Doors structure problem...

The separation wall of my studio wil be made by 2 sheet rock 15 mm + 40 mm rockwool 70 kg/m3 and 50 mm air space and then 40 mm rock wool and 30 mm sheet rock. But installing the door the installer want to do a better installation reinforcing the one of this walls with another sheet rock in the middle. So the wall will be 2x15 mm sheetrock / 40 mm rock wool / 1x15 mm sheetrock/ 50 mm air gap / 40 mm rock wool / 2x15 mm sheetrock what happens with this inner sheet rock?? is worse on isolation terms

If I'm understanding your post correctly then the extra layer of sheetrock will create a 3 leaf wall which will worsen your low end isolation.

but if I don't use the inner leaf in all the wall?? only in the door place??

The "weakest link" theory applies - if part of your wall is weaker, you may as well make ALL the wall weaker. Can you post some sort of sketch of what you're doing? Maybe there's a way to fix it that's better for isolation... Steve

2 pics of the door:

I'm adding up your dimensions, and come up with about 200mm total thickness; not seeing that in the pix. Can you add a drawing or explain more where your man want's to put a third leaf? Thanks... Steve

this is the draw of the double wall: In the picture there is only one wall with the door, but there will be another wall with another door.

the 2nd wall is made... I hope I'll have no problems... the inner layer is not installed...