NRCratings.com, a collaborative arm of Acoustics.com.
This site aligns with our goals of promoting the importance of acoustics and acoustic-related
issues across a variety of related industries.
The NRC is a single-number index determined in a lab
test and used for rating how absorptive a particular material is. This industry
standard ranges from zero (perfectly reflective) to 1* (perfectly absorptive).
It is simply the average of the mid-frequency sound absorption coefficients (250,
500, 1000 and 2000 Hertz) rounded to the nearest 5%.
*(Based on the
testing methodology, and depending upon the material's shape or surface area,
some products can test at an NRC above 1.)
To learn more...
you need to know
NRC ratings of common building materials
is widely used and accepted, it can also be abused or misunderstood. Be aware
of the following items before specifying a particular material based on NRC:
It is advisable
to seek an un-biased third-party, such as an acoustical consultant, for NRC confirmation
on a particular product and installation. Click here to find an acoustical consultant
in your area.
- The NRC rating is an average
of how absorptive a material is at four frequencies (250, 500, 1000 and 2000 Hz).
This rating is appropriate for assessing how well a material absorbs sound within
the speech frequencies, but can be inadequate for sound generated by music, mechanical
equipment or other low-frequency sounds.
this rating is an average, two materials with the same rating might not perform
the same in identical applications.
- The NRC
is based on lab tests. Because the lab is a near 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. A product that receives high ratings in the lab may not perform as
well in the field.
- Make sure the mounting procedure
used in the tests is consistent with your intended installation if you expect
the same results.
- NRC does not have anything
to do with the material's barrier effect (STC). Click
here for our tutorial on the differences between NRC and STC.
of NRC ratings by manufacturers can be misleading and sometimes deceitful for
the following reasons:
- Some manufacturers
will quote absorption at the more-desirable higher frequencies. NRC should be
based only on the absorptive characteristics at 250, 500, 1000, and 2000 Hz. Make
sure the product data you're reviewing is at these frequencies.
manufacturer of a wall carpet product could provide an NRC rating of .80, which
is extremely good. But, if there is fine print be sure to read it, you may see
that 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.
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