Audibility of infrasound

Abstract

The distortion of pure tones (1–16 Hz) caused by the nonlinearities of the middle ear was calculated. It is shown that the slope of the audibility curves for infrasound of Yeowart and Evans could be predicted, thus implying that infrasound might not be heard in the normal sense, but only heard as distortion after being transduced through the middle ear. To verify this result, subjects were exposed simultaneously with the 1–10-Hz stimuli to a low-frequency masking noise (10–100 Hz). This noise was shown to mask pure tones of infrasound of 1–10 Hz even when the SPLs of these tones were 15–25 dB above the masking noise overall sound-pressure level. Clearly, this result implies that the pure tones of infrasound below 10 Hz are not heard in the same manner as tones above 16 Hz. The implications of these results to the importance of the infrasound components of any broad-band noise and to the auditory effects of infrasound are discussed.