The audibility of low-frequency sounds

Contours of equal loudness and threshold of hearing under binaural free-field conditions for the frequency range 20–15 000 Hz were standardized internationally in 1961. This paper describes an extension of the data in the low-frequency range down to 3·15 Hz, at l levels from threshold to 70 phon. The latter corresponds to nearly 140 dB sound pressure level at the lowest frequency. Direct loudness comparisons were made between tones at intervals of an octave, and the resulting contours were checked by numerical loudness estimation.