Nature has been playing symphonies since long before man discovered ‘music’. They resonate through landscapes and urban cities all around the world to remind us that we aren’t alone. I have been doing extensive research into sound, it's uses in the animal kingdom, and it's effects in extreme ranges on humans. If you are not so much into the science of things, I apologize in advance for the lengthy amount of scientific references and findings in my article.
The variety of sounds, from the rustle of the leaves to the call of the Langurs, produced in different ways, convey their own unique meanings. This has been studied for hundreds of years in order to understand how similar animal communication is to that of us humans. Sound is converted to an electrical signal when it enters the ear. This signal travels up the auditory nerve to the part of the brain that processes sound, the auditory cortex. From there, the signals travel throughout the brain, creating a variety of responses. The effects of sound in the brain include evoking emotions, triggering the release of stress chemicals and impacting the development of new neural pathways in the brain.
Click Here for Leopard Monkey Alert Sounds! - BBC Video
Amazing footage of how different types of monkey have distinct calls to warn their troop members of an invading big cat predator. Amusing footage of how David Attenborough reveals their hidden behaviors with a special stuffed toy. From BBC's Life of Mammals.
Music impacts the part of the brain that controls the link between sound, memories and emotion, the
medial prefrontal cortex, says the National Institutes of Health. Listening to music can soothe the emotions. A study published in the December 2009 journal Pediatrics found that premature babies demonstrated an increased rate of weight gain when they were exposed to music by Mozart. The music soothed the babies, reducing their resting energy expenditure. Researchers speculate that the weight gain seen in premature babies who are exposed to Mozart results from this lower energy expenditure. In May 2006, the Journal of Advanced Nursing reported that people who listen to music experience less pain and lower levels of depression and disability related to pain than those who don't listen to music. This indicates that music can effect the brain by lifting the mood and alleviating the perception of pain.
Loud noises evoke an instinctive fight or flight reaction in the brain, according to The Franklin Institute. The fight or flight reaction is a release of chemicals that stimulates immediate action. This reaction has been crucial to ensure human survival in the wilderness, and remains important in the modern world. If you hear a loud honk from a car horn, your brain and body respond quickly to move you out of harm’s way. Once danger has passed, the brain releases tranquilizing chemicals that counteract the stimulating chemicals.
Among the more consistent findings in humans were changes in blood pressure, respiratory rate, and balance. These effects occurred after exposures to infrasound at levels generally above 110 dB. Physical damage to the ear or some loss of hearing has been found in humans and/or animals at levels above 140 dB. Similar results were found in studies relating to excessive ultrasound dB.
Many creatures tend to fall prey to those at higher trophic levels. In order to survive, many organisms
have their own unique way of communicating, in order to protect themselves from predators. What are these ways of communicating? How do organisms convey ideas using these different methods and sounds? Much of this communication involves infrasound. An ongoing debate about the elusive Bigfoot creature revolves around the issue of infrasound. After reading this article though, if you are a researcher who leans toward this infrasound theory, you may be asking yourself, "is it infrasound, or could it be ultrasound, as with the primate distant cousins mentioned in the article below?"
First I would like to talk a little bit about sound, and animal communications. Sound is a vibration that is transmitted in a medium (e.g. air), that can be heard by a human ear. If you were an ant or a bird, the meaning of sound would be different. Sound specifically refers to what the human ear can hear. All vibrations, including sound, have a frequency. Frequency is a measure of how often something “vibrates “ per second. The unit of frequency is Hertz, the official symbol being Hz, and can be thought of as “vibrations per second “ (in layman's terms). The human ear can hear between frequencies of about 20 Hz to 20,000 Hz. So “sound is vibrations in this frequency range.
The extent of biodiversity in our world means that organisms are able to use a large number of different techniques to communicate with one another. Although my topic focuses on auditory communication, organisms effectively use all their other senses to interact with other animals as well:
- Visual
- Olfactory
- Electrocommunication – fish create an electric field, that if disturbed, convey information
- Touch
- Seismic – vibrations created by the organism itself are used as signals
- Thermal
- Autocommunication – the signal is sent by an organism and received back by the same organism after the environment has modified it.
Auditory communication is further classified based on the methods of sound production and the type of sounds produced. When looking at classification based on the method of sound production, we must understand that any movement that causes molecules in the air to vibrate about or causes pressure waves will produce sound. In order to carry out these actions, many organisms have adapted body features. These include:
- A Vibrating Membrane that is attached to a muscle. This membrane is like a drum. It is often found in insects and is used to producing mating calls.
- A Stridulatory Organ that consists of a ‘scraper’ and a rough surface, present on two different parts of the body. When these are rubbed together they produce a ‘chirp,’ which is higher pitched based on the speed at which the two surfaces are rubbed together. This, again, is found in insects.
- A vibrating membrane present in the Larynx of amphibians and mammals, and the Syrinx of birds. The vibration is caused by air pushed up along it by the lungs. The pitch can be changed based on how fast the vibrations are. These vibrations are controlled by muscles, which contract and relax to control the membrane.
- A surface, which is struck to produce sounds. This technique is used by a large number of creatures. For example, beavers use their tails to hit the surface of water to create a warning or alarm signal. This is an efficient method of communication, as sound travels very quickly in water.
Why do organisms need to use so many different methods of communication? What would happen if all of organisms of just one species used only a single method to communicate?
One theory could be that animals may not be able to convey all their ideas using just one method of communication. They may require more complex techniques to share more complex messages. Further, I believe that if all organisms used the same technique to exchange information, then the ‘soundscape’ of the organisms, may get ‘saturated’ with sound. The soundscape may get so full of the same sound that messages may be interrupted and organisms may not be able to communicate efficiently. So, by having diversity in the methods of communication, the environment is less full of the same sound, and organisms are able to interact properly.
Another question to consider is what originally influenced the development of these methods of communication. Was it the physiology of the animal, or was it the features of the environment itself? For example, the beaver uses its tail to strike the water and create sound. Did this technique develop because the beaver’s tail was able to create the sound, or because the water was already present in the environment and the beaver could use it to communicate? Although this is a question that may not have a definite answer just yet, it is an interesting one to think about.
When auditory communication is classified based on the type of sound produced, it is usually categorized into the following:
- Infrasound – sounds that are below the lower bound of the frequency range that humans can hear.
- Audible sound – sounds that humans are able to hear.
- Ultrasound – sounds that are above the upper bound of the frequency range that is audible to human.
The most common use of ultrasound is in echolocation, which is carried out by many organisms,
including bats, whales, dolphins, and a few species of birds. This process involves the emission of ultrasound from an organism into the environment. The animal waits and ‘listens’ for the echoes after the sound waves reflect off surfaces. The process of echolocation is used to locate and identify objects. Most organisms use it as a form of navigation system, a process known as biosonar. This is used to locate and capture their prey. Many fish, such as herring, are only able to hear up to 4 kHz. However, there are many other fish of the subfamily Alosinae, which are able to hear up to 180 kHz. Porpoises also have one of the highest known frequency ranges, with an upper limit of 160 kHz.
Interestingly, it has been found that a few individuals, who are blind, are also able to use echolocation to help ‘visualize’ their surroundings.
Sound is energy that travels in waves. Our ears are capable of receiving the waves and transmitting them through the eardrum and ear bones to the cochlea, which converts the vibrations into electrical impulses that the brain can interpret. People with hearing loss may benefit from a cochlear implant, a device that “assists” the ear electronically. Sound is measured in decibels—40 decibels is normal talking volume, while 120 is the sound of a plane taking off. Scientists have found ways to get rid of noise by using sound waves to mirror the noise waves and cancel them out. You would not want to cancel the sounds of a good pianist. When keys strike and vibrate strings inside a piano, the result is beautiful music. Sound is far more than music to many animals. For elephants, infrasound is a way to communicate across long distances. Bats use high-frequency sounds in echolocation. Their clicks bounce off objects, helping them navigate in darkness and find prey in the form of flying insects. Scientists suspect that bats may effectively be able to slow down time in order to process the echoes returning from their clicks. Now that is a superpower.
Acoustic communication is the sending and receiving of messages using sound. Bird song, the roars of lions and the chirping of cicadas are all examples of this. Sometimes the messages are outside the range of human hearing, such as the ultrasonic squeaks of baby rats or the infrasound rumbles of elephants. Most acoustic communication is not language, in the sense that humans use it, although language is one aspect of this adaptation. Howler monkeys for example, are usually only active during the day. But before night falls, they climb trees to escape ground-based predators and sleep. However, if nocturnal arboreal threats wake them, the howler monkeys produce a very eerie call.
Click Here for One Minute of Howler Monkeys Video
Awesome sounds of howler monkeys taken in the Osa Peninsula of Costa Rica. It was too dark to see anything, but the sounds were hauntingly beautiful.
The Rhino's Silent Call
In the biological world, the ability to produce or perceive infrasound has been considered a rarity. Source: Discover Magazine
One day the San Diego Zoo, a female Sumatran rhinoceros named Barakas was singing a mournful,
whalelike song punctuated with grunts and moans. Through a window in her indoor enclosure she occasionally rubbed noses with Ipuh, a newly arrived male from Indonesia. Ipuh was munching abstractedly on ficus leaves and looking bored. But animal behaviorist Elizabeth Von Muggenthaler, crouching among buckets and hay bales in an adjoining storeroom, was not deceived. She watched the fluttering needle on her tape recorder, which was hooked up to a microphone in Ipuh’s stall, and she suspected the rhino was rumbling--but in a basso so profundo as to be below the hearing range of human eavesdroppers. Elizabeth Von Muggenthaler is president of Fauna Communication Research Institute, where amazing breakthroughs are being made that may forever change the way we listen to the animals.
Elizabeth Von Muggenthaler is a bioacoustician, a scientist that studies natural sound, in the air, underwater and seismically. She is president of Fauna Communications Research Institute, www.animalvoice.com and former chair of the Acoustical Society of America, American Institute of Physics North Carolina Chapter, which covers the Southeast. She is the first to investigate the infrasonic (below) and ultrasonic (above) human hearing range communication of dozens of animals. Von Muggenthaler was invited to the American Institute of Physics international acoustics conference for her design of equipment capable of real-time computer analysis and storage of ultrasonic and infrasonic signals.
Elizabeth has an interdisciplinary and creative approach to research. Paleontologists, marine biologists, and zoologists helped determine that the Sumatran rhino (the most critically endangered rhino) sing like whales because they may be genetically related. After recording over 200 species that have infrasonic and ultrasonic vocalizations, many sound and look like whale under analysis. There may be such a thing as an “ancestral song” of the planet. Interviews with 50 experts in human medicine, veterinary medicine, biology, genetics, paleontology, and acoustics and over 3000 veterinary, human medical, and acoustic scientific journals and books, allowed Elizabeth to solve the mystery of why cats purr. Felines that purr are healing themselves; indeed all cats that purr do so at pitches that correlate exactly to bio-mechanical stimulation vibration frequencies used in the human medical community for osteoporosis, fracture healing, muscle tendon and ligament repair, wound healing, pain relief, Chronic Pulmonary disease, and many other ailments.
Part of their song is very low frequency. They also have a whistle blow that will travel for miles through the forest. In my mind it seems to be some sort of meditation. When I watch them, they will stand there singing in their little mud wallow and being really peaceful.
I can't help but feel that while they're doing this they are somehow singing with the forest, connecting with the Earth. I get emotional about them. They are so beautiful. And as I said, there are only around 200 left in the world, and not much is being done about that.
An example of infrasound can be seen when you're in your car stopped at a traffic light, and you look over and see that the car next to you is shaking because the music is so loud. It's the infrasound that's making the car shake. It's below our normal range of hearing. Another example of how infrasound affects people is in car sickness. The reason some one gets car sick is not always that the car is moving. Car sickness is sometimes caused by the car's vibration — around 4 Herz. In fact, cars are interesting; you get all kinds of low-frequency vibrations from them — 4 Herz, 7 Hertz — that kind of thing. Frequencies of 7 Hertz can cause osteoporosis.
Low frequencies like 18 Hertz can cause dizziness, blackouts, and feelings of terror. There is a theory that some ghost hauntings are actually caused by low-frequency vibrations of around 18 Hertz in a building. That's a fairly common frequency in structures. But what about high frequencies? We are going to address that in this article as well. We know that certain frequencies of both, infrasound and ultrasound are used for healing. We also know from the medical field that we can aim ultrasound waves....they then hit their target and travel back to you; Therefore the distance to the boundary is half the total distance. If a subject is using ultrasound, it may have numerous uses, but unlike infrasound, ultrasound can be used to read your surroundings, and even your subject. We all know that bats and dolphins use ultrasound to navigate. Since ultrasound bounces off objects, they are easily able to determine location of objects in their surroundings, and calculate distance to these objects. So what determines how far ultrasound waves can travel? The frequency of the transducer....the higher the frequency, the less it can penetrate. The lower the frequency, the deeper it can penetrate. Attenuation is directly related to frequency, which I find very interesting in the Cryptozoology field of study as it relates to sound frequencies.We can only assume that the Bigfoot creature is much like humans, but probably more attuned to its senses. Humans rely heavily on our sense of sound. We can hear a relatively normal range of sound waves, from about 16 - 200000 Hz. Ultrasound waves are similar to the ones we can hear. However, the major difference is that they are higher pitched. They vary in frequency from 20 000 Hz to 15 MHz (15 000 000 Hz). As a result of the higher frequency (cycles per second) of the sound waves, humans cannot hear ultrasound waves, nor see them.
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| Source: David Gregg, Michael Teachings |
Tigers roar at around 18 Hz. It doesn't matter that you can't see the tiger. Just hearing the sound is
pretty terrifying. Although we haven't been able to 100% prove that the infrasound made by a Tiger paralyzes or stuns it's victims, Elizabeth says they have recorded the exact frequency of the tiger's range and found that its highest frequency is right around 18 Hertz. So theoretically the tiger's roar could cause temporary paralysis, weakening of the muscles, feelings of terror, coldness, blackouts, and headaches — that kind of thing. So many organisms do use infrasound for purposes other than communication and protection. An interesting use of infrasound is when a tiger roars. Elizabeth's studies showed that the tiger’s infrasound roar has the ability to temporarily paralyze an animal or human. Although it remains a mystery as to how this happens, it is clear that the roar is felt by the organism, but not heard. She carried out the research by playing infrasound and checking whether the tiger would react to it. The reaction by the tiger showed that they were able to hear and therefore produce sounds at very low frequencies. The use of this infrasound roar aids the tiger when it is stalking its prey, as it helps to stall the prey, giving the tiger an opportunity to kill it.
The wave of infrasound actually goes between particles and molecules of an object rather than bouncing off them, because it's a long wave, therefore it can travel through objects. It goes through buildings, through mountains, through whatever, and travels great distances.
An interesting thing happens when the space shuttle takes off, for example. It creates infrasound that travels the earth about seven times before it dissipates. In fact, if you go about 30 miles south of Coco Beach there's a little place called Satellite Beach where there is a hotel built mostly of glass. If you are in one of those rooms when the space shuttle is taking off, you will see the panes of glass bow inward about two-and-a-half inches!
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| Discovery lifts off at the start of STS-120. |
The most acute human ear can perceive frequencies as low as 20 hertz. Frequencies lower than that are called infrasound. Unbeknownst to us, the physical world throbs with infrasonic noise, a symphony of deep booms produced by thunder, air turbulence, jet engines, volcanoes, earthquakes, crashing ocean waves, and even shuddering buildings. (Of course, these phenomena produce audible frequencies as well.)
In the biological world, however, the ability to produce or perceive infrasound has been considered a rarity. Until Elizabeth Von Muggenthaler, an undergraduate at Old Dominion University in Norfolk, taped her first rhino in 1990, only blue whales, elephants, and alligators were known to produce infrasonic calls. Indeed, Von Muggenthaler was at the Virginia Zoological Park trying to tape an African elephant named Monica when she lucked onto her infravocal rhino. Analyzing the recording, she found that the frequency pattern was unusual for an elephant. The infrasound turned out to be coming from Monica’s neighbor, a male white rhino named Rufus.
With the help of her adviser, reproductive biologist Joseph C. Daniel Jr., Von Muggenthaler has since recorded more than two dozen rhinos of four different species (blacks, whites, Sumatrans, and Indians) at zoos around the nation. She picked up sounds in the 5 to 75 hertz range from all of them. (A human bass, in contrast, rarely dips below 100 hertz.) Some of the sounds appeared to be dialogues between the animals; at the very least, judging from their nonrandom patterns, the sounds were more than mere breathing noises or stomach rumblings.
During one of the rhino recording sessions, Von Muggenthaler caught an excited hippopotamus cutting loose in infrasound, too. More recently she has added okapis, zebra-size relatives of the giraffe, to the list of infrasound vocalists. Von Muggenthaler suspects that other animals may also have the ability, and she is trying to pin down the skull characteristics that are required to send and receive infrasound.
She also hopes to find out whether rhinos actually communicate in infrasound, as opposed to merely sounding off. For instance, female rhinos may use infrasound to indicate when they are receptive to male advances; unlike some other animals, rhinos don’t send obvious (to us) signals when they’re in heat. I recorded one female white rhino, Von Muggenthaler recalls, and when I looked at the graph of spectral activity I thought, ‘Wow, what she must be going through!’ All that noise and yet you couldn’t hear anything. That’s what’s fascinating.
The advantage of infrasound for communicating is that it travels long distances. Low-frequency
sounds have long wavelengths, and long waves are less prone than short ones to being scattered by trees and hills. Astonishingly, elephants appear to communicate by infrasound over distances of several miles--at least, that’s one hypothesis to explain why widely separated herds seem to synchronize their maneuvers. Wildlife ecologist Kes Hillman Smith of Garamba National Park in Zaire has observed similar coordinated movements among female white rhinos, and she now thinks infrasound communication may account for it. Von Muggenthaler hopes to take her recording equipment to Africa to find out. We don't have as much research to reference on increased Ultrasound waves. Ultrasound is high frequency mechanical vibrations or pressure waves above a frequency the human ear can hear. Ultrasound uses a pulse-echo technique of imaging the body. Pulses transmitted into patient and give rise to echoes when they encounter interfaces/reflectors. These interfaces/reflectors are caused by variations in the "acoustic impedence" between different tissues.
Her long-term dream is to show that the animals she studies have something akin to human language. Von Muggenthaler’s interest in the issue is more than academic. It’s an important question because we humans equate language with intelligence, and we value intelligence, she says. I think people will value animals more and do more to save them if they consider them intelligent. She has done extensive studies into the infrasound from a cat's purr, and how it has healing properties...so according to Elizabeth, not all infrasound effects are frightening.
We as humans can't even begin to understand what a dog smells, for example. Their noses are many times more efficient than ours. A scallop has a hundred eyes, so it really does see us as we're ripping it from its home. Birds see in the ultraviolet spectrum. We can't see that. We're so limited. It would be nice to spend a day inhabiting the body of several different creatures, just to experience what they're able to see, hear and smell, that we can't.
Interesting stories behind activity in the Mysterious Forest of Hoia Baciu (see video below). Although apparently not Bigfoot related, you may find it of interest since most of us researchers spend much of our lives in the forest. The symptoms exhibited in this forest sound much like infrasound effects. A tiger’s roar, for example, has been measured and emits infrasound around 19 HZ, inducing fear in its prey. Is it possible that the elusive Bigfoot creature uses infrasound as a fear tactic to keep away possible predators, and avoid being seen?
Infrasound can also be man-made. Controlled experiments by British scientists demonstrated that infrasound produces a range of bizarre effects in people, including anxiety, dizziness, nausea, headache, extreme sorrow/oppression, chills, apparitions and hallucinations, supporting the link between infrasound and strange sensations attributed to allegedly haunted sites. So if infrasound is produced by natural disasters, why didn’t humans detect infrasound sensations during the tsunami? It’s quite possible that some did, especially those with certain types of brain signatures, but didn’t associate it with impending danger. It’s worth noting that sleep paralysis, accompanied by hallucinations, is a common phenomena in geodynamic areas along the Pacific Ring of Fire. Many myths exist due to sleep paralysis. Infrasound is sound below 20 Hz in frequency, lower than humans can perceive. It is a frequency that is difficult for humans to hear, but can still cause physiological effects, and can make windows, doors, and other objects vibrate. These lower frequencies have the advantage of carrying farther.
Click Here for Alien Star's Video Story of the Creepy Forest of Hoia Baciu
Transylvania's Bermuda Triangle: The Mysterious Forest of Hoia Baciu
Infrasound can result naturally from severe weather, surf, lee waves, avalanches, earthquakes, volcanoes, bolides, waterfalls, calving of icebergs, auroras, lightening and upper-atmospheric lighting, and has also been used in government experiments. The government is exploring the use of audio to influence humans physically and psychologically as a means of non-lethal warfare methods. The device known as the ‘Wirbelwind Kanonew’ , is perhaps the only known fully developed infrasonic weapon created in order to physically effect it’s target, with the intention of countering enemy aircraft and infantry by creating a vortex of sound (Crab, 2008). The effect of emotional and psychological change as a result of infrasonic exposure can later be found during the second Indochina war. In 1973, The United States deployed the Urban Funk Campaign, a psychoacoustic attack during the war with the intention of altering mental states of their enemies (Goodman, 2010). The device utilized both infrasonic and ultrasonic frequencies, which emitted high
All objects have a property known as their resonant frequency, this involves the “re- enforcement of vibrations of a receiving system due to a similarity to the frequencies of the source” (Pellegrino & Productions, 1996). It is this property that is held within all matter, that we can apply sound as a means of resonance within the human body. It is resonance within the human body that is thought to create the psychological effects of that mentioned in this article.
NASA technical report mentions a resonant frequency for the eye as 18 Hz (NASA Technical Report 19770013810). If this were the case then the eyeball would be vibrating which would cause a serious ‘smearing of vision. Another NASA report (NASA Technical Report 19870046176) mentions hyperventilation as a symptom of whole body vibration. Hyperventilation is characterized by quick
From about 1000 Hz, the dynamic range of the auditory system decreases with decreasing frequency.
This compression is observable in the equal-loudness-level contours, 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 thresholds 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 supernatural events are taking place. Engineer Vic Tandy provided such an explanation in his investigations in the 1980s. Tandy, while working in his laboratory, started to feel uneasy and as if a supernatural presence was with him. Later, he could attribute these feelings to a broken metal fan that was causing noises of a frequency that triggered them. The noise could not be perceived by the human ear, but Tandy's body reacted to the 19Hz sounds.
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 vestibular system, and this has shown in animal models an effect similar to sea sickness.
In 2006 research about the impact of sound emissions from wind turbines on 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. Later studies, however, have linked inaudible infrasound to effects such as fullness, pressure or tinnitus, and acknowledged the possibility that it could disturb sleep. 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.
In a study at Ibaraki University in Japan, researchers said EEG tests showed that the infrasound produced by wind turbines was “considered to be an annoyance to the technicians who work close to a modern large-scale wind turbine.” Source: Wikipedia
Elephants, whales, hippopotamuses, the okapi and rhinoceroses, on the other hand, appear to hear and produce sounds well below our range. And it’s not just the large animals that hear infrasound. Pigeons, guinea fowl, cod, cuttlefish, octopus, squid and the capercaille, a Eurasian grouse, all hear infrasound.
Sound, as vertebrates hear it, consists of waves of relatively high and low air pressure. When these waves reach the eardrum, they push it in and pull it out, setting in motion a vibration transmitted through the middle ear bones to the cochlea, where specialized cells produce nerve impulses. Our brains interpret these impulses as sound. The waves we hear best range from about a yard peak to peak down to tiny fractions of an inch. Infrasound waves range from tens of yards to miles in length.
These long waves travel through brush and trees relatively unimpeded because the ability of an object to reflect a sound wave depends on the ratio of the wavelength to the size of the object. Normal objects such as grass stems, leaves and trees have no effect on very long infrasound waves. On the other hand, they reflect and scatter higher frequencies easily. Even the molecules in air absorb a good deal of high frequency sound, while leaving infrasound unaffected. This makes infrasound ideal for long-distance communication.
Sound travels from its source in all directions losing about 6 decibels for every doubling of distance. With no interruption, the sound will spread spherically. (Certain shapes can modify this spreading effect. A horn couples the sound source—a trumpet player’s lips or the tiny speaker in a horn-loaded audio speaker system—with the air. The larger opening then becomes the sound source, and sound spreads from there.) In a field study of infrasound in Africa, Langbauer found that environments such as bare ground, tall grass and woodland had little or no effect on sounds below 60 Hz projected from a custom-made Pachyderm 2 loudspeaker and recorded at four distances from about 10 to 125 yards from the speaker.
Even very large speakers can’t duplicate the power of elephant infrasonic calls, which have been measured at near-thunder levels about five yards from the elephant. The speakers used in field experiments, although huge by home stereo standards, can only produce volumes half that. Extrapolating from playback experiments, Langbauer estimates elephants can hear infrasonic calls at least 2.5 miles away. Source: eugraph
As humans, we can hear the rumble of distant thunder but can’t hear the crack of lightning unless it strikes close by. We hear the bass but not the treble because powerful low-frequency sound travels long distances well. But since the bass humans hear cuts off at about 20 Hz – below that, you can only feel the sound at close range as it vibrates your chest. If we were capable of hearing bass frequencies lower than 20Hz, we would be able to hear our own muscles moving.
In an edition of Science, an international team of voice researchers and cognitive biologists led by Christian Herbst, Angela Stoeger and Tecumseh Fitch, provides new insights into the production of Elephant communication. The so-called "infrasounds," i.e. sounds with pitches below the range of human hearing, are found to be produced with the same physical mechanism as human speech or singing.
Elephants can communicate using very low frequency sounds, with pitches below the range of human hearing. These low-frequency sounds, termed "infrasounds," can travel several kilometers, and provide elephants with a "private" communication channel that plays an important role in elephants' complex social life. Their frequencies are as low as the lowest notes of a pipe organ.
Although the sounds themselves have been studied for many years, it has remained unclear exactly how elephant infrasounds are made. One possibility, favored by some scientists, is that the elephants tense and relax the muscles in their larynx (or "voice box") for each pulse of sound. This mechanism, similar to cats purring, can produce sounds as low in pitch as desired, but the sounds produced are generally not very powerful.
The other possibility is that elephant infrasounds are produced like human speech or singing, but
because the elephant larynx is so large, they are extremely low in frequency. Human humming is produced by vibrations of the vocal folds (also called "vocal cords"), which are set into vibration by a stream of air from the lungs, and don't require periodic muscle activity. By this hypothesis, elephant infrasounds result simply from very long vocal folds slapping together at a low rate, and don't require any periodic tensing of the laryngeal muscles.
To find out, researchers at the University of Vienna, led by voice scientist Christian Herbst and elephant communication expert Angela Stoeger, removed the larynx from an elephant (which died of natural causes), and brought it into the larynx laboratory of the Department of Cognitive Biology (headed by Tecumseh Fitch). By blowing a controlled stream of warm, humid air through the larynx (substituting for the elephants lungs), and manually placing the vocal folds into the "vocal" position, the scientists coaxed the vocal folds into periodic, low-frequency vibrations that match infrasounds in all details.
Since there can be no periodic tensing and relaxing of vocal fold muscles without a connection to the elephant's brain, low-frequency vibrations in the excised larynx clearly demonstrate that the "purring" mechanism is unnecessary to explain infrasounds. Thus, elephants "sing" using the same physical principles as we do, but their immense larynx produces very low notes.
As an additional insight, the scientists were able to get a very clear look at some fascinating types of vibration called "nonlinear phenomena." When a baby cries, or a heavy metal singer screams, the vocal folds vibrate in an irregular manner, which is very grating to our ears. Young elephants also scream and roar, and the mechanism they use is again identical to that seen in humans.
This research shows that the physical principles underlying the human voice extend over a remarkable range, from bat's incredibly high vocalizations (too high for us to hear), all the way down to elephants' subaudible infrasounds. How whales, the largest animals, make their even lower frequency sounds remains to be determined. Source: University of Vienna
Although the sounds themselves have been studied for many years, it has remained unclear exactly how elephant infrasounds are made. One possibility, favored by some scientists, is that the elephants tense and relax the muscles in their larynx (or "voice box") for each pulse of sound. This mechanism, similar to cats purring, can produce sounds as low in pitch as desired, but the sounds produced are generally not very powerful.
The other possibility is that elephant infrasounds are produced like human speech or singing, but
To find out, researchers at the University of Vienna, led by voice scientist Christian Herbst and elephant communication expert Angela Stoeger, removed the larynx from an elephant (which died of natural causes), and brought it into the larynx laboratory of the Department of Cognitive Biology (headed by Tecumseh Fitch). By blowing a controlled stream of warm, humid air through the larynx (substituting for the elephants lungs), and manually placing the vocal folds into the "vocal" position, the scientists coaxed the vocal folds into periodic, low-frequency vibrations that match infrasounds in all details.
Since there can be no periodic tensing and relaxing of vocal fold muscles without a connection to the elephant's brain, low-frequency vibrations in the excised larynx clearly demonstrate that the "purring" mechanism is unnecessary to explain infrasounds. Thus, elephants "sing" using the same physical principles as we do, but their immense larynx produces very low notes.
As an additional insight, the scientists were able to get a very clear look at some fascinating types of vibration called "nonlinear phenomena." When a baby cries, or a heavy metal singer screams, the vocal folds vibrate in an irregular manner, which is very grating to our ears. Young elephants also scream and roar, and the mechanism they use is again identical to that seen in humans.
This research shows that the physical principles underlying the human voice extend over a remarkable range, from bat's incredibly high vocalizations (too high for us to hear), all the way down to elephants' subaudible infrasounds. How whales, the largest animals, make their even lower frequency sounds remains to be determined. Source: University of Vienna
Meet the world's tiniest cryptographers. Philippine Tarsiers (Tarsius syrichta), primates native to
Southeast Asia that are often no bigger than a human hand, pass messages using an unbreakable code: ultrasonic sounds. A new study shows that these tree-dwellers emit squeaky calls well above the vocal range of any known monkey or ape, perhaps to dodge eavesdropping predators.
New Scientist told us about the only known primate that communicates using pure ultrasound. A Tarsier could be screaming its head off and you would never know it. Uniquely among primates, some of the diminutive mammal’s calls are made up of pure ultrasound. Marissa Ramsier of Humboldt State University in California and her colleagues were puzzled to sometimes hear no sound when Philippine Tarsiers (Tarsius syrichta) opened their mouths as if to call. Placing 35 wild animals in front of an ultrasound detector revealed that what they assumed to be yawns were high-pitched screams beyond the range of human hearing.
While some primates can emit and respond to calls with ultrasonic components, none are known to use only ultrasonic frequencies in a call. The dominant frequency of the Philippine Tarsier’s ultrasonic call was 70 kilohertz, amongst the highest recorded for any terrestrial mammal. They can hear up to 91 kHz, well beyond the 20 kHz limit of human hearing. Whales, dolphins, domestic cats and some bats and rodents are the only other mammals known to communicate in this way.
Having the equivalent of a private communication channel could help Tarsiers warn others of predators such as lizards, snakes and birds which can’t detect such frequencies, says Ramsier. Eavesdropping on insects could also help them locate their prey. Tarsiers are pint-size primates from Southeast Asia who produce some of the most extreme ultrasonic calls in the animal kingdom, well beyond the threshold of human hearing.
Although the Tarsier’s hidden talent may be unique, future studies could reveal that more primates use pure ultrasound calls. “Many primatologists have observed ‘silent’ mouth-opening behaviors in other primates,” says Ramsier. “It is certainly possible that some of these behaviors are accompanied by ultrasonic vocalizations.” Tarsiers' ultrasonic calls -- among the most extreme in the animal kingdom -- give them a "private channel" of communication, says an anthropologist.
Tarsiers from Borneo and the Philippines have conventionally been described as "ordinarily silent." This apparent lack of vocalizations led investigators to suspect that the animals were indeed engaged in these critical communications. We just couldn't hear them.
Nathaniel Dominy, an associate professor of anthropology at Dartmouth, describes the Tarsier's ultrasonic vocalizations as "extreme, and comparable to the highly specialized vocalizations of bats and dolphins, which are used primarily for echolocation."
Dominy and a cadre of colleagues have been studying the hearing and vocalizations of one Tarsier species in the Philippines, Tarsius syrichta. Results of their research appeared online in the Royal Society journal Biology Letters, on February 8, 2012.
Recent technical advances allowed the investigators to test the hearing of six wild Tarsiers on the island of Mindanao. They found "an audible range that extended substantially into the ultrasound," reaching a high of 91 kilohertz (kHz), "a value that surpasses the known range of all other primates and is matched by few animals."
The researchers observed that Tarsiers emitted their ultrasonic call when humans were near, suggesting they were voicing alarm. "Ultrasonic alarm calls can be advantageous to both the signaler and receiver as they are potentially difficult for predators to detect and localize," they write.
Dominy and his group conclude that there may be selective advantages to vocalizations in the pure ultrasound. They call them "private channels of communication with the potential to subvert detection by predators, prey, and competitors."
"Our findings not only verify that Tarsiers are sensitive to the ultrasound, but also that Tarsius syrichta can send and receive vocal signals in the pure ultrasound," Dominy says.
Like any good code, ultrasound works because it's rarely used. Few land mammals—bats and kittens are exceptions—coo or call at frequencies above the normal range of human hearing (about 20 kilohertz). That's largely because ultrasonic waves, unlike other sound waves, spread out quickly; that makes it harder for animals to pinpoint the locations of faraway calls, says study co-author Marissa Ramsier, an anthropologist at Humboldt State University in Arcata, California.
The first clue that Tarsiers use ultrasound came from observing an odd behavior. The big-eyed, nocturnal creatures occasionally open their mouths as if ready to shout, but no sound humans can hear comes out. On a whim, co-author Sharon Gursky-Doyen, a biological anthropologist at Texas A&M University in College Station, brought a microphone used for recording bat chirps to a Philippine jungle frequented by the primates. The animals, it turns out, are boisterous—just not to human ears. "Philippine Tarsiers have often been described as quiet," Ramsier says. But "they're screaming and talking away, and we just didn't know it." To see more about the study findings on their sound frequencies, click here.
The ultrasonic calls possessed the same tone-like structure heard in the audible calls of the other Tarsier species, suggesting they really are using these frequencies for the same sorts of communication. You can hear a recording of one of these ultrasonic calls at this link, as it's been slowed down to an eighth of its normal speed so that it's audible to human ears. Though I'll warn you now - it is not a pleasant sound.
Many people are aware of the effects of infrasound, but are you aware of the effects of ultrasound on humans? Ultrasound at high decibels produces the same physical, psychological and psychoaccoustic effects on the body and the brain. To use ultrasound "to find things", we first need to have a way of generating them. In the medical field for example, we need something to create vibrations that will travel in the tissues in a patient. Some of the ultrasound waves are attenuated. That is, the body absorbs the ultrasound energy, making the waves disappear. These waves don’t return to the probe and are therefore “wasted”. The more the body tissues that the ultrasound waves have to cross, the more attenuation the waves suffer. The sound waves travel at different speeds depending on the type of tissue encountered — fastest through bone tissue and slowest through air. The speed at which the sound waves are returned to the transducer, as well as how much of the sound wave returns, is translated by the transducer as different types of Tissue.
Many people think our mammal friends, the bat is blind, but in fact they can see almost as well as humans. However, at night, their ears are more important than their eyes - they use a special sonar ultrasound system called 'echolocation,' meaning they find things using echoes. As bats fly they make shouting sounds, which are too high for most humans to hear. The echoes they get back from their shouts give them information about anything that is ahead of them, including the size and shape of an insect and which way it is going.
So how does ultrasound work? Ultrasonic sensors measure distances by sending out an ultrasonic
pulse wave then wait for it to bounce back. The sound will be reflected off structures inside the body, and the ultrasound machine will analyze the information from the sound waves. Notably, thermal imaging also assesses its environment by creating images based on differences in surface temperature & by detecting infrared radiation (heat) that emanates from objects and their surrounding environment. Is it possible that some animals use ultrasound in the thermal range to read other animals in much the same way, in order to assess their intent? This brings me to infrared light. devices are also used as proximity sensors similar to ultrasound sensors. Instead of using ultrasound waves, IR sensors use infrared light which is not visible to the human eye. It is believed in the field that Bigfoot creatures avoid infrared light, so let's take a look. Infrared radiation is emitted or absorbed by molecules when they change their rotational-vibrational movements. It excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range. Since ultrasound is used to read its subject or environment, and IR light changes vibration and frequency range, it would stand to reason that IR light would interfere with ultrasound readings.
Sunlight, at an effective temperature of 5,780 kelvins, is composed of near thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation. Nearly all the infrared radiation in sunlight is near infrared, shorter than 4 micrometers. On the surface of Earth, at far lower temperatures than the surface of the Sun, almost all thermal radiation consists of infrared in mid-infrared region, much longer than in sunlight. Of these natural thermal radiation processes only lightning and natural fires are hot enough to produce much visible energy, and fires produce far more infrared than visible-light energy. Infrared Light has low attenuation losses. So on a more logical level, perhaps these creatures are familiar with, and can possibly visibly see, thermal radiation, and thus they tie infrared light to lightning and natural fires, so they would naturally avoid it for those reasons alone. Or perhaps it is something more scientific.
The effects of Ultrasound technology have been proven to have many effects on the fetal bodies. Fetuses are not the only ones effected by the possibly damaging effects of ultrasound. One of the most well known effects of ultrasound is that as Ultrasound waves pass through a tissue they tend to heat it up. The tissue can easily be warmed to 40 degrees Celsius. Although in vivo the heat is usually easily carried away by blood circulation or simply dissipated into surrounding tissues. this regiment can be applied in a technique called Ultrasound therapy where this heat is used to stimulate repair to damaged internal tissues. Another well known effect of Ultrasound are cavitations - The main non-thermal effect is called cavitation. Body tissues and fluids contain dissolved gases. When some of the sound energy is absorbed by the tissue, the energy could create bubbles from the dissolved gases. The bubbles then vibrate due to more absorption and finally burst, causing very intense, localized effects. Cavitations are normal bubbles of gas that are released upon exposure to extreme negative pressure. These bubbles can cause cells or even tissues to rupture. Thermal: When the sound waves pass through the tissue, not all of the waves pass through the tissue or get reflected, some are absorbed by the material. Only a very normal amount gets absorbed, and often the heat generated by the energy is quickly dissipated. But what about higher decibels? Although Ultrasound cannot be heard by humans, at high decibels it can still cause direct damage to human ears. Ultrasound in excess of 120 decibels may cause Hearing damage. Exposure to 155 decibels causes heat levels that are harmful to the body. 180 decibels may even cause death.
Sounds with a frequency of 20 kHz and higher are referred to as ultrasound (or ultrasonic sound).
High frequency sound is sound of which the frequency lies between 8 and 20 kHz. High frequency sound with a frequency over 16 kHz can hardly be heard, but it is not completely inaudible. High frequency sound and even ultrasound in the lower frequency zone (up to 24 kHz) can be audible if the sound level is high enough. The sound threshold (the sound level where sound can be perceived) rises sharply once the frequency (and therefore, the tone) becomes higher. Younger persons hear high frequency sound better and their hearing range is greater toward the high frequencies. It is assumed that high frequency sound and ultrasound with sufficient intensity can be traumatic for the hearing, and can cause other effects as well. High frequency sound causes two types of health effects: on the one hand objective health effects such as hearing loss (in case of protracted exposure) and on the other hand subjective effects which may already occur after a few minutes: headache, tinnitus, fatigue, dizziness and nausea. Depending on the personal sensitivity (this can be age-related or health-realted) people may already experience these subjective effects at a sound level of 75 dB. Note that ultrasound (and sound of high frequencies) is expressed in dB contrary to normal sound which is measured in dB(A). Source: Belgium Government Health Dept
Research in the effects of higher range ultrasound is currently in its infancy but there are some interesting research results coming out. Click here for more research information. The aim of one half
of this project was to explore whether hearing thresholds could be extended into the infrasound and ultrasound ranges making use of various approaches including looking for brain activation through the use of MEG and fMRI imaging. From the results in this project it is clear that some people are much more affected by low frequency ultrasound than others. At the upper frequency limit of human hearing there is a very steep drop in the sensitivity of the ear but the frequency of onset can vary significantly between different people. As a result some people are very sensitive to frequencies above 20 kHz whilst others have no conscious perception at all. However, a lack of perception does not mean that there is no brain activity. As the MEG ultrasound testing was the last part of the project the full set of results are yet to be published but hopefully they will give us some insight and help with developing improved guidelines on ultrasound exposure.
In conclusion regarding ultrasound effects, I would say that anecdotal evidence shows that high
amplitude ultrasound does have an impact on humans, but there is currently not enough research to answer the questions of what frequency range, what amplitude, what exposure time and at what distance. The work in the EARS project mentioned above is a first step towards developing a dose-response relationship but there is plenty more to be done and if you find personally that you experience negative effects from the presence of an ultrasound source currently the best solution is to avoid the source as much as possible.
John Mitani is a primate behavioral ecologist who investigates the behavior of our closest living relatives, the apes. His current research involves studies of an extremely large community of wild chimpanzees at Ngogo, Kibale National Park, Uganda. During the past 39 years, has conducted fieldwork on the behavior of all five kinds of apes: gibbons and orangutans in Indonesia, gorillas in Rwanda, bonobos in the Democratic Republic of Congo, and chimpanzees in Uganda and Tanzania. He found a decided trend for primates with larger home ranges to have loud calls with lower frequencies to travel further distances. Lower frequency sounds are also less susceptible to interference from surrounding environment.
Male chimpanzees produce a species-typical call, the pant hoot, to communicate to conspecifics over long-distances. Calls given by males from the well-known Gombe and Mahale populations typically consist of four different phases: an introduction, build-up, climax, and let-down. Recent observations suggest that chimpanzees living in the Kibale National Park, Uganda, consistently give calls that lack a build-up and are thus qualitatively distinguishable acoustically from those made by other East African conspecifics. We analyzed additional recordings from Mahale and Kibale to re-examine geographic variation in chimpanzee calls. Results indicate that males from both sites produce pant hoots containing all four parts of the call. Calls made by chimpanzees from the two populations, however, differ in quantitative acoustic measures. Specifically, males at Kibale initiate their calls with significantly longer elements and buildup over briefer periods at slower rates than individuals from Mahale. Kibale males also deliver acoustically less variable calls than chimpanzees at Mahale. Although climax elements do not differ between populations in any single acoustic feature, discriminant function analysis reveals that acoustic variables can be used in combination to assign calls to the correct population at rates higher than that expected by chance. Ecological factors related to differences in habitat acoustics, the sound environment of the local biota, and body size are likely to account for these observed macrogeographic variations in chimpanzee calls.
Chimpanzees pant-hooting Video
The pant-hoot is an awesome chimpanzee vocalization, made during times of excitement and to communicate with others. This video has clips of the dominant female chimpanzee at the sanctuary pant-hooting.
Pant hoots, for example, can consist of four distinct parts. Calls may begin with a brief introductory phase consisting of relatively long, tonal elements that emitted at low frequencies and amplitudes. The introduction is characterized by a sequential alternation of relatively high frequency elements followed by lower frequency sounds. The introduction grades into the build-up, a series of relatively short elements typically delivered at faster rates than those heard in the introduction and emitted both on inhalation and exhalation. Build-ups are followed by the climax, the loudest and highest frequency component of the call. Calls may end with a brief let-down phase, whose elements do not appear to differ appreciably from those emitted during the build-up. Male subjects at Mahale use pant hoots selectively to maintain contact with preferred associates and allies over long distances [Mitani & Nishida, 1993], and Kibale chimpanzees at Ngogo appear to employ these calls in the same fashion over similar distances. See more study results in frequencies here. Am. J.Primatol. 47:133–151, 1999.
In the 1950’s and the 1960’s, about 50,000 whales were killed each year, until the discovery of
something special by Roger Payne. The discovery of the Song of the Humpback Whale. This finding took place when military researcher, Frank Watlington, handed over recordings of submarines and dynamite explosions to Roger Payne, as he could not figure out what the noise in the background was. “These sounds are, with no exception that I can think of, the most evocative, most beautiful sounds made by any animal on Earth,” (May 2014) said Payne.
Payne discovered that the sound the whale was producing was a complex song, as the whale was continuously repeating itself. He realized that he may be able to use this beautiful sound to produce some changes in the whaling industry. In the year 1965, whaling was very severe and humpback whales became endangered. The International Whaling Commission did not allow whaling for a certain period of time, until the whale population increased once more. “Do you make cat food out of composer-poets? I think that’s a crime,” (May 2014) said Payne, as he began to think of ways to make everyone aware of these whale songs. His aim was to integrate the songs into our culture. He distributed the recordings to singers and composers all over the world. A singer crucial to the success of the project was Judy Collins. In her album Whales and Nightingales that was released in 1970, she included the song “Farewell to Tarwathie.” This song, which included actual recordings of whale songs that were given to her, became an instant hit. It spread the idea of whale songs to millions all across the globe.
A couple of years later, after hearing the songs, Greenpeace started their own movement called “Save the Whales,” which was a huge success. The song of the whale seemed to completely change the mindset of people. In this way, recordings of animals can really help in the conservation of the species.
After listening to the recordings, I felt guilt. Guilt for being part of a race that has been destroying these creatures. Guilt for doing nothing to protect these creatures. I am sure this was the same way people felt during the mid 20th century, when the movement was introduced. The songs also give us an opportunity to think about the intelligence of the creatures. As former Greenpeace director Rex Weyler said, “It certainly was a huge factor in convincing us that the whales were an intelligent species here on planet Earth and actually made music, made art, created an aesthetic” (May 2014). Why would one kill organisms that are creating art, and are doing nothing to harm us?
By incorporating whale songs into our own songs, we tend to anthropomorphise (ascribe human features to) the whales. Why do we do this? Why do we incorporate them into human culture? By doing so, it feels as though they are now great parts of our lives. It is as if they have a role to play in our lives, whether it involves aiding in music production, or helping us relax. From my research, I also believe that by anthropomorphising the whales, we tend to feel as though the whales are expressing themselves. We tend to feel emotions as if the whales are feeling them too. Although the idea of animals communicating emotion in their sounds is complex, some investigations have been carried out in the field, and documents have been produced, in order to support this idea.
The basic idea of using recordings to convince individuals to help conserve a species can also be used for other animals as well. One example is the recording of tiger roars. Many countries are trying to introduce the recording of tiger roars in order to estimate the tiger population and whether each individual tiger is male or female. The recording is put into computer software that generates spectrograms showing each individual tiger’s roar. Each roar acts as an identity to each individual tiger and can be used to identify it. In the same way, these recordings are being used to estimate animal densities of various creatures all over the world.
Whale Song
Balaena universus hominis - Whale as one with Human Whale Song recording and mastering by The Oceania Project: https://soundcloud.com/iwhales Established in 1988, The Oceania Project is an independent, nonprofit, scientific research organization dedicated to the conservation and protection of Whales, Dolphins and the Oceans.
Around 5% of the studies carried out on human impact on animal communication show that, effects
such as hunting, habitat fragmentation, chemical and noise pollution, “introduced diseases,” “direct human disturbance,” and urbanization, tend to affect acoustic communication (Laiolo, 2010). Therefore, another way recordings can help with conservation is by helping in identifying how humans have affected the organism’s bioacoustics. By comparing previous and current recordings, changes in the animal’s call can be identified. Although many organisms tend to adapt to their environment in this way, many adaptations may be disadvantageous to the species. This may be because other groups of the species are no longer able to communicate with them, sometimes sexual signs of animals are affected, echolocation of bats and cetaceans can be severely interrupted, habitat loss can affect the way birds select their nesting grounds based on acoustic cues, and noise pollution can also affect social signs of mammals. So through the use of recordings, identification of anthropogenic changes to bioacoustics is made easier. This could help with improvements in conservation of animals, as it is now clear what changes need to be made.
Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion and reception in animals (including humans).
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| artist Bill Asmussen |
Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion and reception in animals (including humans).
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Notes on Ultrasound:
Properties of an ultrasound wave
- Frequency higher than 20 000Hz (20kHz)
- Propagation of sound waves longitudinal, the mechanical displacement being in the same direction as propagation.
- A medium is needed for sound waves to go through, no medium = no soundwaves
- This propagation is whereby the particles of the medium which the sounds is going through oscillate (move) back and forth from their original rest positions, in the same line as the wave. This is also know as Simple Harmonic Motion
- The motion of the these particles is cause by 2 factors; the pressure of the wave (which forces them to move in the beginning) and the forces of the restoring molecules (also known as the elasticity of the medium)
Interactions of ultrasound with soft tissues
When an ultrasound wave passes through tissues
- Attenuation: Reduction in amplitude and intensity of wave
- Refraction: Change in direction & velocity of wave
Attenuation is the rate at which intensity wave diminishes with the depth it covers or its penetration.
3 Types:
- Reflection.
- Scattering
- Absorption
Affecting attenuation:
- Frequency of wave - Higher the frequency, higher the attenuation and less penetration of the wave
- Type of tissue the wave is traveling
- Depth the wave travels - more distance wave has to travel the more energy is lost.
Reflection
When a sound wave is incident on a interface between two tissues, part of it is reflected back into the original medium. The amount of energy reflected back depends on impedance.
The greater the difference in impedance between the tissues forming the interface the greater the amount of energy that is reflected back.
Impedance is a property of a tissue defined as density of tissue and velocity of sound in that tissue.
Reflection co-efficient ( R) is the ratio of the intensity of the reflected wave to the incident wave.
R = (Z2 –Z1) ²
( Z2+Z1) 2
The greater R, the greater the degree of reflection. i.e. R for a soft tissue interface such as liver and kidney is 0.01, i.e. only 1% of the sound is reflected. Muscle/bone interface 40% is reflected and for a soft tissue/air interface 99% is reflected.
This is the basis of ultrasound as different organs in the body have different densities and acoustic impedance and this creates different reflectors. In some cases the acoustic impedance can be so great that all the sound waves energy can be reflected, this happens when sound comes in contact with bone and air. This is the reason why ultrasound is not used as a primary imaging modality for bone, digestive tract and lungs.
Absorption
Absorption is the main form of attenuation. Absorption happens as sound travels through soft tissue, the particles that transmit the waves vibrate and cause friction and a loss of sound energy occurs and heat is produced. In soft tissue sound intensity decreases exponentially with depth.
Diffuse Scatter
Diffuse scatter when an objects size relative to the wave length becomes normaler. Imagine placing a thin stick upright in large rippling puddle or lake shore. The waves striking the stick will barely change course. The same applies to sound when the wave length of the sound waves are much larger than the object they are striking little or no sound waves will be reflected back. Because of this no strong reflections are seen as the sound, if reflected at all does not go directly back to the transducer. An example of this can be seen as speculation of an ultrasound image.
Echo Ranging
Echo ranging is a technique used to determine the distance of an object from the transducer. This technique relies on reflection.
The echo ranging equation is z=ct.
z = distance c = speed of ultrasound in tissue t = time
A sound beam is transmitted into a medium and is reflected back from an object. The elapsed time between the transmitted pulse and the received echo is converted into the total distance traveled. (The z value is only half of the distance traveled away and back to the transducer. )
Sound speed (c) is equal to one over the square root of the density times compressibility.OR c= square root compressibility / square root density.This indicates that if the density of a material is increased the speed of sound in that material will also be increased.Sound travels faster in media that are denser than air because of reduced compressibility.The velocity of ultrasound remains constant for a particular medium.Where c=frequency X wavelength.Indicating that for a constant velocity as the frequency is increased the wavelength is reduced.Ultrasonic waves are reflected at boundaries where there is a difference in acoustic impedance (Z) of the materials on each side of the boundary.
Worthy of Noting: Light will travel through a vacuum, sound never will regardless of its frequency.
When ultrasound waves reach a boundary between two media (substances) with different densities, they are partly reflected back. The remainder of the ultrasound waves continue to pass through. What effects can higher Ultrasound waves have on an object, or a human when they pass through? Food for thought.
Southern SASquatch Expeditions
Author: Angela Ashton, Founder
#southernsasquatchexpeditions #bigfoot #sasquatch
https://www.facebook.com/southernsasquatchexpeditions/
Southern SASquatch Expeditions
Author: Angela Ashton, Founder
#southernsasquatchexpeditions #bigfoot #sasquatch
https://www.facebook.com/southernsasquatchexpeditions/
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