Frequency Extremes · spectrum
Infrasound and ultrasound beyond the musical set
Below 20 Hz and above 20 kHz: perception, hazards, myths, and art.
What is measured
Infrasound (<~20 Hz) can be felt more than heard; industrial and natural sources exist; very high levels can cause discomfort. Ultrasound (>~20 kHz) is used in imaging and industry. Consumer “silent subliminal” ultrasound claims are mostly bunk for headphones.
What is claimed
Ghost-hunter and ritual lore sometimes blames infrasound for dread. Possible physiological contribution in some environments; not a default spirit detector.
Related
Editorial dual-lens guide. Physics and history first; myth as myth. Not medical advice.