NRC Explained: How to Read Sound Absorption Ratings
Every acoustic panel spec sheet leads with an NRC figure, Noise Reduction Coefficient, and most buyers treat it as the whole story. It isn't. NRC is a useful shorthand, but understanding what's actually being averaged, and what it leaves out, is the difference between a product that solves your problem and one that just looks good on paper.
What NRC actually is
NRC is the average of a material's sound absorption coefficients at four frequencies: 250 Hz, 500 Hz, 1000 Hz and 2000 Hz, rounded to the nearest 0.05. An NRC of 0.85 means the material absorbs, on average, 85% of the sound energy that hits it across that frequency range, with the rest reflected back into the room. It's tested under controlled lab conditions to ISO 354 internationally, or ASTM C423 in the US, with the material mounted in a reverberation chamber and the room's decay time measured before and after installation.
The gap NRC doesn't cover: low frequency
NRC's four test frequencies start at 250 Hz, which means bass performance, below roughly 200 Hz, isn't captured in the headline number at all. This matters more than most buyers realise: a panel with an excellent NRC of 0.90 can still perform poorly against low-frequency rumble, mechanical hum, or bass-heavy music, because that range simply isn't part of what NRC measures. If low-frequency control matters for your space, ask for the full octave-band absorption data, not just the single NRC figure.
How the rating translates to a class under UK and European standards
BS EN ISO 11654 converts absorption performance into a letter class, Class A through E, based on a weighted absorption coefficient across a wider frequency range than NRC alone. Class A represents the highest-performing products, broadly aligning with an NRC around 0.90 or above. This is the classification referenced directly in BS ISO 22955:2021's office ceiling requirements, which is why you'll see "Class A" rather than "NRC 0.90" quoted in some specifications.
Real-world figures by material type
Fibreglass panels typically achieve the highest NRC ratings, often in the 0.90 to 1.0 range. Mineral wool, rockwool-based panels sit close behind at roughly 0.85 to 0.95, with the added benefit of natural fire resistance. PET felt, made from recycled polyester fibre, typically lands around 0.75 to 0.85, lower than fibreglass or mineral wool but without the fibre-shedding concerns some specifiers have about glass-based products. Melamine foam varies more widely, from around 0.65 up to 0.95 depending on thickness and mounting method, since foam performance is unusually sensitive to how far it sits off the wall.
Why mounting method changes the number you actually get
A panel's tested NRC assumes a specific mounting condition, and moving it further off the wall, adding an air gap, generally improves low-frequency absorption specifically, sometimes meaningfully. The NRC printed on a spec sheet is a starting point, not a guarantee, once it's installed in your actual room under your actual mounting conditions.
Common questions
Is a higher NRC always better? Not necessarily, once you're treating enough of the room to hit your target reverberation time, additional absorption beyond that can make a space feel acoustically flat or dead.
What's the difference between NRC and SAA? SAA, Sound Absorption Average, is a similar single-number rating but calculated across twelve one-third octave bands rather than four, giving a slightly more precise figure; NRC remains the more commonly quoted spec in UK and European markets.
Choosing the right product for your room
See our guide to acoustic panel materials compared or browse our acoustic solutions to find a product matched to your actual frequency problem, not just the headline number.
Related product guides: acoustic wall panels, PET acoustic panels.
From first survey to final finish
One team handles all seven stages, the same way on every project, so you always know what happens next.
A surveyor visits the site, or works from your drawings and photos when a visit isn't practical. Either way, the room, its surfaces and how it is used are recorded before any advice is given.
Reverberation, ambient noise and noise transfer are read against what the space is used for. The findings arrive as a written report with recommendations, yours to keep with no obligation to proceed.
Treatment is modelled against a reverberation target, then drawn up with panel positions, fixings and finishes. Nothing moves forward until you have approved the design.
Every quotation comes with the specification behind it, listing products by type, quantity and finish with costs set out line by line. What is quoted is what the design calls for.
Panels, baffles, ceilings and screens come from our Acoustic Solutions range and are supplied to the approved specification. What arrives on site matches what was designed.
Our own engineers fit to the approved drawings, checking positions and fixings as they go. One team supplies and installs, so nothing is handed between contractors.
Optional: after fit-out the space can be measured again and compared with the original survey, so the improvement is measured rather than assumed. Results are reported against the relevant standards and the written record goes into your building file.
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