Ghost Story: Low Frequency Illusions Created By Standing Waves?

July 03, 2013, by Vic Tandy


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.

As I arrived one morning, I reached for the door handle and came face to face with the cleaning lady who was in a state of distress. She told me she had just been crept up on by something, which she took to be a ghost.

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 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. I investigated but there was no one around.

Back at the desk, the feelings got stronger, and 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.

But 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 believed 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 therefore, 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 halfway down the room.

From the measurements, I formed the hypothesis that a low frequency (LF) standing wave of about 19 Hz 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 not only 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.

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 20 Hz.

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”, also 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 19 Hz would be implicated at this stage. However, Dunn did find a 19 Hz 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 19 Hz, 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 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 350 Hz 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.

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Ghost Story: Low Frequency Illusions Created By Standing Waves?