Loudness Level

1. In acoustics: measured in phons it is numerically equal to the median sound pressure level (dB) of a free progressive 1000 Hz wave presented to listeners facing the source, which in a number of trials is judged by the listeners to be equally loud. Loudness level can be calculated according to ISO 532B. 2. In audio production: measured in loudness units (LU) according to ITU BS.1770.