Infrasound Theory


By: Jacqueline Shields

Infrasound/Ultrasound and how it relates to EVP’s and paranormal phenomena – Or in other words, frequencies that we can’t hear, even though the decibel level is very high. Examples include dog whistles, bar sonar, dolphin sonar, etc. There is a potential that motors from fans/heaters can give off a low frequency (15-20 Hz) that is not audible to our ears, but is deafening to others. I’d be interested if you can pull some numbers on what humans can hear and can’t hear, and if its possible that you can talk in a range that we can’t hear, but recorders can pick up. And learn WHY recorders can pick up that infrasound/ultrasound (if at all).

The detection range for human hearing is 0 decibels (dB) through 130 dB. 130 db is the threshold of pain for humans. The audible frequency range of human is roughly 20 Hertz (Hz) to 20 kHz. 1 A typical person begins to identify sounds at 10-15dB.2 A small number of people may be able to detect sound below 10dB, thus being able to hear sounds normally viewed as inaudible. This may explain why some people hear “phenomenon” and others don’t. In order for words and conversations to be comprehensive to human ears/brains the crucial range is 500-3,000 Hz.2

In theory, a sound may be recorded on a digital recording device at a specific Hz. If the device allows for lower frequency recording (below human detection) and is played back at a different speed, a variation in frequency may occur, thus making the sound audible to human ears. I have put a research call in to a sound technician to verify this statement. I am waiting for his response. Syracuse Paranormal commonly uses the Olympus VN-4100PC digital recorder. The sampling frequency varies with the speed of the recording. 3

The human voice range is 200-4,000 Hz.2 If a voice-like frequency is produced from an unknown source, it must be in this range when heard. If human ears detect a human voice at the high end of the range, it is very commonly unintelligible. The best range to hear and comprehend the words occur with sounds between 3000-4000 Hz. 1

All in all, it is possible for a human (other) source to produce sound in a frequency range that is inaudible. It is, in theory, possible to record those sounds and replay at a different speed to change the frequency to detectable levels.

1. http://hyperphysics.phy-astr.gsu/Hbase/sound/earsens.html 2. http://grounds-mag.com/,ag/grounds_maintenance_equipment_decibel_levels/ 3. http://www.olympusamerica.com/cpg_section/cpg_archhived_product_details.asp?fl=2&id+1291

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