Avoiding a third leaf...

I'm planning a 2 leaf outdoor construction, but one of my walls will be near to a thick stone wall. How far away should my building be for it not to be considered a 3rd leaf, and does it even matter given the wall is very thick? Incidentally, I cant include this wall in my construction because it is very old and listed / protected, and not mine! For this reason I'll be putting my building 1 metre away from it. Will that be enough? Thanks James

1 meter should be more than enough. You could probably tighten that up a bit, if you need to. The goal with any MSM wall is to get the resonant frequency down one octave below the lowest frequency you need to isolate. Increasing the surface density forces the frequency down. Increasing the distance forces the frequency down. In your case, you have stone (which is massive) and thick (implying high surface density), and you have it far away (one meter). At a rough estimate, the resonant frequency of that setup will be below 10Hz, meaning that it isolates well at 20 Hz already, which is VERY low: there's no instruments that get down that low (unless maybe you have a huge cathedral pipe organ in your studio?), so you'll be fine there. At that distance, and with that mass, it won't be an issue. - Stuart -