“Everywhere explore all the time,

What is great and beautiful"

M. V. Lomonosov

What is sound?

• What is sound?

• Is every wave sound?

• Can this statement be verified experimentally?

• What should be the frequency range of an oscillating body in order for a person to hear a sound?

• What characteristics of elastic waves, including sound waves, do you know?

• What are the objective physical characteristics of sound waves?

• What characteristics of sound would you classify as subjective characteristics?

• How do you explain the loudness of the sound?

• Can this statement be verified experimentally?

• What determines the pitch of a sound?

• How can sounds of the same frequency and volume differ from each other?

• What medium does sound travel in?

• It is known that elastic waves can be longitudinal and transverse. What are sound waves?

Ear

Ear- a complex vestibular-auditory organ that performs two functions: it perceives sound impulses and is responsible for the position of the body in space and the ability to maintain balance.

The human ear perceives sound waves with a length of approximately 20.625 m to 1.65 cm, which corresponds to 16 - 20,000 Hz (cycles per second).

outer ear

• outer ear

• Middle ear

• inner ear

• I give an answer to every call, but there is no soul, no body.

• You screamed - it screamed, you were silent - it was silent.

• Lives without a body, speaks without a language.

No one sees it, but everyone hears it.

• In a dark forest, behind any pine,

A marvelous wonder of the forest is hiding.

I will shout: “Ay!” - and it will respond.

And I laugh - and it laughs.

Hydroacoustics

Hydroacoustics- a section of acoustics that studies the emission, reception and propagation of sound waves in a real aquatic environment for the purposes of underwater location, communications, etc.

The main feature of underwater sounds is their low attenuation, as a result of which sounds can propagate under water to much greater distances than, for example, in air.

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.

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 vertical distribution of the speed of sound:

• isotherm

• positive refraction

• negative refraction

• heterogeneous distribution

ultrasonic cleaning

• ultrasonic cleaning

• Mixing

• ultrasonic soldering

• Spot ultrasonic welding

• Ultrasonic holography

• Ultrasound tomography

• Electronics

• Biology

• The medicine

• Chemistry

• There are several methods for excitation of ultrasonic waves in the object under study. The most common is the use of the piezoelectric effect and the EMA method.

n

n

Ultrasonic examination does not destroy or damage the test sample, which is its main advantage. It is possible to carry out control of products from various materials, both metals and non-metals. In addition, we can highlight the high speed of research at low cost and danger to humans (compared to X-ray flaw detection) and the high mobility of the ultrasonic flaw detector.

• The use of piezoelectric transducers requires preparation of the surface for introducing ultrasound into the metal, in particular, the creation of a roughness of at least class 5, in the case of welded joints, also the direction of roughness (perpendicular to the seam). The slightest air gap can become an insurmountable obstacle.

It is used in medical technology, namely, in a device for orientation of the blind in space, i.e. to warn of obstacles in their path. Small size, light weight and long battery life

When detecting an obstacle, the electrosonar gives a sound or vibration signal of different duration. The duration of the signal depends on the distance to the obstacle. By pointing the device in different directions, you can get a clear picture of the surrounding obstacles, such as curbs, steps, walls.

• Obstacle detection range - up to 7 meters

• Weight - less than 150 grams

• Size - no more than 7 x 7 x 3.5 cm (LxWxH)

• Battery life - more than 3 hours

• Power supply - from a battery or accumulator "Krona"

It has long been known that ultrasonic radiation can be made narrowly directed. However, only relatively recently has a truly scientific approach to the analysis of phenomena arising from the interaction of ultrasonic radiation with a biological medium begun to emerge. There are many different aspects associated with the use of ultrasound in medicine.

The problem of interpreting the interaction of acoustic radiation with the biological environment is greatly simplified if the latter is considered not as a solid, but as a liquid. The fact that the interaction of ultrasound with tissue can be modeled by its interaction with liquids is important factor, increasing the practical value of medical ultrasound diagnostics.

Reception and measurement of ultrasound

In medical or biological applications, the need to receive and measure ultrasound arises in three broad areas. Ultrasound, by definition, is not perceived directly by the human senses, and therefore it is necessary to use some kind of physical effect or a sequence of such effects so that the effect of ultrasound can manifest itself, and mainly quantitatively. Thus, the choice of a method for a specific problem is made in terms of the convenience of its application, as well as the accuracy of measuring the acoustic field parameter of interest.

Methods of ultrasonic echo-pulse imaging have already found wide and varied applications in medicine.

Echo-pulse methods have now become widely used in many areas of medicine.

The second type of procedures

already habitual,

assessment of fetal development

by the measurement of one or

over its size

such as diameter

and head circumference

chest area

or abdomen.

Finally, it is necessary

note ultrasonic

motion study

fetus. This phenomenon is only

has recently become

detailed

research.

Here, the main interest is the study of the physiology and development of the fetus.

Accuracy is also important here.

and equipment calibration,

necessary

also give special

attention to effects

refraction

ultrasound in the lens and cornea.

Topic: Mechanical oscillations and waves. Sound

Lesson 36 Sound vibrations. Pitch, timbre, sound volume

Yeryutkin Evgeny Sergeevich

The topic of the lesson is devoted to sound sources, sound vibrations. We will also talk about the characteristics of sound - pitch, volume and timbre. Before talking about sound, about sound waves, let's remember that mechanical waves propagate in elastic media. Part of the longitudinal mechanical waves, which is perceived by the human hearing organs, is called sound, sound waves. Sound is mechanical waves that are perceived by human hearing organs, which cause sound sensations. .

Experiments show that the human ear, human hearing organs perceive vibrations with frequencies from 16 Hz to 20,000 Hz. It is this range that we call the sound range. Of course, there are waves whose frequency is less than 16 Hz (infrasound) and more than 20,000 Hz (ultrasound). But this range, these sections are not perceived by the human ear.

Infrasound Sound Ultrasound

|________________|_______________________________|______________________

0 16–20 20000 Hz

Rice. 1. Human ear hearing range

As we said, the areas of infrasound and ultrasound are not perceived by human hearing organs. Although they can be perceived, for example, by some animals, insects.

What ? Sound sources can be any bodies that oscillate with sound frequency (from 16 to 20,000 Hz)

Rice. 2. An oscillating ruler clamped in a vise

could be the source of the sound

Let us turn to experience and see how a sound wave is formed. To do this, we need a metal ruler, which we clamp in a vise. Now, acting on the ruler, we can observe vibrations, but we do not hear any sound. And yet, a mechanical wave is created around the ruler. Note that when the ruler moves to one side, an air seal forms here. On the other side, there is also a seal. Between these seals, an air vacuum is formed. Longitudinal wave - this is a sound wave, consisting of seals and air discharges. The vibration frequency of the ruler in this case is less than the audio frequency, so we do not hear this wave, this sound. Based on the experience that we have just observed, at the end of the 18th century an instrument called a tuning fork was created.

Rice. 3. Propagation of longitudinal sound waves

from a tuning fork

As we have seen, sound appears as a result of vibrations of the body with a sound frequency. Sound waves propagate in all directions. There must be a medium between the human hearing aid and the source of sound waves. This medium can be gaseous, liquid, solid, but it must be particles capable of transmitting vibrations. The process of transmission of sound waves must necessarily occur where there is matter. If there is no substance, we will not hear any sound.

For sound to exist:

1. Sound source

2. Wednesday

3. Hearing aid

4. Frequency 16-20000Hz

5. Intensity

Now let's move on to discussing the characteristics of sound. The first is the pitch. Sound pitch - characteristic, which is determined by the frequency of oscillation. The higher the frequency of the body that produces vibrations, the higher the sound will be. Let's turn again to the ruler, clamped in a vise. As we have already said, we saw the vibrations, but did not hear the sound. If now the length of the ruler is made smaller, then we will hear the sound, but it will be much more difficult to see the vibrations. Look at the line. If we act on it now, we will not hear any sound, but we observe vibrations. If we shorten the ruler, we will hear a sound of a certain pitch. We can make the length of the ruler even shorter, then we will hear the sound of even higher pitch (frequency). We can observe the same thing with tuning forks. If we take a large tuning fork (it is also called a demonstration tuning fork) and hit the legs of such a tuning fork, we can observe the oscillation, but we will not hear the sound. If we take another tuning fork, then, by striking it, we will hear a certain sound. And the next tuning fork, a real tuning fork, which is used to tune musical instruments. It produces a sound corresponding to the note la, or, as they say, 440 Hz.

The next characteristic is the timbre of the sound. Timbre called sound color. How can this characteristic be illustrated? Timbre is the difference between two identical sounds played by different musical instruments. You all know that we have only seven notes. If we hear the same note A, taken on the violin and on the piano, then we will distinguish them. We can immediately tell which instrument created this sound. It is this feature - the color of the sound - that characterizes the timbre. It must be said that the timbre depends on what sound vibrations are reproduced, in addition to the fundamental tone. The fact is that arbitrary sound vibrations are quite complex. They consist of a set of individual vibrations, they say vibration spectrum. It is the reproduction of additional vibrations (overtones) that characterizes the beauty of the sound of a particular voice or instrument. Timbre is one of the main and striking manifestations of sound.

Another feature is volume. The loudness of the sound depends on the amplitude of the vibrations. Let's take a look and make sure that the loudness is related to the amplitude of the vibrations. So, let's take a tuning fork. Let's do the following: if you hit the tuning fork weakly, then the oscillation amplitude will be small and the sound will be quiet. If now the tuning fork is hit harder, then the sound is much louder. This is due to the fact that the amplitude of oscillations will be much larger. The perception of sound is a subjective thing, it depends on what the hearing aid is, what the person's well-being is like.

List of additional literature:

Are you familiar with the sound? // Quantum. - 1992. - No. 8. - C. 40-41. Kikoin A.K. On musical sounds and their sources // Kvant. - 1985. - No. 9. - S. 26-28. Elementary textbook of physics. Ed. G.S. Landsberg. T. 3. - M., 1974.

Sound (sound wave ) –is an elastic wave perceived by the human and animal hearing organ. In other words, sound is the propagation of density (or pressure) fluctuations in an elastic medium, arising from the interaction of particles of the medium with each other.

The atmosphere (air) is one of the elastic media. The propagation of sound in air obeys the general laws of propagation of acoustic waves in ideal gases, and also has features due to the variability of density, pressure, temperature and humidity. The speed of sound is determined by the properties of the medium and is calculated from the formulas for the speed of an elastic wave.

There are artificial and natural sources sound. Artificial emitters include:

Vibrations of solid bodies (strings and decks of musical instruments, loudspeaker diffusers, telephone membranes, piezoelectric plates);

Air vibrations in a limited volume (organ pipes, whistles);

Beat (piano keys, bell);

Electric current (electroacoustic transducers).

Natural sources include:

Explosion, collapse;

Air flow around obstacles (wind blowing the corner of a building, the crest of a sea wave).

There are also artificial and natural receivers sound:

Electroacoustic transducers (microphone in air, hydrophone in water, geophone in the earth's crust) and other devices;

Hearing apparatus of man and animals.

During the propagation of sound waves, phenomena characteristic of waves of any nature are possible:

Reflection from an obstacle

Refraction at the boundary of two media,

interference (addition),

Diffraction (obstacle avoidance),

Dispersion (dependence of the speed of sound in a substance on the frequency of sound);

Absorption (decrease in the energy and intensity of sound in the medium due to the irreversible conversion of sound energy into heat).

Objective sound characteristics

sound frequency

The frequency of the sound audible to a person lies in the range from 16 Hz before 16 - 20 kHz . Elastic waves with frequency below audible range called infrasound (including concussion), s higher frequency – ultrasound , and the highest frequency elastic waves are hypersonic .

The entire frequency range of sound can be divided into three parts (Table 1.).

Noise has a continuous spectrum of frequencies (or wavelengths) in the region of low-frequency sound (Tables 1, 2). continuous spectrum means that the frequency can have any value from the given interval.

Musical , or tonal , sounds have a line frequency spectrum in the region of mid-frequency and partially high-frequency sound. The rest of the high-frequency sound is occupied by a whistle. line spectrum means that musical frequencies have only strictly defined (discrete) values ​​from the specified interval.

In addition, the interval of musical frequencies is divided into octaves. Octave is the frequency interval enclosed between two boundary values, the upper of which is twice the lower(Table 3)

Common octave frequency bands

Examples of frequency intervals for sound produced by the human vocal apparatus and perceived by the human auditory apparatus are shown in Table 4.

Examples of the frequency ranges of some musical instruments are shown in Table 5. They cover not only the audio range, but also the ultrasonic range.

Animals, birds and insects create and perceive sound in other frequency ranges than humans (Table 6).

In music, each sinusoidal sound wave is called simple tone, or tone. The pitch depends on the frequency: the higher the frequency, the higher the tone. Main tone complex musical sound is called the tone corresponding to lowest frequency in its spectrum. Tones corresponding to other frequencies are called overtones. If overtones multiples frequency of the fundamental, then the overtones are called harmonic. The overtone with the lowest frequency is called the first harmonic, with the next - the second, etc.

Musical sounds with the same root note may differ timbre. The timbre depends on the composition of the overtones, their frequencies and amplitudes, the nature of their rise at the beginning of the sound and the decay at the end.

Sound speed

For sound in various environments, general formulas(22) - (25). In this case, it should be taken into account that formula (22) is applicable in the case of dry atmospheric air and, taking into account the numerical values ​​of the Poisson's ratio, molar mass and universal gas constant, can be written as:

However, real atmospheric air always has humidity, which affects the speed of sound. This is because Poisson's ratio  depends on the ratio of the partial pressure of water vapor ( p steam) to atmospheric pressure (p). In moist air, the speed of sound is determined by the formula:

.

From the last equation it can be seen that the speed of sound in moist air is slightly greater than in dry air.

Numerical estimates of the speed of sound, taking into account the influence of temperatures and humidity of atmospheric air, can be carried out using the approximate formula:

These estimates show that when sound propagates along the horizontal direction ( 0 x) with an increase in temperature by 1 0 C the speed of sound increases by 0.6 m/s. Under the influence of water vapor with a partial pressure of not more than 10 Pa the speed of sound increases by less than 0.5 m/s. But in general, at the maximum possible partial pressure of water vapor near the Earth's surface, the speed of sound increases by no more than 1 m/s.

Sound pressure

In the absence of sound, the atmosphere (air) is an undisturbed medium and has a static atmospheric pressure (

).

When sound waves propagate, an additional variable pressure is added to this static pressure, due to condensation and rarefaction of air. In the case of plane waves, we can write:

where p sv, max is the sound pressure amplitude,  - cyclic frequency of sound, k - wave number. Therefore, the atmospheric pressure at a fixed point in this moment time becomes equal to the sum of these pressures:

Sound pressure is a variable pressure equal to the difference between the instantaneous actual atmospheric pressure at a given point during the passage sound wave and static atmospheric pressure in the absence of sound:

Sound pressure during the period of oscillation changes its value and sign.

Sound pressure is almost always much less than atmospheric pressure.

It becomes large and commensurate with atmospheric pressure when shock waves occur during powerful explosions or when a jet aircraft passes.

The sound pressure units are as follows:

- pascal in SI

,

- bar in GHS

,

- millimeter of mercury,

- atmosphere.

In practice, devices measure not the instantaneous value of sound pressure, but the so-called effective (or current )sound pressure . It equals the square root of the average value of the square of the instantaneous sound pressure at a given point in space at a given time

(44)

and therefore also called RMS sound pressure . Substituting expression (39) into formula (40), we obtain:

. (45)

Sound impedance

Sound (acoustic) impedance called the amplitude ratiosound pressure and vibrational velocity of particles of the medium:

. (46)

The physical meaning of sound impedance: it is numerically equal to the sound pressure, causing oscillations of the particles of the medium with a unit speed:

The unit of measurement of sound impedance in SI is pascal second per meter:

.

In the case of a plane wave particle oscillation speed is equal to

.

Then formula (46) takes the form:

. (46*)

There is also another definition of sound resistance, as the product of the density of the medium and the speed of sound in this medium:

. (47)

Then it physical meaning is that it is numerically equal to the density of the medium in which the elastic wave propagates with unit velocity:

.

In addition to acoustic resistance in acoustics, the concept is used mechanical resistance (R m). Mechanical resistance is the ratio of the amplitudes of the periodic force and the oscillatory velocity of the particles of the medium:

, (48)

where S is the surface area of ​​the sound emitter. Mechanical resistance is measured in newton seconds per meter:

.

Energy and power of sound

A sound wave is characterized by the same energy quantities as an elastic wave.

Each volume of air in which sound waves propagate has an energy that is made up of the kinetic energy of oscillating particles and the potential energy of elastic deformation of the medium (see formula (29)).

Sound intensity is calledsound power . She is equal

. (49)

That's why the physical meaning of sound power is similar to the meaning of the energy flux density: numerically equal to the average value of the energy that is transferred by a wave per unit of time through the transverse surface of a unit area.

The unit of sound intensity is watts per square meter:

.

The sound power is proportional to the square of the effective sound pressure and inversely proportional to the sound (acoustic) pressure:

, (50)

or, taking into account expressions (45),

, (51)

where R ak – acoustic impedance.

Sound can also be characterized by sound power. Sound power is the total amount of sound energy radiated by a source for a certain time through a closed surface surrounding the sound source:

, (52)

or, taking into account formula (49),

. (52*)

Sound power, like any other, is measured in watts:

.

Periodic in time and space, the process of propagation of deformations in an elastic medium is called a wave process or a wave. When a wave propagates, the particles of the medium perform forced oscillations.

The main property of all waves is the transfer of energy without the transfer of matter. Energy transfer is a dynamic sign of wave motion. And the kinematic sign of wave motion is the propagation of the oscillation phase. Waves are classified into elastic, waves on the surface of a liquid and electromagnetic. Waves are longitudinal and transverse. An elastic wave is called longitudinal if the displacement of each particle of the medium occurs along the same line as the direction of wave propagation. This is how sound travels. Longitudinal waves arise from compression and expansion deformations of an elastic medium and can propagate in a solid, liquid and gaseous medium. When driving a nail with a hammer, a longitudinal impulse (wave) of high density sweeps along the nail, driving its end deeper into the wood. The direction along which the vibration propagates is called the beam.

An elastic wave is called transverse if the particles of the medium oscillate in planes perpendicular to the direction of wave propagation. Transverse waves arise from shear deformations only in solids. Such an effect is observed, for example, when an impulse is sent along the rope with a sharp lateral movement. Transverse also electromagnetic radiation. Water waves are usually a mixture of longitudinal and transverse waves. Each individual drop, excited by a passing wave, moves along an ellipse, moving up and down, forward and backward.

According to the nature of propagation, linear, surface and spatial, or one-, two- and three-dimensional waves are distinguished. The boundary separating oscillating particles from particles that have not yet begun to oscillate is called the wave front. All particles of the wavefront oscillate with the same phase. The wavefront is perpendicular to the beam. A ray is the direction in which a wave propagates. An elastic wave is called harmonic or sinusoidal if the oscillations of its constituent particles are harmonic.

Regardless of the longitudinal or transverse nature of the wave motion, the displacement of each individual particle in an elastic medium can be expressed as a function of time. On fig. 15.1 shows the relationship between the offset (x, t). particles of the medium participating in the wave process, and the distance x of these particles from the source of oscillations for a fixed time t, s. Thus, the wave graph expresses the dependence of the displacement of all particles of the medium on the distance to the source of oscillations at a given time.

Recall that the oscillation plot gives the dependence of the displacement of a given particle on time. For particle B (Fig. 15.1), which lags in its oscillation relative to particle O for the propagation time of oscillations from O to B, equal to = x / v, the oscillation equation has the form

Any of the equations allows you to determine the displacement of any point of the wave at any time and is called the equation of the wave. Here: A - wave amplitude, m; = 2 /T - cyclic (circular) wave frequency, rad/s; T - oscillation period, s; t - x/ + = t - kx+ - phase of a plane wave, equal to the phase of oscillations at an arbitrary point with coordinate x, rad; - the initial phase of oscillations at the points of the coordinate plane x = 0, rad; X/ = T = - wavelength - the distance between the nearest particles oscillating in the same phase, m; k \u003d 2 / \u003d 2 / ( T) ​​\u003d / - wave number (indicates how many wavelengths fit on a segment of length 2, rad / m).

The speed of sound depends on the elastic properties of the gas (and the medium as a whole) and on the temperature.

Longitudinal mechanical waves propagating in an elastic medium in the form of alternating compressions and expansions with a frequency of 20 to 20 * 10 3 Hz are called sound or acoustic. They are perceived by the organs of human hearing. Waves with a higher frequency are called ultrasound, with a lower frequency - infrasound: infra- and ultrasound are not heard by the human ear.

Sounds are classified into musical tone, consonance (musical sound), noise and explosion. The ear responds to mechanical vibrations with a sense of tone. Each tone (do, re, mi, fa, salt, la, si) has a certain height. Pitch is the quality of the sensation of sound, and mainly depends on the length and frequency of the sound wave (Fig. 15.2). The higher the frequency, the higher the sound, and vice versa.

Consonance is the result of the simultaneous sounding of several musical tones. The resulting oscillation cannot be sinusoidal. To the ear, musical sounds (consonance) differ in pitch and loudness. The tone of the lowest frequency in consonance is called the main tone. We perceive the frequency of the fundamental tone of a complex sound as the pitch of the sound. The rest of the tones, called overtones, give the sound a specific shade, "color". They are also called the timbre of sound. It is the timbre that distinguishes the tone “la”, published by one musical instrument, from the tone "la" of another musical instrument.

Noise - irregular oscillations, a mixture of numerous oscillations with approximately the same amplitude and with a wide variety of frequencies. An explosion from an acoustic “point of view” is a short-term and strong sound effect.

The energy characteristic of sound waves is the intensity (strength) of sound, equal to the ratio of the amount of energy W passing through the surface every second, perpendicular to the direction of wave propagation, to the area s of this surface J = W / (st), W / m 2. Because the total energy harmonic vibration of the body is W = 0.5m 2 A 2 , J, it is obvious that the sound power is proportional to the square of the amplitude. The human ear picks up and recognizes a sound wave with an intensity of 2*10 -12 W/m 2 , but at the same time withstands a sonic shock of 110 W/m 2 . Perhaps no other physical device has such a range of perception of the strength of sound. The minimum value of the sound intensity is called the hearing threshold. Thus, in order for a sound wave to create an auditory sensation, it is necessary that it has a frequency of the sound range and an intensity corresponding to the frequency that is not less than the minimum value (Fig. 15.3). The maximum value of the sound intensity is called the pain threshold.

It is approximately 10 14 times higher than the threshold of 10 4 Hz audibility. The values ​​of both thresholds are different for different frequencies and are presented in Figs. 15.3. The area covered by the curves is called the hearing area.

We evaluate the power of sound subjectively as the loudness of the sound. The loudness of sound is determined by the amplitude of oscillations in the sound wave (Fig. 15.4). Loudness takes into account the different sensitivity of human hearing to sound waves of different frequencies, even if they have the same power. The minimum volume level perceived by a person is 1 dB. A whisper corresponds to a volume level of 10 dB, speech - 60, the sound of an aircraft engine - 120 dB.

Let in an elastic medium at some distance from the source of sound waves there is a device that perceives vibrations of the medium, called a receiver. If the sound source and receiver move relative to each other in the direction of their approach or removal, then the receiver will perceive the frequency v pr, different from the frequency of the source v ist.

This phenomenon is called the Doppler effect. (15.1)

where a is the speed of propagation of a sound wave in the medium under consideration. Formula (15.1) is a quantitative description of the Doppler effect.

Wave interference is the superposition in space of two or more coherent waves, as a result of which, depending on the ratio between the phases of these waves, the resulting wave is strengthened or weakened. Waves are called coherent if their phase difference is constant in time. For coherent waves, the frequency must be the same. These are monochromatic waves.

Standing waves are a special case of interference. They are formed when two reversible, running towards each other, harmonic waves with the same frequencies and amplitudes are superimposed (Fig. 15.11). Standing waves propagate at the same speed but in opposite directions. standing wave equation m.

Diffraction is the phenomenon of non-rectilinear propagation of waves through holes commensurate with the wavelength. The energy of the incident wave is unevenly distributed in separate directions. It is the smaller, the larger the diffraction angle.

living in the world various waves, a person constantly experiences the influence of sound. Sound vibrations are not just a phenomenon that accompanies it everywhere, but also a source of pleasure, as well as a powerful information tool. Performing a wide variety of functions, sound is able to warn of danger, give pleasure, and become a means of communication. We listen with delight to birds singing, pleasant music, enter into conversation with other people.

Sound vibrations are important not only for humans, but also for animals that use sound to survive.

By its nature, sound is a mechanical elastic wave that can propagate in solids, liquids, gases. Sound sources cause sound vibrations by vibration (mechanical vibration), which is often invisible to the eye. Sound sources include physical bodies, carrying out oscillations per second (trembling or vibration) with a frequency of 16-20000 times. Sound vibrations can cause solid bodies (string, earth's crust), gaseous (air jet), liquid

Among the characteristics of sound, it is customary to distinguish two parameters: timbre - the frequency of sound vibrations; loudness - the amplitude of the sound wave. The unit of sound volume is considered to be 1 Bel (it was named after one of the inventors of the telephone - Alexander Graham Bell). Almost one Bel is not used, it is more convenient to use decibels equal to one tenth of Bel. To have a visual representation of the volume dimension, it should be taken into account that 10 dB is a whisper; 20-30 dB correspond to normal residential noise; 50 dB is the average volume of a conversation; a truck engine is running with a noise level of 80 dB; physiological in humans occurs at 130 dB; 180 dB can lead to rupture of the eardrum.

Considering sound vibrations of different frequencies, birdsong is referred to as high-frequency waves, and the sound of a truck engine can be attributed to low sounds. Possessing the whole range of properties and characteristics that distinguish waves of different nature, sound waves have found wide application in various fields. The property of a liquid to conduct sound is actively used in the exploration of the deep sea. The well-known echo, for example, is used to determine distances in echolocation. Bats are a striking example of natural echolocators.

A special type of sound vibrations is ultrasound, a very effective tool in the hands of physicians and other researchers. These oscillations include waves with frequencies over 20,000 Hz. This type of oscillation has a number of unique properties. Passing through water, ultrasound causes it to boil (cavitate) with the appearance. Using ultrasound, you can tear off elements from the surface of the metal, crush solid bodies. Ultrasonication allows the mixing of liquids that would normally not mix, such as oil-based emulsions. Ultrasound allows the saponification of fats. This principle lies in the design of washing machines. The property of ultrasound to produce a crushing effect has found application in ultrasonic soldering irons.

A special type of vibration up to 16 Hz is called infrasound. It is known that fluctuations of this frequency can have a painful effect on the human body. At frequencies of 4-8 Hz, vibration of the internal organs is felt, a frequency of 12 Hz provokes an attack

Infrasound sources can be machines and mechanisms with large surfaces that perform mechanical vibrations (mechanical origin) or flows of liquids and gases with turbulent properties (hydrodynamic or aerodynamic origin).