Study on the measurement of infrasound and perceptible response to infrasound in life environment.

To investigate the occurrence of infrasound in life environment, sound presure levels were measured at various places. In addition to this, levels of inf arsound perceptible to humans were examined. This experiment was performed in such places as under a bridge, inside an automobile and beside a cooling tower, where a single frequency in infarsound was predominantly observed. The results were as follows: 1) Beside a refrigerator, in a computer room and beside a cooling tower, the sound pressure levels of inf rasound were considerably low. 2) Beside a washing machine, a level of 81 dB, the highest level, was recorded at dehydration process. 3) The sound pressure level in wooden houses was found to be higher than that in concrete buildings, and the highest level in a wooden house was over 100 dB. 4) Considerably high sound pressure levels, 100 dB at 20 m from a running railroad carriage and 83 dB at 20 m from a running motor truck, were recorded. 5) Inside an automobile, levels over 110 dB were recorded when the wind-up vibration was generated. 6) The response rate of the subjects rose with an increase in the sound pressure level under each frequency. 7) Concerning the relations between frequency, sound pressure level and response rate, the 50% response levels of total response were 102 dB at 6 Hz, 93 dB at 10 Hz, 92 dB at 13 Hz, 85 dB at 20 Hz and 82 dB at 22 Hz respectively. 8) The 50% response level of total response decreased at a rate of -10 dB/octave. 9) The 20% and 80% response levels were located at +6 dB relative to the 50% response level, respectively.