Code: This industry standard (also an ANSI standard)
usually pertains to HVAC or mechanical noise impact.
This standard is often required for certain certifications (such as government
medical facilities) or included in client specifications/standards (for example,
some companies have NC standards that their buildings must meet).
Information: An NC level is a standard that describes the relative loudness
of a space, examining a range of frequencies (rather than simply recording the
decibel level). This level illustrates the extent to which noise interferes with
speech intelligibility. NC should be considered for any project where excessive
noise would be irritating to the users, especially where speech intelligibility
is important. There are a few spaces where speech intelligibility is absolutely
- Recording studios
- Lecture halls
- Worship centers
For some areas, such as machine shops
or kitchens, it is not essential to maintain a particularly low NC level.
NC Level Strength: It is important for design professionals to specify
NC ratings to protect their designs (within reason specifying an acceptable
NC level does not have to be a burden on the budget). Doing so speaks to your
reputation as a responsible architect or designer and limits your liability.
NC Level Weakness: NC does not account for sound at very low frequencies.
In spite of numerous efforts to establish a widely accepted, useful, single-number
rating method for evaluating noise in a structure, a variety of techniques exist
today. The vast majority of acoustic professionals use the NC standard, but it
is still important to be aware of the other acceptable methods that do account
for low frequency levels, including (but not limited to):
Criteria (RC) measures background sound in a building over the frequency range
16 Hz to 4000 Hz. This rating system requires two steps: determining the mid-frequency
average level and determining the perceived balance between high and low frequency
sound. To view the recommended ANSI levels for room criteria for various activity
areas, click here.
- Balanced Noise Criteria (NCB)
is based on the ANSI threshold of audibility for pure-tones and is defined as
the range of audibility for continuous sound in a specified field from 16 Hz to