Room within a room insolation: completely filling the gap?

[sxx]

When building a room within a room, is it OK to comlpetely fill the air gap with rockwool? (touching both the inner and outer partition)
Or is leaving an air gap between both partitions mandatory to acheive a good sound isolation?

[Soundman2020]

Yes, you should completely fill the cavity with suitable insulation. Do not "cram" in the insulation much that you over-compress it: just put in enough to fill the cavity, without forcing it in.

- Stuart -