Infrasound

Acoustic waves below 20Hz are normally inaudible, but may be experienced as being in a region of high pressure.

• 2-5Hz range played at 100-125dB may produce difficulty in swallowing and slight post-exposure headache.
• 2-5Hz range played at 125-137dB may produce chest wall vibration; difficulty in speaking and voice modulation; swaying sensations; lethargy and drowsiness; and post-exposure fatigue and headaches.
• 5-15Hz range played at 125-137dB may produce middle-ear pain; difficulty in speaking and voice modulation; severe chest wall vibration; severe abdomen vibration and associated feelings of nausea; a falling sensation; lack of concentration and drowsiness; tinnitus; and severe post-exposure fatigue and headaches.
• 7Hz is possibly the most disturbing frequency, being close to the natural resonance frequency of many of the internal body organs and being the same frequency as the alpha brainwaves.
• 15-20Hz range played at 125-137dB may produce severe middle ear pain; respiratory difficulties (gagging sensations); nasal cavity vibration; persistent eye watering; tinnitus; sensation of fear; excessive perspiration and shivering; and severe post-exposure fatigue and headaches.

See also: Acoustics, Audio Frequency, G Weighted Overall Level.