Every day, you encounter sounds that you can’t technically hear. Some of these are produced at incredibly high pitches, but many others occur as infrasound. This range of ultra-low frequencies below 20 Hertz (Hz) are found everywhere—during thunderstorms, inside factories, and even amid rush hour traffic. But a growing body of evidence suggests that infrasound is regularly detectable in spookier situations. More specifically, the seemingly imperceptible tones may frequently show up in “haunted” hotspots.
This isn’t to say that ghosts generate ultra-low rumblings like crocodiles. Instead, researchers writing in the journal Frontiers in Behavioral Neuroscience suggest that infrasound may help explain why some places simply feel more creepy or foreboding than others.
“Consider visiting a supposedly haunted building. Your mood shifts, you feel agitated, but you can’t see or hear anything unusual,” Rodney Schmaltz, a psychologist at Canada’s MacEwan University and study co-author, said in a statement. “In an old building, there is a good chance that infrasound is present, particularly in basements where aging pipes and ventilation systems produce low-frequency vibrations.”
To better understand the potential relationship between unconscious auditory influences on human psychology, Schmaltz’s team asked 36 volunteers to sit by themselves in a room and listen to either unsettling or calming music clips. During half of the sessions, the study authors also exposed their volunteers to 18 Hz infrasound tones through hidden subwoofer speakers. Each person then filled out a survey to record their emotional responses to the music, as well as whether or not they suspected any exposure to infrasound. Finally, they provided a saliva sample to assess their cortisol levels.
Researchers discovered that participants’ salivary cortisol was higher when infrasound was present, whether or not the individual successfully flagged low-frequency audio. The volunteers also consistently reported higher levels of irritability and ranked the music as sadder overall. Interestingly, there was no statistical evidence suggesting people could reliably identify infrasound.
“Participants could not reliably identify whether infrasound was present, and their beliefs about whether it was on had no detectable effect on their cortisol or mood,” explained Schmaltz.
While cortisol levels are directly related to irritability and stress in humans, the experiment indicated the hormone may also be swayed by more subtle influences.
“This study suggests that the body can respond to infrasound even when we can’t consciously hear it,” Schmaltz added.
Past research supports their theory, including a famous incident from over 40 years ago. During the 1980s, a British engineer named Vic Tandy began noticing odd shapes at the corners of his vision while working in a factory for medical equipment. Coworkers had long alleged that the building itself was haunted. However, Tandy’s “visions” disappeared soon after discovering and disabling a nearby fan that was generating infrasound rumblings.
“As someone who studies pseudoscience and misinformation, what stands out to me is that infrasound produces real, measurable reactions without any visible or audible source,” said Schmaltz.
The study’s authors stress that they haven’t reached any definitive conclusions yet, citing the small sample pool and focus on a single frequency. That said, their work is one more indication that a ghost may not be what’s raising the hairs on the back of your neck—it may simply be some faulty plumbing.
