Question about floating floor

Hi all! I've learned a lot reading here, but i'm in big trouble!! I'm a spaniard engineer/musician, now living in north Argentina, 1.500 Km north of Buenos Aires, and I'm building my own studio, the one and only studio in this zone. I've builded the exterior shell of brick and concrete, and I'm doing the inner walls of drywall on metal studs. I did not float the control room floor, but i floated the live room floor with 20mm fiberglass (80 Kg/m3) and a 40mm concrete slab. I wanted to isolate the floor of the vibrations of the road i got at 25m. My surprise was that when finished, it resonates like a tuning fork, it vibrates freely as one piece (that really is). the dimensions are 5,50m x 7m. My first instinct is to rip it and leave the floor unfloated, but I wonder if there's a better solution. My contractor says the drywall and ceiling will absorb the vibration, but i think it will vibrate like a drum, floor and walls, and the mechanical transmission will do any recording impossible. Please need some advice. Here in Tucuman there's nobody I can ask. Thank you in advance and forgive my english.

i would check and make sure the floating slab isn't actually touching the floor underneath or walls somehow - maybe some rebar is touching or a gap in forms allowed cement to get through and bridge the top floor to the lower one. does the floor seem resilient or stiff? it could be the insulation is too stiff (dynamic stiffness) for the mass of the floor - that's not good. if its too resilient, you might consider another 40-60mm layer on top to add more mass. although, it might be that the rest of the construction on top of the floor will add enough weight to compress the insulation to the desired value and add some dampening.

Thanks for your help. It seems the slab is not touching the walls anywhere, in fact you can't hear anything in the wall if you hit the floor, but it makes a big low noise and a great vibration all over the slab. I followed the process and I think everything is well done. Yes I think the fiberglass is too resilient, maybe I need more mass on the slab. I'll try this and see what happens. How can I calculate the weight of all the structure of the drywall? If the weight of the slab plus the structure presses too much I won't have a floating floor, right?

yes, if there is too much compression you'll end up without a floating floor... to calculate the weight you'll need to add up the wall board, framing, any electrical, any ducting, fasteners, mud, caulk, etc and bear in mind this weight will be on the edges of the floor so the compression on the edges will be highest. any photos of the construction process or a more detailed description of the floor?

Sorry to tell you this - but the design is doomed for failure right off the bat........ And your contractor doesn't have a clue what he's talking about (as regards the walls absorbing the problem) You cannot just arbitrarily pick a spring and slab and ever expect the assembly close enough to a center frequency that won't be problematic for you........ So figure to begin by jackhammering up the top slab you have now........ Next - I would not approach this with that method at all....... Either polymer pucks - or (even better) a slab lift design - using tested materials whose properties are well known........ all designed around a center frequency (for the slab ) of 10Hz or less......... Of course you aren't going to be able to do this yourself unless you start studying - which you probably should have done before throwing your money away on what you have now............ So figure to hire a designer to figure it all out for you........... someone reasonably local so they truly understand the properties of the earth the lower slab is sitting on - and what it might bring into the mix as well........ Good luck, Rod

You're right Rod, nobody here know a word about acoustics, and the few consultors in this country are 1.500 km from here. I can't afford it. So do you think i might unfloat it? This is the first thing I thought, but given that I have the slab already done, I wanted to know if there's something I can do to solve the problem before demolishing it. I did know I didn't be able to build a floating floor the common way, but I never thought a concrete slab will sound as it does, this was my mistake. Thanks for your help, I will post some photos of my construction.

opaqueman wrote:

You're right Rod, nobody here know a word about acoustics, and the few consultors in this country are 1.500 km from here. I can't afford it. So do you think i might unfloat it? This is the first thing I thought, but given that I have the slab already done, I wanted to know if there's something I can do to solve the problem before demolishing it. I did know I didn't be able to build a floating floor the common way, but I never thought a concrete slab will sound as it does, this was my mistake. Thanks for your help, I will post some photos of my construction.

There isn't anything I can think of to change the center frequency of an object after it's constructed. You'll just have to remove it........ Rod

Haven't read too closely here, but what about drilling holes in the floating slab and piping cement into the gap? I don't know if that would be too much weight, or not as economic or easy as ripping it out, but just to cover all your bases....

Thanks pianojam, but there's no gap. It's a concrete subfloor (4 cm I think), 2 cm fiberglass panels (80 Kg/m3) an a concrete slab of 4 cm or a little more. I think is a problem of weight, but I agree with Rod that nobody here (nor me) can calculate the resonant frequency of the whole system. I will try a couple of things, but I think I will remove it at last.

Here are some photos of the construction of the floor:

It's the first time I attach photos