What NRC actually measures
NRC is a 0–1 rating of how much sound a material absorbs, averaged across four mid-band frequencies: 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz. An NRC of 0 means the material reflects all sound; an NRC of 1 means it absorbs everything at those frequencies.
NRC is measured in a reverberation chamber against ASTM C423 or ISO 354, with the sample mounted in a specified way. Change the mounting, change the number — which is why comparing NRC across brands only works when the mounting method matches.
How to read NRC numbers on a datasheet
A good product datasheet gives NRC by thickness and mounting. If a datasheet only shows one NRC number with no mounting info, treat that number with caution.
- NRC 0.30–0.50 — light treatment, good for background surfaces
- NRC 0.55–0.75 — solid mid-frequency absorption, most offices and restaurants
- NRC 0.80+ — studio-grade absorption for recording and control rooms
What NRC doesn't tell you
NRC averages four mid-band frequencies. A panel with NRC 0.80 might be fantastic at 1000 Hz and useless below 250 Hz — which is exactly the frequency range you care about for a home theatre or bass-heavy podcast studio.
For bass control, look at Sabin absorption at 125 Hz, not NRC. For speech-heavy spaces (offices, classrooms), NRC is a good enough proxy.
Comparing two acoustic quotes by NRC — the right way
Always compare NRC at the same thickness and mounting. A 25 mm panel with NRC 0.85 sounds impressive until you notice the competitor's 50 mm panel gets 0.90 with less coverage needed.
Ask your supplier for the third-party test certificate. Reputable manufacturers — Acoustimart included — will send it.