In the engineering building where Tandy worked, cleaning staff as well as fellow researchers complained of feeling dread, depression and a strange feeling that someone was watching them. But what made the situation really worthy of a Scooby-Do episode was the fact that every so often the staff would see dark figures out of the corners of their eyes.
You can get the same sensation by going four days without sleep.
Now we're talking.
After one particularly strange experience when a gray shape sat next to his desk for several minutes, Vic Tandy was determined to figure out what the hell was going on. Being a man of science, he was going to skip the part where he had an exorcist come and bless the facility.
After eliminating gas poisoning and rogue equipment, Vic realized that the ghostly apparitions seemed to almost always occur in a certain section of the lab. He also realized that if he put a metal sheet in a vice, it would spontaneously vibrate uncontrollably for no apparent reason. Poltergeist, right?
No. Just infrasound.
Specifically, a "silent" exhaust fan was sending out low frequency vibrations that bounced back and forth on the lab's walls until they formed a powerful wave at... 18.9Hz. Right at the top of the panic range.
And, according to a NASA study, it was powerful enough to resonate with the average human eyeball, causing "smeared" vision. This is a phenomenon where the eye vibrates just enough to register something static -- say, the frame of your glasses or a speck of dust -- as large, moving shapes.
Predictably enough, once the vibrating fan was removed, the strange apparitions and feelings of fear disappeared.
Convinced that he had stumbled onto something, Vic Tandy went on to test this explanation for ghostly apparitions in the cellar of a nearby "haunted" abbey. According to the locals, as soon as someone would step into the cellar they would freeze up, see strange gray ghosts and have to leave because of nausea. Vic discovered that the shape of the cellar, the hallway leading to it as well as nearby factories all contributed in making the haunted cellar a perfect resonating chamber. The vibrations created were exactly 18.9Hz and were most powerful at the threshold of the cellar, where most people became sick and terrified.
Could it be? All of these hauntings, all of this folklore, all of it caused by something so, so stupid?
Pictured: fucking pipes.
Also, could somebody with an infrasound generator use this against you? You bet. They even experimented with this during Vietnam, blasting sounds of various frequencies from helicopters, trying to induce panic or at least severe annoyance in the Viet Cong below. Instead of driving away the enemy, infrasound only made them scared and trigger happy. While this was not ideal during a war situation infrasound was later used by the British as a successful method of crowd control.
The problem is it doesn't affect everyone the same way -- obviously not everyone at the abbey saw a ghost. And if you're trying to do it artificially, you need very large and very powerful equipment.
Still, if you want to make people who enter your building feel an otherworldly sense of fear or awe, install an infrasound generator. A large pipe organ will do.
Better home defence than a 12 gauge shotgun.
So if you're ever troubled by strange noises in the middle of the night or you experience feelings of dread in your basement or attic or even if someone in your family sees a spook, specter, or ghost ...
Well, call the repair guy, because it might be caused by a malfunctioning ventilation fan.
Sadly, it turns out these guys AREN'T who you need to call.