John Huntington and his friends decided to test the reported phenomenon of infrasound (very low-frequency sounds) causing people to feel spooky chills and thrills, a phenomenon blamed for ghost sightings and reports of hauntings. They created a spook-house with a double-blind randomized infrasound generator and used surveys to check for a correlation between infrasound and creepy feelings. John exhaustively documented the experimental setup (and the setbacks encountered in getting things up and running), and the results. Spoiler alert: they didn’t find a correlation.
We picked a 19 Hertz (Hz, or cycles per second) sine wave as our infrasound source, since that’s the frequency Tandy and Lawrence had found in their initial investigation of a “haunted” space (see Part I of this series for details). For our initial tests last spring, we used an Audio Toolbox as our signal generator, and connected it up to our ancient Apogee P-10 subwoofer processor and a Crown K2 amp, which drove an Apogee AE-10 double 18″ subwoofer (these units work just fine, but haven’t been made in years.) We got the sound going, but after a minute or so, it would cut out. I figured out that the processor was apparently protecting the subs against the “bad” infrasound, and was cutting out. So, I bypassed the processor and its protection circuits, and (carefully) drove the subwoofers directly from the amp. This worked just fine, but I was a bit concerned about damaging the speakers themselves. Fortuitously, over the summer I managed to get for our department a massive, modern Meyer Sound 650-P powered subwoofer. And after some tests in late summer we determined that the unit could generate quite a bit of 19Hz without clipping, and we figured the level was pretty good because by the time we pushed the 650-P up to its limits, the effects of the infrasound would be obvious to anyone in the room, which wouldn’t have been acceptable for our purposes.
Part 1,
Part 2,
Part 3,
Part 4,
Part 5
(Thanks, John!)