Improving soundproofing while lowering resonance point

Hi I´m planning to have a double leaf wall, first leaf is a 15 cm brickwall and second leaf is a 2x6 wood stud with insulation and a 12mm plywood. Both leafs are decoupled with 10 cm from leaf to leaf. I have 3 questions: Regarding soundproofing and lowering resonance point: 1. Obviously my two leafs have different mass... How will this affect soundproofind and resonance point? Will I improve things by adding this second leaf or will I make things worse? I can´t match both masses... I´m thinking like containing water here... I have a strong barrier and making the whole system a little stronger by adding a new but weaker extra barrier. What will happen to soundproofing and with resonance point of the wall? 2. Im planing both leafs to be decoupled but my acoustic window will sit on top of these two walls... Will this couple the walls again? Is there any point or gain in decouple walls if I plan to install the window this way? 3. Is there a way to decouple the window? is this recommendable? could you point to a resource where I can learn more about this?

1. Obviously my two leafs have different mass... How will this affect soundproofind and resonance point? Will I improve things by adding this second leaf or will I make things worse? I can´t match both masses... I´m thinking like containing water here... I have a strong barrier and making the whole system a little stronger by adding a new but weaker extra barrier. What will happen to soundproofing and with resonance point of the wall?

Use my calculator to see how your performance will change. Gregwor & audiomutt’s MSM Transmission Loss Calculator Version 2.02 Thread

2. Im planing both leafs to be decoupled but my acoustic window will sit on top of these two walls... Will this couple the walls again? Is there any point or gain in decouple walls if I plan to install the window this way?

First off, it this was your ONLY option, you'd have to have a very very thick window in order to match the mass of both leaves combined. Secondly, yes, this will be the flanking point of your walls and severely compromise the MSM system.

3. Is there a way to decouple the window? is this recommendable? could you point to a resource where I can learn more about this?

Yes, put one window in each leaf. Here's a thread with pictures to show how it's accomplished: viewtopic.php?f=2&t=21396&p=144643&hilit=BRAUS#p144643 Greg

Thank you for all your answers. They´re very helpfull...

Gregwor wrote:

Use my calculator to see how your performance will change. Gregwor & audiomutt’s MSM Transmission Loss Calculator Version 2.02 Thread

Regarding your calculator... My second leaf is a 15cm brickwall... But I don´t know how to tell the system this. I think brickwall is now one of the options. Update: I decided to use a two leaf system... 15 cm thick Brickwall (I don´t know the density since this is an existing wall) 15 cm air gap between inner leafs 2X6 wood stud (filled with insulation) 3 5/8 drywall (10.74kg/m2 each plate) The whole widht of the system is calculated to be 35cm In order to get the desnsity of any material I tend to divide the weight / m2 ... Can you confirm this is a correct way? Your calculator is super cool... I´m still trying to fit all my data there haha =)

In order to get the desnsity of any material I tend to divide the weight / m2 ... Can you confirm this is a correct way?

There is a conversion calculator on the calculator ;-) Greg