Infrasound

<h2 id="history-and-study">History and study</h2>
One of the pioneers in infrasonic research was French scientist <a href="/facts/Vladimir_Gavreau/sxfKFep0">Vladimir Gavreau</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> His interest in infrasonic waves first came about in 1957 in the large concrete building that he and his research team were working in. The group was experiencing bouts of periodic and deeply unpleasant nausea. After weeks of speculation on the source of the nausea — the team was convinced that it was a pathogen or an untraced leak of noxious chemical fumes in the facility — they discovered that a "loosely poised low speed motor... was developing [these] 'nauseating vibrations'".<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a>
When Gavreau and the team attempted to measure an amplitude and pitch, they were shocked when their equipment detected no audible sound. They concluded the sound being generated by the motor was so low in pitch that it was below their biological ability to hear, and that their recording equipment was not capable of detecting these frequencies. Nobody had conceived that sound might exist at such low frequencies, and so no equipment had been developed to detect it. Eventually, it was determined that the sound inducing the nausea was a 7 cycle per second infrasound wave that was inducing a resonant mode in the ductwork and architecture of the building, significantly amplifying the sound.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> In the wake of this serendipitous discovery, the researchers soon got to work preparing further infrasonic tests in the laboratories. One of his experiments was an infrasonic whistle, an oversized <a href="/facts/Organ_pipe/eddLTo55">organ pipe</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a><a class="footnote-ref" id="fnref:7" href="#fn:7">7</a><a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> As a result of this and similar incidents, it has become routine in new architecture construction to inspect for and eliminate any infrasonic resonances in cavities and the introduction of sound-proofing and materials with specialized sonic properties.

<h2 id="sources">Sources</h2>

Infrasound can result from both natural and man-made sources:

<ul><li>Natural events: infrasonic sound sometimes results naturally from <a href="/facts/Severe_weather/9kD3FWWU">severe weather</a>, <a href="/facts/Ocean_surface_wave/7IsEqwJp">surf</a>,<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> <a href="/facts/Lee_wave/DbL3qpGu">lee waves</a>, <a href="/facts/Avalanche/xm5qLRSC">avalanches</a>, <a href="/facts/Earthquake/NGjIzagw">earthquakes</a>, <a href="/facts/Volcano/c2M5upml">volcanoes</a>,<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a><a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> <a href="/facts/Bolide/2wftckSU">bolides</a>,<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> <a href="/facts/Waterfall/CDyaLQIQ">waterfalls</a>, <a href="/facts/Ice_calving/3xRnvKFs">calving</a> of <a href="/facts/Iceberg/2xFa1Xb2">icebergs</a>, <a href="/facts/Aurora_(astronomy)/6agpj9Qs">aurorae</a>, <a href="/facts/Meteor/gcoGYw6o">meteors</a>, <a href="/facts/Lightning/dLTuxz8n">lightning</a> and <a href="/facts/Upper-atmospheric_lightning/487v0T6w">upper-atmospheric lightning</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> <a href="/facts/Nonlinear/4aYItALC">Nonlinear</a> <a href="/facts/Ocean_surface_wave/7IsEqwJp">ocean wave</a> interactions in ocean storms produce pervasive infrasound vibrations around 0.2 Hz, known as <a href="/facts/Microbarom/lJY729ul">microbaroms</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> According to the Infrasonics Program at <a href="/facts/National_Oceanic_and_Atmospheric_Administration/IvcuqNJg">NOAA</a>, infrasonic arrays can be used to locate avalanches in the Rocky Mountains, and to detect <a href="/facts/Tornado/HSGNQzHa">tornadoes</a> on the high plains several minutes before they touch down.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a></li></ul>
<ul><li>Animal communication: <a href="/facts/Whales/EMJBgXfb">whales</a>, <a href="/facts/Elephants/6prrEFFK">elephants</a>,<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a> <a href="/facts/Hippopotamus/hFGDPWRI">hippopotamuses</a>,<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a> <a href="/facts/Rhinoceros/PYIvDdvU">rhinoceroses</a>,<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a><a class="footnote-ref" id="fnref:19" href="#fn:19">19</a><a class="footnote-ref" id="fnref:20" href="#fn:20">20</a> <a href="/facts/Giraffes/up0Jqouf">giraffes</a>,<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> <a href="/facts/Okapi/FIGeHfQj">okapis</a>,<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a> <a href="/facts/Peacock/mfhnT3h8">peacocks</a>,<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a> and <a href="/facts/Alligator/8eVwtou3">alligators</a> are known to use infrasound to communicate over distances—up to hundreds of miles in <a href="/facts/Whale_sound/H5HaPmgj">the case of whales</a>. In particular, the <a href="/facts/Sumatran_rhinoceros/lH8cvGb1">Sumatran rhinoceros</a> has been shown to produce sounds with frequencies as low as 3 Hz which have similarities with the <a href="/facts/Whale_song/H5HaPmgj">song of the humpback whale</a>.<a class="footnote-ref" id="fnref:24" href="#fn:24">24</a> The <a href="/facts/Roar_(utterance)/MBGYFrF0">roar</a> of the <a href="/facts/Tiger/0cWH5o9T">tiger</a> contains infrasound of 18 Hz and lower,<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a> and the <a href="/facts/Purr/ong9oQqg">purr</a> of <a href="/facts/Felidae/Fryfw7gm">felines</a> is reported to cover a range of 20 to 50 Hz.<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a><a class="footnote-ref" id="fnref:27" href="#fn:27">27</a><a class="footnote-ref" id="fnref:28" href="#fn:28">28</a> It has also been suggested that migrating birds use naturally generated infrasound, from sources such as <a href="/facts/Turbulent/NpgFUhG5">turbulent</a> airflow over mountain ranges, as a <a href="/facts/Navigation/sGGAJ0AQ">navigational</a> aid.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a> Infrasound also may be used for long-distance communication, especially well documented in <a href="/facts/Baleen_whale/hYfEGyEK">baleen whales</a> (see <a href="/facts/Whale_vocalization/H5HaPmgj">whale vocalization</a>), and <a href="/facts/African_elephant/vMA6IWh1">African elephants</a>.<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a> The frequency of baleen whale sounds can range from 10 <a href="/facts/Hertz/6Wshj5qm">Hz</a> to 31 kHz,<a class="footnote-ref" id="fnref:31" href="#fn:31">31</a> and that of elephant calls from 15 Hz to 35 Hz. Both can be extremely loud (around 117 <a href="/facts/Decibel/0LyxAPXh">dB</a>), allowing communication for many kilometres, with a possible maximum range of around 10 km (6 mi) for elephants,<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a> and potentially hundreds or thousands of kilometers for some whales. Elephants also 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. These calls may be used to coordinate the movement of herds and allow <a href="/facts/Mating_elephants/6prrEFFK">mating elephants</a> to find each other.<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a></li></ul>
<ul><li>Human singers: some vocalists, including <a href="/facts/Tim_Storms/HNKAFIHd">Tim Storms</a>, can produce notes in the infrasound range.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a></li></ul>
<ul><li>Man-Made sources: infrasound can be generated by human processes such as <a href="/facts/Sonic_boom/Hfnr1Vlz">sonic booms</a> and <a href="/facts/Explosion/Utp8Wv9D">explosions</a> (both chemical and <a href="/facts/Nuclear_explosion/BtpfgcUg">nuclear</a>), or by machinery such as <a href="/facts/Diesel_engine/9B9opxvA">diesel engines</a>, <a href="/facts/Wind_turbine/lUfWqfLg">wind turbines</a> and specially designed mechanical <a href="/facts/Transducers/YS7zfv9d">transducers</a> (industrial vibration tables). Certain specialized <a href="/facts/Loudspeaker/tqEjnJ2z">loudspeaker</a> designs are also able to reproduce extremely low frequencies; these include large-scale <a href="/facts/Rotary_woofer/a1HVM8CK">rotary woofer</a> models of <a href="/facts/Subwoofer/RYD1sR7V">subwoofer</a> loudspeaker,<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a> as well as large <a href="/facts/Loudspeaker_enclosure/H2n9Xyg9">horn loaded</a>, <a href="/facts/Loudspeaker_enclosure/H2n9Xyg9">bass reflex</a>, <a href="/facts/Loudspeaker_enclosure/H2n9Xyg9">sealed</a> and <a href="/facts/Loudspeaker_enclosure/H2n9Xyg9">transmission line</a> loudspeakers.<a class="footnote-ref" id="fnref:36" href="#fn:36">36</a><a class="footnote-ref" id="fnref:37" href="#fn:37">37</a></li></ul>
<h2 id="animal-reaction">Animal reaction</h2>
Main article: <a href="/facts/Perception_of_infrasound/1XPgfAhl">Perception of infrasound</a>
Further information: <a href="/facts/Tsunami/N3xGNHBl">Tsunami § Possible animal reaction</a>, and <a href="/facts/Rayleigh_wave/QAlu9lQo">Rayleigh wave § Possible animal reaction</a>
Some animals have been thought to perceive the infrasonic waves going through the earth, caused by natural disasters, and to use these as an early warning. An example of this is the <a href="/facts/2004_Indian_Ocean_earthquake_and_tsunami/GpHsI7Wu">2004 Indian Ocean earthquake and tsunami</a>. Animals were reported to have fled the area hours before the actual tsunami hit the shores of Asia.<a class="footnote-ref" id="fnref:38" href="#fn:38">38</a><a class="footnote-ref" id="fnref:39" href="#fn:39">39</a> It is not known for sure that this is the cause; some have suggested that it may have been the influence of <a href="/facts/Electromagnetic_waves/Ynx7ujCW">electromagnetic waves</a>, and not of infrasonic waves, that prompted these animals to flee.<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a>
Research in 2013 by Jon Hagstrum of the US Geological Survey suggests that <a href="/facts/Homing_pigeons/4oeMCg2q">homing pigeons</a> use low-frequency infrasound to navigate.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a>

<h2 id="human-reactions">Human reactions</h2>
Further information: <a href="/facts/Health_effects_from_noise/6A2Fz81a">Health effects from noise</a>
20 Hz is considered the normal low-frequency limit of human hearing. When pure sine waves are reproduced under ideal conditions and at very high volume, a human listener will be able to identify tones as low as 12 Hz.<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a> Below 10 Hz it is possible to perceive the single cycles of the sound, along with a sensation of pressure at the eardrums.
From about 1000 Hz, the dynamic range of the auditory system decreases with decreasing frequency. This compression is observable in the <a href="/facts/Equal-loudness_contour/TamhqmSc">equal-loudness-level contours</a>, and it implies that even a slight increase in level can change the perceived loudness from barely audible to loud. Combined with the natural spread in <a href="/facts/Absolute_threshold_of_hearing/Fn3TzQ3p">thresholds</a> within a population, its effect may be that a very low-frequency sound which is inaudible to some people may be loud to others.
One study has suggested that infrasound may cause feelings of awe or fear in humans. It has also been suggested that since it is not consciously perceived, it may make people feel vaguely that odd or <a href="/facts/Supernatural/qSlTK0Ss">supernatural</a> events are taking place.<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a>
A scientist working at Sydney University's Auditory Neuroscience Laboratory reports growing evidence that infrasound may affect some people's nervous system by stimulating the <a href="/facts/Vestibular_system/h2gYqtSq">vestibular system</a>, and this has shown in animal models an effect similar to <a href="/facts/Sea_sickness/kBs72ygo">sea sickness</a>.<a class="footnote-ref" id="fnref:44" href="#fn:44">44</a>
In research conducted in 2006 focusing on the impact of sound emissions from wind turbines on the nearby population, perceived infrasound has been associated to effects such as annoyance or fatigue, depending on its intensity, with little evidence supporting physiological effects of infrasound below the human perception threshold.<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a> Later studies, however, have linked inaudible infrasound to effects such as fullness, pressure or tinnitus, and acknowledged the possibility that it could disturb sleep.<a class="footnote-ref" id="fnref:46" href="#fn:46">46</a> Other studies have also suggested associations between noise levels in turbines and self-reported sleep disturbances in the nearby population, while adding that the contribution of infrasound to this effect is still not fully understood.<a class="footnote-ref" id="fnref:47" href="#fn:47">47</a><a class="footnote-ref" id="fnref:48" href="#fn:48">48</a>
In a study at <a href="/facts/Ibaraki_University/u3zD87u2">Ibaraki University</a> in Japan, researchers said EEG tests showed that the infrasound produced by <a href="/facts/Wind_turbine/lUfWqfLg">wind turbines</a> was "considered to be an annoyance to the technicians who work close to a modern large-scale wind turbine".<a class="footnote-ref" id="fnref:49" href="#fn:49">49</a><a class="footnote-ref" id="fnref:50" href="#fn:50">50</a><a class="footnote-ref" id="fnref:51" href="#fn:51">51</a>
Jürgen Altmann of the <a href="/facts/Technical_University_of_Dortmund/mbWpIHcQ">Technical University of Dortmund</a>, an expert on <a href="/facts/Sonic_weapon/xDlu1sE3">sonic weapons</a>, has said that there is no reliable evidence for nausea and vomiting caused by infrasound.<a class="footnote-ref" id="fnref:52" href="#fn:52">52</a>
High volume levels at concerts from subwoofer arrays have been cited as causing <a href="/facts/Lung_collapse/oaCPSynh">lung collapse</a> in individuals who are very close to the subwoofers, especially for smokers who are particularly tall and thin.<a class="footnote-ref" id="fnref:53" href="#fn:53">53</a>
In September 2009, London student Tom Reid died in a club of <a href="/facts/Cardiac_dysrhythmia/ooEpr46Q">sudden arrhythmic death syndrome (SADS)</a> after complaining that "loud bass notes" from the club's speakers were "getting to his heart". The inquest recorded a verdict of natural causes, although some experts commented that the bass could have acted as a trigger.<a class="footnote-ref" id="fnref:54" href="#fn:54">54</a>
Air is a very inefficient medium for transferring low frequency vibration from a transducer to the human body.<a class="footnote-ref" id="fnref:55" href="#fn:55">55</a> Mechanical connection of the vibration source to the human body, however, provides a potentially dangerous combination. The U.S. space program, worried about the harmful effects of rocket flight on astronauts, ordered vibration tests that used cockpit seats mounted on vibration tables to transfer "brown note" and other frequencies directly to the human subjects. Very high power levels of 160 dB were achieved at frequencies of 2–3 Hz. Test frequencies ranged from 0.5 Hz to 40 Hz. Test subjects suffered motor ataxia, nausea, visual disturbance, degraded task performance and difficulties in communication. These tests are assumed by researchers to be the nucleus of the current <a href="/facts/Urban_legend/zBubH9kG">urban myth</a> surrounding the "brown note" and its effects.<a class="footnote-ref" id="fnref:56" href="#fn:56">56</a><a class="footnote-ref" id="fnref:57" href="#fn:57">57</a>
The report "A Review of Published Research on Low Frequency Noise and its Effects"<a class="footnote-ref" id="fnref:58" href="#fn:58">58</a> contains a long list of research about exposure to high-level infrasound among humans and animals. For instance, in 1972, Borredon exposed 42 young men to tones at 7.5 Hz at 130 dB for 50 minutes. This exposure caused no adverse effects other than reported drowsiness and a slight blood pressure increase. In 1975, Slarve and Johnson exposed four male subjects to infrasound at frequencies from 1 to 20 Hz, for eight minutes at a time, at levels up to 144 dB SPL. There was no evidence of any detrimental effect other than middle ear discomfort. Tests of high-intensity infrasound on animals resulted in measurable changes, such as cell changes and ruptured blood vessel walls.
Infrasound is one hypothesized cause of death for the nine Soviet hikers who were <a href="/facts/Dyatlov_Pass_incident/0W3MXemj">found dead at Dyatlov Pass</a> in 1959.<a class="footnote-ref" id="fnref:59" href="#fn:59">59</a>

<h3>Hygienic standards in the workplace</h3>
US: Maximum levels for frequencies from 1 to 80 Hz are no more than 145 dB. Overall level (for all frequencies) - no more than 150 dB.<a class="footnote-ref" id="fnref:60" href="#fn:60">60</a>

RF<a class="footnote-ref" id="fnref:61" href="#fn:61">61</a><table><tbody><tr><th colspan="4">Equivalent sound pressure levels, dB, in octave bands with geometric mean frequencies, Hz</th><th rowspan="2">Equivalent overall sound pressure level, dB</th><th rowspan="2">Maximum overall infrasound level, dB</th></tr><tr><td>2</td><td>4</td><td>8</td><td>16</td></tr><tr><td>100</td><td>95</td><td>90</td><td>85</td><td>100</td><td>120</td></tr></tbody></table>
<h3>Brown note</h3>
Main article: <a href="/facts/Brown_note/ReWRoSwx">Brown note</a>
The brown note is a hypothetical infrasonic frequency capable of causing fecal incontinence by creating acoustic resonance in the human bowel. Attempts to demonstrate the existence of a "brown note" using sound waves transmitted through the air have failed.
In February 2005 the television show <a href="/facts/MythBusters/cJ4j9XAr">MythBusters</a> attempted to verify whether the "brown note" was a reality. They tested notes down to 5 Hz in frequency and up to 153 dB in <a href="/facts/Sound_pressure/MgJAcp2I">sound pressure</a>. They used a type subwoofer used for major rock concerts, and which had been specially modified for deeper bass extension. The rumored physiological effects did not materialize. The show declared the brown note myth "busted."<a class="footnote-ref" id="fnref:62" href="#fn:62">62</a><a class="footnote-ref" id="fnref:63" href="#fn:63">63</a><a class="footnote-ref" id="fnref:64" href="#fn:64">64</a><a class="footnote-ref" id="fnref:65" href="#fn:65">65</a>

<h3>Infrasonic 17 Hz tone experiment</h3>
On 31 May 2003, a group of UK researchers held a mass experiment, where they exposed some 700 people to music laced with soft 17 Hz <a href="/facts/Sine_waves/mD1CB09M">sine waves</a> played at a level described as "near the edge of hearing", produced by an extra-long-stroke subwoofer mounted two-thirds of the way from the end of a seven-meter-long plastic sewer pipe. The experimental concert (entitled Infrasonic) took place in the <a href="/facts/Purcell_Room/V7mWl7uC">Purcell Room</a> over the course of two performances, each consisting of four musical pieces. Two of the pieces in each concert had 17 Hz tones played underneath.<a class="footnote-ref" id="fnref:66" href="#fn:66">66</a><a class="footnote-ref" id="fnref:67" href="#fn:67">67</a>
In the second concert, the pieces that were to carry a 17 Hz undertone were swapped so that test results would not focus on any specific musical piece. The participants were not told which pieces included the low-level 17 Hz near-infrasonic tone. The presence of the tone resulted in a significant number (22%) of respondents reporting feeling uneasy or sorrowful, getting chills down the spine or nervous feelings of revulsion or fear.<a class="footnote-ref" id="fnref:68" href="#fn:68">68</a><a class="footnote-ref" id="fnref:69" href="#fn:69">69</a>
In presenting the evidence to the <a href="/facts/British_Association_for_the_Advancement_of_Science/q1DLURYh">British Association for the Advancement of Science</a>, Professor <a href="/facts/Richard_Wiseman/WXnnA3Kl">Richard Wiseman</a> said "These results suggest that low frequency sound can cause people to have unusual experiences even though they cannot consciously detect infrasound. Some scientists have suggested that this level of sound may be present at some <a href="/facts/List_of_reportedly_haunted_locations/SVKp2Fs7">allegedly haunted sites</a> and so cause people to have <a href="/facts/Apparitional_experience/hzYmghwf">odd sensations</a> that they attribute to a ghost—our findings support these ideas."<a class="footnote-ref" id="fnref:70" href="#fn:70">70</a>

<h3>Suggested relationship to ghost sightings</h3>
<a href="/facts/Psychologist/J4l4QdX2">Psychologist</a> <a href="/facts/Richard_Wiseman/WXnnA3Kl">Richard Wiseman</a> of the <a href="/facts/University_of_Hertfordshire/e2urd0uG">University of Hertfordshire</a> suggests that the odd sensations that people attribute to ghosts may be caused by infrasonic vibrations. <a href="/facts/Vic_Tandy/XDC3rKKC">Vic Tandy</a>, experimental officer and part-time lecturer in the school of international studies and law at <a href="/facts/Coventry_University/Gm0gLVk1">Coventry University</a>, along with Dr. Tony Lawrence of the University's psychology department, wrote in 1998 a paper called "Ghosts in the Machine" for the Journal of the <a href="/facts/Society_for_Psychical_Research/qIKAxANh">Society for Psychical Research</a>. Their research suggested that an infrasonic signal of 19 Hz might be responsible for <a href="/facts/Apparitional_experience/hzYmghwf">some ghost sightings</a>. Tandy was working late one night alone in a supposedly haunted laboratory at <a href="/facts/Warwick/QlWsG9pL">Warwick</a>, when he felt very anxious and could detect a grey blob out of the corner of his eye. When Tandy turned to face the grey blob, there was nothing.
The following day, Tandy was working on his <a href="/facts/Fencing/9h2HHTvy">fencing</a> <a href="/facts/Foil_(fencing)/MLnJpJzQ">foil</a>, with the handle held in a <a href="/facts/Vice_(tool)/JWJRfIkA">vice</a>. Although there was nothing touching it, the blade started to vibrate wildly. Further investigation led Tandy to discover that the extractor fan in the lab was emitting a frequency of 18.98 Hz, very close to the <a href="/facts/Resonant_frequency/q7VLALUz">resonant frequency</a> of the eye given as 18 Hz by NASA.<a class="footnote-ref" id="fnref:71" href="#fn:71">71</a> This, Tandy conjectured, was why he had seen a ghostly figure—it was, he believed, an optical illusion caused by his eyeballs resonating. The room was exactly half a wavelength in length, and the desk was in the centre, thus causing a <a href="/facts/Standing_wave/n134E8TC">standing wave</a> which caused the vibration of the foil.<a class="footnote-ref" id="fnref:72" href="#fn:72">72</a>
Tandy investigated this phenomenon further and wrote a paper entitled The Ghost in the Machine.<a class="footnote-ref" id="fnref:73" href="#fn:73">73</a> He carried out a number of investigations at various sites believed to be haunted, including the basement of the Tourist Information Bureau next to <a href="/facts/Coventry_Cathedral/aKuLRH9s">Coventry Cathedral</a><a class="footnote-ref" id="fnref:74" href="#fn:74">74</a><a class="footnote-ref" id="fnref:75" href="#fn:75">75</a> and <a href="/facts/Edinburgh_Castle/U0G3KwuB">Edinburgh Castle</a>.<a class="footnote-ref" id="fnref:76" href="#fn:76">76</a><a class="footnote-ref" id="fnref:77" href="#fn:77">77</a>

<h2 id="detection-and-measurement">Detection and measurement</h2>
See also: <a href="/facts/Infrasonic_sensing_array/gqKV7kmd">Infrasonic sensing array</a>
<a href="/facts/NASA_Langley/UrNAPV7g">NASA Langley</a> has designed and developed an infrasonic detection system that can be used to make useful infrasound measurements at a location where it was not possible previously. The system comprises an <a href="/facts/Electret_microphone/j5omEm2H">electret condenser microphone</a> PCB Model 377M06, having a 3-inch membrane diameter, and a small, compact windscreen.<a class="footnote-ref" id="fnref:78" href="#fn:78">78</a> Electret-based technology offers the lowest possible background noise, because <a href="/facts/Johnson_noise/ur238TgX">Johnson noise</a> generated in the supporting electronics (preamplifier) is minimized.<a class="footnote-ref" id="fnref:79" href="#fn:79">79</a>
The microphone features a high membrane compliance with a large backchamber volume, a prepolarized backplane and a high impedance preamplifier located inside the backchamber. The windscreen, based on the high transmission coefficient of infrasound through matter, is made of a material having a low acoustic impedance and has a sufficiently thick wall to ensure structural stability.<a class="footnote-ref" id="fnref:80" href="#fn:80">80</a> Close-cell polyurethane foam has been found to serve the purpose well. In the proposed test, test parameters will be sensitivity, background noise, signal fidelity (harmonic distortion), and temporal stability.
The microphone design differs from that of a conventional audio system in that the peculiar features of infrasound are taken into account. First, infrasound propagates over vast distances through the Earth's atmosphere as a result of very low atmospheric absorption and of refractive ducting that enables propagation by way of multiple bounces between the Earth's surface and the stratosphere. A second property that has received little attention is the great penetration capability of infrasound through solid matter – a property utilized in the design and fabrication of the system windscreens.<a class="footnote-ref" id="fnref:81" href="#fn:81">81</a>
Thus the system fulfills several instrumentation requirements advantageous to the application of acoustics: (1) a low-frequency microphone with especially low background noise, which enables detection of low-level signals within a low-frequency passband; (2) a small, compact windscreen that permits (3) rapid deployment of a microphone array in the field. The system also features a data acquisition system that permits real time detection, bearing, and signature of a low-frequency source.<a class="footnote-ref" id="fnref:82" href="#fn:82">82</a>

<h3>Infrasound for nuclear detonation detection</h3>
Infrasound is one of several techniques used to identify if a nuclear detonation has occurred. A network of 60 infrasound stations, in addition to seismic and hydroacoustic stations, comprise the <a href="/facts/International_Monitoring_System/sFAGq1pT">International Monitoring System</a> (IMS) that is tasked with monitoring compliance with the <a href="/facts/Comprehensive_Nuclear-Test-Ban_Treaty/PJukufKN">Comprehensive Nuclear Test-Ban Treaty</a> (CTBT).<a class="footnote-ref" id="fnref:83" href="#fn:83">83</a> IMS Infrasound stations consist of eight <a href="/facts/Microbarometer/7oJuySvG">microbarometer</a> sensors and space filters arranged in an array covering an area of approximately 1 to 9 km2.<a class="footnote-ref" id="fnref:84" href="#fn:84">84</a><a class="footnote-ref" id="fnref:85" href="#fn:85">85</a> The space filters used are radiating pipes with inlet ports along their length, designed to average out pressure variations like wind turbulence for more precise measurements.<a class="footnote-ref" id="fnref:86" href="#fn:86">86</a> The microbarometers used are designed to monitor frequencies below approximately 20 hertz.<a class="footnote-ref" id="fnref:87" href="#fn:87">87</a> Sound waves below 20 hertz have longer wavelengths and are not easily absorbed, allowing for detection across large distances.<a class="footnote-ref" id="fnref:88" href="#fn:88">88</a>
Infrasound wavelengths can be generated artificially through detonations and other human activity, or naturally from earthquakes, severe weather, lightning, and other sources.<a class="footnote-ref" id="fnref:89" href="#fn:89">89</a> Like <a href="/facts/Forensic_seismology/shxFsYn2">forensic seismology</a>, algorithms and other filter techniques are required to analyze gathered data and characterize events to determine if a nuclear detonation has actually occurred. Data is transmitted from each station via secure communication links for further analysis. A digital signature is also embedded in the data sent from each station to verify if the data is authentic.<a class="footnote-ref" id="fnref:90" href="#fn:90">90</a>
The <a href="/facts/Comprehensive_Test_Ban_Treaty/PJukufKN">Comprehensive Nuclear-Test-Ban Treaty Organization Preparatory Commission</a> uses infrasound as one of its monitoring technologies, along with <a href="/facts/Seismology/Lony1LYX">seismic</a>, <a href="/facts/Hydrophone/yLwe7VYY">hydroacoustic</a>, and <a href="/facts/Radionuclide/5WpCfbdq">atmospheric radionuclide</a> monitoring. The loudest infrasound recorded to date by the monitoring system was generated by the 2013 <a href="/facts/Chelyabinsk_meteor/4wpcyS0q">Chelyabinsk meteor</a>.<a class="footnote-ref" id="fnref:91" href="#fn:91">91</a>

<h2 id="in-popular-culture">In popular culture</h2>
The 2017 film <a href="/facts/The_Sound_(film)/XB61aHuM">The Sound</a> uses infrasound as a major plot element.<a class="footnote-ref" id="fnref:92" href="#fn:92">92</a><a class="footnote-ref" id="fnref:93" href="#fn:93">93</a>
In "Fermata", a 2020 episode of the Franco-Belgian TV series <a href="/facts/Astrid_et_Rapha%25C3%25ABlle/Dyw5wVfV">Astrid et Raphaëlle</a>, infrasound from a generator hidden in the pipe organ of the <a href="/facts/Grand_Auditorium_(Maison_de_la_Radio)/bAt05fk5">Grand Auditorium</a> in the <a href="/facts/Maison_de_la_Radio_et_de_la_Musique/M1BPFNN3">Maison de la Radio et de la Musique</a>, the Paris headquarters of <a href="/facts/Radio_France/BUlIXgkv">Radio France</a>, is used as a murder weapon.
The 'ghost frequency' phenomenon is mentioned in Season 3 Episode 4 of the TV Series <a href="/facts/Evil_(TV_series)/csn91vqp">Evil</a>, The Demon of the Road.

<h2 id="see-also">See also</h2>

<ul><li><a href="/facts/Bioacoustics/MvvMaYKN">Bioacoustics</a></li>
<li><a href="/facts/Blaster_beam/l8lNYuyQ">Blaster beam</a></li>
<li><a href="/facts/Brown_note/ReWRoSwx">Brown note</a></li>
<li><a href="/facts/Clear-air_turbulence/WfwxwR52">Clear-air turbulence</a></li>
<li><a href="/facts/Contrabass_tuba/IXLDfJ0q">Contrabass tuba</a></li>
<li><a href="/facts/Feraliminal_Lycanthropizer/29csNfRj">Feraliminal Lycanthropizer</a></li>
<li><a href="/facts/Havana_syndrome/2jehFr49">Havana syndrome</a></li>
<li><a href="/facts/Helmholtz_resonance/Qn3p9Qxr">Helmholtz resonance</a></li>
<li><a href="/facts/The_Hum/8B66dGKT">The Hum</a></li>
<li><a href="/facts/Low-frequency_oscillation/kxPocUsz">Low-frequency oscillation</a></li>
<li><a href="/facts/Microbarom/lJY729ul">Microbarom</a></li>
<li><a href="/facts/Sonic_weapon/xDlu1sE3">Sonic weapon</a></li>
<li><a href="/facts/Subcontrabass_tuba/T9yfVKqX">Subcontrabass tuba</a></li>
<li><a href="/facts/Ultrasound/31Pa5IH9">Ultrasound</a></li></ul>

Notes

Bibliography
<ul><li>Gundersen, P. Erik. The Handy Physics Answer Book. Visible Ink Press, 2003.</li>
<li>Chedd, Graham. Sound; From Communications to Noise Pollution. <a href="/facts/Doubleday_%2526_Company/QIy49hM9">Doubleday & Company</a>, 1970.</li>
<li>O'Keefe, Ciaran, and Sarah Angliss. <a href="https://web.archive.org/web/20131225083806/http://www.uni-graz.at/richard.parncutt/cim04/proceedings_.htm">The Subjective Effects of Infrasound in a Live Concert Setting</a>. <a href="https://web.archive.org/web/20131225084105/http://www.uni-graz.at/richard.parncutt/cim04/welcome.htm">CIM04: Conference on Interdisciplinary Musicology</a>. <a href="/facts/Graz/NVCdhqkU">Graz</a>, Austria: Graz UP, 2004. 132–133.</li>
<li>Discovery's Biggest Shows aired at 8:00 pm (Indian Standard Time) on <a href="/facts/The_Discovery_Channel/mmhjAhgr">The Discovery Channel</a>, India on Sunday, 7 October 2007</li></ul>
<h2 id="external-links">External links</h2>

Look up infrasound in Wiktionary, the free dictionary.

<ul><li><a href="https://web.archive.org/web/20200408192005/https://psl.noaa.gov/programs/infrasound/">NOAA Infrasonics Program (archived)</a></li>
<li><a href="https://web.archive.org/web/20070904211118/http://www.rdss.info/index_ns.html">US Army Space and Missile Defense Command Monitoring Research Program (archived)</a></li>
<li><a href="https://web.archive.org/web/20041024230907/http://www.ees.lanl.gov/Resources/infra_collab.shtml">Los Alamos Infrasound Monitoring Laboratory (archived)</a></li>
<li><a href="https://pubs.usgs.gov/pinatubo/tahira/index.html">Infrasonic and Acoustic-Gravity Waves Generated by the Mount Pinatubo Eruption of 15 June 1991</a>, Makoto Tahira, Masahiro Nomura, Yosihiro Sawada and Kosuke Kamo</li>
<li><a href="https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090009968.pdf">Sub-surface windscreen for the measurement of outdoor infrasound</a> Qamar A. Shams, Cecil G. Burkett and Toby Comeaux NASA Langley Research Center, Allan J. Zuckerwar Analytical Services and Material, and George R. Weistroffer Virginia Commonwealth University</li></ul>

<h2 id="references">References</h2>

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<li id="fn:13">Haak, Hein (1 September 2006). "Probing the Atmosphere with Infrasound : Infrasound as a tool" (PDF). CTBT: Synergies with Science, 1996–2006 and Beyond. Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization. Archived from the original (PDF) on 2 July 2007. <a href="https://web.archive.org/web/20070702200640/http://www.ctbto.org/reference/symposiums/2006/haak/0901probingtheatmosphere.pdf" target="_blank">https://web.archive.org/web/20070702200640/http://www.ctbto.org/reference/symposiums/2006/haak/0901probingtheatmosphere.pdf</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">"Microbaroms". Infrasonic Signals. University of Alaska Fairbanks, Geophysical Institute, Infrasound Research Group. Archived from the original on 15 February 2008. Retrieved 22 November 2007. The ubiquitous five-second-period infrasonic signals called "microbaroms", which are generated by standing sea waves in marine storms, are the cause of the low-level natural-infrasound background in the passband from 0.02 to 10 Hz. <a href="https://web.archive.org/web/20080215074429/http://www.gi.alaska.edu/infrasound/Infrasound254.htm" target="_blank">https://web.archive.org/web/20080215074429/http://www.gi.alaska.edu/infrasound/Infrasound254.htm</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">"NOAA ESRL Infrasonics Program". Archived from the original on 8 April 2020. Retrieved 10 April 2012. <a href="http://www.esrl.noaa.gov/psd/programs/infrasound/" target="_blank">http://www.esrl.noaa.gov/psd/programs/infrasound/</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Payne, Katharine B.; Langbauer, William R.; Thomas, Elizabeth M. (1986). "Infrasonic calls of the Asian elephant (Elephas maximus)". Behavioral Ecology and Sociobiology. 18 (4): 297–301. doi:10.1007/BF00300007. S2CID 1480496. <a href="/wiki/Katharine_Payne" target="_blank">/wiki/Katharine_Payne</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Barklow, William E. (2004). "Low-frequency sounds and amphibious communication in Hippopotamus amphibious". Journal of the Acoustical Society of America. 115 (5): 2555. Bibcode:2004ASAJ..115.2555B. doi:10.1121/1.4783854. Archived from the original on 8 February 2013. <a href="https://web.archive.org/web/20130208150037/http://asadl.org/jasa/resource/1/jasman/v115/i5/p2555_s1?bypassSSO=1" target="_blank">https://web.archive.org/web/20130208150037/http://asadl.org/jasa/resource/1/jasman/v115/i5/p2555_s1?bypassSSO=1</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">von Muggenthaler, E.K.; Stoughton, J.W.; Daniel, J.C., Jr. (1993). "Infrasound from the rhinocerotidae". In Ryder, O.A. (ed.). Rhinoceros biology and conservation: Proceedings of an international conference, San Diego, U.S.A. Zoological Society of San Diego. pp. 136–140. <a href="http://www.rhinoresourcecenter.com/index.php?act=refs&CODE=ref_detail&id=1165238239" target="_blank">http://www.rhinoresourcecenter.com/index.php?act=refs&CODE=ref_detail&id=1165238239</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">von Muggenthaler, Elizabeth (2003). "Songlike vocalizations from the Sumatran Rhinoceros (Dicerorhinus sumatrensis)". Acoustics Research Letters Online. 4 (3): 83. doi:10.1121/1.1588271. <a href="https://doi.org/10.1121%2F1.1588271" target="_blank">https://doi.org/10.1121%2F1.1588271</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">Marrin, West (3 November 2004). Infrasonic signals in the environment (PDF). Acoustics 2004: Transportation Noise & Vibration — The New Millennium. Gold Coast, Australia: Australian Acoustical Society. Archived from the original (PDF) on 26 March 2012. <a href="https://web.archive.org/web/20120326095047/http://www.watersciences.org/documents/Infrasound-Marrin.pdf" target="_blank">https://web.archive.org/web/20120326095047/http://www.watersciences.org/documents/Infrasound-Marrin.pdf</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">von Muggenthaler, E.; Baes, C.; Hill, D.; Fulk, R.; Lee, A. (1999). Infrasound and low frequency vocalizations from the giraffe; Helmholtz resonance in biology. Riverbanks Consortium on biology and behavior. Archived from the original on 15 February 2012. <a href="https://web.archive.org/web/20120215233027/http://www.animalvoice.com/giraffe.htm" target="_blank">https://web.archive.org/web/20120215233027/http://www.animalvoice.com/giraffe.htm</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">E. Von Muggenthaler: Infrasound from the okapi, invited presentation, student competition award, proceedings from the 1992 American Association for the Advancement of Science (A.A.A.S) 158th conference, 1992 <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">Freeman, Angela R.; Hare, James F. (1 April 2015). "Infrasound in mating displays: a peacock's tale". Animal Behaviour. 102: 241–250. doi:10.1016/j.anbehav.2015.01.029. ISSN 0003-3472. S2CID 53164879. <a href="http://www.sciencedirect.com/science/article/pii/S0003347215000391" target="_blank">http://www.sciencedirect.com/science/article/pii/S0003347215000391</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">von Muggenthaler, Elizabeth (2003). "Songlike vocalizations from the Sumatran Rhinoceros (Dicerorhinus sumatrensis)". Acoustics Research Letters Online. 4 (3): 83. doi:10.1121/1.1588271. <a href="https://doi.org/10.1121%2F1.1588271" target="_blank">https://doi.org/10.1121%2F1.1588271</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
<li id="fn:25">Work by Muggenthaler et al, also referred to in: The Secret Of A Tiger's Roar, ScienceDaily, 1 December 2000, American Institute of Physics, Inside Science News Service (1 December 2000), Retrieved 25 December 2011 <a href="https://www.sciencedaily.com/releases/2000/12/001201152406.htm" target="_blank">https://www.sciencedaily.com/releases/2000/12/001201152406.htm</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></li>
<li id="fn:26">Von Muggenthaler, E., Perera, D. (2002), The cat's purr: a healing mechanism?, In review, presented 142nd Acoustical Society of America International Conference, 2001. <a href="#fnref:26" class="footnote-back-ref">↩</a></li>
<li id="fn:27">Work by Muggenthaler et al, referred to in: David Harrison: Revealed: how purrs are secret to cats' nine lives, The Telegraph, 18 March 2001, Retrieved 25 December 2011 <a href="https://www.telegraph.co.uk/news/worldnews/northamerica/usa/1326953/Revealed-how-purrs-are-secret-to-cats-nine-lives.html" target="_blank">https://www.telegraph.co.uk/news/worldnews/northamerica/usa/1326953/Revealed-how-purrs-are-secret-to-cats-nine-lives.html</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></li>
<li id="fn:28">von Muggenthaler, (2006) The Felid Purr: A Biomechanical Healing Mechanism, Proceedings from the 12th International Low Frequency Noise and Vibration Conference, pp. 189–208 <a href="#fnref:28" class="footnote-back-ref">↩</a></li>
<li id="fn:29">"Science Question of the Week - 07 April 2000". 2 November 2004. Archived from the original on 2 November 2004. Retrieved 12 March 2022. <a href="https://web.archive.org/web/20041102004955/http://pao.gsfc.nasa.gov/gsfc/educ/science/2000/04-07-00.htm" target="_blank">https://web.archive.org/web/20041102004955/http://pao.gsfc.nasa.gov/gsfc/educ/science/2000/04-07-00.htm</a> <a href="#fnref:29" class="footnote-back-ref">↩</a></li>
<li id="fn:30">Langbauer, W.R.; Payne, K.B.; Charif, R.A.; Rapaport, L.; Osborn, F. (1991). "African elephants respond to distant playbacks of low-frequency conspecific calls" (PDF). The Journal of Experimental Biology. 157 (1): 35–46. doi:10.1242/jeb.157.1.35. Retrieved 27 May 2009. <a href="http://jeb.biologists.org/cgi/reprint/157/1/35.pdf" target="_blank">http://jeb.biologists.org/cgi/reprint/157/1/35.pdf</a> <a href="#fnref:30" class="footnote-back-ref">↩</a></li>
<li id="fn:31">W. John Richardson; Charles R. Greene, Jr.; Charles I. Malme; Denis H. Thomson (1995). Marine Mammals and Noise. Academic Press. ISBN 978-0-12-588440-2. <a href="978-0-12-588440-2" target="_blank">978-0-12-588440-2</a> <a href="#fnref:31" class="footnote-back-ref">↩</a></li>
<li id="fn:32">Larom, D.; Garstang, M.; Payne, K.; Raspet, R.; Lindeque, M. (1997). "The influence of surface atmospheric conditions on the range and area reached by animal vocalizations" (PDF). The Journal of Experimental Biology. 200 (3): 421–431. doi:10.1242/jeb.200.3.421. PMID 9057305. Retrieved 27 May 2009. <a href="http://jeb.biologists.org/cgi/reprint/200/3/421.pdf" target="_blank">http://jeb.biologists.org/cgi/reprint/200/3/421.pdf</a> <a href="#fnref:32" class="footnote-back-ref">↩</a></li>
<li id="fn:33">Garstang, Michael (1 January 2010), Brudzynski, Stefan M. (ed.), "Chapter 3.2 - Elephant infrasounds: long-range communication", Handbook of Behavioral Neuroscience, Handbook of Mammalian Vocalization, vol. 19, Elsevier, pp. 57–67, doi:10.1016/B978-0-12-374593-4.00007-3, retrieved 27 January 2020 <a href="http://www.sciencedirect.com/science/article/pii/S156973391070014X" target="_blank">http://www.sciencedirect.com/science/article/pii/S156973391070014X</a> <a href="#fnref:33" class="footnote-back-ref">↩</a></li>
<li id="fn:34">Hsu, Christine (24 August 2012). "Man With World's Deepest Voice Hits Notes That Only Elephants Can Hear". Medical Daily. Retrieved 2 August 2016. American singer Tim Storms who also has the world's widest vocal range can reach notes as low as G-7 (0.189Hz) [...] so low that even Storms himself cannot hear it. <a href="http://www.medicaldaily.com/man-worlds-deepest-voice-hits-notes-only-elephants-can-hear-242157" target="_blank">http://www.medicaldaily.com/man-worlds-deepest-voice-hits-notes-only-elephants-can-hear-242157</a> <a href="#fnref:34" class="footnote-back-ref">↩</a></li>
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<li id="fn:89">"IMS Infrasound Network". can-ndc.nrcan.gc.ca. Natural Resources Canada. 30 March 2020. Retrieved 25 April 2017. <a href="http://can-ndc.nrcan.gc.ca/is_infrasound-en.php" target="_blank">http://can-ndc.nrcan.gc.ca/is_infrasound-en.php</a> <a href="#fnref:89" class="footnote-back-ref">↩</a></li>
<li id="fn:90">"Infrasound monitoring". Ctbto.org. CTBTO Preparatory Commission. Archived from the original on 3 February 2017. Retrieved 25 April 2017. <a href="https://web.archive.org/web/20170203034207/https://www.ctbto.org/verification-regime/monitoring-technologies-how-they-work/infrasound-monitoring/" target="_blank">https://web.archive.org/web/20170203034207/https://www.ctbto.org/verification-regime/monitoring-technologies-how-they-work/infrasound-monitoring/</a> <a href="#fnref:90" class="footnote-back-ref">↩</a></li>
<li id="fn:91">Harper, Paul (20 February 2013). "Meteor explosion largest infrasound recorded". The New Zealand Herald. APN Holdings NZ. Retrieved 31 March 2013. <a href="http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=10866592" target="_blank">http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=10866592</a> <a href="#fnref:91" class="footnote-back-ref">↩</a></li>
<li id="fn:92">Lowe, Justin (3 October 2017). "'The Sound': Film Review". The Hollywood Reporter. Retrieved 29 March 2021. Continuing her search, Kelly soon encounters ghostly apparitions and overwhelming low-frequency sound waves below the threshold of human hearing that emanate from a source she's unable to identify with her audio gear. <a href="https://www.hollywoodreporter.com/review/sound-1044371" target="_blank">https://www.hollywoodreporter.com/review/sound-1044371</a> <a href="#fnref:92" class="footnote-back-ref">↩</a></li>
<li id="fn:93">Kermode, Jennie (27 September 2017). "The Sound (2017) Movie Review from Eye for Film". Eye For Film. Retrieved 29 March 2021. <a href="https://www.eyeforfilm.co.uk/review/the-sound-2017-film-review-by-jennie-kermode" target="_blank">https://www.eyeforfilm.co.uk/review/the-sound-2017-film-review-by-jennie-kermode</a> <a href="#fnref:93" class="footnote-back-ref">↩</a></li>
</ol>

Infrasound open-in-new

Infrasound