TL;DR: An absorption table lists a material's sound absorption coefficient at each frequency band. 0 means fully reflective, 1.0 means fully absorptive (lab figures can read slightly above 1.0). Read across the bands to see which frequencies a panel actually controls — a single number like NRC hides that.
What the numbers mean
The absorption coefficient (often written α or αs) is the fraction of sound energy a surface absorbs rather than reflects, measured per frequency band (typically 125, 250, 500, 1000, 2000 and 4000 Hz).
- 0.0 — reflects everything
- 0.5 — absorbs about half
- 1.0 — absorbs (almost) everything
Values slightly above 1.0 are normal in the reverberation-room test method (an edge-diffraction effect), not an error.
Why the shape matters more than one number
Single-figure ratings such as NRC average several mid-band values. Two products with the same NRC can behave completely differently — one might absorb evenly, another only the highs. Reading the full curve tells you whether a panel matches the problem you have (e.g. low-mid muddiness vs high-frequency harshness).
Watch the test conditions
- Standard: reputable data cites BS EN ISO 354 (reverberation-room method).
- Mounting: results depend on how the sample was fixed — bonded vs free, on a wall vs in a corner. (See mounting and absorption.)
- αs vs Aobj: a coefficient (α) applies per unit area; some items are reported as equivalent absorption area (m² per object) when used discretely, e.g. corner bass control.
See it in practice
C-ATS publishes its independently measured figures — read them in the C-ATS absorption data.
FAQ
What is a good absorption coefficient?
It depends on the job. For broadband absorption you want high values across the mids and highs; for bass control you care about the low bands. Match the curve to the problem.
Why can a coefficient exceed 1.0?
It's a known characteristic of the ISO 354 reverberation-room method (edge diffraction), not a mistake.
Is NRC enough?
No — NRC is a single averaged number that hides the frequency detail. Read the full band-by-band table.