The major difference is that CNEL can be measured using ordinary dBA readings (see Sound Level Meter), as opposed to the computer calculation of Effective Perceived Noise Level used in the NEF. As ...

Consequently, 30dB is about twice as loud as 20dB, and a computer producing 40dB of noise would be approximately four times louder than one generating 20dB. A PC emitting only 20dB of noise would ...