Pnc Preferred Noise Criteria

Overview

Engineering reference data for Pnc Preferred Noise Criteria in acoustics.

Key Formulas

Speed of Sound

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

Speed of sound in an ideal gas.

Sound Level

$L = 10 \log_{10}(I/I_0)$

Decibel level.

Wavelength

$\lambda = c / f$

Wavelength = speed / frequency.

Variables

PNC Curves Data Table

Example Calculation

For a noise spectrum with the following measured sound pressure levels:

• 31.5 Hz: 40 dB
• 63 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

The PNC rating is determined by identifying the lowest PNC curve that is not exceeded by the measured spectrum at any frequency. In this example, the spectrum exceeds the PNC-50 curve at 500 Hz (60 dB vs. 54 dB) but remains below the PNC-60 curve at all frequencies, resulting in a PNC rating of *PNC-57.

Important Notes

• PNC curves were developed to address limitations of the earlier Noise Criterion (NC) system, particularly regarding low-frequency noise from air-conditioning systems
• PNC criteria are more stringent at lower frequencies than NC criteria
• These criteria do not provide protection against low-frequency sound exposure
• The PNC system may reflect public tolerance to background noise rather than optimal acoustic environments
• PNC ratings are commonly used to evaluate continuous background noise in spaces like offices, studios, and hospitals

Interactive Charts

References

• Original Source