M
Mass
Weight in the boundary, because a heavier construction is harder to drive.
Isolation
Isolation is a different problem from treatment
Treatment controls resonance, reverberation and reflection inside a room. Isolation stops sound crossing the boundary between that room and the building around it. The two are not interchangeable.
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The framework it is engineered on
A
Airtightness
A gap conducts sound past everything else in the build-up.
I
Isolation
Breaking the mechanical path, so structure-borne energy is not carried through.
D
Damping
Turning the energy that does reach the boundary into heat rather than sound.
It comes first, and it is specified on its own
Isolation is the layer that reaches a project earliest, because it is built into the shell rather than fitted to the finished room. It does not determine treatment performance: it provides the conditions in which treatment behaves predictably. Where a room needs both, they are specified separately.