In sound frequencies, ultrasound is frequencies of sound waves that are above the range of human hearing--too high pitched. On the opposite end of the frequency spectrum--sound too low for human hearing (anything below about 20Hz)--we have infrasound. It has been known for some time that exposure to infrasound can have quite an interesting effect on the human central nervous system.

Infrasonic frequencies can cause feelings of temperature drop, nervousness, feelings of being watched, and paranoia. In addition, within the 15-20Hz region, we find the resonant frequency of the human retina (approximately 19Hz). This sound frequency can actually cause the retina to vibrate, which can cause object in your peripheral vision to blur.

This blurred object combined with a feeling of not being alone causes the mind to assume that the blur in their vision is a person, and when they turn to see them, the blur that they assumed was a person, vanished instantly.

Clearly, these phenomena are categorically similar with many standard paranormal phenomena. But, how do we know when infrasound is the cause of the "haunting?" The answer is complex. There are many causes of infrasound, both manmade and natural in origin. Manmade sources can range from subways to exhaust vents. Natural sources can include storms, tornados, earthquakes, or even ocean waves.

I would be willing to be that a great number of paranormal experiences could be debunked by detecting, locating and if possible, isolating causes of infrasound throughout a location. However, this in itself poses a problem.

Using equipment to detect infrasound on a modest budget can be quite the challenge. For more information on how S.P.I. approaches infrasonic detection, please be sure to frequently visit our Research and Development section.

Be safe in your investigations.