Sound absorption · Glass wool
SCG Cylence Zoftone
- Thickness
- 25–50 mm
- Density
- 32–64 kg/m³
- Sound absorption (NRC)
- up to 1.00
What is NRC?
In short
NRC (noise reduction coefficient) is a single number that tells you how much a material absorbs sound in the speech range. It is the average of the sound absorption coefficients at 250, 500, 1000 and 2000 Hz. Close to 0 means almost everything is reflected; close to 1 means almost everything is absorbed. NRC does not tell you how well a material blocks sound through a wall.
- 1Sound reaches the surface
- 2Part is reflected back into the room
- 3Part is absorbed — NRC summarises mid-frequency absorption as one number; it depends on the thickness and mounting tested
- 4STC / Rw belong to the complete tested wall (linings, frame, insulation, joints), not to one piece of insulation
- 5Sound transmitted to the other side — the higher the rating, the less gets through
What NRC tells you
How well a surface reduces reflections inside a room. Use it to compare absorption panels, acoustic ceilings and other materials used against echo.
How NRC is calculated
Average the absorption coefficients (α) at the four frequencies and round to the nearest 0.05, as set out in the test standard (for example ASTM C423).
| Frequency | 250 Hz | 500 Hz | 1000 Hz | 2000 Hz | NRC |
|---|---|---|---|---|---|
| --- | --- | --- | --- | --- | --- |
| α (made-up example) | 0.40 | 0.80 | 0.95 | 0.90 | 0.75 |
A made-up example to show the method, not a real product: (0.40 + 0.80 + 0.95 + 0.90) ÷ 4 = 0.7625, rounded to 0.75.
Reading NRC in a datasheet
- Check the thickness and mounting it was measured at — an air gap behind the panel changes the result
- Check the test standard, e.g. ASTM C423 or ISO 354
- For low-frequency problems, look at the 125–250 Hz values too, not only NRC
- Some datasheets show values above 1.00; this comes from the laboratory test method
What NRC does not tell you
High NRC does not mean good sound insulation
Blocking sound through a wall is rated by the STC or Rw of the whole wall system — a different thing from NRC. See Sound insulation vs sound absorption.
Sources
- ASTM C423 — Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method
- ISO 354 — Acoustics — Measurement of sound absorption in a reverberation room
Related products
Categories and example products for this topic
- SCG Cylence Zoftone — A reading example: NRC 0.85 (grade L) and 1.00 (grade M) at 50 mm thickness
- ISO TONE — Thickness changes NRC: 0.69 at 25 mm and 0.86 at 50 mm
- Aeroflex ACOUSTEX — Duct lining with NRC 0.65 at 25 mm and absorption values published by frequency
- Micro Duct Liner PFL — States the test mounting: NRC 0.70–0.85 by model (Type A mounting)
Sound absorption · Polyester fibre
ISO NOISE ISO TONE
- Thickness
- 25–50 mm
- Sound absorption (NRC)
- 0.69–0.86
Duct and HVAC insulation · Acoustic foam
Aeroflex ACOUSTEX
- Thickness
- 25 mm
- Sound absorption (NRC)
- 0.65
- Service temp.
- -20 – 85 °C
Duct and HVAC insulation · Glass wool
Microfiber Micro Duct Liner PFL
- Thickness
- 25–50 mm
- Density
- 32–48 kg/m³
- Sound absorption (NRC)
- 0.70–0.85