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It all stems from the human ear. And information on these is scant, though Volcer bravely attempts to piece together the material, her consensus being that despite numerous trials, very few sonic weapons have moved beyond a testing phase. She also cites the use of repellent sound technologies not just in a military capacity, but in the public sphere. Increasingly military designed technology is finding its way into the hands of police as a mechanism for crowd control. It reportedly offers an instant migraine and can push people off their feet.
Around the world, different types of sonic devices are used for crowd control, to protect areas of attack and to incapacitate soldiers or workers. Here are some examples of devices that use sound to disperse or attack:.
Since the early s, long-range acoustic devices -- also known as LRADs -- have helped authorities control crowds of people, especially protesters. They emit a loud, painful sound over a long distance and make people run away. In the US, police used such devices during demonstrations at the G20 Summit meeting in Pittsburgh. They were also used more recently, during the protests in Ferguson, Missouri , following the fatal shooting of Michael Brown.
The popularity of the devices among law enforcement has risen now that the LRAD Corporation, the company that originally created the device, now sells them to more than 70 countries, the company said in a recent financial report. The so-called "mosquito" produces a very high-pitched sound that can be perceived by teenagers, but not to adults.
It's used in several countries to prevent people from loitering. The middle ear includes the eardrum and the chain of three small bones or ossicles: the eardrum receives acoustical vibrations from the air, which cause it to tremble like the skin of a drum, and transmits them to the three bones.
While frequencies useful to communication are amplified, basses and strong sounds are filtered. The internal ear is composed of the organs of equilibrium the vestibular apparatus and of hearing the cochlea. The spiral-shaped cochlea transmits the vibrations of the ossicles to the brain. It is covered by the basilar membrane, which serves as a base to the organ of Corti, itself composed of nerve receptors equipped with hair cells. When a sound reaches the receptors, these hair cells, distributed throughout the long membrane, begin to move like the keys of a piano, and thus transmit the different frequencies to the brain.
The ear functions therefore as a microphone, transforming acoustic energy into electrical energy. The sound spectrum, which includes all sounds, can be broken into frequencies the number of oscillations of the mechanical vibration in one second , the unit of measurement of which is the hertz Hz. Rapid vibrations high frequency produce a high sound, whereas slower vibrations low frequency produce a low sound — the "la" of the tuning fork corresponds, for example, to Hz.
One characteristic that interests the military in particular is that the human ear hears only a part of the sound spectrum. Generally we don't hear sounds below 20 Hz infrasounds or above 20, Hz ultrasounds — the sound exists, but we don't hear it, or not much. Between the two is what's called the audible range: low frequencies deep sounds are between 20 and Hz, medium frequencies medium sounds fall between Hz and 2, Hz, and high frequencies high-pitched sounds between 2, and 20, Hz.
Elephants can hear sounds starting at 0. When a sound is made up solely of its fundamental frequency , its base frequency, we speak of pure tone. Such sound, which is usually of electronic origin for example, the frequency of an alarm , is aggressive to the ear. It is represented in the form of a sinusoidal waveform the same movement repeating periodically; see figure 1. In music, as in nature, we find mainly complex tones , which is to say composed not only of their fundamental frequency but also of harmonic frequencies , which are multiples of the fundamental frequency.
The fundamental frequency is the lowest and the one with the greatest breadth, so we hear it with the greatest intensity. The timbre of an instrument is determined by the combination of the fundamental frequency and the harmonics that it emits, the relative intensity of which varies, as does its evolution in time: that is why the "la" of a piano sounds different from the same "la" played on the violin.
Finally, we speak of octaves to designate the interval between two base frequencies, one of which is the double of the other for example, the "la" at Hz and the "la" at 1, Hz.beernearme.com/2623-cellphone-snapchat-tracking.php
A complex tone can be represented in the form of a period wave that is non-sinusoidal see figure 2. A complex sound can also be non-sinusoidal and non-periodic, if it doesn't repeat the same vibration regularly see figure 3. Noise is an aleatory or irregular wave see figure 4. In acoustics, therefore, noise is not an unpleasant or unaesthetic sound, but a continuous signal in which no particular frequency can be distinguished.
Over the course of the twentieth century, contemporary music, notably bruitism, questioned, reinterpreted, and deconstructed these definitions in their relationship to the concept of aesthetics. What we call white noise is a noise containing all the frequencies at the same intensity as when a television is not properly adjusted. The capacity to hear low and high frequencies varies from person to person, according to age and health. The ear is far more sensitive to frequencies between 1, Hz and 4, Hz, which are useful for oral communication, than to low frequencies. Another notable characteristic of our bodies is that it is not only the ear that reacts to sound: in proximity to a loudspeaker or a subwoofer , which sends low notes at a high volume, our intestines vibrate.
Extremely Loud: Sound as a Weapon by Juliette Volcler, Hardcover | Barnes & Noble®
We call this the extra-auditive effects of sound. Our body perceives a part of the infrasounds and the ultrasounds that are inaudible to the ear. A deaf person may dance perfectly well, therefore, since he or she may feel the vibrations of the sounds in his or her body. A final clarification concerning frequency: every physical body object or organism has its own particular frequency, or resonance frequency , which causes maximal vibration in the object harmonic frequencies also cause vibration, but less so.
Sound touches every body around it and is transformed into mechanical energy, into vibration — like the surface of water when you throw a stone. When the frequency of sound coincides with the resonance frequency of an object, the object vibrates more strongly. When Bianca Castafiore, the "Milanese Nightingale" in the Tintin series of comic books, manages to break glass with her voice, it is because the frequency she emits is the same as the resonance frequency of glass: under the combined effects of the frequency the note , the intensity or volume , and the length how long the singer holds the note , glass vibrates with increasing force to the point of breaking.
The same holds true for a bridge, which can be destroyed by a weak gust of wind if the wind's resonance frequency corresponds to that of the bridge. For vertical vibratory excitation of a standing or sitting human body, below 2 Hz the body moves as a whole. Above, amplification by resonances occurs with frequencies depending on body parts, individuals, and posture. A main resonance is at about 5 Hz where the greatest discomfort is caused; sometimes the head moves strongest at about 4 Hz. The voice may warble at 10 to 20 Hz, and eye resonances within the head may be responsible for blurred vision between 15 and 60 Hz.
In-phase movement of all organs in the abdominal cavity with consequent variation of the lung volume and chest wall is responsible for the resonance at 4—6 Hz. But we often get too excited about the vibrational potential of infrasounds, forgetting one important thing: that low-frequency acoustic waves, which are not unidirectional, apply the same pressure to the whole body. The result is that "air pressure variations impinging on the human body produce some vibration, but due to the large impedance mismatch nearly all energy is reflected. The stronger vibration of the thoracic cavity comes into play between 40 Hz and 60 Hz.
This particular sensitivity of the human body to certain frequencies is exploited in a positive manner by certain medical techniques or in some spiritual practices mantras.