Measurement of human body surface vibrations induced by complex low-frequency noise composed of two pure tones

To clarify the mechanical responses of the human body to airborne vibrations, six male subjects were exposed to eight kinds of low-frequency noise stimuli: airborne white noise, two pure tones (31.5 and 50 Hz), and five complex noises composed of pure tones. The vibrations induced on the body surface were measured at five locations: the forehead, the right and left anterior chest, and the right and left anterior abdomen. It was found that the vibration acceleration levels of both the 31.5- and 50-Hz components in the chest vibration increased as an approximately linear function of the sound pressure levels of each corresponding frequency component in the noise stimulus. No clear interference was found between the 31.5- and 50-Hz components in the chest vibration. Similar characteristics were also found in the vibrations induced at the forehead and abdomen. These findings suggest that within the limited range of frequency and sound pressure level used here, the human body acts as a mechanically linear system in response to airborne vibrations induced by complex low-frequency noise.