If I have home brick wall rendered 10 inch ,I build a stud wall like in picture how dB I get isolation theoretically ..
Here you ask how many decibels of isolation you get, but in the diagram you want to know what the STC rating is. So I'm really not sure what you are asking! Do you want the STC rating for that construction, or do you want to know how many dB of isolation that construction will provide? That is two very, very different things.
Calculating STC rating is a pain, and I don't have the time to do that. Besides, STC numbers are useless for studios, since they don't tell you anything about isolation in low frequencies. So i did not bother calculating the STC rating.
But I did calculate the isolation for that construction: You would get roughly 55 dB of isolation with that. I used:
250 mm brick
100 mm air gap
12 mm plywood
Considering that you do not have any insulation in the cavity, the isolation would not be good in low frequencies. The resonant frequency of that wall would be about 72 Hz, so the wall would not isolate below about 100 Hz. It would only isolate well, starting at about 150 Hz and above. There is not enough mass on the inner-leaf, the air gap is small, and there is no insulation in the air gap, so that wall just will not perform very well.
- Stuart -