insulation in between, then a layer of sheetrock. Did this also worsen the situation? The wall was originally just concrete with wallpaper on it, as you can see in the photos.


So I'd appreciate any professionals on here that could explain what has gone wrong with the floor or the wall. Or maybe there is nothing wrong with the wall? Thank you

PICS: https://www.dropbox.com/sh/c5d5ifgwdeeg ... lJxqa?dl=0

[Soundman2020]

Hi "soundbanana". Please read the forum rules for posting (click here). You seem to be missing a couple of things!

in the living room to reduce noise from downstairs neighbours I put "pressure resistant" insulation

Do you have the specs on that insulation that you used? Link to the manufacturer's website?

with fibreboard on top, as a floating floor.

That floor is not floating, and nor should it be. Here's why:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

However, it also is not doing you any good! More on that below...

Sadly I am experiencing a "booming" sound when walking on this floor now, like a drum.

Correct. That is to be expected.

It's surprising to me as I thought the insulation would be dense enough to absorb any sound. I was recommended this procedure when talking to professionals about sound-insulating a floor.

You should probably be looking for a different "professional". Any true expert in acoustics and isolation would have not recommended such a thing.

Firstly, insulation does NOT stop sound. That's not what it is for, or what it is supposed to do. It damps resonance, and absorbs some sound, but that is very different from stopping sound. (That's why most acoustic professionals don't use the term "soundproofing", because there is no such thing).

So your floor started out on several incorrect acoustical principle. Insulation does not stop sound, floating floors cannot be built they way you were told to build yours (see link), and you likely do not need a true floating floor anyway.

I was wondering if someone could explain to me what is going on with this floor?

It is exactly what you said it is: a drum. It is a flexible membrane stretched across a resonant cavity. That is precisely what it is. Therefore, it does what it is supposed to do: it resonates at the frequencies to which it is tuned, just like any other drum. From the way you built it, as seen in those photos, I'd estimate that the resonant frequency is likely somewhere in the region of 40 - 60 Hz.

Triple-leafing effect should not occur as to my knowledge there would be only one airspace in this floor. Concrete + airspace/insulation + fibreboard + sheetrock.

You are assuming that the neighbors down below do not have any other ceiling that hangs below the concrete...

Have this floor actually made it worse? Making the noise from my neighbours resonate?

Quite possibly. And likely in the other direction too: your walking on that floor will possibly now be louder than it was before, for them.

I also insulated the wall. 2x4 on the wall with insulation in between, then a layer of sheetrock. Did this also worsen the situation?

Once again, quite possibly. You have not actually isolated that wall at all, since you attached the framing directly to the existing concrete wall, and you also laid the 2x4's flat. So you have a very thin cavity in there, with a very high resonant frequency. Probably around 80 to 100 Hz. So that wall will amplify sound traveling through it for all frequencies up to about 130 Hz. It starts isolating reasonably at about 190 Hz, and only isolates well above about 290 Hz. However, that "isolates well" is not so great either: limited to maybe 30-something dB, total.

So I'd appreciate any professionals on here that could explain what has gone wrong with the floor or the wall. Or maybe there is nothing wrong with the wall?

There is something wrong in both cases. The advice you received was not correct, and what you have built will not do what you are hoping it will do. Your suspicions are founded: what you have done probably won't help, and very possibly could make things considerably worse.

OK, so let's start by taking several steps back: What are you trying to accomplish here? It seems to me, that you have noisy neighbors and want to isolate yourself from them so that you are not so annoyed by their noise. Is that it? Or are you trying to build a studio in there, and you don't want to annoy the, with your noise? Those are two very, very different scenarios.

If you could explain in more detail your goals here, as well as the types of noise you are trying to deal with, and the levels of noise you are dealing with, then we can suggest ways of accomplishing that. Right now, we don't have enough information to go on! If your goals is to isolate your piccolo playing so that your neighbor's don't hear it, then what you have is probably not to far off from what you need. But if your neighbors have a thumping, blasting home theater down there, with earth-shaking subs, and you have a sleeping baby in your room, then that's a very, VERY different thing. If you have a sound level meter, then it would be great of you could measure the actual levels that are causing you problems.


- Stuart -

[soundbanana]

Hi Soundman2020, thank you for your reply, I appreciate it a lot in this time of great frustration.

* 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. http://www.rockwool.no/produkter/u/2011 ... /markplate

* You say my floor is not floating. Why not? The fibreboard is resting on top of the insulation, nothing is nailed down. I have read the "floating floor" thread, though I still didn't quite understand why I shouldn't have used it in my case. Is it because I simply cannot get enough weight on top of my insulation in order to eliminate the resonance beneath? And if I in fact was able to put enough weight on there, wouldn't it then be a good solution?

* Regarding the drum aspect: why on earth would this building technique be a standard in households in Norway? Proponents brag that it eliminates impact sounds, at least to the people underneath. What they obviously failed to mention to me is that it also creates a drum, worsening MY situation.

* Triple-leaf: I'm fairly certain that my downstairs neighbours concrete roof is only painted, as is the standard in the building. In the event that they do have a cavity - I have still expanded the thickness of the floor/roof with more materials - so even if it would be triple-leaf, wouldn't it be better than nothing? I.e: 100cm tripleleaf must be better than 30cm doubleleaf?

* 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?

* 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. Seems like I haven't done myself any favours, eh? One for the history books, I'm sure.

EDIT: I did a sound test where I played different HZ and it was the loudest at 48hz, 58hz and 88hz....

[Soundman2020]

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 -