Two British scientists have shown that "infrasound" - sound
pitched too low for human hearing - can induce such feelings. It's
the latest report from a research frontier that has fascinated
scientists for decades.
Human-made and natural infrasound is around us all the time. Some
animals, such as elephants and whales, use it for long-distance
communication. Nuclear test ban monitors use it as part of their
strategy to detect illegal bomb tests. Atmospheric scientists use it
for a variety of purposes, including listening instrumentally for
the rumble of distant storms. Some infrasound sources, such as ocean
waves, can be detected thousands of miles away.
Humans can't hear anything pitched lower than 20 hertz. But we
often can feel it just as we can feel (as well as hear) the bass
booms from the souped-up audio system in a car a block away. If you
tune into this low-frequency sound range, you find what two
scientists call "a virtual symphony" of infrasound.
Reviewing the subject in Physics Today, Alfred Bedard (with the
National Oceanic and Atmospheric Administration) and Thomas Georges
(with the NOAA/Colorado State University Corroborative Institute for
Research in the Atmosphere) note that these unheard, but sometimes
felt, sounds are as intense as sounds we can hear. They report that
the infrasound power radiated by the strongest atmospheric storms is
estimated to be equivalent to the electric power consumed by a city
with 100,000 population. That kind of power makes it possible to
isolate the signature of a distant storm or other infrasound source
from the cacophony that instruments detect. There's even an
infrasound background called "the voice of the sea" that probably is
generated by ocean waves in storms around the world.
Drs. Bedard and Georges also point out that winds blowing over
mountain ranges can generate infrasounds that last for days. They
speculate that increases in suicides reported from the Alps and the
western United States "may be due to some as yet unknown biological
response" to such infrasound events. The British experiments,
reported during the recent meeting of the British Association for
the Advancement of Science in Manchester, England, may shed light on
Richard Lord with Britain's National Physical Laboratory and
Richard Wiseman at the University of Hertfordshire described
experiments in which infrasound was mixed into contemporary music.
Some listeners reported uneasy, nervous, or chills-down-the-spine
feelings. Professor Wiseman told the meeting that "these results
suggest that low-frequency sound can cause people to have unusual
experiences even though they cannot consciously detect infrasound,"
according to a Reuters report.
The unheard infrasound "symphony" has become an important tool
for nuclear test-ban monitoring and for atmospheric, avalanche, and
earthquake research. And it now appears that, if you have creepy
feelings in creepy places, you don't have to look for supernatural
sources. Just blame them on the real-life acoustics of "The Twilight