Ghost Story: Low Frequency Illusions
Standing Firm in the Presence of Standing Waves
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Before working at Coventry University in Coventry, UK, I designed
anesthetic machines in a lab that was two garages end to end. The
lab was long and thin, rather like a railway carriage. There was
no hint of the strange events that would unfold. |
Aided by a healthy dose of skepticism, I decided to take a look. The thing
was described as gray, very tall and less than attractive. But when I
entered the lab, there was nothing to be seen.
I checked to confirm there were no leaking anesthetic gases. We were extremely
careful with the anaesthetic agents. Everything checked out. The cleaning
lady returned, and we did what anyone would expect of the British in a
crisis…had a cup of tea.
Over the following weeks, we experienced weird events. For example, my
boss would talk to me as if I was standing next to him, when I was on
the other end of the room. In addition, we were unusually depressed and
suffered headaches. The room could be oppressively hot in the summer,
but this was different and unpleasant.
Sitting at the desk when I was working late one night, I had an intense
feeling that someone was watching me. There were windows at each end of
the lab, so it was possible, although unlikely. I investigated but there
was no one around. Back at the desk, the feelings got stronger, I began
to notice something moving by my shoulder. Immediately the hackles stood
up on the back of my neck and a cold chill ran through me.
There was clearly something else in the room. The door was in front of
me, so no one could have entered without my knowing. Whatever it was came
from behind me and glided silently to my side. I was partly aware that
my attempts to give this gray mass form were influencing what I saw, but
I was absolutely terrified of what was happening.
Time Seemed to Slow
I considered a range of options, mainly centered on escape. In the end,
with the gray mass established between the door and myself, I decided
to confront it. When I turned to look at the apparition, it retreated
and faded away. With skepticism still marginally intact, I decided I was
working too hard and went home.
The following day, I discovered what I believe to have been the cause
of the apparition. I was entering a fencing competition and had come in
early to fit my favorite handle to a foil blade. When I put the blade
into the vise, the free end began to move on its own. As I wondered what
might happen next, it dawned on me that this vibration required energy
and something a little less supernatural might be involved.
I transferred the foil blade to a drill vise and slid it along the floor.
The amplitude of the blade movement peaked next to the desk, which was
half way down the room. From the measurements, I formed the hypothesis
that a low frequency (LF) standing wave of about 19Hz with significant
amplitude was the cause of this supernatural encounter.
Finding the source was easy. I asked the maintenance staff if any work
had been done near our lab; indeed a fan had been installed the previous
weekend. Turning the fan off stopped the blade moving, but also lifted
the oppressive feeling from the room and effectively exorcised the ghost,
which was not reported again.
My interest in the effects of LF sound ignited. I dug out a work by W.
Tempest from 1976, titled Infrasound and Low Frequency Vibration (Academic
Press, London), which contained a couple of interesting case studies.
“Noise consultants were asked to examine one of a group of bays in a factory
where workers reported feeling uneasy. The bay had an oppressive feel
not present in the adjacent areas, although the noise level appeared the
same.
“Management workers and consultants were all aware of the unusual atmosphere,
and on investigation it was found that LF sound was present at a slightly
higher level than in other bays. However, the actual frequency of the
offending noise was not obvious. The cause of the noise was a fan in the
air conditioning system.
“Workers in a university radiochemistry building experienced the same
oppressive feeling together with dizziness when the fan in a fume cupboard
was switched on. Conventional soundproofing had reduced the audible sound
to the point where there was hardly any difference in the noise with the
fan on as off.
“The situation affected some people so much that they refused to work
in the lab. It was concluded that the LF component of the sound was responsible.”
(p.81-82)
Symptomology
Infrasound can cause hyperventilation, which may lead to feelings of panic.
At the same time panic can cause hyperventilation, so it is possible to
establish a positive feedback loop, the final effects of which can be
quite profound. Other works suggest the mechanism for the physical manifestation
could be the vibration of the eyeball, which has a resonant frequency
around 20Hz.
With help from parapsychologist Dr. Tony Lawrence, I published “The Ghost
in the Machine” in a 1998 issue of Journal of the Society for Psychical
Research. From the publicity, people began contacting me with their own
experiences of similar ghosts: gray objects and feelings of a presence.
Unfortunately, I had limited resources, but when one group of experiences
centered on a medieval cellar near Coventry University, it was too good
to miss. I published a second paper on this topic in 2000, “Something
in the Cellar,” in the Journal of the Society for Psychical Research.
“In 1997, a Coventry tour guide accompanied a Canadian journalist touring
Britain into the [Coventry] cellar. He noticed that the journalist gave
the appearance of being taken ill as he crossed the threshold of the room...The
journalist described a feeling as if a balloon was being pushed between
his shoulder blades and an intense feeling of a presence.
“Eventually he reported that the face of a woman seemed to be peering
over his right shoulder. The guide was unable to feel or see anything
but the visitor had become ‘ashen’ and looked extremely unwell. The journalist
exhibited the physical symptoms for some time before recovering.”
Other reports followed, including a former assistant manager at the Information
Center above the cellar, who felt an intense presence in the cellar to
the extent that she would talk to it. Two witches investigated and declared
the cellar to be haunted but by a friendly ghost; a third witch investigated
alone and was less charitably received.
I discussed the events with Bill Dunn, a colleague in our School of Engineering
who was aware of my work. He offered his services and a spectrum analyzer
to do measurements.
Infrasound in the Cellar
The hypothesis was that we would find infrasound in the cellar. I did
not suggest to him that 19Hz would be implicated at this stage. However,
Dunn did find a 19Hz signal, which we discovered peaked in amplitude at
the door, the point where most of the witnesses report a feeling of presence.
The dimensions of the medieval cellar would not support resonance at 19Hz,
but the modern corridor attached to it could. In fact, this fits with
the witnesses’ comments because they did not always enter the cellar itself.
I believe they experience the infrasound effects in the corridor approaching
the cellar, rather than the cellar itself.
At the cellar door, these feelings peak and, if a supernatural cause is
considered, the blame is usually placed on the cellar because of its spooky
appearance. This would lead me to suggest that these particular apparitions
are a combination of infrasound and spookiness.
So, Infrasound + Spookiness = Apparition.
The apparition only appeared in the lab when the person seeing it was
alone and either early in the morning or at night when the light outside
was dim. With colleagues around, the feeling of security is increased
and an apparition is less likely to be perceived. The level of signal
in the cellar is low but the ambient noise level down there is also extremely
low. We don’t know if the signal’s level is constant or if it is higher
during the apparitional experiences.
The mechanism for the effect on humans is not completely clear. However,
there seems little doubt that infrasound can affect humans in ways which
are dependent on the environment and the individual’s sensitivity. It
would be useful to test these more subtle effects in a controlled environment
without too many harmonics.
Standing Waves
Most Performance Audio professionals are familiar with urban night clubs,
where standing waves are a common problem. Resulting from symmetrically
shaped, usually rectangular rooms, these standing waves are a predictable
challenge to usable gain-before-feedback. Many a graphic equalizer has
failed to filter a 350Hz howl from a downtown bar.
Where musical, especially stringed, instruments are concerned, standing
waves are also a major component of desirable harmonic content. In addition,
harmonic content, as we know, plays a major role in nearly everyone’s
psychoacoustic response.
It’s all about vibrations. Often, these are “Good Vibrations” where the
psychoacoustic energy is all good. Other times however, harmonic vibrations
can manifest foreboding moods and an emotional sense of dread.
In terms of wave propagation, standing waves are naturally formed by the
interference of two harmonic waves of identical frequency and amplitude
(and therefore same wavelength), traveling in opposite directions.
One characteristic of every standing wave pattern is that there are points,
which appear to be standing still. These points, sometimes referenced
as points of no displacement, are commonly called as nodes.
There are other points along the atmospheric medium which undergo vibrations
between large positive and large negative displacements. These points
undergo the maximum displacement during each vibrational cycle of the
standing wave. Functionally, these points are the opposite of nodes, and
hence called anti-nodes.
Vic Tandy teaches at the School of International Studies and Law at Coventry University in the UK. His Web page has full text versions of the papers, links and contact details at http://193.61.107.61/cyberclass/vicweb/parapsychology.htm
January/February 2002 Live Sound International