What the numbers mean
The sound absorption coefficient α shows the share of sound energy that a surface absorbs at a given frequency. NRC is an average at 250, 500, 1000 and 2000 Hz. αw is a single weighted value from EN ISO 11654, which also gives a class from A (best) to E.
Why mounting matters
A thin porous panel placed directly on a wall absorbs mainly high frequencies. Leave an air gap behind the panel and it absorbs far more in the mid range. Published figures for 9 mm PET felt show this: for example NRC 0.65 with a 50 mm cavity and 0.80 with a 200 mm cavity. Results come from different products, so this is illustration, not a formula. A ceiling baffle hanging in space is measured differently again.
How to read a report
Look for the standard (ISO 354), the laboratory, date, sample thickness and mounting type, and the full table of frequencies. If a data sheet gives a single number without mounting, ask for the report.
What panels cannot do
Absorbers reduce reverberation in a room. They do not stop sound passing through walls, and desk screens only offer limited shielding. Surfaces covered with non-porous film largely lose their absorption. For a whole room, ask an acoustician to calculate reverberation time for the room’s purpose.
Our approach
We give you values only from a report for the product you buy. See the acoustic panels section.
