Nc Noise Criterion

Reference data and engineering information about nc noise criterion for acoustics applications.

Overview

Engineering reference data for Nc Noise Criterion in acoustics.

Key Formulas

Speed of Sound

$c = \sqrt{\gamma R T}$

Speed of sound in an ideal gas.

Wavelength

$\lambda = c / f$

Wavelength = speed / frequency.

Variables

Symbol	Description	Unit
$c$	Speed of sound	m/s
$L$	Sound level	dB
$\lambda$	Wavelength	m
$f$	Frequency	Hz

Example Calculation

The following measured sound pressure levels can be used to estimate an NC rating.

Frequency	Measured SPL
62.5 Hz	40 dB
125 Hz	50 dB
250 Hz	55 dB
500 Hz	60 dB
1000 Hz	50 dB
2000 Hz	55 dB
4000 Hz	45 dB
8000 Hz	45 dB

Plotting these values against the NC curves yields an NC rating of *NC-57.

Balanced Noise Criteria (NCB) curves are an alternative to the standard NC curves. They are used to specify acceptable background noise levels in occupied spaces, encompassing noise from air-conditioning systems and other ambient sources.

Interactive Charts

References

Original Source