Equal-loudness contours flatten at low frequencies as level rises

Evidence

The equal-loudness contours outlined in Fig. 8.1 have a shape for low loudness levels such as 20 phon that is almost parallel to the threshold in quiet. This is especially true for frequencies above about 200 Hz and, in that frequency range, also holds for larger loudness levels. At low frequencies, however, equal-loudness contours become shallower with higher levels. A 50-Hz tone of 50 dB sound pressure level reaches a loudness level of about 20 phon, but a 50-Hz tone of 110 dB sound pressure level reaches 100 phon. The difference between the numbers in phon and the numbers in dB is 30 at low levels but only 10 at high levels. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1172

Categorization

• SHARE: A concrete numerical example (50 Hz: 20 phon from 50 dB, vs 100 phon from 110 dB) worth sending to anyone into audio engineering or sound design.