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PostPosted: Thu Sep 28, 2017 11:31 pm 
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Hi everyone

First time here, really enjoyed reading through the posts. I have quite a specific issue so I would really appreciate any advice. I have been running my recording and rehearsal studio successfully for 8 years. The business directly below me recently changed hands and they have complained about the noise from my ground floor live room. The previous tenant must have been a very chilled out chap because he never complained once. So I need to re-think the floor. I believe there is just a single concrete layer between my unit and the one below.

Details:
The live room is 17.5' x 13' inside measurements. The walls are the standard 'Mass Air Mass' design with two layers of stud and insulation with air gap in the middle.
The floor is currently just a single layer of rubber matting with chipboard and carpet (I know, don't take the piss, I was clueless when I built it).

So.... I need to know, is a wooden floating floor the best option or should i be looking at concrete? I've read to much contradicting information, with some recommending the rubber 'u boat' isolators with others saying they're a waste of time and to not bother with isolation and just focus on mass. The noise that is being transferred is both airborne and impact. Luckily the neighbours are being understanding so aren't rushing me to do the work, so I want to make sure I get it right.

Any advice would be greatly appreciated.

Dan
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PostPosted: Fri Sep 29, 2017 4:31 am 
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Hi Dan, and welcome. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

Quote:
The business directly below me recently changed hands and they have complained about the noise from my ground floor live room.
Just trying to understand here: You are on the ground floor, so they must be in the basement? Is this an office building of some sort?

Quote:
The walls are the standard 'Mass Air Mass' design with two layers of stud and insulation with air gap in the middle.
And the ceiling?

Quote:
The floor is currently just a single layer of rubber matting with chipboard and carpet
:shock: Mmmmm.... :)

Quote:
is a wooden floating floor the best option
No. Here's why: viewtopic.php?f=2&t=8173

Quote:
or should i be looking at concrete?
Yes, assuming that it is PROPERLY floated.

Quote:
I've read to much contradicting information, with some recommending the rubber 'u boat' isolators with others saying they're a waste of time and to not bother with isolation and just focus on mass.
Take a careful look at the specs for those rubber pucks: You'll find that there aren't any! That should tell you something straight away. Go to the web site of the manufacturers, and see if you can find any real technical specs, any reports from independent acoustic test labs, that clearly define the transmission loss curves that such products produce.... Have fun searching! :)

Here's the absolute real down-to-earth technical truth:

It's also the part that the purveyors of "plywood deck floated on our magic rubber pucks" don't tell you. Here's how it goes...

First, there's a graph that explains the problem in simple terms:

Attachment:
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 fail to 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 upper 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 floor joists, 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.

Which brings up the question: What would you need to do, to get a 60 PSF floor? Well, let's consider using OSB for your floor deck: the density of OSB is roughly 610 kg/m3, which works out to 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! :shock: 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 (which is great if you only record sopranos accompanied by piccolos! :) )

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. The people telling you to forget U-boats and plywood are correct.

Now, all of the above assumes that the "deck" is fully isolated from the underlying subfloor, and that the only "spring" down 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 those rubber pads you mentioned, 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" (it makes the spring stiffer, which implies a higher resonant frequency). 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 really 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 somewhere in the range 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 unicorn hair, 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! Well ... Until you stand on it.... :shock: 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 :shock: Gulp! I think you see where this is going.... You just flattened your rubber pads into oblivion! Pancakes would be jealous of how flat your pucks are! 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 here, but I can keep on adding numerous scenarios, such as a desk, chair, couch, your DAW, other gear, more people, instruments, 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 and Kinetics Noise Control 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.

---

OK, rant mode = off...

Quote:
The floor is currently just a single layer of rubber matting with chipboard and carpet
That, right there, is probably a big part of the problem!

In Canada, the National Research Council has done a huge amount of extensive testing on acoustic isolation, and all of their documents are available on-line for free! Unfortunately, the have now made it impossible to find them... it used to be simple to go to their web-site and browse through lists of fascinating documents, but a couple of years ago they "greatly improved" their website ( :!: :roll: :cen: ), so now you pretty much need to know the exact title and location of the document in order to get it... Wonderful! But anyway, there's a document called IR-802, with the title that only a scientist could love: "Impact Sound Measurements on Floors Covered with Small Patches of Resilient Materials or Floating Assemblies". And it actually does tell you all about that subject. There's dozens of pages of analysis of tests they did in their acoustic labs, and one of the graphs is rather interesting, since it shows what you have:

Attachment:
floating-floor-negative-isolation-1--various-decks-on-rubber-mat.jpg
I'm not sure which of those best fits your case, but I'm guessing the 15mm OSB is close. But regardless, there's an interesting thing about all of those. They all have NEGATIVE ISOLATION for the entire low end of the spectrum, below about 300 Hz! There's another word for "negative isolation": it's called "amplification". In other words, your floor is probably AMPLIFYING sounds in that range, making them LOUDER down below than they would have been if you would have done nothing at all to the floor...

So that's the first issue: simply taking out your current floor would likely improve things, assuming that you have the situation shown in that graph.

Second, the REAL solution here, is to float a concrete slab instead. And that is complex, and it is expensive. It's not something that you want to try on your own! As I showed above, you need to do a whole bunch of calculations involving point loads, line loads, area loads, resilience, deflections, mass, frequencies, and other fun stuff, to make sure that your slab actually will float. If it does not float, then you are back to the same situation: you make things worse, not better.

Quote:
The noise that is being transferred is both airborne and impact.
Yep, but it's the impact noise that is a bitch to deal with, since that is in the actual building structure. Of course, a correctly floated floor will deal with both of those, assuming that your walls and ceiling are already doing what they are supposed to do, and also that you have correctly isolated your HVAC ducts, with suitably designed silencer boxes, and also that your electrical system was installed correctly, with proper attention to acoustic isolation of the outlets, switches, lights, wall penetrations, etc...

I would suggest that you hire an expert to do the math and do the design for you, and you'll also need a structural engineer to check that you really can load up the existing floor with another few thousand pounds of dead load, in addition to the existing dead load, and the live load. There's a lot involved here.

There might also be another solution, but it's unlikely to be as effective: it might be possible to re-build the ceiling in the room down below, such that it provides improved isolation. I would not bet on that working well, though. The real solution is to float your floor properly.


- Stuart -


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PostPosted: Fri Sep 29, 2017 8:07 pm 
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Hi Stuart

Many thanks for your reply and apologies if I missed the board rules.

I will definitely take that on board and forget about a wooden floating floor. I'll get a builder in to assess the possibility of a concrete floating floor. The rest of the room (walls, ceiling, air ducts etc) were all done well and there's very little noise escaping into the rest of my unit... it's purely the sound travelling below. Thanks to your comments I have a good idea of what to do.

Kind Regards
Dan


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PostPosted: Fri Sep 29, 2017 11:27 pm 
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Quote:
I'll get a builder in to assess the possibility of a concrete floating floor.
It's not a builder that you need. Not at all. A builder would not have the faintest idea about how to do it correctly. What you need is a specialist. Floating a floor is not something the typical builder would have any expertise in. Call someone like Mason Industries, or Kinetics, or a studio designer, and get one of their qualified engineers to look at your situation and design the solution. Then, once you have the plans, get a structural engineer to examine your building to see if it is even feasible to do it. And once you have all that in place, with an approved plan and a structural engineers blessing, then and only then can you approach a qualified builder for an actual quote.

This is the only sane way to approach the problem. Asking a builder to do it is sort of like getting the service station attendant why pumps your tires and cleans your windshield, to tune the power train on a Lamborghini... :)

- Stuart -

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PostPosted: Fri Sep 29, 2017 11:41 pm 
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Soundman2020 wrote:
Quote:
I'll get a builder in to assess the possibility of a concrete floating floor.
It's not a builder that you need. Not at all. A builder would not have the faintest idea about how to do it correctly. What you need is a specialist. Floating a floor is not something the typical builder would have any expertise in. Call someone like Mason Industries, or Kinetics, or a studio designer, and get one of their qualified engineers to look at your situation and design the solution. Then, once you have the plans, get a structural engineer to examine your building to see if it is even feasible to do it. And once you have all that in place, with an approved plan and a structural engineers blessing, then and only then can you approach a qualified builder for an actual quote.

This is the only sane way to approach the problem. Asking a builder to do it is sort of like getting the service station attendant why pumps your tires and cleans your windshield, to tune the power train on a Lamborghini... :)

- Stuart -


Thank-you, I have actually been in touch with Mason Insustries.


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