EFFECTIVE PERCEIVED NOISE LEVEL (EPNL)
A modification of the PERCEIVED NOISE LEVEL to take into account tone components in aircraft BROAD BAND NOISE, as well as the duration of the noise. It is measured in EPNdB, and defined as the Perceived Noise Level (PNL) in PNdB plus a tone correction and a duration correction. It is in general use by the U.S. Federal Aviation Administration in aircraft certification.
The EPNL measurement is based on the following equation:
EPNL= PNLmax+ 10 log (t10/20) + F (dB)
where PNLmax is the maximum perceived noise level during flyover in PNdB, t10 is the duration (in seconds) of the noise level within 10 dB of the peak PNL, and F is a correction for PURE TONEs (which are generally found to be more annoying than broad band noise without perceived tones). In practice, F is about +3 dB.
The NOISE EXPOSURE FORECAST (NEF) is based on EPNL measurement and thus requires computer calculation.