NC curves

NC curves

A series of curves of octave-band sound spectra, used to provide a single-number rating of the noisiness of an indoor space. A measured octave-band spectrum is compared with this set of curves to determine the NC level of the space in which the measurements were made.
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The measured octave bands for a space are compared with the NC curves. These curves were developed with lines that represent constant perceived loudness by the human ear.
Applying octave band measures obtained in the classrooms to the NC curves, all but Classroom D exceed this 35 NC rating.
These curves are similar to the NC curves but have been adjusted in frequency range and nominally based on modern equal loudness curves.
The highest NC curve to which an octave band level is tangent is the NC rating.
NC curves are commonly used as an alternative to dBA values or RC curves.