I think many people are confused. This may help.
Chris from what i can tell your going to want to rip out the outside layer of plasterboard to the existing room and then build something like what is in the picture.
Chris' control room and rehearsal rooms space dilemma.
Originally posted at johnlsayers.com, topic 14228.
Chris, You are at the right place, and Stuart is still the right guy to help you out. I have to agree with him that you are not clear in your purpose. In order to establish a proper mass/spring/mass you have a lot of demolition work in front of you based on your current construction. That said...the exterior of this building has not been included in your plans, as best as I can read, and that makes a difference. It can be the deciding factor in how well your isolation performs so it needs to be included as part of your plan. Based on what I have read, you have two framed leafs with mass on both sides...but no mention of the exterior of the building? The exterior in your part of the world will most likely be a concrete/block perimeter. One leaf also the first part of the "mass" in your search for mass/spring/mass. So it reads like a double framed assembly with mass coupled on both sides, what is often mentioned as a four leaf, acoustically. Clear information, from the outside of the building into the proposed room areas is required...it is essential and can not be overlooked or thought of as unnecessary. Unless the rooms you have on the inside of this building are 36 inches away from the exterior walls...it can be more than the four leaf you already are confused about having. It isn't rocket science...but it is a science that many here try to get a handle on. The good thing is that as a community, it takes everyone here to help fill in the blanks that an actual scientist would be able to do single handedly...Difference is, it can be understood by the Average Joe :)I'm here for help and advice, and I apologise if I've managed to annoy anyone.