Low-frequency loudness growth compresses as level rises

Evidence

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. The most sensitive area of threshold in quiet, the frequency range between 2 and 5 kHz, corresponds to a dip in all equal-loudness contours. For high levels, this dip seems to become even deeper, i.e. tones in that frequency range are even louder than expected from a parallel shift of threshold in quiet. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1172

Categorization

• XREF: Recruitment-like nonlinear loudness growth at low frequencies connects to hearing-impaired loudness phenomena. — connects to: An Indian temple bell’s low tone grows louder over seconds after striking — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1319