Please help confirm wall structure design

[Lunatique]

Hi guys, I need some more advice before entering the next phase of construction. Right now I've been debating with my construction guy on what to do about the 2nd layer of walls. Please take a look at the following images:

For this one, the idea is that the original existing brick/concrete wall already counts as a leaf, and all I need to do is leave 2" of air gap, and then erect my stud/fiberglass/gypsum layer as the 2nd leaf. This is the idea I'm supporting.



In this image, the construction guy is saying that we should add a layer of stud/fiberglass to the existing brick/concrete wall to add even more soundproofing. His idea sounds fine on paper, but I can't tell if adding that layer of stud/fiberglass would screw up the two-leaf structure. Since that additional layer of stud/fiberglass does not contain gypsum boards (originally he wanted to put gypsum boards on it and I told him that's a big nono as it'll make it three-leaf instead of two), I would assume it technically does not count as an extra leaf, right? But what does it mean? The extra layer of stud/fiberglass only increases the air gap between the gypsum and the existing brick/concrete wall?

So guys, your suggestions?

[andrebrito]

If it is low density rockwool it won't act as a third leaf. Filling the cavity will held slightly larger value at medium-high frequencies.