Technical Booklet G Resistance to the Passage of Sound·Page 26·2.7
Wall type 4: Framed walls with absorbent material
Framed walls achieve sound resistance through the combined effect of leaf mass, frame isolation, and sound absorption in the cavity between frames.
The resistance to airborne sound depends on the mass per unit area of the leaves, the isolation of the frames, and the absorption in the cavity between the frames.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet G - Resistance to the Passage of Sound.pdf