Infrasound is acoustic energy below roughly 20 Hz — under the nominal human hearing threshold, but still very much a real pressure wave that a room, a body, and its organs can respond to mechanically. At 19 Hz in air (c ≈ 343 m/s) the wavelength is about 18 m, so it is common for one full room dimension, or a simple fraction of it, to be comparable to a half- or full wavelength — which is exactly the condition needed for an axial standing wave to form between two parallel walls, with pressure antinodes at the walls and a node at the room's midpoint for the lowest mode.
f_mode(nx,ny,nz) = (c/2)·√[(nx/L)² + (ny/W)² + (nz/H)²]
λ = c / f (≈18.1 m at 19 Hz)
This simulation solves for the axial/tangential room mode (nx, ny, nz — small integers, each along one wall pair) whose natural frequency is closest to the frequency slider for the current room dimensions, then renders that mode's real pressure shape, cos(nx·πx/L)·cos(ny·πy/W)·cos(nz·πz/H), oscillating in time — a simplified rigid-wall model that ignores damping, furnishings, and non-modal energy, so treat the pattern as illustrative of the underlying physics, not a acoustic-engineering prediction for a real room.
Why 19 Hz specifically? In 1998, engineer Vic Tandy investigated reports of a "haunted" laboratory and traced an unexplained sense of unease and a fleeting grey shape at the edge of vision to a fan producing an infrasonic tone measured near 19 Hz. He proposed that this frequency sits close to a resonance of the human eyeball, and that strong exposure could cause the eye to vibrate enough to blur or distort vision, producing a sensed "presence." It is a genuinely researched hypothesis with a documented case behind it — not a settled or universally reproduced mechanism, and later attempts to generalize it to all reports of unease near infrasound remain debated among acousticians and psychologists. High-SPL infrasound is separately well established to cause discomfort, chest/organ vibration and disorientation at sufficient exposure, independent of the eye-resonance question.
- Frequency — sweep across 5–40 Hz; watch the standing-wave pattern reorganize as the nearest room mode changes, and note how close 19 Hz sits to typical room-scale axial modes.
- Sound pressure level — scales the visual amplitude of the field (brighter/larger points), standing in for how strongly a subwoofer is driven; it does not change the pattern's shape.
- Room dimensions — length, width and height each shift which integer mode falls nearest the chosen frequency, which is why the "haunted room" effect is reported as room-dependent rather than universal.