If you go to our resource page and look in the right column there's an article on sound isolation. Hopefully it will be helpful in answering your question.
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Rives, I have read so many articles abt sound isolation etc. Obviously building a room within a room concept is the most ideal solution. However its not a solution I m prepare to carry out due to time constraints and lost of width and depth of the room. I m not looking for perfect isolation but just sufficient so that it doesnt disturb my neighbour. Sound leak to my house is immaterial. Some how most articles I read use stud and gypsum board construction and not much on brickwall and RC construction. Also I can hardly find any company that deal in HT sound isolation in Malaysia. probably has to just take a risk and isolate only party wall. Reckon that even though wall/ceiling/floor are rigidly connected, the vibration effect may not transmit to much sound to neighbour. I also felt that flanking prob may not be a big prob as sound is travelling thru a big void in ceiling et.
The article points out one of the really big caveats of sound isolation. Namely that sound is largely transmitted through structure. Thus isolating the wall without dealing with the floor, ceiling, etc may be relatively useless. It really depends on the structure of the building and how the structure is connected. It's impossible for me to have any idea about the specifics of your situation and give you reasonable advice beyond--as you say--a room within a room. The other issue which you may not be aware of is that STC are quoted at 125 Hz only. Thus the subwoofer that is rattling things at 40 to 60 hz is not even considered in the STC calculations. You could do things that do a great job in terms of specifications for STC, but actually have no affect on the actual intrusion to your neighbors.