Wall frame construction

Hello everybody, first of all let me say that this forum is fantastic, great informations and nice people. I'm looking for some basic tips about sound isolation. I'm doing this between the control room and the live room. Separating the two rooms there is a brick wall of about 15 "(40 cm) Do you think this may be a proper framing ? or do you recommend something better to improve STC? I read the various discussion about the triple leaf problem, but I don't understand how to compare it with this situation becasue the wall is thick. Maybe you have more experience than me so you can you give me more tips and suggestions. Thank you for your help. Nico

Hi Nico, and Welcome! :) Yes, that's the correct way to do it if there is a massive wall that cannot be removed. Even though it is 3-leaf, there is so much mass on the middle leaf, and the air gaps are big enough, that you shouldn't have a problem like that. However, that is assuming that the drywall (gypsum board) continues around the rest of each room, all four sides and the ceiling, without touching the existing structure at any point. - Stuart -

Thanks Soundman you kind support, So the mass of brick wall will give me further Trasmission loss. ;-) Do you think it will be better to vary the two airspace cavities ?? 8 cm of airspace on one side and 5 cm on the other side ? ......... to improve resonance effects ....... And about the rockwool position inside the two cavities.....what's the difference between covering the two side of the airspace or just attach all the insulation to the Plasterboards ??? ( like in this image ) ..... i am not able to understand the differences in trasmission lost of the two solutions ..,, any hint ?

So the mass of brick wall will give me further Trasmission loss.

Well, sort of.... The entire wall is a tuned resonant system, and the final TL depends on how you tune it. It turns out that, for any given total mass, you get the best results when most of that mass is on the middle leaf. As long as the mass in the middle leaf is at least as great as the sum of the other two masses, then you are getting the best optimization. Worst case is where there is not much mass on the middle leaf.

Do you think it will be better to vary the two airspace cavities ?? 8 cm of airspace on one side and 5 cm on the other side ? ......... to improve resonance effects .......

Logically, that's what you would expect, but "truth is stranger than fiction", as they say: here too it turns out that you get the best TL when the cavities are the same size, provided that most of the mass is on the middle leaf.

And about the rockwool position inside the two cavities.....what's the difference between covering the two side of the airspace or just attach all the insulation to the Plasterboards ??? ( like in this image ) ..... i am not able to understand the differences in trasmission lost of the two solutions ..,, any hint ?

In this case, there is no difference. You can put it against the brick wall, or against the drywall, or in the middle of the cavity, and it does not make much difference. What DOES make a difference is the AMOUNT of insulation: The purpose of the insulation is to increase the damping inside the cavity. Damping is very necessary to deal with the multiple different types of resonance going on inside the wall. You get the best TL when the entire cavity is filled with insulation, but without compressing it!: just filled, not over-filled, not forced in. The difference in TL between a wall that has no insulation in it and one that is filled, can be as much as 16 dB. That's a HUGE difference. In your case, at a rough guess if you just put 3" in each side of your wall, you'd be getting about 5 to 8 dB better than empty, but filled with 6" of insulation on both sides, you'd be getting about 10 to 12 dB more than empty. However, you might not be allowed to fill the cavity entirely: Rod has pointed out that there might be fire code restrictions on how much you are allowed to fill. So check your building code, to find out. - Stuart -