Features of sound propagation in different materials. Sound propagation. Sound sounding of the depths

We know that sound travels through the air. That is why we can hear. No sound can exist in a vacuum. But if sound is transmitted through the air, due to the interaction of its particles, will it not be transmitted by other substances? Will be.

Propagation and speed of sound in different media

Sound is not only transmitted by air. Probably everyone knows that if you put your ear to the wall, you can hear conversations in the next room. AT this case sound is transmitted through the wall. Sounds propagate in water and in other media. Moreover, the propagation of sound in different environments occurs in different ways. The speed of sound varies depending on the substance.

Curiously, the speed of sound propagation in water is almost four times higher than in air. That is, fish hear "faster" than we do. In metals and glass, sound travels even faster. This is because sound is a vibration of the medium, and sound waves are transmitted faster in environments with better conductivity.

The density and conductivity of water is greater than that of air, but less than that of metal. Accordingly, the sound is transmitted differently. When moving from one medium to another, the speed of sound changes.

The length of a sound wave also changes as it passes from one medium to another. Only its frequency remains the same. But that's why we can distinguish who specifically speaks even through the walls.

Since sound is vibrations, all the laws and formulas for vibrations and waves are well applicable to sound vibrations. When calculating the speed of sound in air, one should also take into account the fact that this speed depends on the air temperature. As the temperature increases, the speed of sound propagation increases. At normal conditions the speed of sound in air is 340,344 m/s.

sound waves

Sound waves, as is known from physics, propagate in elastic media. That is why sounds are well transmitted by the earth. Putting your ear to the ground, you can hear from afar the sound of footsteps, the clatter of hooves, and so on.

In childhood, everyone must have had fun by putting their ear to the rails. The sound of train wheels is transmitted along the rails for several kilometers. For creating reverse effect sound absorption, use soft and porous materials.

For example, in order to protect a room from extraneous sounds, or, conversely, in order to prevent sounds from escaping from the room to the outside, the room is treated and soundproofed. The walls, floor and ceiling are upholstered with special materials based on foamed polymers. In such an upholstery, all sounds subside very quickly.

1. The source of sound can be any body that vibrates.

2. How does sound travel?

2. Sound propagates in the form of longitudinal waves in the air.

3. Can sound propagate in a space devoid of matter?

3. In a space devoid of matter, sound will not propagate. Since the sound wave cannot propagate.

4. Does any wave that reaches the human ear cause a sensation of sound?

4. No, it all depends on the frequency of oscillations in the wave.

5. Why are not perceived as the sounds of the wave caused by the beating of the heart? Fluctuations in lung volume during breathing?

5. Waves caused by the beating of the heart and lung volume during breathing are not perceived as sounds, since their frequency is very low (less than 20 Hz). For example, in the case of heartbeats, if we take into account that the average human pulse is 100 beats per minute, we get that the heartbeat frequency is v ≈ 1.67 Hz, which is much lower than 20 Hz. The same happens in the case of fluctuations in lung volume during breathing.

The singing of birds, the sound of rain and wind, thunder, music - everything that we hear, we consider sound.

From a scientific point of view, sound is a physical phenomenon, which is mechanical vibrations propagating in a solid, liquid and gaseous medium. They evoke auditory sensations.

How does a sound wave come about?

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All sounds propagate in the form of elastic waves. And waves arise under the action of elastic forces that appear when the body is deformed. These forces tend to return the body to its original state. For example, a stretched string in a stationary state does not sound. But one has only to take it aside, as under the influence of the force of elasticity, it will tend to take its original position. Vibrating, it becomes a source of sound.

Any oscillating body can be a sound source, for example, a thin steel plate fixed on one side, air in a musical wind instrument, human vocal cords, a bell, etc.

What happens in the air when a vibration occurs?

Like any gas, air has elasticity. It resists compression and immediately begins to expand when the pressure is reduced. It evenly transfers any pressure on it in different directions.

If you compress the air sharply with the help of a piston, then the pressure will immediately increase in this place. It will immediately be transferred to neighboring layers of air. They will shrink, and the pressure in them will increase, and in the previous layer it will decrease. So along the chain, alternating zones of increased and reduced pressure are passed on.

Deviating to the sides alternately, the sounding string compresses the air, first in one direction, and then in the opposite direction. In the direction in which the string deviated, the pressure becomes higher than atmospheric pressure by some amount. FROM opposite side the pressure decreases by the same amount, as the air there is rarefied. Compression and rarefaction will alternate and spread in different directions, causing air vibrations. These vibrations are called sound wave . And the difference between atmospheric pressure and pressure in a layer of compression or rarefaction of air is called acoustic, or sound pressure.

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A sound wave propagates not only in air, but also in liquid and solid media. For example, water is an excellent conductor of sound. We hear the impact of a rock under the water. The noise of the propellers of a surface ship picks up the acoustics of the submarine. If we put a wrist watch on one end of a wooden board, then, putting our ear to the opposite end of the board, we will hear it ticking.

Will sounds be different in a vacuum? The English physicist, chemist and theologian Robert Boyle, who lived in the 17th century, placed a clock in a glass vessel, from which the air was pumped out. He did not hear the ticking of the clock. This meant that sound waves do not propagate in airless space.

Sound Wave Characteristics

The form of sound vibrations depends on the sound source. Most simple form have uniform or harmonic vibrations. They can be represented as a sinusoid. Such oscillations are characterized by amplitude, wavelength and frequency of propagation of oscillations.

Amplitude

Amplitude in general case called the maximum deviation of the body from the equilibrium position.

Since a sound wave consists of alternating regions of high and low pressure, then it is often considered as a process of propagation of pressure fluctuations. Therefore they talk about air pressure amplitude in a wave.

The loudness of the sound depends on the amplitude. The larger it is, the louder the sound.

Each sound of human speech has a form of vibrations, peculiar only to him. Thus, the form of vibrations of the sound "a" differs from the form of vibrations of the sound "b".

Wave frequency and period

The number of vibrations per second is called wave frequency .

f = 1/T

where T is the period of oscillation. This is the amount of time it takes for one complete oscillation to occur.

The longer the period, the lower the frequency, and vice versa.

The unit of frequency in the international measurement system SI is hertz (Hz). 1 Hz is one oscillation per second.

1 Hz = 1 s -1 .

For example, a frequency of 10 Hz means 10 oscillations in 1 second.

1000 Hz = 1 kHz

The pitch depends on the vibration frequency. The higher the frequency, the higher the tone of the sound.

The human ear is not capable of perceiving all sound waves, but only those that have a frequency of 16 to 20,000 Hz. It is these waves that are considered sound waves. Waves whose frequency is below 16 Hz are called infrasonic, and those above 20,000 Hz are called ultrasonic.

A person does not perceive either infrasonic or ultrasonic waves. But animals and birds can hear ultrasound. For example, an ordinary butterfly distinguishes sounds that have a frequency of 8,000 to 160,000 Hz. The range perceived by dolphins is even wider, it ranges from 40 to 200 thousand Hz.

Wavelength

Wavelength call the distance between two nearest points of a harmonic wave that are in the same phase, for example, between two crests. Designated as ƛ .

In a time equal to one period, a wave travels a distance equal to its length.

Wave propagation speed

v = ƛ /T

Because T = 1/f

then v = ƛ f

Sound speed

Attempts to determine the speed of sound with the help of experiments were made in the first half of the 17th century. The English philosopher Francis Bacon, in his work The New Organon, proposed his own way of solving this problem, based on the difference in the speeds of light and sound.

It is known that the speed of light is much higher than the speed of sound. Therefore, during a thunderstorm, we first see a flash of lightning, and only then we hear thunder. Knowing the distance between the source of light and sound and the observer, as well as the time between the flash of light and sound, the speed of sound can be calculated.

Bacon's idea was used by the French scientist Marin Marsenne. An observer at some distance from the man firing the musket recorded the time elapsed from the flash of light to the sound of the shot. Then the distance was divided by the time to get the speed of sound. According to the results of the experiment, the speed was equal to 448 m/s. It was a rough estimate.

At the beginning of the 19th century, a group of scientists from the Paris Academy of Sciences repeated this experience. According to their calculations, the speed of light was 350-390 m/s. But this figure was not accurate either.

Theoretically, Newton tried to calculate the speed of light. He based his calculations on the Boyle-Mariotte law, which described the behavior of gas in isothermal process (at constant temperature). And this happens when the volume of the gas changes very slowly, managing to give the environment the heat that occurs in it.

Newton also assumed that between the areas of compression and rarefaction, the temperature levels off quickly. But these conditions do not exist in a sound wave. Air does not conduct heat well, and the distance between the layers of compression and rarefaction is large. The heat from the compression layer does not have time to pass into the rarefaction layer. And there is a temperature difference between them. Therefore, Newton's calculations turned out to be incorrect. They gave a figure of 280 m / s.

The French scientist Laplace was able to explain that Newton's mistake was that a sound wave propagates in air in adiabatic conditions at varying temperatures. According to Laplace's calculations, the speed of sound in air at a temperature of 0 o C is 331.5 m/s. Moreover, it increases with increasing temperature. And when the temperature rises to 20 ° C, it will already be equal to 344 m / s.

Sound waves travel at different speeds in different media.

For gases and liquids, the speed of sound is calculated by the formula:

where With -sound speed,

β - adiabatic compressibility of the medium,

ρ - density.

As can be seen from the formula, the velocity depends on the density and compressibility of the medium. In air, it is less than in liquid. For example, in water at a temperature of 20 ° C, it is equal to 1484 m / s. Moreover, the higher the salinity of the water, the faster the sound propagates in it.

For the first time, the speed of sound in water was measured in 1827. This experiment was somewhat reminiscent of the measurement of the speed of light by Maren Marsenne. A bell was lowered into the water from the side of one boat. At a distance of more than 13 km from the first boat was the second. On the first boat, the bell was struck and gunpowder was set on fire at the same time. On the second boat, the time of the flash was recorded, and then the time of arrival of the sound from the bell. By dividing the distance by the time, we get the speed of the sound wave in water.

Sound has the highest speed in a solid medium. For example, in steel it reaches more than 5000 m/s.

We perceive sounds at a distance from their sources. Sound usually travels to us through the air. Air is an elastic medium that transmits sound.

If the sound transmission medium is removed between the source and the receiver, then the sound will not propagate and, therefore, the receiver will not perceive it. Let's demonstrate this experimentally.

Let's place an alarm clock under the bell of the air pump (Fig. 80). As long as there is air in the bell, the sound of the bell is heard clearly. When air is pumped out from under the bell, the sound gradually weakens and finally becomes inaudible. Without a transmission medium, the vibrations of the bell's cymbal cannot propagate, and the sound does not reach our ear. Let the air under the bell and hear the ringing again.

Rice. 80. An experiment proving that in a space where there is no material medium, sound does not propagate

Elastic substances, such as metals, wood, liquids, gases, conduct sounds well.

Let's put a pocket watch on one end of the wooden board, and we ourselves will move to the other end. Putting your ear to the board, we will hear the clock.

Tie a string to a metal spoon. Attach the end of the string to the ear. By hitting the spoon, we will hear a strong sound. We will hear an even stronger sound if we replace the twine with wire.

Soft and porous bodies are poor conductors of sound. To protect any room from the penetration of extraneous sounds, the walls, floor and ceiling are laid with layers of sound-absorbing materials. As interlayers, felt, pressed cork, porous stones, various synthetic materials (for example, foam plastic) made on the basis of foamed polymers are used. The sound in such layers quickly attenuates.

Liquids conduct sound well. Fish, for example, hear footsteps and voices well on the shore, this is known to experienced anglers.

So, sound propagates in any elastic medium - solid, liquid and gaseous, but cannot propagate in space where there is no substance.

Oscillations of the source create an elastic wave of sound frequency in its environment. The wave, reaching the ear, acts on the eardrum, causing it to vibrate at a frequency corresponding to the frequency of the sound source. Trembling of the tympanic membrane is transmitted through the ossicles to the endings auditory nerve, irritate them and thus cause a sensation of sound.

Recall that only longitudinal elastic waves can exist in gases and liquids. Sound in air, for example, is transmitted by longitudinal waves, i.e., by alternating condensations and rarefactions of air coming from the sound source.

A sound wave, like any other mechanical waves, does not propagate in space instantly, but at a certain speed. This can be seen, for example, by observing the firing of a gun from afar. First we see fire and smoke, and then after a while we hear the sound of a shot. Smoke appears at the same time as the first sound vibration occurs. By measuring the time interval t between the moment the sound occurs (the moment the smoke appears) and the moment when it reaches the ear, we can determine the speed of sound propagation:

Measurements show that the speed of sound in air at 0 °C and normal atmospheric pressure is equal to 332 m/s.

The speed of sound in gases is the greater, the higher their temperature. For example, at 20 °C the speed of sound in air is 343 m/s, at 60 °C - 366 m/s, at 100 °C - 387 m/s. This is explained by the fact that with increasing temperature, the elasticity of gases increases, and the greater the elastic forces that arise in the medium during its deformation, the greater the mobility of the particles and the faster the vibrations are transmitted from one point to another.

The speed of sound also depends on the properties of the medium in which the sound propagates. For example, at 0 °C, the speed of sound in hydrogen is 1284 m/s, and in carbon dioxide it is 259 m/s, since hydrogen molecules are less massive and less inert.

Nowadays the speed of sound can be measured in any medium.

Molecules in liquids and solids are located closer to each other and interact more strongly than gas molecules. Therefore, the speed of sound in liquid and solid media is greater than in gaseous media.

Since sound is a wave, to determine the speed of sound, in addition to the formula V = s / t, you can use the formulas known to you: V = λ / T and V = vλ. When solving problems, the speed of sound in air is usually considered equal to 340 m/s.

Questions

1. What is the purpose of the experiment shown in Figure 80? Describe how this experiment is carried out and what conclusion follows from it.
2. Can sound propagate in gases, liquids, solids? Support your answers with examples.
3. Which body conducts sound better - elastic or porous? Give examples of elastic and porous bodies.
4. What kind of wave - longitudinal or transverse - is a sound propagating in the air; in water?
5. Give an example showing that a sound wave does not propagate instantly, but at a certain speed.

Exercise 30

1. Can the sound of a massive explosion on the Moon be heard on Earth? Justify the answer.
2. If you tie one half of a soap dish to each end of the thread, then with the help of such a phone you can even whisper while in different rooms. Explain the phenomenon.
3. Determine the speed of sound in water if a source oscillating with a period of 0.002 s excites waves of 2.9 m in length in water.
4. Determine the wavelength of a 725 Hz sound wave in air, water, and glass.
5. One end of a long metal pipe was hit once with a hammer. Will the sound from the impact propagate to the second end of the pipe through the metal; through the air inside the pipe? How many blows will the person standing at the other end of the pipe hear?
6. An observer standing near a straight section railway, I saw steam above the whistle of a steam locomotive going in the distance. After 2 s after the appearance of steam, he heard the sound of a whistle, and after 34 s the steam locomotive passed by the observer. Determine the speed of the locomotive.

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 we even eyes closed, without seeing anything, only by the sound we can guess 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?

Sounds perceived 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 the 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 sound, a person can experience various feelings.The complex complex of sounds that we call music causes a wide variety of 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 projectiles in flight, the howl of the wind, the roar of a 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 leg on a resonator box. 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 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 according to a strictly defined rule - the angle of reflection equal to the angle falling - the concept of echo is connected 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

Main physical characteristics sound - 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 of 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 quality characteristic 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. Sound of the same intensity can create various people auditory perception unequal in its loudness. 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 eardrum 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 internal and outside eardrum. Usually Eustachian tube 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 with 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

Over the past decades, the number of various kinds of cars and other sources of noise has sharply increased, the spread of portable radios and tape recorders, often turned on at high volume, and the 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 noradrenaline), 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 disrupted, energy metabolism begins to prevail over plastic, which leads to premature aging organism.

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 standards permissible noise for the premises for this purpose. The normalized parameters of constant noise 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 established 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 last years medicine ascribes to her healing properties. 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 the air and water environment, as well as in the 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 experience a sense of danger much earlier than humans. They react in advance to a distant hurricane or an impending earthquake. On the other hand, scientists have found 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 installations. 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 cause 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 commonly 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 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, there are a number of features in the propagation of ultrasound.

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 stream 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 must 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 beautiful world 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 organ pipes produce two sounds at the same time, only slightly different in pitch, then periodic amplifications of sound are heard, similar to drum roll. Saver explained this phenomenon by the periodic coincidence of the oscillations 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 the 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 works of Saver, 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 indicate that any sound source 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 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. Place a bell under the bell of the air pump 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 I again start to let in air 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 is connected with the propagation of sound in solids for a long time didn't seem very convincing. 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, 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 a 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 wave crests, 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. Getting into the liquid filling the cochlea, air waves affect 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, disturb silence, have harmful or irritant effect on the human body, reducing 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 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 is random sound vibrations of a 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. At different people it is different, and therefore conventionally the threshold of hearing is considered to be a sound pressure equal to 2x10 "5 N / m2 at 1000 Hz, corresponding to a power of 10" 12 W / m2. 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).

Often the noise is 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 environment 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 (noise traffic). 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 listen loud music, the risk of acoustic neuroma was increased by 2.5 times.

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 of 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 effect on the human nervous system. 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 various diseases as 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. Enough loud noise already after 1 min can cause changes in the electrical activity of the brain, which becomes similar to electrical activity 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 acceptable level sound stimuli.

And yet, road transport is the leader 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. The noise level in living rooms with closed windows facing the highway is only 10-15 dB lower than on the street.

The noise of cars depends on many factors: 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 have been noted functional state central nervous and cardiovascular systems caused by noise. Ischemic disease 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.

The noises are causing 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.

More and more doctors are talking about noise disease, predominant lesion hearing and 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, must be taken out of central parts cities to sparsely populated areas and create green spaces around them that absorb noise well. Planes should not fly over cities.

SOUNDPROOFING

To avoid harmful effects soundproofing helps a lot

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

Acoustics Laboratory MNIIP is developing sections "Acoustic Ecology" as part of project documentation. Projects on sound insulation of premises, noise control, calculations of sound amplification systems, acoustic measurements are being carried out. Although in ordinary rooms people are increasingly looking for acoustic comfort - good noise protection, intelligible speech and the absence of the 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, the chestnut tree decomposes toxic gases with almost no damage to its “health”.

The importance of planting greenery in city streets is very dense - 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 beneficial influence 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 science Center was laid 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.

← We must fight harmful influence noise by controlling the noise level, as well as by using special measures to reduce noise levels.