Insulation atlas/Foundation
Absorption is not insulation. Confusing them ruins the schedule.
A ceiling absorber shortens the tail inside the room. An isolating wall stops sound reaching the next room. Neither does the other’s job.
What an absorber changes
Absorption turns part of the wave’s energy into heat in a porous material or a resonator. The measure is α or αw, and classes A to E under ISO 11654. The effect shows up in reverberation time RT60 and in speech clarity inside the same volume. A class A ceiling panel does not raise the wall’s insulation and does not stop a neighbour hearing you.
What insulation changes
Airborne insulation is the level difference between a source room and a receiving room. In the laboratory it is measured as R and reduced to Rw under ISO 717-1. In a finished building flanking enters, and the number becomes R'w or DnT,w under ISO 16283-1. Impact insulation is a different measure: Ln,w and L'nT,w under ISO 717-2. The American STC is close to Rw and not identical to it.
A suspended absorbing ceiling under a concrete slab treats the echo of the room below. Insulation between storeys is the slab itself, a floating floor if there is one, and the closing of openings. A line that says ‘acoustic insulation’ and then supplies only felt panels delivers a room that is calmer inside and still audible outside.
How the two lines are written
An absorption line names the system, thickness, position, area, and the αw class of that system. An insulation line names the element (wall, door, glass, floor), the required figure (Rw, DnT,w or L'nT,w), whether the figure is laboratory or field, and what is excluded from flanking. This atlas keeps the two lines apart. The absorber catalogue stays on the systems pages and is not a substitute for the wall.