Hi "elseano". Please read the
forum rules for posting (click here). You seem to be missing a couple of things!
I noticed in this thread a recommendation for 48kg is there any reason why you would choose 48kg over 60kg/m3?
48 kg/m3 is the optimum density if you are using mineral wool, but if you are using fiberglass it would need to be about 30 kg/m3.
In fact, it isn't really the density that matters, but rather a characteristic known as "gas flow resistivity" (GFR). That's the actual acoustic parameter that defines how the insulation behaves with sound waves moving through it. The problem is that most manufacturers of insulation don't bother measuring or publishing that number, because it doesn't have much relationship to the main purpose of their product: thermal insulation. It is only meaningful for what we studio builders want: acoustic porous absorption. Fortunately, there is a rough relationship between GFR and the density of each type of material. The relationship isn't precise, and it isn't linear, but it is close enough to be useful.
48 kg/m3 is slightly better than 60 kg/m3 for low frequency absorption. The more dense the insulation is, the better it is for HIGH frequencies, and the worse it is for LOW frequencies. Roughly. That's not intuitive, but it's the way it works, to a certain extent. If you draw a graph of overall acoustic performance vs. density, you get a gentle curve, which peaks at about 48 kg/m3. If you go higher in density, then it is better for highs. If you go lower, it is better for highs. Of course, if you go very high or very low, then all bets are off, but in general, that's how it works.
But like I said, each type of insulation is different: aprox 50kg/m3 applies to mineral wool, aprox. 30 kg/m3 applies to fiberglass. If you use something else, then you'd have to look up the acoustic characteristics of that specific material to find out what density you'd need.
- Stuart -
