What is noise reduction coefficient (NRC)?

The Noise Reduction Coefficient (NRC) describes the general performance of a materials sound absorptive quality. It is represented by a numerical value between 0 and 1, with 0 representing perfect reflection and 1 representing perfect absorption.

The image below helps us to understand absorption, transmission and reflection of sound in walls, pointing out why it is so important in spaces such as schools and restaurants to use decorative sound absorption panels.


It is calculated from the arithmetic average across the middle frequencies of the octave band sound absorption coefficients (250, 500, 1000 and 2000 Hertz) to the nearest 5%.

Does NRC Have Limitations?

The short answer is yes. Given that NRC is an average, comparisons between materials across the frequency spectrum cannot be accurately measured. This is important as the overall frequency spectrum is required when correctly specifying or substituting acoustic room treatment solutions. These limitations are most pronounced when we compare the effects of decorative soundproof wall panels to sound absorbing wall panels.

The below table demonstrates that a material can have an identical NRC rating to another material, however possess differences across the frequency spectrum;

Material 1 Material 2
Frequency Absorption Coefficient Absorption Coefficient
250 0.1 0.5
500 0.3 0.45
1000 0.7 0.5
2000 1 0.55
NRC 0.50 0.50

Is it OK to Use NRC?!

Yes! It is perfectly fine to use NRC as an indication of a materials absorption performance, especially when dealing with architects and those who may not be familiar with the advanced areas of acoustics.

NOTE: It is important to remember that the overall absorption performance of a material cannot be determined by the NRC alone.

What are Scattering Coefficients? (Acoustics)

Scattering coefficients are now featured on our acoustic data sheets. This is in response to a high demand from acoustic consultants.

The practical use for this data is that it can be inputted in programs such as Odeon and EASE. These programs are used to simulate room acoustics in critical and/or complicated acoustic geometries.

If asked – the testing has been conducted at Sydney University in a 1:6 scale model reverberation room. The testing was conducted in general accordance with ISO 17497-1.

As far as I am aware, Supawood is the only manufacturer in Australia that provides this data!

Definition; Scattering refers to the ‘non-specular’ reflection of sound waves. Specular meaning ‘mirror like reflection’, non-specular meaning diffuse. Although, in acoustics a diffusion coefficient refers to the ‘evenness’ of non-specular reflections and that itself has its own measurement criteria. This can be confusing. The best way to consider scattering is that it refers to the non-specular reflection of sound waves that are not necessarily reflected evenly.

If you have any further questions that haven’t been answered, feel free to reach out to us and our customer care team will be happy to help.

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