Infrasound
Infrasound is sound below roughly 20 Hz — too low to hear, strong enough to feel. Engineer Vic Tandy famously traced a lab haunting (dread, a gray figure in peripheral vision) to a fan resonating at 18.9 Hz; wind, machinery and organ pipes can do the same to houses and churches. It is the skeptic's most elegant ghost explanation, and this glossary presents it as such. The accounts it cannot reach — activity that follows a family between buildings, events with witnesses in acoustically unrelated rooms — are the ones that stay on trial.
Related on this site: /haunted-house-stories/ /tag/unexplained-events/ /night-shift-stories/