OK, now I understand. It's not your actual concrete slab studio floor that is resonating, but rather the light-weight wood assembly sitting on top of it. That's quite common. It happens all the time to first-time studio builders. Any time you put a thin, flexible sheet of material (such as OSB) over an air cavity, it does, indeed, create a resonant system, and any resonant system will NOT isolate the room. In fact, at the exact frequency of peak resonance, that system can amplify the sound going through to the other side. So if you are hearing an F# in your room, then whoever is down below you, is also hearing it, and loud!
I'm starting to feel a little stupid. It's all a bit more difficult than I had anticipated. But I'm doing it right or I'm not doing it.
Great! So you should first investiage this a bit, to find out how to do it right. There's three things here on the forum that will help you to get your floating floor right:
The first one is a research paper with results of extensive testing of various floating floors, some of them similar to your. This paper basically demonstrates that it is really, really hard to get a floating floor to work
without creating a resonant system:
https://digistar.cl/Forum/viewtopic.php ... g+floor#p4 Look for the document title "IR-802 - Floating floors", about half way down that list. It's a very interesting paper, and fairly easy to follow.
The other two, are articles I wrote about floating floors a few years ago:
What is a floating floor? How to do it wrong, and how to do it right:Floating your floor: How and why... and why not.Those should give you a good idea of what the real issues are here, and how to go about building your floor correctly... if you even need one!
That's the basic issue here: whether or not you actually need a full floating floor. That's why I asked what is below your studio. If there is another important down there (a parking garage, laundry, bathroom, or some such) then you might not need one. It might be simpler just to mount any noisy instruments on Glenn's "drum riser", if you plan to track in that room, or just do nothing at all if you only plan to mix in there (as long as you isolate your speakers from the soffits!).
But if there is something important down there as an angry neighbor's bedroom, or something like that, then you
might need one. Maybe. It does depend on what you are going to do in your room! If you are going to play live acoustic drums, bass guitar on a big amp, or anything else that makes a noise and also causes vibrations in your floor, then yes, you would need to do that, and you are right: it is NOT easy to do. See the links above.
You would first need to determine how much of a problem you are causing, and that would involve going down into that room under yours and doing a spectrum analysis while someone else is making that annoying noise in your room. That way, you can determine what frequencies are causing the problems, and ho loud each of those is. Based on that, you can "tune" your floor to reduce those frequencies as much as possible, to acceptable levels. It might be possible to adapt Glenn's Drum Riser concept to cover the entire floor, if the problem isn't too serious.
In the worst-case scenario, your "loud noise" would also be causing "structure-borne" vibrations in the building structure itself (eg, from kick-drum impact sounds, or bass amp vibrations, or stomping musicians with clogs on....). In that case, you would, indeed, need to float your floor properly, which would imply that you'll need to hire a structural engineer to make sure the existing floor is capable of supporting the large additional weight of a properly floated floor.
The diagram you posted that your fried sent to you, is not an option. That is a three-leaf system, which would likely make matters WORSE in the low end of the spectrum. It might do something of the mid range and the highs, but it would resonant at two different frequencies in the low end, perhaps even in the low mids, since it doesn't have anywhere near enough mass, and the are gas are very tiny. To understand the concepts involved here, especially the issue with 3-leaf systems, I'd strongly suggest that you should read this article about how studio isolation works:
What is MSM? How does it work? That's mostly about walls, but the same principles apply to floors as well.
Unfortunately, floating a floor is a big deal if it has to isolate the entire audible spectrum by a large amount. If you just need some reduction at certain frequencies in the low mids or mids, then there are simpler alternatives. But not that system that your friend suggested.
Isolation is a science. It is well understood. Sound follows the laws of physics, and is therefore easy to predict. There are systems for creating isolation, and equations for calculating things, such as the frequencies that will be isolated, the frequencies that will not be isolated, and how much isolation you will get. Unfortunately, many well-meaning people on the internet do not know this, and think you can just sort of cobble together bits and pieces of things, and keep on trying until it works. Or they heard about an uncle of their wife's second cousins boss, whose son's girlfriend once worked in a studio, and he thinks the did it like XYZ... Reality is a bit different! Isolating a studio is simple in concept, because the laws of physics are well understood. I can design you an isolation system for as much isolation as you need, at any frequency where you need it. The design isn't a problem. It's the implementation that is a problem, because the laws of physics dictate the, in order to get isolation, you need mass. The more isolation you need, the more mass you need. Major mass takes up space. Major mass is expensive. Major mass is hard to handle in practice, and can easily overload whatever structure that it is sitting on. High isolation at low frequencies also implies a large air cavity (because small cavities resonate at higher frequencies). Large cavities take up space. ANd high isolation also implies acoustic damping of the right type, the right amount, and in the right place.
That's why your current floor is resonating: it is light-weight (low mass), and the air gap is small, which implies a relatively high resonant frequency, and there isn't enough damping of the right type.
The articles above should get you on the right path for doing this right, if indeed you need to do it.
EDIT: I did take a look at the link you posted... that's not a floating floor. You cannot build a successful studio floating floor like that. Way too little mass, way to little air gap. That floor is going to resonate, just like yours, but perhaps at a slightly lower frequency. See the above articles to understand why. Any company that uses the words "soundproofing" in their name, probably isn't going to be a good source of reliable information (with some exceptions). Professional acousticians and acoustic designers don't use that word, because it has no meaning. There is no technical definition for what "soundproofing" is. We tend to use terms like "isolation" and "transmission loss", which are real technical terms that do have meaning, and can be measured.
- Is it a good idea to do a few steps back and redo the floor construction?
Yes, definitely! You certainly do not want to have your studio sitting on top of a resonant cavity!
- Did i damaged the Rockwool?
Probably not. It's probably OK. Mineral wool is pretty tough. Once you get it out, measure it to see if it is still roughly as thick as it was originally. If it is, then you are OK. It's pretty hard to damage mineral wool!
- The floor is now 12cm's high. There is concrete underneath so there must be another way, right?
Right!
I suspect that you might be better off without that floor at all! Then you can re-use those materials for the walls, ceiling, soffits, acosutic treatment, etc. But if it turns out that you do need something down there, then there are still options for you that don't need a full floating floor, which is expensive to do, and complicated. Those options aren't as good as a floating floor, but might be enough for your case. And they also don't cause strong resonance!
- Stuart -