The average frequency range of hearing for human beings is about 20 to 20,000Hz. Frequencies below 20Hz are called infrasounds, and above 20,000Hz are called ultrasounds. Infrasound is the sound that extends below the range of human hearing (from 20 Hz down to 0.001 Hz), and it is produced by many natural and human-made sources.
Some natural sources of infrasonic sound waves are animals, such as whales, elephants, and giraffes, which communicate using infrasound over long distances. Volcanoes, earthquakes, ocean waves, waterfalls, meteors, and asteroids generate infrasonic sound waves. Some sources of human-made infrasound are nuclear and chemical explosions, mechanical engines, machinery, and airplanes.
Infrasonic waves propagate with extremely low attenuation i.e., their amplitude reduces very slowly and hence are capable of spreading over great distances. The infrasonic sound spectrum is filled with sources, and distinguishing between these sources is essential since their identification influences—the decisions regarding the responses. Many sources of infrasonic waves are with different periods and wavelength scale for each type of infrasonic wave source.
RECENT ENCOUNTERS WITH INFRASOUND
In recent years the human health effects of infrasound arise from health concerns expressed by the residents of Kokomo, Indiana. Several individuals in the local area have complained of non-specific symptoms, including sleep disturbance, headaches, and nausea. Several state and federal agency officials and experts in the academic community and private sector have been called to help investigate these concerned health complaints.
No conclusions have been made regarding the relationship between this low-frequency noise and the residents’ health complaints. Health concerns expressed by the residents of Kokomo, Indiana region, is a mystery so far.
HARMFUL EFFECTS OF INFRASOUND
During a scientific study, when people started listening to an orchestra were exposed to infrasound at irregular time intervals, about 22 percent reported discomfort every time the sounds were emitted. So, while hearing to sounds below 20Hz, we will choose to isolate the machine by a formwork using some absorbent materials at a shallow frequency or lower the exposure time of persons to that sound. The rule regarding exposure time reduces an exposure level by 4 dB if the exposure time is halved and applies to both infrasound and the audible sound spectrum.
SCIENTIFIC APPROACH TO INFRASOUNDS
Scientists confirm that high-level infrasound may harm the basilar membrane of the human ear and perhaps be capable of canceling noise-induced hearing loss. Chinchilla was exposed to a 30 Hz tone in 100 dB SPL and 108 HB SPL in 4 DHP SPL for 1.75 hours or 86 dB SPL for 24 h at 30 Hz tone. For each animal, the tympanic membrane (TM) was perforated (~ 1 mm2) in one ear, before exposure to infect that cochlea by approximately 50 dB SPL.
Controls included animals that were exposed only or only in 4-kHz OBN infusion. The ABR threshold shifts (TSs) and DPOAE level shifts were determined before pre- and post-TM-perforation and immediately after exposure before cochlear fixation. The cochlea was sterilized, embedded in plastic, and dissected into a flat preparation of Corti’s organ (OC). Each dissected section was evaluated for loss of inner hair cells (IHCs) and outer hair cells (OHCs).
For each chinchilla, the patterns and patterns of loss of functional and hair cells are compared between their right and left cochlea. TM perforation produced no ABR TS during frequency, but 10–21 dB DPOAE LS from 0.6–2 kHz. Infrasonic sound exposure resulted in 10–35 dB ABR TS and below 2 kHz, there was no DPOAE LS, and no IHC or OHC losses. Exposure to 4-kHz OBN at 108 dB produced 1050 dB ABR TS for 0.5–12 kHz, 1060 dB DPOAE LS for 0.6–2 kHz, and OHC losses in the first turn.
When infrasound was present at exposure to 108 dB for the 4-kHz OBN, functional impairment and loss of OHC were significantly increased compared to the apical and basal tips of the OC, with exposure to the 4 kHz BBN in the cochleae alone. Exposure for only 4-kHz OBN at 86 dB produces 10–40 dB ABR TS for 3–12 kHz and 10–30 base LS for 3–8 kHz, but little or no OHC in between the first turns. There is no loss. No difference in the functional or hair-cell loss was found, the presence or absence of presence at 86 dB upon exposure to 4-kHz OBN.
We are exposed to infrasound and increase the cochlear damage of an intensive 4-kHz OBN, as fluid movements more significant than infrasound caused greater inhibition of cochlear fluid through the damaged reticular lamina. Simultaneous violations and a moderate 4-kHz OBN do not increase cochlear damage because the lattice lamina rarely ruptures during this average level of exposure.
Ghostbusters and paranormal activity experts use advanced devices to capture infrasonic sounds to conclude the presence of any supernatural entity in the haunted place.