Infrasonic Sound

 *sound science series # 3

Infrasound  

Infrasound is a sound that is lower in frequency than 20 Hz (Hertz) or cycles per second, the "normal" limit of human hearing. 

                      Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher levels it is possible to feel infrasound vibrations in various parts of the body.

                 The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.001 Hz.

Sources: Infrasound sometimes results naturally from severe weather, surf, lee waves, avalanches, earthquakes, volcanoes, bolides, waterfalls, calving of icebergs, aurorae, lightning and upper-atmospheric lightning. Nonlinear ocean wave interactions in ocean storms produce pervasive infrasound vibrations around 0.2 Hz, known as microbaroms. According to the Infrasonics Program at the NOAA, infrasonic arrays can be used to locate avalanches in the Rocky Mountains, and to detect tornadoes on the high plains several minutes before they touch down.

                   Infrasound can also be generated by human-made processes such as sonic booms and explosions (both chemical and nuclear), by machinery such as diesel engines and older designs of down tower wind turbines and by specially designed mechanical transducers (industrial vibration tables) and large-scale subwoofer loudspeakers such as rotary woofers. The Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission uses infrasound as one of its monitoring technologies (along with seismic, hydroacoustic, and atmospheric radionuclide monitoring).

              
Whales, elephants, hippopotamuses, rhinoceros, giraffes, okapi, and alligators are known to use infrasound to communicate over distances—up to hundreds of miles in the case of whales. In particular, the Sumatran Rhinoceros has been shown to produce sounds with frequencies as low as 3 Hz which have similarities with the song of the humpback whale. The roar of the tiger contains infrasound of 18 Hz and lower, and the purr of felines is reported to cover a range of 20 to 50 Hz. It has also been suggested that migrating birds use naturally generated infrasound, from sources such as turbulent airflow over mountain ranges, as a navigational aid. Elephants, in particular, produce infrasound waves that travel through solid ground and are sensed by other herds using their feet, although they may be separated by hundreds of kilometres.

Elephants use infrasonic sounds to communicate

wind turbines produce major infrasound

Battle of Jericho: what about sound guns and other directed noise-based attacks

Low frequency acoustic waves were first discovered after the eruption of the Krakatoa (Indonesia) in August 27, 1883. Due to its low frequency content, the infrasound traveled up to four times around the globe while reaching altitudes over 100 km.

storms and ocean waves generate infrasound

      Animal reactions to infrasonics:   

•  Animals have been known to perceive the infrasonic waves going through the earth by natural disasters and can use these as an early warning.

•   Infrasound may also be used for long-distance communication in African elephants.  
 

Human reactions to infrasonics:

1. Sound frequencies below 20 Hz affect on our internal body organs. Each organ is susceptible to these subsonic frequencies. They start vibrating when their critical frequency is reached.

2. Our human body behaves like a resonating chamber ( like an ear) for the infrasonic sound.

3. These silent, mysterious sound affect thousands of our internal organs in our abdominal or cranial cavity.

 

Aweful feeling: One study has suggested that infrasound may cause feelings of awe or fear in humans. It was also suggested that since it is not consciously perceived, it can make people feel vaguely that supernatural events are taking place.

Ghost feelings: Research by Vic Tandy, a lecturer at Coventry University, suggested that an infrasonic signal of 19 Hz might be responsible for some ghost sightings.
           More recent research seem to indicate that, while infrasound does seem to have effects on human emotions, some of Tandy's findings are inaccurate.

 Alarming infrasonics: Waves of infrasound are invisible, but slam into living tissue and physical structures with great force.
The sensation vibrates internal organs and buildings, flattening objects as the sonic wave strikes.
At certain pitches, it can explode matter.
          Long pipe organs, such as those found in churches and cathedrals produce infrasound. In one UK study, the extreme bass frequencies instilled strange feelings at a concert hall. Effects were "extreme sense of sorrow, coldness, anxiety, and even shivers down the spine."

Infrasonics as weapon: High-intensity/low-frequency sound and infrasound are powerful forces, and governments have tested and used them as a weapon of war.

# (for the reference reading)

http://www.lowertheboom.org/trice/infrasound.htm

*Note: all pictures thankfully shared from various sources..