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
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 materials shape or surface area, some products can test at an NRC above 1.)
Strength: This standard is widely used and accepted.
- 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 youre 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,
youll 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.