Concrete Plate vs Rockwool Drywall Ceiling

Hi, I would like to know, what if I use concrete plate for ceiling soundproofing? Since it got mass, very airtight, and would support a floor above, I think it would be a better solution. How much STC is a 12 cm concrete plate? How is it compared to usual rockwool-double drywall-channel system? Ari

About STC 45 or so - mass is great, but not everything. Doubling its thickness raises STC about 5 points, depending on the original thickness. There are other factors, but I'm out of time for now. I'll go into this more this evening... Steve

Ari, if you have a concrete ceiling that will support a floor above, you can add a couple of layers of Homosote above the concrete, then a layer or two of gypsum wallboard, then underlayment (plywood or MDF) and finally the flooring material, and get STC in the range of 55-60, possibly a little better. Even with heavy mass, which is good for low frequencies, you still need that "air space" (the two layers of Homosote) and a second layer of mass (the gypboard and plywood and floor covering) in order to get good isolation through the entire frequency band. The other thing that makes what I suggested above a good way to go, is that the two "mass centers" have different resonant frequencies because of their dissimilarity. This keeps any one frequency from finding a "resonance path" and getting through... Steve