The Mythbusters (Discovery Channel TV show) entered the world of audio during their Halloween special by testing the haunted hum or fear frequency. It is often said, as in a famous UK experiment that infrasonic audio - that is audio below the frequency of 20 Hz - can make people feel odd, anxious, uneasy, nervous or frightened if they don't perceive the sound consciously. In fact infrasonic sound is thought by some to be the basis for people supposedly experiencing supernatural or ghostly events.
So what better urban myth to test on Halloween than this for the Mythbusters? And so in a segment called The Haunted Hum, Jamie and Adam went out to a remote location where there were four empty cabins with nearly identical layouts. They set up nine huge sub-woofer type, stadium concert-sized speakers (Meyer Sound 1100-LFCs) underneath one of them and turned them up to just below the volume where they were causing things to rattle. And since the range of human hearing bottoms out at 20 Hz, the sound would not be heard.
Then they enlisted 10 volunteers to spend time in each of the cabins and report whether they felt different in any of them. I don't want to spoil the surprise in case you have not seen the episode (you can see the Aftershow for it on the Mythbusters site to get the answer), but Jamie did report feeling a bit anxious, like he had had too much caffeine.
Watch for the episode on the Discovery Channel.