Codes & Testing :: Noise Reduction Coefficient (NRC)

Standard: NRC is a laboratory rating of a material's sound absorption quality. (Click here to view the NRC of various common building materials.)

Enforcement: This is more of an industry standard and not necessarily enforced.

General Information: The NRC rating is an average of how absorptive a material is at only four frequencies (250, 500, 1000 and 2000 Hz). This industry standard ranges from zero (perfectly reflective) to 1* (perfectly absorptive). It is always expressed as a decimal rounded to the nearest .05.

*(Based on the testing methodology, and depending upon the material’s shape or surface area, some products can test at an NRC above 1.)

Strength: This standard is widely used and accepted.

Weakness:

  • The NRC rating is only measured at 250, 500, 1000 and 2000 Hz. This is perfectly acceptable for speech, but can be inadequate for music (and other low-frequency sounds).
  • Because this rating is an average, two materials with the same rating might not perform the same.
  • Communication of product ratings by manufacturers can be misleading and sometimes deceitful for the following reasons:
    • The information provided is based on lab tests. Because the lab is a perfect environment that is rarely duplicated in everyday applications, some products will not test the same in the field. Certain factors, such as installation variables, are not accounted for in the lab.
    • Some manufacturers will quote absorption at the more-desirable higher frequencies without clearly explaining the testing conditions. NRC is based only on absorptive characteristics at the following frequencies: 250, 500, 1000, 2000 Hz. Make sure the product data you’re reviewing is of these frequencies.
    • Make sure the mounting procedure used in the tests is consistent with your intended installation if you expect the same results. For example, a manufacturer of a wall carpet product provides an NRC rating of .80, which is extremely good. But, if you know how to read the fine print, you’ll see this rating was achieved while the carpet was installed over fiberglass. In this installation configuration, the fiberglass, not the carpet, acts as the sound absorber. Without the acoustic material behind, the wall carpet will probably only achieve an NRC of .20.

A responsible design professional will not rely solely on information provided by manufacturers. While some do provide accurate information, it is advisable to seek an un-biased third-party for product confirmation. Visit the Products & Materials section or contact us if you are looking for a specific product not currently listed in our database.



 
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