Sound, Infrasound & Vibration

Infrasound and human physiological effects

Infrasound below 20 Hz can induce unease, anxiety, dread, and mild disorientation without the subject being consciously aware of any sound source. Detection appears to occur through bone conduction, inner-ear structures, and resonance within body cavities rather than normal hearing. A 2026 peer-reviewed study (Schmaltz et al., Frontiers in Behavioral Neuroscience) found that even five minutes of exposure at around 18 Hz raised salivary cortisol and increased self-reported irritability and sadness in participants who could not consciously detect the signal. The effects sat below conscious awareness — percipients attributed the feelings to their surroundings, not to a sound.

The 18–19 Hz eyeball-resonance hypothesis

A widely cited hypothesis, originating with Vic Tandy's work and references to NASA biomechanics research, proposes that infrasound near 18–19 Hz may approach the resonant frequency of the human eyeball. The suggested mechanism is that vibration of the vitreous humour smears peripheral vision, producing shadowy or indistinct shapes at the edge of the visual field. This claim is weakly evidenced (see Uncertainties): the frequency of eyeball resonance is not firmly established, the mechanism predicts whole-field rather than peripheral-only disturbance, and the visual effects Tandy described have not been replicated under controlled conditions. Treat it as a plausible but unconfirmed hypothesis, not an established mechanism.

Natural infrasound sources

Naturally occurring infrasound spans a wide frequency range: large tornadoes produce energy around 0.2–1 Hz; microbaroms from ocean-wave interactions occur near 0.2 Hz; wind over terrain generates broadband infrasound up to around 5 Hz; volcanic eruptions and severe thunderstorms also produce infrasonic signatures. These background signals are everywhere but generally too low in frequency and amplitude to produce the physiological effects attributed to the 18–19 Hz range. They are detectable by sensitive equipment and provide a baseline "floor" against which man-made sources must be judged.

Man-made infrasound sources: HVAC, fans, and machinery

HVAC fans, large ventilation ducts, industrial compressors, and transformer rooms are among the most common sources of infrasound in buildings. A 2023 case study (Environmental Research and Public Health, via PMC) found that in one administrative building, turning off the ventilation system caused a very large drop in noise level across the entire 0.05–10 Hz range, confirming it as the dominant continuous source. HVAC noise concentrates heavily below 250 Hz; the standard A-weighted measurements used in most regulatory contexts substantially underestimate its impact, because A-weighting attenuates low frequencies.

Wind turbines

Wind turbines produce infrasound and LFN as a by-product of blade rotation and mechanical drive components. Multiple national health reviews — including a 2014 Frontiers in Public Health review and a 2017 Acoustics Australia article — concluded that measured infrasound levels from operational turbines at typical setback distances fall well below established perception thresholds. Self-reported symptoms in some residents near turbines are real, but controlled studies consistently point to a nocebo mechanism (the expectation of harm producing symptoms) rather than a direct acoustic effect. This remains an area of active scientific and regulatory debate.

Road, rail, and airport LFN

UK Department for Environment, Food & Rural Affairs (Defra) strategic noise mapping (most recent round: 2022) estimates that around 40% of adults in England are exposed to long-term road traffic noise above 50 dB — the level at which health effects become detectable. In 2018 alone, around 100,000 disability-adjusted life years were attributed to road noise in the UK, 13,000 to rail, and 17,000 to aircraft. These figures cover all noise frequencies; the low-frequency component penetrates building fabric most effectively and is the hardest to attenuate. The UK Civil Aviation Authority and Defra publish receptor-level exposure data under the Open Government Licence.

Structural resonance and standing waves

Physical room dimensions determine where modal resonances fall. Most rooms have fundamental resonances in the 20–200 Hz range, each tied to the room's length, width, or height. When a source drives energy at a modal frequency, standing waves produce large spatial variation in sound pressure level — sometimes 20 dB or more across a few metres. These pressure variations are felt as well as heard, producing sensations of pressure, heaviness, or vibration that depend strongly on exactly where a person is standing. An investigator who moves two paces may notice a complete change in perceived atmosphere that tracks the acoustic node/antinode pattern rather than any feature of the room.

Tunnels, ducts, and pipework

Underground tunnels, building service ducts, drainage channels, and heating pipework act as waveguides, carrying low-frequency sound with very low attenuation over long distances. A sound generated in a basement plant room can arrive at an upper-floor corridor intact in frequency and only modestly reduced in level. Cellar spaces, Victorian tunnels, and industrial underfloor voids are particularly effective waveguides — directly relevant to Vic Tandy's investigations (see Examples).

Tandy & Lawrence (1998): "The Ghost in the Machine"

Vic Tandy, a lecturer at Coventry University, and Dr Tony R. Lawrence published their foundational paper in the Journal of the Society for Psychical Research (vol. 62, pp. 360–64, 1998). Tandy had been working in a research laboratory where staff experienced feelings of depression, cold, and a sense of presence; Tandy himself reported seeing a grey figure at the edge of his peripheral vision that vanished when he turned to face it. The next day he noticed his fencing foil vibrating in its vice when clamped in the lab. Investigation traced the cause to a recently installed extractor fan producing a standing wave estimated mathematically (not directly measured) at approximately 18.98 Hz. The fan was switched off and the phenomena stopped. Tandy and Lawrence proposed that infrasound near 19 Hz might, under certain conditions, generate sensory phenomena consistent with a haunting. Methodological note: the frequency was calculated, not directly measured, and no instrumental record of the reported visual effect was made (see Uncertainties). [1]

Tandy (2000): "Something in the Cellar" (Coventry)

Tandy went on to investigate the medieval cellar beneath Coventry's Tourist Information Centre, where some visitors had reported feelings of a "presence." Using acoustic measuring equipment, he found a near-19 Hz standing wave in the connecting corridor between the modern building and the 14th-century cellar — consistent with his earlier laboratory findings. This was the first time a 19 Hz standing wave was instrumentally detected (rather than calculated) in a reportedly haunted location. [2]

Wiseman, Lord & Watt / Infrasonic Concert (2003)

Psychologist Richard Wiseman and colleagues Sarah Angliss and Ciarán O'Keeffe organised two public concerts at the Purcell Room, London (31 May 2003), under the title Soundless Music. Around 700 attendees heard four musical pieces, two of which were secretly laced with a 17 Hz infrasonic tone at near-threshold amplitude. Participants were surveyed immediately afterwards. Those exposed to the pieces carrying the 17 Hz tone reported a statistically significant 22% increase in anomalous experiences, including chills, unease, inexplicable sadness, and a sense of presence. Wiseman concluded that "low-frequency sound can cause people to have unusual experiences even though they cannot consciously detect infrasound." Note: the effect size was modest, and the experiment has not been formally replicated under peer-reviewed conditions. [6]

French et al. (2009): "The Haunt Project"

Researchers at Goldsmiths College, University of London (Christopher French, Usman Haque, Rosie Bunton-Stasyshyn, Rob Davis) built a purpose-made chamber and exposed 79 participants to infrasound (18.9 Hz and 22.3 Hz), complex electromagnetic fields (EMF), both, or neither, in a 2×2 factorial design over 50-minute sessions. Some 79.7% of participants reported unusual sensations of some kind — but there were no statistically significant differences between the infrasound and non-infrasound conditions. The strongest predictor of a reported anomalous experience was individual suggestibility, not acoustic or electromagnetic condition. French concluded that simply telling participants they might experience something unusual was more predictive than the physical conditions applied. [4]

Schmaltz et al. (2026): Infrasound, Cortisol, and Aversive Responding

Published 27 April 2026 in Frontiers in Behavioral Neuroscience, this controlled experiment exposed 36 participants to either horror-themed or calming music, with 18 Hz infrasound (~75–78 dB) either present or absent. Participants could not accurately tell when infrasound was present. Even so, infrasound exposure significantly raised salivary cortisol and increased self-reported irritability, sadness, and disinterest, independently of music type. The authors proposed an evolutionary arousal-vigilance mechanism: infrasound — common near traffic, industrial machinery, and ageing HVAC systems — engages subconscious threat-detection pathways without triggering conscious hearing. This is the most methodologically rigorous recent study to find a positive physiological effect at environmental-level intensities. [3]