Note 01
Reading acoustic data: NRC, αw and what they leave out.
A single number cannot describe how a panel behaves in a room. It is still the number that ends up in the specification, so it is worth knowing what it hides.
NRC is the arithmetic average of absorption at 250, 500, 1000 and 2000 Hz, rounded to the nearest 0.05. It is quick, blunt and standard in North America. Our 12 mm board measures 0.85 to ISO 354.
αw weights the same measurements according to EN ISO 11654, with a shape indicator (L, M or H) for how absorption behaves at low and high frequency. A product with αw 0.80 (MH) is not the same as one with αw 0.80 (L): the first absorbs speech, the second absorbs motor noise better.
Mounting matters more than the panel. The same board on a batten with a 50 mm air gap absorbs differently from the same board glued flat. Test reports are only comparable when the mounting condition matches — that is why a report should state the build-up, not just the board.
Reverberation is a room property. Adding 10 m² of absorber to a 200 m² hard room will not fix a 1.8 s reverberation time. We can help estimate quantities, but the target should come from an acoustic consultant working from the room volume and use.