Sound is vibration, i.e., periodic mechanical perturbation in elastic media – gaseous, liquid and solid. Such outrage, which represents a physical change in the environment (e.g., change density or pressure, the displacement of particles), distributed in the form of sound waves. The sound can be inaudible, if its frequency is outside the sensitivity of the human ear, or it applies in this environment as a rigid body, which may not have direct contact with the ear, or its energy dissipates rapidly in the environment. Thus, a common process of sound perception – is only one aspect of acoustics.
Sound waves
Sound wave [10]
Sound waves are an example of the oscillatory process. Any fluctuation associated with the violation of the equilibrium state of the system and is expressed in deviation of its characteristics from the equilibrium values, then return to the original value. For sound waves this characteristic is the pressure at the point of the medium, and the deviation of the sound pressure. [4]
Consider a long tube filled with air. From the left end is inserted closely adjacent to the walls of the piston. If the piston to move sharply to the right and stopped, then the air in the immediate vicinity, momentarily compressed. Then compressed air expands, pushing the air adjacent to it on the right, and the compression area, initially emerged near the piston will move along the tube with constant speed. This compression wave is a sound wave in the gas.
Then there is a sharp displacement of the particles of an elastic medium in one place, will increase the pressure in this place. Thanks to the elastic relations of particles, the pressure is transmitted to neighboring particles which, in turn, affect the following, and the area of high pressure moved as though in an elastic medium. For a region of high pressure follows an area of low pressure, and thus forms a series of alternating regions of compression and rarefaction propagating through the medium in wave form. Each particle of an elastic medium in this case will oscillate.
A sound wave in a gas is characterized by excess pressure, excess density, particle displacement and velocity. For sound waves, these deviations from equilibrium values is always small. Thus, the excess pressure associated with the wave is much less than the static pressure of the gas. Otherwise, we are dealing with another phenomenon – the shock wave. In the sound wave corresponding to normal speech, the excessive pressure is only about one millionth of atmospheric pressure.
It is important the fact that the substance is not carried away by the sound wave. The wave is merely passing through the air temporal, according to the passage which the air is returned to equilibrium.
Wave motion, of course, is characteristic not only of sound: in the form of waves propagated light signals and radio signals, and everyone is familiar with waves on the surface of the water. [4]
Thus sound, in the broadest sense — of the elastic wave in any elastic medium and creating mechanical vibrations; in a narrow sense — the subjective perception of these oscillations special sense organs of animals or man.
Like any wave, sound is characterized by amplitude and frequency spectrum. Usually the person hears the sounds transmitted through the air, in the frequency range 16-20 Hz to 15-20 kHz. Sound below the range of human audibility are called infrasound; higher: up to 1 GHz, — ultrasound, 1 GHz — hypersound. Among audible sounds should also highlight the phonetic, speech sounds and phonemes (which is oral) and musical sounds (which is music).
[5]
Distinguish between longitudinal and transverse sound waves in the direction of wave propagation and direction of mechanical vibrations of the particles of the propagation medium.
In liquid and gaseous environments where there are no significant density fluctuations, sound waves are longitudinal in nature, that is, the direction of oscillation of the particles coincides with the direction of travel of the wave. In solids, in addition to longitudinal deformation, there are also elastic shear strain, causing the excitation of transverse (shear) waves; in this case the particles oscillate perpendicular to the direction of wave propagation. The speed of propagation of longitudinal waves is much greater than the speed of propagation of shear waves. [3]
The air is not homogeneous everywhere for the sound. It is known that the air is constantly in motion. Its speed in different layers are not the same. In the layers close to the ground, the air in contact with its surface buildings, forests and so the speed here is less than at the top. Due to this, the sound wave is not equally fast at the top and bottom. If the air movement, i.e. wind — companion sound, that in the upper layers of air, the wind will be stronger to customize the sound wave than in the lower. With a headwind the sound is travelling slower at the top than the bottom. This difference in velocity affects the shape of the sound wave. As a result of distortion of a wave sound travels not in a straight line. With the tailwind line of propagation of the sound wave bends downwards, with a cross — up.
Another reason of the uneven distribution of sound in the air. It has different temperature of individual layers.
Differently heated layers of air, like the wind, change the direction of the sound. Day the sound wave is bent up, because the speed of sound in the lower warmer layers higher than the top layers. In the evening, when the earth and the surrounding layers of air, quickly cooled, the upper layers become warmer, lower speed of sound in them is greater and the line of propagation of sound waves is bent down. So at night the blue is better.
Observing clouds, you can often see how at different heights they are moving not only at different speeds and sometimes in different directions. So the wind at different heights from the ground may have a different speed and direction. Form the sound waves in such layers will also be varied from layer to layer. Suppose, for example, the sound against the wind. In this case, the line of sound propagation should be bent and head up. But if on her way to meet a layer of slow moving air, it again changes direction and may again return to earth. That's when the space from where the wave rises in height, to the place where she returns to earth, and there is a "zone of silence". [11]
The organs of sound perception
Hearing — the ability of biological organisms to perceive sounds by the organs of hearing; a special feature of the hearing aid, sound vibrations excited by the environment, e.g., air or water. One of the biological five senses, also called acoustic perception.
The human ear perceives the sound wave length from about 20 m to 1.6 cm, which corresponds to 16 — 20 000 Hz (cycles per second) in the transmission of vibrations through the air, and up to 220 kHz when sound transmission through the bones of the skull. These waves have important biological significance, for example, sound waves in the range of 300-4000 Hz correspond to the human voice. Sounds above 20,000 Hz are of little practical value, as rapidly inhibited; vibration below 60 Hz are perceived due to vibration sense. The frequency range that can hear, called the hearing or audible range; higher frequencies are called ultrasound, and the lower — infrasound.
The ability to discern audio frequencies strongly depends on the individual: his age, sex, exposure to auditory diseases, fitness and fatigue of hearing. Individuals are able to perceive sounds up to 22 kHz, or even higher.
People can distinguish several sounds at the same time due to the fact that the cochlea can be some standing waves. [1]
The ear is a complex vestibular-auditory organ which performs two functions: it perceives sound impulses and is responsible for the body's position in space and the ability to keep balance. This paired organ, which is located in the temporal bones of the skull, limited to outside ears.
The organ of hearing and equilibrium is represented by three departments: external, middle and inner ear, each of which performs its specific functions.
The outer ear consists of the auricle and the external auditory canal. The auricle is a complex form elastic cartilage, covered with skin, the lower part, called the lobe, is a skin fold, which consists of skin and adipose tissue.
Auricle in living organisms acting as a receiver of sound waves that are then transmitted into the inner part of the hearing aid. The value of the auricle in humans is much less than in animals, so human it is almost stationary. But many animals, handling ears, capable of much more accurate than people, to determine the location of the sound source.
The folds of the human auricle are making in entering the auditory canal sound, small distortion of frequency-dependent horizontal and vertical sound localization. Thus, the brain receives additional information to clarify the location of the sound source. This effect is sometimes used in acoustics, including to create a feeling of surround sound when using headphones or hearing AIDS.
The function of the ear — catching sounds; it is a continuation of the cartilage of the external auditory canal, whose length on average is 25-30 mm. Cartilaginous part of the auditory canal enters the bone, and the whole external auditory meatus is lined with skin containing sebaceous and sulfur glands, which is a modified sweat. This passage ends blindly from the middle ear it is separated by the eardrum. Caught the ear sound waves hit the eardrum and cause vibrations.
In turn, the vibrations of the eardrum are transmitted to the middle ear.
The middle ear
The main part of the middle ear is the tympanic cavity is a small space with a volume of approximately 1см3 located in the temporal bone. Here are three auditory ossicles: the hammer, anvil, and stirrup — they transmit sound vibrations from the outer ear to the inner at the same time reinforcing them.
The auditory ossicles — as the smallest fragments of the human skeleton, represent a chain, transmitting vibrations. The handle of the hammer is closely merged with the eardrum, the head of the hammer is connected to the anvil, and that, in turn, its long process to the stapes. The base of the stapes closes the window of the vestibule, connecting thus with the inner ear.
The middle ear cavity is connected with the nasopharynx by the Eustachian tube, through which is aligned with the average pressure of the air inside and outside of the eardrum. If you change the external pressure sometimes "lays" ears that usually is solved in that the reflex is called a yawn. Experience shows that even more effective in the ears is solved by swallowing movements, or if in this moment to blow into a pinched nose.
The inner ear
Of the three parts of the organ of hearing and balance is the most difficult inner ear, which is due to its intricate form called the labyrinth. The bony labyrinth consists of the vestibule, cochlea and semicircular canals, but directly relevant to the hearing only has a snail, filled with lymph fluids. Within the cochlea is the membranous canal is also filled with liquid, the bottom wall of which is a receptor apparatus of the auditory analyzer, covered voloskovye cells. Hair cells detect vibrations of the liquid filling the channel. Each hair cell is tuned to a certain audio frequency, with cells tuned to low frequencies are located in the upper part of the cochlea, and high frequencies are captured by the cells of the lower part of the cochlea. When the hair cells with age or for other reasons to die, a person loses the ability to perceive sounds of appropriate frequencies.[2]
The limits of perception
The human ear can nominally hear sounds in the range of 16 to 20,000 Hz. The upper limit tends to decrease with age. Most adults can't hear the sound of a frequency above 16 kHz. The ear itself does not respond to frequencies below 20 Hz, but they can be felt through the organs of touch.
The range of loudness of perceived sound is huge. But the eardrum in the ear is sensitive only to pressure changes. The sound pressure level generally measured in decibels (dB). The lower threshold of audibility is defined as 0 dB (20 micropascal) and the definition of the upper limit of audibility is more related to the threshold of discomfort and further to the hearing impaired, contusion, etc. This limit depends on how long the time we listen to the sound. The ear can tolerate short-term increase in volume up to 120 dB without consequences, but long-term perception of sound volume over 80 dB can cause hearing loss.
A more thorough study of the lower boundary of the hearing showed that the minimum threshold at which the sound is heard depends on the frequency. This graph has been called the absolute threshold of hearing. On average, it has a plot of maximum sensitivity in the range from 1 kHz to 5 kHz, although with age, the sensitivity decreases in the range above 2 kHz.
There is also a way of listening without the participation of the tympanic membrane — the so-called microwave auditory effect, when the modulated radiation in the microwave range (1 to 300 GHz) effects on the tissues around the cochlea, causing the person to perceive different sounds.
Sometimes a person can hear sounds in the low frequency region, although in reality the sounds of this frequency were not. This happens due to the fact that the vibrations of the basilar membrane in the ear are not linear and there can be fluctuations with the difference frequency between the two higher frequency. [9]
Synesthesia
One of the most unusual neuropsychiatric phenomena, which are not the same kind of stimulus and the type of sensations that the person experiences. Synesthetic perception is reflected in the fact that in addition to the usual qualities may be additional, more simple sensations or stable "elementary" experience - for example, color, smell, sounds, tastes, tactile qualities of surface, transparency, dimension and shape, location in space and of other qualities that are not received through the senses, and existing only in the form of reactions. These additional qualities can either occur as isolated sensory impressions, or even be manifested physically. [7]
Isolated, for example, auditory synesthesia. It is the ability of some people to "hear" sounds when monitoring moving objects or flashes, even if they are not accompanied by real sound effects.[1]
Note that synesthesia rather neuropsychiatric feature of a person and is not a mental disorder. Such a perception of the world can feel an ordinary person by the use of certain drugs.
The General theory of synesthesia (scientifically proven, universal ideas about it) yet. At day time there are many hypotheses and conducted a lot of research in this area. Already there was the original classification and mapping, it became clear certain strict patterns. For example, we scientists have found that synesthetes have a special character of attention - as if "dosnateli" - to those phenomena that cause them to have synesthesia. Synesthetes - slightly different brain anatomy and radically different its activation for synaesthetic "incentives". [7] researchers from Oxford University (UK) delivered a series of experiments which found that the cause of synesthesia can be trigger the neurons. [8] the Only thing you can say for sure that this perception is obtained at the level of the brain, and not at the level of primary perception.
Conclusion
Pressure waves passing through the outer ear, the eardrum and ossicles of the middle ear and reach the fluid-filled inner ear having the shape of a snail. Liquid, hesitate, hits the membrane is covered with tiny hairs, cilia. Sinusoidal components of a complex sound cause vibrations of various parts of the membrane. Oscillating together with the membrane of the cilia excite the associated nerve fibers; they have a series of pulses in which "encoded" the frequency and amplitude of each component of the complex wave; this data is electrochemically transferred to the brain.[5]
From the whole range of sounds primarily emit audible range: 20 to 20,000 Hz, the infrasound (20 Hz) and ultrasound – from 20,000 Hz and above. The infrasound and the ultrasound person can not hear, but that doesn't mean they're not affected by it. It is known that infrasound, especially below 10 Hz, can affect the human psyche, cause depression. Ultrasounds can cause asthenic-vegetative syndromes, etc.
Kisimul part of the range of sound is divided into low-frequency sounds up to 500 Hz, mid – 500-10000 Hz and high frequency – 10,000 Hertz.
Such a unit is very important because the human ear is unequally sensitive to different sounds. The ear is most sensitive to a relatively narrow range of midfrequency sounds from 1000 to 5000 Hertz. To more low - and high-frequency sounds, the sensitivity drops sharply. This leads to the fact that a person is able to hear mid-frequency range sounds with an energy of about 0 dB and not hear low-frequency sounds in 20-40-60 dB. That is, sounds with the same energy in mid-frequency range can be perceived as loud and quiet or low frequency as to not be heard.
This feature of the sound generated by nature is not accidental. The sounds needed for its existence, the sounds of nature are mainly in the midfrequency range.
Perception of sounds is much disturbed, if at the same time heard other sounds, noise is similar in frequency or harmonics. So, on the one hand, the human ear poorly perceives low-frequency sounds, on the other hand, if the room background noise, the perception of these sounds can further be broken and subverted. [6]
Translated by «Yandex.Translator»
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