Study finds infrasound the likely horror in hauntings
by Rob Beschizza · Boing BoingNoise below the range of human hearing from old pipes, machinery and ventilation systems can induce stressful sensations, according to a study published by Canadian researchers in Frontiers in Behavioral Neuroscience. The findings offer a compelling scientific explanation for why I feel ill-at-ease in the basement of the abandoned 19th-century sanitarium, built over an old cemetery, that I've been squatting in rural West Pennsylvania. It's not the faslely-accused murderer they executed without trial in 1844 here or the spirits of all those kids who died in that fire the one time; it's that 48" steel ventilation fan whirring away at 17Hz.
The new study, led by Kale R. Scatterty, Trevor J. Hamilton, and Rodney M. Schmaltz of MacEwan University in Edmonton, Alberta (with co-authors Dawson VonStein, Lisa B. Prichard, and Brian C. Franczak), set out to test whether infrasound exposure could measurably shift mood and stress physiology in humans, even if it was beyond the range of audibility.
Infrasound refers to sound waves with frequencies below 20 Hz, the lower threshold of what the human ear can consciously detect. It's generated by unusual events such as volcanic eruptions and severe storms, but also the mundane hum of human-made machinery: HVAC systems, traffic, and long, thin metal things such as pipes. The key point is that "non-audible" doesn't mean "non-perceptible." The body, it turns out, may be picking up signals the conscious mind never registers.
For the study, thirty-six undergrads were randomly assigned to one of four conditions in a 2×2 design: they listened to either calming meditation music or horror-themed ambient audio, with infrasound (~18 Hz, at 75–78 decibels) either present or absent. The infrasound was produced by two subwoofers positioned out of sight. Participants provided saliva samples immediately before and 20 minutes after exposure (the cortisol in it being an established hormonal marker of stress) and completed a mood questionnaire afterward.
Participants couldn't consciously detect whether the infrasound was on; their guesses were no better than chance. But those exposed to infrasound reported higher irritability, lower interest in the music, and rated the audio as sadder irrespective of whether they were hearing calming or unsettling tracks. Moreover, their cortisol levels were also measurably elevated, a physiological effect that persisted even after statistically accounting for self-reported mood.
Past research in this area has been murky. Some studies found infrasound linked to fatigue, nausea, and anxiety; others reported no significant effects at all. The inconsistencies were largely attributed to weak experimental controls, unverified sound exposures, and over-reliance on self-report. The new MacEwan study addressed these gaps directly by pairing verified infrasonic delivery with both psychological and biological measures, and by ruling out expectancy effects (which is to say that participants' beliefs about whether the infrasound was on had no bearing on their cortisol response.)
Nautilus has more on Schmaltz, a pseudoscience fan fascinated by "why people believe weird stuff."
Infrasound has also been in the news lately as it may be generated by all those AI datacenters being too-quickly built; "All sub-audible infrasounds issues are fake," writes one pro-AI writer, who describes infrasound itself as a pseudoscientific idea.
Before it was shown how katabatic winds and a slab avalanche together explains the deeply unnerving Dyatlov Pass incident, in which a team of expert young hikers fled their tent half-naked into the snow and perished in the night, infrasound was one of the more convincing explanations for their seemingly irrational behavior.
I made an infrasound musical instrument once out of very large PVC piping, but it was so big and hideous that the most unsease-inducing thing about it was the sight of it; my Dread Chime was repurposed as a French drain.