Sound is one of the components of our life, and a person hears it everywhere. In order to consider this phenomenon in more detail, we first need to understand the concept itself. To do this, you need to turn to the encyclopedia, where it is written that "sound is elastic waves propagating in any elastic medium and creating mechanical vibrations in it." In simpler terms, these are audible vibrations in any medium. The main characteristics of the sound depend on what it is. First of all, the speed of propagation, for example, in water is different from another medium.

Any sound analogue has certain properties (physical features) and qualities (reflection of these features in human sensations). For example, duration-duration, frequency-pitch, composition-timbre, and so on.

The speed of sound in water is much higher than, say, in air. Therefore, it spreads faster and is much farther audible. This happens because of the high molecular density of the aqueous medium. It is 800 times denser than air and steel. It follows that the propagation of sound depends largely on the medium. Let's turn to specific numbers. So, the speed of sound in water is 1430 m/s, in air - 331.5 m/s.

Low-frequency sound, such as the sound of a running ship's engine, is always heard a little before the ship enters the field of view. Its speed depends on several things. If the temperature of the water rises, then naturally the speed of sound in the water rises. The same happens with an increase in water salinity and pressure, which increases with increasing depth of the water space. Such a phenomenon as thermal wedges can have a special role on speed. These are places where layers of water of different temperatures meet.

Also in such places it is different (due to the difference in temperature regime). And when sound waves pass through such layers of different density, they lose most of their strength. Faced with a thermocline, the sound wave is partially, and sometimes completely, reflected (the degree of reflection depends on the angle at which the sound falls), after which, on the other side of this place, a shadow zone is formed. If we consider an example when a sound source is located in the water space above the thermocline, then it will be almost impossible to hear something even lower.

Which are published above the surface, are never heard in the water itself. And vice versa happens when under the water layer: it does not sound above it. A striking example of this is modern divers. Their hearing is greatly reduced due to the fact that water affects and the high speed of sound in water reduces the quality of determining the direction from which it is moving. This dulls the stereophonic ability to perceive sound.

Under a layer of water, they enter the human ear most of all through the bones of the cranium of the head, and not, as in the atmosphere, through the eardrums. The result of this process is its perception simultaneously by both ears. The human brain is not able at this time to distinguish the places where the signals come from, and in what intensity. The result is the emergence of consciousness that the sound, as it were, rolls from all sides at the same time, although this is far from being the case.

In addition to the above, sound waves in the water space have such qualities as absorption, divergence and scattering. The first is when the strength of sound in salt water gradually disappears due to the friction of the aquatic environment and the salts in it. Divergence is manifested in the removal of sound from its source. It seems to dissolve in space like light, and as a result, its intensity drops significantly. And fluctuations completely disappear due to scattering on all sorts of obstacles, inhomogeneities of the medium.

Have you ever thought that sound is one of the most striking manifestations of life, action, movement? And also about the fact that each sound has its own “face”? And even with our eyes closed, without seeing anything, we can only guess by the sound what is happening around. We can distinguish the voices of acquaintances, hear rustling, roaring, barking, meowing, etc. All these sounds are familiar to us from childhood, and we can easily identify any of them. Moreover, even in absolute silence, we can hear each of the listed sounds with our inner hearing. Imagine it as if it were real.

What is sound?

The sounds perceived by the human ear are one of the most important sources of information about the world around us. The noise of the sea and wind, the singing of birds, the voices of people and the cries of animals, the peals of thunder, the sounds of moving ears, make it easier to adapt to changing external conditions.

If, for example, a stone fell in the mountains, and there was no one nearby who could hear the sound of its fall, did the sound exist or not? The question can be answered both positively and negatively equally, since the word "sound" has a double meaning. Therefore, we need to agree. Therefore, we need to agree what is considered sound - a physical phenomenon in the form of propagation of sound vibrations in the air or the sensation of the listener. is essentially a cause, the second is an effect, while the first concept of sound is objective, the second is subjective.In the first case, the sound is really a stream of energy flowing like a river stream.Such a sound can change the environment through which it passes, and is itself changed by it "In the second case, by sound we understand the sensations that arise in the listener when a sound wave acts through the hearing aid on the brain. Hearing a sound, a person can experience various feelings. The complex complex of sounds that we call music evokes in us the most diverse emotions. Sounds form the basis of speech, which serves as the main means of communication in human society. Finally, there is such a form of sound as noise. Sound analysis from the standpoint of subjective perception is more complicated than with an objective assessment.

How to create sound?

Common to all sounds is that the bodies that generate them, that is, the sources of sound, oscillate (although most often these vibrations are invisible to the eye). For example, the sounds of the voices of people and many animals arise as a result of the vibrations of their vocal cords, the sound of wind musical instruments, the sound of a siren, the whistle of the wind, the peals of thunder are due to fluctuations in air masses.

On the example of a ruler, you can literally see with your eyes how sound is born. What movement does the ruler make when we secure one end, pull back the other, and release it? We will notice that he seemed to tremble, hesitated. Based on this, we conclude that the sound is created by a short or long oscillation of some objects.

The source of sound can be not only vibrating objects. The whistle of bullets or shells in flight, the howl of the wind, the roar jet engine are born from breaks in the air flow, during which its rarefaction and compression also occur.

Also, sound oscillatory movements can be noticed with the help of a device - a tuning fork. It is a curved metal rod, mounted on a resonator box on a leg. If you hit the tuning fork with a hammer, it will sound. Vibration of the tuning fork branches is imperceptible. But they can be detected if a small ball suspended on a thread is brought to a sounding tuning fork. The ball will periodically bounce, which indicates the fluctuations of the Cameron's branches.

As a result of the interaction of the sound source with the surrounding air, air particles begin to contract and expand in time (or "almost in time") with the movements of the sound source. Then, due to the properties of air as a fluid medium, vibrations are transmitted from one air particle to another.

Toward an explanation of the propagation of sound waves

As a result, vibrations are transmitted through the air over a distance, i.e., a sound or acoustic wave, or, simply, sound propagates in the air. The sound, reaching the human ear, in turn, excites vibrations in its sensitive areas, which are perceived by us in the form of speech, music, noise, etc. (depending on the properties of the sound dictated by the nature of its source).

Propagation of sound waves

Is it possible to see how the sound "runs"? In transparent air or in water, the oscillations of the particles themselves are imperceptible. But it is easy to find an example that will tell you what happens when sound propagates.

A necessary condition for the propagation of sound waves is the presence of a material environment.

In vacuum, sound waves do not propagate, since there are no particles transmitting interaction from the source of vibrations.

Therefore, on the Moon, due to the absence of an atmosphere, complete silence reigns. Even the fall of a meteorite on its surface is not audible to the observer.

The speed of propagation of sound waves is determined by the rate of transfer of interaction between particles.

The speed of sound is the speed of propagation of sound waves in a medium. In a gas, the speed of sound turns out to be of the order (more precisely, somewhat less) of the thermal speed of molecules and therefore increases with increasing gas temperature. The greater the potential energy of interaction of the molecules of a substance, the greater the speed of sound, so the speed of sound in a liquid, which, in turn, exceeds the speed of sound in a gas. For example, in sea water the speed of sound is 1513 m/s. In steel, where transverse and longitudinal waves can propagate, their propagation speed is different. Transverse waves propagate at a speed of 3300 m/s, and longitudinal at a speed of 6600 m/s.

The speed of sound in any medium is calculated by the formula:

where β is the adiabatic compressibility of the medium; ρ - density.

Laws of propagation of sound waves

The basic laws of sound propagation include the laws of its reflection and refraction at the boundaries of various media, as well as the diffraction of sound and its scattering in the presence of obstacles and inhomogeneities in the medium and at the interfaces between media.

The sound propagation distance is influenced by the sound absorption factor, that is, the irreversible transfer of sound wave energy into other types of energy, in particular, into heat. An important factor is also the direction of radiation and the speed of sound propagation, which depends on the medium and its specific state.

Acoustic waves propagate from a sound source in all directions. If a sound wave passes through a relatively small hole, then it propagates in all directions, and does not go in a directed beam. For example, street sounds penetrating through an open window into a room are heard at all its points, and not just against the window.

The nature of the propagation of sound waves at an obstacle depends on the ratio between the dimensions of the obstacle and the wavelength. If the dimensions of the obstacle are small compared to the wavelength, then the wave flows around this obstacle, propagating in all directions.

Sound waves, penetrating from one medium to another, deviate from their original direction, that is, they are refracted. The angle of refraction can be greater or less than the angle of incidence. It depends on the medium from which the sound penetrates. If the speed of sound in the second medium is greater, then the angle of refraction will be greater than the angle of incidence, and vice versa.

Encountering an obstacle on its way, sound waves are reflected from it in a strictly certain rule- the angle of reflection is equal to the angle of incidence - the concept of echo is associated with this. If sound is reflected from several surfaces at different distances, multiple echoes occur.

Sound propagates in the form of a diverging spherical wave that fills an ever larger volume. As the distance increases, the oscillations of the particles of the medium weaken, and the sound dissipates. It is known that in order to increase the transmission distance, sound must be concentrated in a given direction. When we want, for example, to be heard, we put our hands to our mouths or use a mouthpiece.

Diffraction, that is, the bending of sound rays, has a great influence on the range of sound propagation. The more heterogeneous the medium, the more the sound beam is bent and, accordingly, the shorter the sound propagation distance.

Sound properties and characteristics

The main physical characteristics of sound are the frequency and intensity of vibrations. They also affect the auditory perception of people.

The period of oscillation is the time during which one complete oscillation occurs. An example is a swinging pendulum, when it moves from the extreme left position to the extreme right and returns back to its original position.

The oscillation frequency is the number of complete oscillations (periods) in one second. This unit is called the hertz (Hz). The higher the oscillation frequency, the higher the sound we hear, that is, the sound has a higher tone. In accordance with the accepted international system units, 1000 Hz is called kilohertz (kHz), and 1.000.000 is called megahertz (MHz).

Frequency distribution: audible sounds - within 15Hz-20kHz, infrasounds - below 15Hz; ultrasound - within 1.5 (104 - 109 Hz; hypersound - within 109 - 1013 Hz.

The human ear is most sensitive to sounds with a frequency of 2000 to 5000 kHz. The greatest acuity of hearing is observed at the age of 15-20 years. Hearing deteriorates with age.

The concept of the wavelength is associated with the period and frequency of oscillations. The length of a sound wave is the distance between two successive concentrations or rarefications of the medium. Using the example of waves propagating on the surface of water, this is the distance between two crests.

Sounds also differ in timbre. The main tone of the sound is accompanied by secondary tones, which are always higher in frequency (overtones). Timbre is a qualitative characteristic of sound. The more overtones superimposed on the main tone, the more "juicy" the sound musically.

The second main characteristic is the amplitude of oscillations. This is the largest deviation from the equilibrium position for harmonic vibrations. On the example of a pendulum - its maximum deviation to the extreme left position, or to the extreme right position. The amplitude of oscillations determines the intensity (strength) of the sound.

The strength of sound, or its intensity, is determined by the amount of acoustic energy flowing in one second through an area of ​​​​one square centimeter. Consequently, the intensity of acoustic waves depends on the magnitude of the acoustic pressure created by the source in the medium.

Loudness is in turn related to sound intensity. The greater the intensity of the sound, the louder it is. However, these concepts are not equivalent. Loudness is a measure of the strength of the auditory sensation caused by a sound. A sound of the same intensity can create different auditory perceptions in different people. Each person has their own hearing threshold.

A person ceases to hear sounds of very high intensity and perceives them as a feeling of pressure and even pain. This strength of sound is called the pain threshold.

The effect of sound on the human ear

Human hearing organs are able to perceive vibrations with a frequency of 15-20 hertz to 16-20 thousand hertz. Mechanical vibrations with the indicated frequencies are called sound or acoustic (acoustics - the study of sound). The human ear is most sensitive to sounds with a frequency of 1000 to 3000 Hz. The greatest hearing acuity is observed at the age of 15-20 years. Hearing deteriorates with age. In a person under 40 years of age, the highest sensitivity is in the region of 3000 Hz, from 40 to 60 years old - 2000 Hz, over 60 years old - 1000 Hz. In the range up to 500 Hz, we are able to distinguish a decrease or increase in frequency even 1 Hz. At higher frequencies, our hearing aid becomes less receptive to this slight change in frequency. So, after 2000 Hz, we can distinguish one sound from another only when the difference in frequency is at least 5 Hz. With a smaller difference, the sounds will seem the same to us. However, there are almost no rules without exception. There are people who have unusually fine hearing. A gifted musician can detect a change in sound by just a fraction of the vibrations.

The outer ear consists of the auricle and auditory canal, which connect it to the eardrum. The main function of the outer ear is to determine the direction of the sound source. The ear canal, which is a two-centimeter long tube tapering inward, protects the inner parts of the ear and acts as a resonator. The ear canal ends at the eardrum, a membrane that vibrates under the action of sound waves. It is here, on the outer border of the middle ear, that the transformation of objective sound into subjective takes place. Behind the tympanic membrane are three small interconnected bones: the hammer, anvil and stirrup, through which vibrations are transmitted to the inner ear.

There, in the auditory nerve, they are converted into electrical signals. The small cavity, where the hammer, anvil and stirrup are located, is filled with air and is connected to the oral cavity by the Eustachian tube. Thanks to the latter, the same pressure is maintained on the inside and outside of the eardrum. Usually the Eustachian tube is closed, and opens only with a sudden change in pressure (when yawning, swallowing) to equalize it. If a person's Eustachian tube is closed, for example, due to a cold, then the pressure does not equalize, and the person feels pain in the ears. Further, vibrations are transmitted from the tympanic membrane to the oval window, which is the beginning of the inner ear. The force acting on the tympanic membrane is equal to the product of the pressure and the area of ​​the tympanic membrane. But the real mysteries of hearing begin at the oval window. Sound waves propagate in the fluid (perilymph) that fills the cochlea. This organ of the inner ear, shaped like a cochlea, has a length of three centimeters and is divided into two parts along the entire length by a septum. Sound waves reach the partition, go around it and then propagate in the direction almost to the same place where they first touched the partition, but from the other side. The septum of the cochlea consists of a basal membrane that is very thick and taut. Sound vibrations create wavy ripples on its surface, while the ridges for different frequencies lie in completely defined sections of the membrane. Mechanical vibrations are converted into electrical vibrations in a special organ (Corti's organ) located above the upper part of the main membrane. The tectorial membrane is located above the organ of Corti. Both of these organs are immersed in a fluid - the endolymph and are separated from the rest of the cochlea by the Reissner membrane. The hairs growing from the organ, Corti, almost penetrate the tectorial membrane, and when sound occurs, they touch - the sound is converted, now it is encoded in the form of electrical signals. A significant role in strengthening our ability to perceive sounds is played by the skin and bones of the skull, due to their good conductivity. For example, if you put your ear to the rail, then the movement of an approaching train can be detected long before it appears.

The effect of sound on the human body

In recent decades, there has been a sharp increase in the number different kind cars and other sources of noise, the spread of portable radios and tape recorders, often turned on at high volume, and a passion for loud popular music. It is noted that in cities every 5-10 years the noise level increases by 5 dB (decibel). It should be borne in mind that for the distant ancestors of man, noise was an alarm signal, indicating the possibility of danger. At the same time, the sympathetic-adrenal and cardiovascular systems, gas exchange, and other types of metabolism changed quickly (the level of sugar and cholesterol in the blood increased), preparing the body for fight or flight. Although in modern man this function of hearing has lost such practical significance, "vegetative reactions of the struggle for existence" have been preserved. So, even a short-term noise of 60-90 dB causes an increase in the secretion of pituitary hormones that stimulate the production of many other hormones, in particular, catecholamines (adrenaline and norepinephrine), the work of the heart increases, blood vessels narrow, and arterial pressure(HELL). At the same time, it was noted that the most pronounced increase in blood pressure is observed in patients with hypertension and persons with a hereditary predisposition to it. Under the influence of noise, brain activity is disrupted: the nature of the electroencephalogram changes, the sharpness of perception and mental performance decrease. There was a deterioration in digestion. It is known that prolonged exposure to noisy environments leads to hearing loss. Depending on individual sensitivity, people differently evaluate noise as unpleasant and disturbing them. At the same time, music and speech of interest to the listener, even at 40-80 dB, can be transferred relatively easily. Usually hearing perceives fluctuations in the range of 16-20000 Hz (oscillations per second). It is important to emphasize that backfire causes not only excessive noise in the audible range of oscillations: ultra- and infrasound in the ranges not perceived by human hearing (above 20 thousand Hz and below 16 Hz) also causes nervous strain, malaise, dizziness, changes in the activity of internal organs, especially the nervous and cardiovascular systems. It has been established that residents of areas located near major international airports have a distinctly higher incidence of hypertension than in a quieter area of ​​the same city. Excessive noise (above 80 dB) affects not only the hearing organs, but also other organs and systems (circulatory, digestive, nervous, etc.), vital processes are disturbed, energy metabolism begins to prevail over plastic, which leads to premature aging of the body .

With these observations-discoveries, methods of purposeful influence on a person began to appear. You can influence the mind and behavior of a person in various ways, one of which requires special equipment (technotronic techniques, zombification.).

Soundproofing

The degree of noise protection of buildings is primarily determined by the norms of permissible noise for premises of this purpose. The normalized constant noise parameters at the calculated points are the sound pressure levels L, dB, in octave frequency bands with geometric mean frequencies of 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz. For approximate calculations it is allowed to use sound levels LA, dBA. The normalized parameters of intermittent noise at the design points are the equivalent sound levels LA eq, dBA, and the maximum sound levels LA max, dBA.

Permissible sound pressure levels (equivalent sound pressure levels) are standardized by SNiP II-12-77 "Noise Protection".

It should be borne in mind that the permissible levels of noise from external sources in the premises are set subject to the provision of normative ventilation of the premises (for residential premises, wards, classes - with open windows, transoms, narrow window sashes).

Isolation from airborne sound is the attenuation of sound energy when it is transmitted through the fence.

Standardized parameters of sound insulation of enclosing structures of residential and public buildings, as well as auxiliary buildings and premises of industrial enterprises are the airborne sound insulation index of the enclosing structure Rw, dB and the index of the reduced impact noise level under the ceiling.

Noise. Music. Speech.

From the point of view of the perception of sounds by the organs of hearing, they can be divided mainly into three categories: noise, music and speech. These are different areas of sound phenomena that have information specific to a person.

Noise is an unsystematic combination a large number sounds, that is, the fusion of all these sounds into one discordant voice. It is believed that noise is a category of sounds that disturbs a person or annoys.

Humans can only handle a certain amount of noise. But if an hour passes - another, and the noise does not stop, then there is tension, nervousness and even pain.

Sound can kill a person. In the Middle Ages, there was even such an execution, when a person was put under a bell and they began to beat him. Gradually, the bell ringing killed a person. But that was in the Middle Ages. In our time, supersonic aircraft have appeared. If such an aircraft flies over the city at an altitude of 1000-1500 meters, then the windows in the houses will burst.

Music is a special phenomenon in the world of sounds, but, unlike speech, it does not convey precise semantic or linguistic meanings. Emotional saturation and pleasant musical associations begin in early childhood, when the child still has verbal communication. Rhythms and chants connect him with his mother, and singing and dancing are an element of communication in games. The role of music in human life is so great that in recent years medicine has attributed healing properties to it. With the help of music, you can normalize biorhythms, ensure the optimal level of activity of the cardiovascular system. But one has only to remember how the soldiers go into battle. From time immemorial, the song has been an indispensable attribute of a soldier's march.

Infrasound and ultrasound

Is it possible to call sound what we do not hear at all? So what if we don't hear? Are these sounds no longer available to anyone or anything?

For example, sounds with a frequency below 16 hertz are called infrasound.

Infrasound - elastic vibrations and waves with frequencies that lie below the frequency range audible to humans. Usually, 15-4 Hz is taken as the upper limit of the infrasonic range; such a definition is conditional, since with sufficient intensity, auditory perception also occurs at frequencies of a few Hz, although in this case the tonal character of the sensation disappears, and only individual cycles of oscillations become distinguishable. The lower frequency limit of infrasound is uncertain. At present, its field of study extends down to about 0.001 Hz. Thus, the range of infrasonic frequencies covers about 15 octaves.

Infrasonic waves propagate in air and water, as well as in earth's crust. Infrasounds also include low-frequency vibrations of large structures, in particular vehicles, buildings.

And although our ears do not "catch" such vibrations, but somehow a person still perceives them. In this case, we experience unpleasant, and sometimes disturbing sensations.

It has long been observed that some animals are much before man feel a sense of danger. They react in advance to a distant hurricane or an impending earthquake. On the other hand, scientists have discovered that during catastrophic events in nature, infrasound occurs - low-frequency vibrations in the air. This gave rise to hypotheses that animals, thanks to their keen senses, perceive such signals earlier than humans.

Unfortunately, infrasound is produced by many machines and industrial plants. If, say, it occurs in a car or plane, then after some time the pilots or drivers are anxious, they get tired faster, and this can be the cause of an accident.

They make noise in the infrasonic machines, and then it is harder to work on them. And everyone around you will have a hard time. It is no better if it “hums” with infrasound ventilation in a residential building. It seems to be inaudible, but people get annoyed and can even get sick. To get rid of infrasonic hardships allows a special "test" that any device must pass. If it “phonites” in the infrasound zone, then it will not receive a pass to people.

What is a very high pitch called? Such a squeak that is inaccessible to our ear? This is ultrasound. Ultrasound - elastic waves with frequencies from approximately (1.5 - 2) (104 Hz (15 - 20 kHz) to 109 Hz (1 GHz); the region of frequency waves from 109 to 1012 - 1013 Hz is usually called hypersound. By frequency, ultrasound is conveniently divided into 3 ranges: low frequency ultrasound (1.5 (104 - 105 Hz), medium frequency ultrasound (105 - 107 Hz), high frequency ultrasound (107 - 109 Hz). Each of these ranges is characterized by its own specific features of generation, reception, distribution and application .

By its physical nature, ultrasound is elastic waves, and in this it does not differ from sound, therefore the frequency boundary between sound and ultrasonic waves is conditional. However, due to higher frequencies and, consequently, short wavelengths, a number of features of the propagation of ultrasound take place.

Due to the short wavelength of ultrasound, its nature is determined primarily by the molecular structure of the medium. Ultrasound in a gas, and in particular in air, propagates with great attenuation. Liquids and solids are, as a rule, good conductors of ultrasound - the attenuation in them is much less.

The human ear is not capable of perceiving ultrasonic waves. However, many animals freely perceive it. These are, among other things, the dogs we know so well. But dogs, alas, cannot “bark” with ultrasound. But the bats and dolphins have the amazing ability to both emit and receive ultrasound.

Hypersound is elastic waves with frequencies from 109 to 1012 - 1013 Hz. By physical nature, hypersound is no different from sound and ultrasonic waves. Due to higher frequencies and, consequently, shorter wavelengths than in the field of ultrasound, the interactions of hypersound with quasiparticles in the medium become much more significant - with conduction electrons, thermal phonons, etc. Hypersound is also often represented as a flow of quasiparticles - phonons.

The hypersound frequency range corresponds to the frequencies of electromagnetic oscillations of the decimeter, centimeter and millimeter ranges (the so-called ultra-high frequencies). Frequency 109 Hz in air at normal atmospheric pressure and room temperature should be of the same order of magnitude as the mean free path of molecules in air under the same conditions. However, elastic waves can propagate in a medium only if their wavelength is noticeably greater than the free path of particles in gases or greater than the interatomic distances in liquids and solids. Therefore, hypersonic waves cannot propagate in gases (particularly in air) at normal atmospheric pressure. In liquids, hypersound attenuation is very large and the propagation range is short. Hypersound propagates relatively well in solids - single crystals, especially at low temperatures. But even in such conditions, hypersound is able to cover a distance of only 1, maximum 15 centimeters.

Sound is mechanical vibrations propagating in elastic media - gases, liquids and solids, perceived by the hearing organs.

With the help of special instruments, you can see the propagation of sound waves.

Sound waves can harm human health and vice versa, help to cure ailments, it depends on the type of sound.

It turns out that there are sounds that are not perceived by the human ear.

Bibliography

Peryshkin A. V., Gutnik E. M. Physics Grade 9

Kasyanov V. A. Physics Grade 10

Leonov A. A "I know the world" Det. encyclopedia. Physics

Chapter 2. Acoustic noise and its impact on humans

Purpose: To investigate the impact of acoustic noise on the human body.

Introduction

The world around us is a beautiful world of sounds. Around us are the voices of people and animals, music and the sound of the wind, the singing of birds. People transmit information through speech, and with the help of hearing it is perceived. For animals, sound is no less important, and in some ways more important because their hearing is more developed.

From the point of view of physics, sound is mechanical vibrations that propagate in an elastic medium: water, air, a solid body, etc. The ability of a person to perceive sound vibrations, listen to them, is reflected in the name of the doctrine of sound - acoustics (from the Greek akustikos - audible, auditory). The sensation of sound in our hearing organs occurs with periodic changes in air pressure. Sound waves with a large amplitude of sound pressure change are perceived by the human ear as loud sounds, with a small amplitude of sound pressure change - as quiet sounds. The loudness of the sound depends on the amplitude of the vibrations. The loudness of the sound also depends on its duration and on individual features listener.

High-frequency sound vibrations are called high-pitched sounds, and low-frequency sound vibrations are called low-pitched sounds.

Human hearing organs are capable of perceiving sounds with a frequency ranging from approximately 20 Hz to 20,000 Hz. Longitudinal waves in a medium with a pressure change frequency of less than 20 Hz are called infrasound, with a frequency of more than 20,000 Hz - ultrasound. The human ear does not perceive infrasound and ultrasound, i.e., does not hear. It should be noted that the indicated boundaries of the sound range are arbitrary, since they depend on the age of people and the individual characteristics of their sound apparatus. Usually, with age, the upper frequency limit of perceived sounds decreases significantly - some older people can hear sounds with frequencies not exceeding 6,000 Hz. Children, on the contrary, can perceive sounds whose frequency is slightly more than 20,000 Hz.

Oscillations whose frequencies are greater than 20,000 Hz or less than 20 Hz are heard by some animals.

The subject of study of physiological acoustics is the organ of hearing itself, its structure and action. Architectural acoustics studies the propagation of sound in rooms, the influence of sizes and shapes on sound, the properties of materials that cover walls and ceilings. This refers to the auditory perception of sound.

There is also musical acoustics, which examines musical instruments and the conditions for their best sound. Physical acoustics deals with the study of sound vibrations themselves, and beyond recent times embraced and fluctuations lying beyond the limits of audibility (ultraacoustics). It widely uses a variety of methods to convert mechanical vibrations into electrical vibrations and vice versa (electroacoustics).

History reference

Sounds began to be studied in antiquity, since a person is characterized by an interest in everything new. The first acoustical observations were made in the 6th century BC. Pythagoras established a connection between the pitch and the long string or trumpet that makes the sound.

In the 4th century BC, Aristotle was the first to correctly understand how sound travels in air. He said that the sounding body causes compression and rarefaction of the air, the echo was explained by the reflection of sound from obstacles.

In the 15th century, Leonardo da Vinci formulated the principle of the independence of sound waves from various sources.

In 1660, in the experiments of Robert Boyle, it was proved that air is a conductor of sound (sound does not propagate in a vacuum).

In 1700-1707. Joseph Saveur's memoirs on acoustics were published by the Paris Academy of Sciences. In these memoirs, Saver discusses a phenomenon well known to organ designers: if two pipes of an organ emit two sounds at the same time, only slightly different in pitch, then periodic amplifications of sound are heard, similar to a drum roll. Saver explained this phenomenon by the periodic coincidence of the vibrations of both sounds. If, for example, one of the two sounds corresponds to 32 vibrations per second, and the other to 40 vibrations, then the end of the fourth vibration of the first sound coincides with the end of the fifth vibration of the second sound, and thus the sound is amplified. From organ pipes, Saver moved on to an experimental study of string vibrations, observing the nodes and antinodes of vibrations (these names, which still exist in science, were introduced by him), and also noticed that when a string is excited, along with the main note, other notes sound, length whose waves are ½, 1/3, ¼,. from main. He called these notes the highest harmonic tones, and this name was destined to remain in science. Finally, Saver was the first to try to determine the limit of the perception of vibrations as sounds: for low sounds, he indicated a limit of 25 vibrations per second, and for high ones - 12,800. After that, Newton, based on these experimental work Saveur, gave the first calculation of the wavelength of sound and came to the conclusion, now well known in physics, that for any open pipe the wavelength of the emitted sound is equal to twice the length of the pipe.

Sound sources and their nature

Common to all sounds is that the bodies that generate them, that is, the sources of sound, oscillate. Everyone is familiar with the sounds that arise when the skin stretched over the drum moves, the waves of the sea surf, the branches swaying by the wind. All of them are different from each other. The "color" of each individual sound strictly depends on the movement due to which it arises. So if the oscillatory movement is extremely fast, the sound contains high frequency vibrations. A slower oscillatory motion creates a lower frequency sound. Various experiments show that any source of sound necessarily oscillates (although most often these oscillations are not noticeable to the eye). For example, the sounds of the voices of people and many animals arise as a result of the vibrations of their vocal cords, the sound of wind musical instruments, the sound of a siren, the whistling of the wind, and the peals of thunder are due to fluctuations in air masses.

But not every oscillating body is a source of sound. For example, a vibrating weight suspended on a thread or spring does not make a sound.

The frequency at which oscillations repeat is measured in hertz (or cycles per second); 1 Hz is the frequency of such a periodic oscillation, the period is 1 s. Note that it is the frequency that is the property that allows us to distinguish one sound from another.

Studies have shown that the human ear is able to perceive as sound the mechanical vibrations of bodies occurring at a frequency of 20 Hz to 20,000 Hz. With very fast, more than 20,000 Hz or very slow, less than 20 Hz, sound vibrations, we do not hear. That is why we need special devices to register sounds that lie outside the frequency limit perceived by the human ear.

If the speed of the oscillatory movement determines the frequency of the sound, then its magnitude (the size of the room) is the loudness. If such a wheel is rotated at high speed, a high frequency tone will occur, slower rotation will generate a lower frequency tone. Moreover, the smaller the teeth of the wheel (as shown by the dotted line), the weaker the sound, and the larger the teeth, that is, the more they cause the plate to deviate, the louder the sound. Thus, we can note one more characteristic of sound - its loudness (intensity).

It is impossible not to mention such a property of sound as quality. Quality is intimately related to structure, which can go from overly complex to extremely simple. The tone of the tuning fork supported by the resonator has a very simple structure, since it contains only one frequency, the value of which depends solely on the design of the tuning fork. In this case, the sound of the tuning fork can be both strong and weak.

You can create complex sounds, so for example, many frequencies contain the sound of an organ chord. Even the sound of a mandolin string is quite complex. This is due to the fact that the stretched string oscillates not only with the main (like a tuning fork), but also with other frequencies. They generate additional tones (harmonics), the frequencies of which are an integer number of times higher than the frequency of the fundamental tone.

The concept of frequency is unlawful to apply in relation to noise, although we can talk about some areas of its frequencies, since it is they that distinguish one noise from another. The noise spectrum can no longer be represented by one or more lines, as in the case of a monochromatic signal or a periodic wave containing many harmonics. It is depicted as a whole line

The frequency structure of some sounds, especially musical ones, is such that all overtones are harmonic with respect to the fundamental tone; in such cases, the sounds are said to have a pitch (determined by the pitch frequency). Most of the sounds are not so melodious, they do not have an integral ratio between frequencies characteristic of musical sounds. These sounds are similar in structure to noise. Therefore, summarizing what has been said, we can say that sound is characterized by loudness, quality and height.

What happens to sound after it has been created? How does it reach, for example, our ear? How does it spread?

We perceive sound with our ears. Between the sounding body (sound source) and the ear (sound receiver) is a substance that transmits sound vibrations from the sound source to the receiver. Most often, this substance is air. Sound cannot propagate in airless space. As waves cannot exist without water. Experiments support this conclusion. Let's consider one of them. Under the bell air pump place a call and turn it on. Then they begin to pump out the air with a pump. As the air becomes rarefied, the sound becomes audible weaker and weaker and, finally, almost completely disappears. When the air again begins to let in under the bell, the sound of the bell again becomes audible.

Of course, sound propagates not only in air, but also in other bodies. This can also be tested experimentally. Even such a faint sound as the ticking of a pocket watch lying at one end of the table can be clearly heard by putting your ear to the other end of the table.

It is well known that sound is transmitted over long distances on the ground, and especially on railroad tracks. Putting your ear to the rail or to the ground, you can hear the sound of a far-reaching train or the tramp of a galloping horse.

If we, being under water, strike a stone against a stone, we will clearly hear the sound of the impact. Therefore, sound also propagates in water. Fish hear footsteps and the voices of people on the shore, this is well known to anglers.

Experiments show that different solid bodies conduct sound differently. Elastic bodies are good conductors of sound. Most metals, wood, gases, and liquids are elastic bodies and therefore conduct sound well.

Soft and porous bodies are poor conductors of sound. When, for example, a watch is in a pocket, it is surrounded by a soft cloth, and we do not hear its ticking.

By the way, the fact that the experiment with a bell placed under a cap seemed not very convincing for a long time is connected with the propagation of sound in solids. The fact is that the experimenters did not isolate the bell well enough, and the sound was heard even when there was no air under the cap, since the vibrations were transmitted through various connections of the installation.

In 1650, Athanasius Kirch'er and Otto Gücke, based on an experiment with a bell, concluded that air was not needed for the propagation of sound. And only ten years later, Robert Boyle convincingly proved the opposite. Sound in air, for example, is transmitted by longitudinal waves, i.e., by alternating condensations and rarefactions of air coming from the sound source. But since the space surrounding us, unlike the two-dimensional surface of water, is three-dimensional, then sound waves propagate not in two, but in three directions - in the form of divergent spheres.

Sound waves, like any other mechanical waves, do not propagate in space instantly, but at a certain speed. The simplest observations make it possible to verify this. For example, during a thunderstorm, we first see lightning and only after a while hear thunder, although the vibrations of the air, perceived by us as sound, occur simultaneously with the flash of lightning. The fact is that the speed of light is very high (300,000 km / s), so we can assume that we see a flash at the time of its occurrence. And the sound of thunder, which was formed simultaneously with lightning, takes a quite tangible time for us to travel the distance from the place of its occurrence to the observer standing on the ground. For example, if we hear thunder more than 5 seconds after seeing lightning, we can conclude that the thunderstorm is at least 1.5 km away from us. The speed of sound depends on the properties of the medium in which the sound propagates. Scientists have developed various ways determination of the speed of sound in any environment.

The speed of sound and its frequency determine the wavelength. Watching the waves in the pond, we notice that diverging circles are sometimes smaller and sometimes larger, in other words, the distance between wave crests or wave troughs can be different depending on the size of the object due to which they arose. By holding our hand low enough above the surface of the water, we can feel every splash that passes us. The greater the distance between successive waves, the less often their crests will touch our fingers. Such a simple experiment allows us to conclude that in the case of waves on the water surface for a given wave propagation speed, a higher frequency corresponds to a smaller distance between the crests of the waves, that is, shorter waves, and, conversely, to a lower frequency, longer waves.

The same is true for sound waves. The fact that a sound wave passes through a certain point in space can be judged by a change in pressure at a given point. This change completely repeats the oscillation of the membrane of the sound source. A person hears sound because the sound wave exerts varying pressure on the eardrum of their ear. As soon as the crest of a sound wave (or area of ​​high pressure) reaches our ear. We feel pressure. If the areas of increased pressure of the sound wave follow each other quickly enough, then the tympanic membrane of our ear vibrates quickly. If the crests of the sound wave are far behind each other, then the eardrum will vibrate much more slowly.

The speed of sound in air is surprisingly constant. We have already seen that the frequency of sound is directly related to the distance between the crests of the sound wave, that is, there is a certain relationship between the frequency of sound and the wavelength. We can express this relationship as follows: wavelength equals speed divided by frequency. It can be said in another way: the wavelength is inversely proportional to the frequency with a proportionality factor equal to the speed of sound.

How does sound become audible? When sound waves enter the ear canal, they cause the eardrum, middle and inner ear to vibrate. Once in the fluid filling the cochlea, the air waves act on the hair cells inside the organ of Corti. The auditory nerve transmits these impulses to the brain, where they are converted into sounds.

Noise measurement

Noise is an unpleasant or unwanted sound, or a set of sounds that interfere with the perception of useful signals, break silence, have a harmful or irritating effect on the human body, and reduce its performance.

In noisy areas, many people develop symptoms of noise disease: increased nervous excitability, fatigue, high blood pressure.

The noise level is measured in units,

Expressing the degree of pressure sounds, - decibels. This pressure is not perceived indefinitely. The noise level of 20-30 dB is practically harmless to humans - this is a natural background noise. As for loud sounds, the permissible limit here is approximately 80 dB. A sound of 130 dB already causes a painful sensation in a person, and 150 becomes unbearable for him.

Acoustic noise - chaotic sound vibrations of different physical nature, characterized by a random change in amplitude, frequency.

With the propagation of a sound wave, consisting of condensations and rarefactions of air, the pressure on the eardrum changes. The unit for pressure is 1 N/m2 and the unit for sound power is 1 W/m2.

The threshold of hearing is the minimum volume of sound that a person perceives. It is different for different people, and therefore it is conventionally considered to be a sound pressure equal to 2x10 "5 N / m2 at 1000 Hz, corresponding to a power of 10"12 W / m2, for the threshold of hearing. It is with these quantities that the measured sound is compared.

For example, the sound power of motors during takeoff of a jet aircraft is 10 W/m2, that is, it exceeds the threshold by 1013 times. It is inconvenient to operate with such large numbers. They say about sounds of different loudness that one is louder than the other not by so many times, but by so many units. The volume unit is called Bel - after the inventor of the telephone A. Bel (1847-1922). Loudness is measured in decibels: 1 dB = 0.1 B (Bel). A visual representation of how sound intensity, sound pressure and volume level are related.

The perception of sound depends not only on its quantitative characteristics (pressure and power), but also on its quality - frequency.

The same sound at different frequencies differs in loudness.

Some people do not hear high frequency sounds. So, in older people, the upper limit of sound perception drops to 6000 Hz. They do not hear, for example, the squeak of a mosquito and the trill of a cricket, which make sounds with a frequency of about 20,000 Hz.

The famous English physicist D. Tyndall describes one of his walks with a friend as follows: “The meadows on both sides of the road were teeming with insects, which filled the air with their sharp buzzing to my ears, but my friend did not hear anything of this - the music of insects flew beyond the boundaries of his hearing” !

Noise levels

Loudness - the level of energy in sound - is measured in decibels. A whisper equates to approximately 15 dB, the rustle of voices in a student auditorium reaches approximately 50 dB, and street noise in heavy traffic is approximately 90 dB. Noises above 100 dB can be unbearable to the human ear. Noises in the order of 140 dB (for example, the sound of a jet plane taking off) can be painful to the ear and damage the eardrum.

For most people, hearing becomes dull with age. This is due to the fact that the ear ossicles lose their original mobility, and therefore the vibrations are not transmitted to the inner ear. In addition, infections of the hearing organs can damage the eardrum and negatively affect the functioning of the bones. If you have any hearing problems, you should immediately consult a doctor. Some types of deafness are caused by damage to the inner ear or auditory nerve. Hearing loss can also be caused by constant noise exposure (such as on a factory floor) or sudden and very loud bursts of sound. You must be very careful when using personal stereo players, as excessive volume can also lead to deafness.

Permissible indoor noise

With regard to the noise level, it should be noted that such a concept is not ephemeral and unsettled from the point of view of legislation. So, in Ukraine to this day, the Sanitary norms for permissible noise in the premises of residential and public buildings and on the territory of residential development adopted back in the times of the USSR are in force. According to this document, in residential premises, the noise level must be ensured, not exceeding 40 dB during the day and 30 dB at night (from 22:00 to 08:00).

Quite often noise carries important information. A car or motorcycle racer listens carefully to the sounds that the engine, chassis and other parts of a moving vehicle make, because any extraneous noise can be a harbinger of an accident. Noise plays a significant role in acoustics, optics, computer technology, and medicine.

What is noise? It is understood as chaotic complex vibrations of various physical nature.

The problem of noise has been around for a very long time. Already in ancient times, the sound of wheels on the cobblestone pavement caused insomnia in many.

Or maybe the problem arose even earlier, when the cave neighbors began to quarrel because one of them knocked too loudly while making a stone knife or ax?

Noise pollution is growing all the time. If in 1948, during a survey of residents of large cities, 23% of the respondents answered in the affirmative to the question of whether they were worried about noise in the apartment, then in 1961 - already 50%. In the last decade, the noise level in cities has increased by 10-15 times.

Noise is a type of sound, although it is often referred to as "unwanted sound". At the same time, according to experts, the noise of a tram is estimated at the level of 85-88 dB, a trolleybus - 71 dB, a bus with an engine capacity of more than 220 hp. With. - 92 dB, less than 220 hp With. - 80-85 dB.

Scientists from State University Ohio concluded that people who are regularly exposed to loud noises are 1.5 times more likely than others to develop acoustic neuroma.

Acoustic neuroma is a benign tumor that causes hearing loss. Scientists examined 146 patients with acoustic neuroma and 564 healthy people. They were all asked questions about how often they had to deal with loud sounds no weaker than 80 decibels (traffic noise). The questionnaire took into account the noise of instruments, motors, music, children's screams, noise at sporting events, in bars and restaurants. Study participants were also asked if they used hearing protection. Those who regularly listened to loud music had a 2.5-fold increased risk of acoustic neuroma.

For those who were exposed to technical noise - 1.8 times. For people who regularly listen to a child's cry, the noise in stadiums, restaurants or bars is 1.4 times higher. When using hearing protection, the risk of acoustic neuroma is no higher than in people who are not exposed to noise at all.

Impact of acoustic noise on humans

The impact of acoustic noise on a person is different:

A. Harmful

Noise causes a benign tumor

Prolonged noise adversely affects the organ of hearing, stretching the eardrum, thereby reducing sensitivity to sound. It leads to a breakdown in the activity of the heart, liver, to exhaustion and overstrain. nerve cells. Sounds and noises of high power affect the hearing aid, nerve centers, can cause pain and shock. This is how noise pollution works.

Noises are artificial, technogenic. They have a negative impact on nervous system person. One of the worst urban noises is the noise of road transport on major highways. It irritates the nervous system, so a person is tormented by anxiety, he feels tired.

B. Favorable

Useful sounds include the noise of foliage. The splashing of the waves has a calming effect on our psyche. The quiet rustle of leaves, the murmur of a stream, the light splash of water and the sound of the surf are always pleasant to a person. They calm him, relieve stress.

C. Medical

The therapeutic effect on a person with the help of the sounds of nature originated with doctors and biophysicists who worked with astronauts in the early 80s of the twentieth century. In psychotherapeutic practice, natural noises are used in the treatment of various diseases as an aid. Psychotherapists also use the so-called "white noise". This is a kind of hiss, vaguely reminiscent of the sound of waves without splashing water. Doctors believe that "white noise" soothes and lulls.

The impact of noise on the human body

But is it only the hearing organs that suffer from noise?

Students are encouraged to find out by reading the following statements.

1. Noise causes premature aging. In thirty cases out of a hundred, noise reduces the life expectancy of people in large cities by 8-12 years.

2. Every third woman and every fourth man suffer from neuroses caused by increased noise levels.

3. Diseases such as gastritis, gastric and intestinal ulcers are most often found in people who live and work in noisy environments. Variety musicians have a stomach ulcer - an occupational disease.

4. Sufficiently strong noise after 1 minute can cause changes in the electrical activity of the brain, which becomes similar to the electrical activity of the brain in patients with epilepsy.

5. Noise depresses the nervous system, especially with repeated action.

6. Under the influence of noise, there is a persistent decrease in the frequency and depth of breathing. Sometimes there is arrhythmia of the heart, hypertension.

7. Under the influence of noise, carbohydrate, fat, protein, salt metabolism changes, which manifests itself in a change in the biochemical composition of the blood (the level of sugar in the blood decreases).

Excessive noise (above 80 dB) affects not only the hearing organs, but also other organs and systems (circulatory, digestive, nervous, etc.), vital processes are disturbed, energy metabolism begins to prevail over plastic, which leads to premature aging of the body .

NOISE PROBLEM

A large city is always accompanied by traffic noise. Over the past 25-30 years, noise has increased by 12-15 dB in large cities around the world (i.e., the noise volume has increased by 3-4 times). If an airport is located within the city, as is the case in Moscow, Washington, Omsk and a number of other cities, this leads to a multiple excess of the maximum permissible level of sound stimuli.

And still automobile transport leading among the main sources of noise in the city. It is he who causes noise up to 95 dB on the sound level meter scale on the main streets of cities. Noise level in living rooms with closed windows facing the highway, only 10-15 dB lower than on the street.

The noise of cars depends on many reasons: the brand of the car, its serviceability, speed, quality of the road surface, engine power, etc. The noise from the engine increases sharply at the time of its start and warming up. When the car is moving at the first speed (up to 40 km / h), the engine noise is 2 times higher than the noise generated by it at the second speed. When the car brakes hard, the noise also increases significantly.

The dependence of the state of the human body on the level of environmental noise has been revealed. Certain changes in the functional state of the central nervous and cardiovascular systems caused by noise were noted. Ischemic heart disease, hypertension, increased blood cholesterol are more common in people living in noisy areas. Noise greatly disturbs sleep, reduces its duration and depth. The period of falling asleep increases by an hour or more, and after waking up, people feel tired and have a headache. All this eventually turns into chronic overwork, weakens the immune system, contributes to the development of diseases, and reduces efficiency.

Now it is believed that noise can reduce the life expectancy of a person by almost 10 years. There are also more mentally ill people due to increasing sound stimuli, especially women are affected by noise. In general, the number of hearing-impaired people in cities has increased, but the most common phenomena have become headache and increased irritability.

NOISE POLLUTION

Sound and noise of high power affect the hearing aid, nerve centers and can cause pain and shock. This is how noise pollution works. The quiet rustle of leaves, the murmur of a stream, the voices of birds, the light splash of water and the sound of the surf are always pleasant to a person. They calm him, relieve stress. This is used in medical institutions, in psychological relief rooms. Natural noises of nature become more and more rare, disappear completely or are drowned out by industrial, transport and other noises.

Prolonged noise adversely affects the organ of hearing, reducing the sensitivity to sound. It leads to a breakdown in the activity of the heart, liver, to exhaustion and overstrain of nerve cells. Weakened cells of the nervous system cannot coordinate their work sufficiently various systems organism. This results in disruption of their activities.

We already know that 150 dB noise is detrimental to humans. Not for nothing in the Middle Ages there was an execution under the bell. The hum of the bell ringing tormented and slowly killed.

Each person perceives noise differently. Much depends on age, temperament, state of health, environmental conditions. Noise has an accumulative effect, that is, acoustic stimuli, accumulating in the body, increasingly depress the nervous system. Noise has a particularly harmful effect on the neuropsychic activity of the body.

Noises cause functional disorders of cardio-vascular system; has a harmful effect on the visual and vestibular analyzers; reduce reflex activity, which often causes accidents and injuries.

Noise is insidious, its harmful effect on the body occurs invisibly, imperceptibly, and breakdowns in the body are not detected immediately. In addition, the human body is practically defenseless against noise.

Increasingly, doctors are talking about noise disease, a primary lesion of hearing and the nervous system. The source of noise pollution can be an industrial enterprise or transport. Especially heavy dump trucks and trams produce a lot of noise. Noise affects the human nervous system, and therefore noise protection measures are taken in cities and enterprises. Railway and tram lines and roads along which freight transport passes should be moved from the central parts of cities to sparsely populated areas and green spaces should be created around them that absorb noise well. Planes should not fly over cities.

SOUNDPROOFING

Soundproofing greatly helps to avoid the harmful effects of noise.

Noise reduction is achieved through construction and acoustic measures. In external enclosing structures, windows and balcony doors have significantly less sound insulation than the wall itself.

The degree of noise protection of buildings is primarily determined by the norms of permissible noise for premises of this purpose.

FIGHTING ACOUSTIC NOISE

The Acoustics Laboratory of MNIIP is developing sections "Acoustic Ecology" as part of the project documentation. Projects on sound insulation of premises, noise control, calculations of sound amplification systems, acoustic measurements are being carried out. Although in ordinary premises more and more people want acoustic comfort - good noise protection, intelligible speech and the absence of so-called. acoustic phantoms - negative sound images formed by some. In constructions intended for additional struggle with decibels, at least two layers alternate - "hard" (gypsum board, gypsum fiber). Also, acoustic design should occupy its modest niche inside. To combat acoustic noise, frequency filtering is used.

CITY AND GREEN SPACES

If you protect your home from noise with trees, then it will be useful to know that the sounds are not absorbed by the foliage. Hitting the trunk, sound waves break, heading down to the soil, which is absorbed. Spruce is considered the best guardian of silence. Even on the busiest highway, you can live in peace if you protect your home next to green trees. And it would be nice to plant chestnuts nearby. One adult chestnut tree cleans up to 10 m high, up to 20 m wide and up to 100 m long from car exhaust gases. At the same time, unlike many other trees, chestnut decomposes toxic substances gases almost without damage to their "health".

The importance of planting greenery in city streets is great - dense plantings of shrubs and forest belts protect against noise, reducing it by 10-12 dB (decibel), reduce the concentration of harmful particles in the air from 100 to 25%, reduce wind speed from 10 to 2 m/s, reduce the concentration of gases from machines up to 15% per unit volume of air, make the air more humid, lower its temperature, i.e., make it more breathable.

Green spaces also absorb sounds, the higher the trees and the denser their planting, the less sound is heard.

Green spaces in combination with lawns, flower beds have a beneficial effect on the human psyche, soothe eyesight, nervous system, are a source of inspiration, and increase people's working capacity. The greatest works of art and literature, the discoveries of scientists, were born under the beneficial influence of nature. Thus were created the greatest musical creations of Beethoven, Tchaikovsky, Strauss and other composers, paintings of the remarkable Russian landscape painters Shishkin, Levitan, works of Russian and Soviet writers. It is no coincidence that the Siberian scientific center was founded among the green plantings of the Priobsky pine forest. Here, in the shadow of the city noise, surrounded by greenery, our Siberian scientists are successfully conducting their research.

The planting of greenery in such cities as Moscow and Kyiv is high; in the latter, for example, there are 200 times more plantings per inhabitant than in Tokyo. In the capital of Japan, for 50 years (1920-1970), about half of "all green areas located within a" radius of ten kilometers from the center were destroyed. In the United States, almost 10,000 hectares of central city parks have been lost over the past five years.

← Noise adversely affects the state of human health, first of all, it worsens hearing, the state of the nervous and cardiovascular systems.

← Noise can be measured using special devices - sound level meters.

← It is necessary to combat the harmful effects of noise by controlling the noise level, as well as through special measures to reduce the noise level.

Over long distances, sound energy propagates only along gentle rays, which do not touch the ocean floor all the way. In this case, the limitation imposed by the medium on the range of sound propagation is its absorption in sea water. The main mechanism of absorption is associated with relaxation processes that accompany the violation of the thermodynamic equilibrium between ions and molecules of salts dissolved in water by an acoustic wave. It should be noted that the main role in the absorption in a wide range of sound frequencies belongs to the magnesium sulphide salt MgSO4, although in percentage terms its content in sea water is quite small - almost 10 times less than, for example, NaCl rock salt, which nevertheless does not play any significant role in the absorption of sound.

Absorption in sea water, generally speaking, is greater the higher the frequency of the sound. At frequencies from 3-5 to at least 100 kHz, where the above mechanism dominates, the absorption is proportional to the frequency to a power of about 3/2. At lower frequencies, a new absorption mechanism is activated (possibly due to the presence of boron salts in water), which becomes especially noticeable in the range of hundreds of hertz; here, the absorption level is anomalously high and decreases much more slowly with decreasing frequency.

To more clearly imagine the quantitative characteristics of absorption in sea water, we note that due to this effect, sound with a frequency of 100 Hz is attenuated by a factor of 10 on a path of 10 thousand km, and with a frequency of 10 kHz - at a distance of only 10 km (Fig. 2). Thus, only low-frequency sound waves can be used for long-range underwater communications, for long-range detection of underwater obstacles, and the like.

Figure 2 - Distances at which sounds of different frequencies attenuate 10 times when propagating in sea water.

In the region of audible sounds for the frequency range of 20-2000 Hz, the range of propagation under water of sounds of medium intensity reaches 15-20 km, and in the region of ultrasound - 3-5 km.

Based on the values ​​of sound attenuation observed in laboratory conditions in small volumes of water, one would expect much greater ranges. However, under natural conditions, in addition to damping due to the properties of water itself (the so-called viscous damping), its scattering and absorption by various inhomogeneities of the medium also affect.

The refraction of sound, or the curvature of the path of the sound beam, is caused by the heterogeneity of the properties of water, mainly along the vertical, due to three main reasons: changes in hydrostatic pressure with depth, changes in salinity, and changes in temperature due to uneven heating of the water mass by the sun's rays. As a result of the combined action of these causes, the speed of sound propagation, which is about 1450 m / s for fresh water and about 1500 m / s for sea water, changes with depth, and the law of change depends on the season, time of day, depth of the reservoir, and a number of other reasons . Sound rays leaving the source at some angle to the horizon are bent, and the direction of the bend depends on the distribution of sound velocities in the medium. In summer, when the upper layers are warmer than the lower ones, the rays bend down and are mostly reflected from the bottom, losing a significant portion of their energy. On the contrary, in winter, when the lower layers of the water maintain their temperature, while the upper layers cool, the rays bend upward and undergo multiple reflections from the surface of the water, during which much less energy is lost. Therefore, in winter, the sound propagation distance is greater than in summer. Due to refraction, so-called. dead zones, i.e. areas located close to the source in which there is no audibility.

The presence of refraction, however, can lead to an increase in the range of sound propagation - the phenomenon of ultra-long propagation of sounds under water. At some depth below the surface of the water there is a layer in which sound propagates at the lowest speed; above this depth, the speed of sound increases due to an increase in temperature, and below this, due to an increase in hydrostatic pressure with depth. This layer is a kind of underwater sound channel. A beam deviated from the axis of the channel up or down, due to refraction, always tends to get back into it. If we place the sound source and receiver in this layer, then even sounds of medium intensity (for example, explosions of small charges of 1-2 kg) can be recorded at distances of hundreds and thousands of kilometers. A significant increase in the sound propagation range in the presence of an underwater sound channel can be observed when the sound source and receiver are located not necessarily near the channel axis, but, for example, near the surface. In this case, the rays, refracting downwards, enter the deep layers, where they deviate upwards and come out again to the surface at a distance of several tens of kilometers from the source. Further, the pattern of propagation of rays is repeated and as a result a sequence of so-called. secondary illuminated zones, which are usually traced to distances of several hundred km.

The propagation of high-frequency sounds, in particular ultrasounds, when the wavelengths are very small, is influenced by small inhomogeneities that are usually found in natural reservoirs: microorganisms, gas bubbles, etc. These inhomogeneities act in two ways: they absorb and scatter the energy of sound waves. As a result, with an increase in the frequency of sound vibrations, the range of their propagation is reduced. This effect is especially pronounced in the surface layer of water, where there are the most inhomogeneities. Scattering of sound by inhomogeneities, as well as by irregularities in the water surface and the bottom, causes the phenomenon of underwater reverberation that accompanies the sending of a sound impulse: sound waves, reflecting from a combination of inhomogeneities and merging, give a delay of the sound impulse, which continues after its end, similar to reverberation observed in enclosed spaces. Underwater reverberation is a rather significant interference for a number of practical applications of hydroacoustics, in particular for sonar.

The limits of the propagation range of underwater sounds are also limited by the so-called. own noises of the sea, which have a twofold origin. Part of the noise arises from the impact of waves on the surface of the water, from the surf, from the noise of rolling pebbles, etc. The other part is related to the marine fauna; this includes sounds produced by fish and other marine animals.

Sound is understood as elastic waves lying within the limits of audibility of the human ear, in the range of oscillations from 16 Hz up to 20 kHz. Oscillations with a frequency below 16 Hz called infrasound, over 20 kHz-ultrasound.

Water is denser and less compressible than air. In this regard, the speed of sound in water is four and a half times greater than in air, and is 1440 m/sec. Sound vibration frequency (nude) is related to the wavelength (lambda) by the relation: c= lambda-nu. Sound propagates in water without dispersion. The speed of sound in water varies depending on two parameters: density and temperature. A change in temperature by 1° entails a corresponding change in the speed of sound by 3.58 m per second. If we follow the speed of sound propagation from the surface to the bottom, it turns out that at first, due to a decrease in temperature, it quickly decreases, reaching a minimum at a certain depth, and then, with depth, it begins to increase rapidly due to an increase in water pressure, which, as is known, increases by approximately 1 atm for every 10 m depths.

Starting from a depth of approximately 1200 m, where the temperature of the water remains practically constant, the change in the speed of sound is due to the change in pressure. “At a depth of approximately 1200 m (for the Atlantic), there is a minimum value for the speed of sound; on the great depths By increasing the pressure, the speed of sound increases again. Since sound rays are always bent towards the areas of the medium where their speed is the lowest, they are concentrated in the layer with the minimum speed of sound” (Krasilnikov, 1954). This layer, discovered by Soviet physicists L.D. Rozenberg and L.M. Brekhovskikh, is called the "underwater sound channel". Sound entering the sound channel can propagate over long distances without attenuation. This feature must be kept in mind when considering the acoustic signaling of deep-sea fish.

Sound absorption in water is 1000 times less than in air. Sound source in the air with a power of 100 kW in the water can be heard at a distance of up to 15 km; sound source in water 1 kW heard at a distance of 30-40 km. Sounds of different frequencies are absorbed differently: high-frequency sounds are most strongly absorbed and low-frequency sounds are the least absorbed. The low absorption of sound in water made it possible to use it for sonar and signaling. The water spaces are filled with a lot of various sounds. The sounds of water bodies of the World Ocean, as the American hydroacousticist Wenz (1962) showed, arise in connection with the following factors: tides, currents, wind, earthquakes and tsunamis, industrial human activity and biological life. The nature of the noise created by various factors differs both in the set of sound frequencies and in their intensity. On fig. Figure 2 shows the dependence of the spectrum and pressure level of the sounds of the World Ocean on the factors that cause them.

In different parts of the World Ocean, the composition of noise is determined by different components. In this case, the bottom and shores have a great influence on the composition of sounds.

Thus, the composition and intensity of noise in different parts of the World Ocean are extremely diverse. There are empirical formulas that show the dependence of the intensity of sea noise on the intensity of the factors that cause them. However, for practical purposes, ocean noise is usually measured empirically.

It should be noted that among the sounds of the World Ocean, industrial sounds created by man are the most intense: the noise of ships, trawls, etc. According to Shane (1964), they are 10-100 times more intense than other sounds of the World Ocean. However, as can be seen from Fig. 2, their spectral composition is somewhat different from the spectral composition of sounds caused by other factors.

When propagating in water, sound waves can be reflected, refracted, absorbed, diffracted, and interfered.

Encountering an obstacle on its way, sound waves can be reflected from it in the case when their wavelength (lambda) less than the size of the obstacle, or go around (diffract) it in the case when their wavelength is greater than the obstacle. In this case, one can hear what is happening behind the obstacle without seeing the source directly. Falling on an obstacle, sound waves in one case can be reflected, in another case they can penetrate into it (be absorbed by it). The value of the energy of the reflected wave depends on how strongly the so-called acoustic impedances of the media “p1c1” and “p2c2” differ from each other, on the interface of which sound waves fall. Under the acoustic resistance of the medium is meant the product of the density of the given medium p and the speed of sound propagation With in her. The greater the difference in the acoustic impedance of the media, the greater part of the energy will be reflected from the separation of the two media, and vice versa. In the case of, for example, sound falling from the air, rs which 41, into the water, rs which is 150,000, it is reflected according to the formula:

In connection with the above, sound penetrates much better into a solid body from water than from air. From air to water, sound penetrates well through bushes or reeds protruding above the water surface.

In connection with the reflection of sound from obstacles and its wave nature, the addition or subtraction of the amplitudes of sound pressures of the same frequencies that have come to given point space. An important consequence such addition (interference) is the formation of standing waves upon reflection. If, for example, a tuning fork is brought into oscillation, bringing it closer and further away from the wall, one can hear the increase and decrease in the sound volume due to the appearance of antinodes and nodes in the sound field. Usually, standing waves are formed in closed containers: in aquariums, pools, etc., with a source sounding for a relatively long time.

In the real conditions of the sea or other natural reservoir, during the propagation of sound, numerous complex phenomena are observed that arise in connection with the heterogeneity of the aquatic environment. A huge influence on the propagation of sound in natural reservoirs is exerted by the bottom and interfaces (water - air), temperature and salt heterogeneity, hydrostatic pressure, air bubbles and planktonic organisms. The water-air interface and the bottom, as well as the heterogeneity of the water, lead to the phenomena of refraction (curvature of sound rays), or reverberation (multiple reflection of sound rays).

Water bubbles, plankton and other suspended matter contribute to sound absorption in the water. Quantification of these numerous factors has not yet been developed. It is necessary to take them into account when setting up acoustic experiments.

Let us now consider the phenomena that occur in water when sound is emitted in it.

Imagine a sound source as a pulsating sphere in infinite space. The acoustic energy emitted by such a source is attenuated inversely with the square of the distance from its center.

The energy of the resulting sound waves can be characterized by three parameters: speed, pressure and displacement of oscillating water particles. The last two parameters are of particular interest when considering the auditory abilities of fish, so we will dwell on them in more detail.

According to Harris and Berglijk (Harris a. Berglijk, 1962), pressure wave propagation and displacement effects are represented differently in the near (at a distance of less than one wavelength of sound) and far (at a distance of more than one wavelength of sound) acoustic field.

In the far acoustic field, the pressure attenuates inversely with the distance from the sound source. In this case, in the far acoustic field, the displacement amplitudes are directly proportional to the pressure amplitudes and are interconnected by the formula:

where R - acoustic pressure in dynes/cm 2 ;

d- particle displacement value in cm.

In the near acoustic field, the dependence between the pressure and displacement amplitudes is different:

where R-acoustic pressure in dynes/cm 2 ;

d - displacement of water particles in cm;

f - oscillation frequency in hz;

rs- acoustic resistance of water equal to 150,000 g/cm2 sec 2 ;

lambda is the wavelength of sound in m; r - distance from the center of the pulsating sphere;

i= SQR i

It can be seen from the formula that the displacement amplitude in the near acoustic field depends on the wavelength, sound, and distance from the sound source.

At distances smaller than the wavelength of the sound in question, the displacement amplitude decreases inversely with the square of the distance:

where BUT is the radius of the pulsating sphere;

D- increase in the radius of the sphere due to pulsation; r is the distance from the center of the sphere.

Fish, as will be shown below, have two different types of receivers. Some of them perceive pressure, while others perceive the displacement of water particles. The above equations are therefore great importance for the correct assessment of fish responses to underwater sound sources.

In connection with the emission of sound, we note two more phenomena associated with emitters: the phenomenon of resonance and directivity of emitters.

The emission of sound by the body occurs in connection with its vibrations. Each body has its own oscillation frequency, determined by the size of the body and its elastic properties. If such a body is brought into oscillation, the frequency of which coincides with its own frequency, the phenomenon of a significant increase in the amplitude of the oscillation occurs - resonance. The use of the concept of resonance allows us to characterize some acoustic properties emitters and receivers of fish. Sound radiation into water can be directional or non-directional. In the first case, sound energy propagates predominantly in a certain direction. A graph expressing the spatial distribution of the sound energy of a given sound source is called its directivity diagram. The directivity of the radiation is observed in the case when the diameter of the emitter is much larger than the wavelength of the emitted sound.

In the case of omnidirectional radiation, sound energy diverges uniformly in all directions. This phenomenon occurs when the wavelength of the emitted sound exceeds the diameter of the emitter lambda>2A. The second case is most typical for low-frequency underwater radiators. Typically, the wavelengths of low-frequency sounds are much larger than the dimensions of the underwater emitters used. The same phenomenon is typical for fish emitters. In these cases, the radiation patterns of the emitters are absent. In this chapter, only some of the general physical properties of sound in the aquatic environment have been noted in connection with the bioacoustics of fish. Some more specific questions of acoustics will be considered in the relevant sections of the book.

In conclusion, let us consider the sound measurement systems used by various authors. Sound can be expressed by its intensity, pressure, or level of pressure.

Sound intensity in absolute units is measured either by a number erg / sec-cm 2, or W / cm 2. At the same time 1 erg/sec=10 -7 Tue.

Sound pressure is measured in bars.

There is a relationship between the intensity and pressure of sound:

which can be used to convert these values ​​from one to another.

No less often, especially when considering the hearing of fish, due to the huge range of threshold values, sound pressure is expressed in relative logarithmic decibel units, db. If the sound pressure of one sound R, and the other R o, then they consider that the first sound is louder than the second by kdb and calculate it according to the formula:

In this case, most researchers take the threshold value of human hearing equal to 0.0002 as the zero reading of the sound pressure P o bar for frequency 1000 Hz.

The advantage of such a system is the possibility of a direct comparison of the hearing of humans and fish, the disadvantage is the difficulty of comparing the results obtained by the sound and hearing of fish.

The actual values ​​of sound pressure created by fish are four to six orders of magnitude higher than the accepted zero level (0.0002 bar), and the threshold levels of hearing of various fish lie both above and below the conditional zero count.

Therefore, for the convenience of comparing the sounds and hearing of fish, American authors (Tavolga and Wodinsky, 1963, etc.) use a different frame of reference.

The sound pressure of 1 bar, which is 74 db higher than previously accepted.

Below is an approximate ratio of both systems.

The actual values ​​in the American reference system are marked with an asterisk in the text.

Hydroacoustics (from Greek. hydro- water, acusticococcus- auditory) - the science of phenomena occurring in the aquatic environment and associated with the propagation, emission and reception of acoustic waves. It includes the development and creation of hydroacoustic devices intended for use in the aquatic environment.

The history of development

Hydroacoustics- a science that is rapidly developing at the present time, and undoubtedly has a great future. Its appearance was preceded by a long path of development of theoretical and applied acoustics. We find the first information about the manifestation of human interest in the propagation of sound in water in the notes of the famous Renaissance scientist Leonardo da Vinci:

The first measurements of distance by means of sound were made by the Russian researcher Academician Ya. D. Zakharov. On June 30, 1804, he flew in a balloon for scientific purposes, and in this flight he used the reflection of sound from the earth's surface to determine the flight altitude. While in the basket of the ball, he shouted loudly into the downward horn. After 10 seconds, a distinctly audible echo came. From this, Zakharov concluded that the height of the ball above the ground was approximately 5 x 334 = 1670 m. This method formed the basis of radio and sonar.

Along with the development of theoretical issues in Russia, practical studies were carried out on the phenomena of the propagation of sounds in the sea. Admiral S. O. Makarov in 1881 - 1882 proposed to use a device called a fluctometer to transmit information about the speed of the current under water. This marked the beginning of the development of a new branch of science and technology - hydroacoustic telemetry.

Scheme of the hydrophonic station of the Baltic Plant, model 1907: 1 - water pump; 2 - pipeline; 3 - pressure regulator; 4 - electromagnetic hydraulic shutter (telegraph valve); 5 - telegraph key; 6 - hydraulic membrane emitter; 7 - board of the ship; 8 - tank with water; 9 - sealed microphone

In the 1890s at the Baltic Shipyard, on the initiative of Captain 2nd Rank M.N. Beklemishev, work began on the development of hydroacoustic communication devices. The first tests of a hydroacoustic transmitter for underwater communication were carried out at the end of the 19th century. in the experimental pool in the Galernaya harbor in St. Petersburg. The vibrations emitted by it were well heard for 7 miles on the Nevsky floating lighthouse. As a result of research in 1905. created the first hydroacoustic communication device, in which a special underwater siren controlled by a telegraph key played the role of a transmitter, and a carbon microphone, fixed from the inside on the ship's hull, served as a signal receiver. The signals were recorded by the Morse apparatus and by ear. Later, the siren was replaced with a membrane-type emitter. The efficiency of the device, called a hydrophonic station, has increased significantly. Sea trials of the new station took place in March 1908. on the Black Sea, where the range of reliable signal reception exceeded 10 km.

The first serial stations for sound underwater communication designed by the Baltic Shipyard in 1909-1910. installed on submarines "Carp", "Gudgeon", "Sterlet", « Mackerel" and " Perch» . When installing stations on submarines, in order to reduce interference, the receiver was located in a special fairing towed astern on a cable-cable. The British came to a similar decision only during the First World War. Then this idea was forgotten, and only at the end of the 1950s was it again used in different countries when creating noise-resistant sonar ship stations.

The impetus for the development of hydroacoustics was the First World War. During the war, the Entente countries suffered heavy losses in the merchant and navy due to the actions of German submarines. There was a need to find means to combat them. They were soon found. A submarine in a submerged position can be heard by the noise generated by the propellers and operating mechanisms. A device that detects noisy objects and determines their location was called a noise direction finder. The French physicist P. Langevin in 1915 suggested using a sensitive receiver made of Rochelle salt for the first noise direction finding station.

Fundamentals of hydroacoustics

Features of the propagation of acoustic waves in water

Components of an echo occurrence event.

The beginning of comprehensive and fundamental research on the propagation of acoustic waves in water was laid during the Second World War, which was dictated by the need to solve the practical problems of the navies and, first of all, submarines. Experimental and theoretical work was continued in the postwar years and summarized in a number of monographs. As a result of these works, some features of the propagation of acoustic waves in water were identified and refined: absorption, attenuation, reflection and refraction.

The absorption of acoustic wave energy in sea water is caused by two processes: the internal friction of the medium and the dissociation of salts dissolved in it. The first process converts the energy of an acoustic wave into thermal energy, and the second process, being converted into chemical energy, brings the molecules out of equilibrium, and they decay into ions. This type of absorption increases sharply with an increase in the frequency of the acoustic vibration. The presence of suspended particles, microorganisms and temperature anomalies in the water also leads to the attenuation of the acoustic wave in the water. As a rule, these losses are small, and they are included in the total absorption, however, sometimes, as, for example, in the case of scattering from the wake of a ship, these losses can be up to 90%. The presence of temperature anomalies leads to the fact that the acoustic wave enters the zones of the acoustic shadow, where it can undergo multiple reflections.

The presence of water-air and water-bottom interfaces leads to the reflection of an acoustic wave from them, and if in the first case the acoustic wave is completely reflected, then in the second case the reflection coefficient depends on the bottom material: it poorly reflects the muddy bottom, well - sandy and rocky . At shallow depths, due to the repeated reflection of an acoustic wave between the bottom and the surface, an underwater sound channel arises, in which the acoustic wave can propagate over long distances. Changing the value of the speed of sound at different depths leads to the curvature of the sound "rays" - refraction.

Refraction of sound (curvature of the path of the sound beam)

Sound refraction in water: a - in summer; b - in winter; on the left - change in speed with depth. The speed of sound propagation varies with depth, and the changes depend on the time of year and day, the depth of the reservoir, and a number of other reasons. Sound rays emerging from a source at a certain angle to the horizon are bent, and the direction of the bend depends on the distribution of sound velocities in the medium: in summer, when the upper layers are warmer than the lower ones, the rays bend downward and are mostly reflected from the bottom, while losing a significant portion of their energy ; in winter, when the lower layers of the water maintain their temperature, while the upper layers cool, the rays bend upward and are repeatedly reflected from the surface of the water, with much less energy being lost. Therefore, in winter, the sound propagation distance is greater than in summer. The vertical sound velocity distribution (VSDS) and the velocity gradient have a decisive influence on the propagation of sound in the marine environment. The distribution of the speed of sound in different regions of the World Ocean is different and varies with time. There are several typical cases of VRSZ:

Scattering and absorption of sound by inhomogeneities of the medium.

Propagation of sound in underwater sound. channel: a - change in the speed of sound with depth; b - path of rays in the sound channel. The propagation of high-frequency sounds, when the wavelengths are very small, is influenced by small inhomogeneities, usually found in natural reservoirs: gas bubbles, microorganisms, etc. These inhomogeneities act in two ways: they absorb and scatter the energy of sound waves. As a result, with an increase in the frequency of sound vibrations, the range of their propagation is reduced. This effect is especially noticeable in the surface layer of water, where there are the most inhomogeneities. Scattering of sound by heterogeneities, as well as irregularities in the surface of the water and the bottom, causes the phenomenon of underwater reverberation that accompanies the sending of a sound pulse: sound waves, reflecting from a combination of heterogeneities and merging, give a tightening of the sound pulse, which continues after its end. The limits of the range of propagation of underwater sounds are also limited by the own noises of the sea, which have a dual origin: some of the noises arise from the impacts of waves on the surface of the water, from the sea surf, from the noise of rolling pebbles, etc.; the other part is associated with marine fauna (sounds produced by hydrobionts: fish and other marine animals). Biohydroacoustics deals with this very serious aspect.

Distance of propagation of sound waves

The propagation range of sound waves is complex function radiation frequency, which is uniquely related to the wavelength of the acoustic signal. As is known, high-frequency acoustic signals are rapidly attenuated due to strong absorption by the aquatic environment. Low-frequency signals, on the contrary, are capable of propagating in the aquatic environment over long distances. So an acoustic signal with a frequency of 50 Hz is capable of propagating in the ocean for distances of thousands of kilometers, while a signal with a frequency of 100 kHz, typical for side-scan sonar, has a propagation range of only 1-2 km. Approximate ranges of modern sonars with different frequencies of the acoustic signal (wavelength) are given in the table:

Areas of use.

Hydroacoustics received wide practical use, since an efficient transmission system has not yet been created electromagnetic waves underwater at any considerable distance, and sound is therefore the only possible means of communication underwater. For these purposes, sound frequencies from 300 to 10,000 Hz and ultrasounds from 10,000 Hz and above are used. Electrodynamic and piezoelectric emitters and hydrophones are used as emitters and receivers in the sound region, and piezoelectric and magnetostrictive ones are used in the ultrasonic region.

The most significant applications of hydroacoustics are:

• To solve military problems;
• Maritime navigation;
• Sound underwater communication;
• Fish-searching reconnaissance;
• Oceanological research;
• Areas of activity for the development of the wealth of the bottom of the oceans;
• Use of acoustics in the pool (at home or in a synchronized swimming training center)
• Marine animal training.

Notes

Literature and sources of information

LITERATURE:

• V.V. Shuleikin Physics of the sea. - Moscow: "Nauka", 1968. - 1090 p.
• I.A. Romanian Fundamentals of hydroacoustics. - Moscow: "Shipbuilding", 1979. - 105 p.
• Yu.A. Koryakin Hydroacoustic systems. - St. Petersburg: "Science of St. Petersburg and the sea power of Russia", 2002. - 416 p.