The specific sensation that we perceive as sound is the result of the impact on the human hearing apparatus of the oscillatory movement of an elastic medium - most often air. Vibrations of the medium are excited by the sound source and, propagating in the medium, reach the receiving apparatus - our ear. Thus, the infinite variety of sounds we hear is caused by oscillatory processes that differ from each other in frequency and amplitude. Two sides of the same phenomenon should not be confused: sound as a physical process is a special case of oscillatory motion; but as a psycho-physiological phenomenon, sound is a certain specific sensation, the mechanism of the origin of which has now been studied in some detail.

Speaking about the physical side of the phenomenon, we characterize the sound by its intensity (strength), its composition and the frequency of the oscillatory processes associated with it; referring to sound sensations, we are talking about loudness, timbre, and pitch.

In solids, sound can propagate both in the form of longitudinal and transverse vibrations. Since liquids and gases do not have shear elasticity, it is obvious that in gaseous and liquid media sound can only propagate in the form of longitudinal vibrations. In gases and liquids, sound waves are alternating thickening and rarefaction of the medium, moving away from the sound source at a certain speed characteristic of each medium. The surface of a sound wave is the locus of particles of the medium having the same phase of oscillations. The surfaces of sound waves can be drawn, for example, in such a way that between the surfaces of adjacent waves there is a thickening layer and a rarefaction layer. The direction perpendicular to the surface of the wave is called the beam.

Sound waves in a gaseous medium can be photographed. For this purpose, behind the sound source is placed

a photographic plate, on which a beam of light from an electric spark is directed from the front so that these rays from an instantaneous flash of light fall on the photographic plate, passing through the air, surrounding source sound. On fig. 158-160 shows photographs of sound waves obtained by this method. The sound source was separated from the photographic plate by a small screen on a stand.

On fig. 158, but it can be seen that the sound wave has just come out from behind the screen; in fig. 158b, the same wave was photographed a second time a few thousandths of a second later. The surface of the wave in this case is a sphere. In the photograph, the image of the wave is obtained in the form of a circle, the radius of which increases with time.

Rice. 158. Photograph of a sound wave at two points in time (a and b). Reflection of a sound wave (c).

On fig. 158c shows a photograph of a spherical sound wave reflected from a flat wall. Here you should pay attention to the fact that the reflected part of the wave, as it were, comes from a point located behind the reflecting surface at the same distance from the reflecting surface as the sound source. It is well known that the phenomenon of reflection of sound waves explains the echo.

On fig. 159 shows the change in the wave surface during the passage of a sound wave through a lenticular bag filled with hydrogen. This change in the surface of the sound wave is a consequence of the refraction (refraction) of sound rays: at the interface between two media, where the speed of the waves is different, the direction of wave propagation changes.

Rice. 160 reproduces a photograph of sound waves with a four-slit screen placed in their path. Passing through the cracks, the waves go around the screen. This phenomenon of wave bending around obstacles encountered is called diffraction.

The laws of propagation, reflection, refraction and diffraction of sound waves can be derived from the Huygens principle, according to which each particle set into vibration

the medium can be considered as a new center (source) of waves; the interference of all these waves produces the actually observed wave (the ways of applying Huygens' principle will be explained in the third volume using the example of light waves).

Sound waves carry with them a certain amount of motion and consequently exert pressure on the obstacles they encounter.

Rice. 159. Refraction of a sound wave.

Rice. 160. Diffraction of sound waves.

To clarify this fact, let us turn to Fig. 161. In this figure, the dotted line shows the sinusoid of the displacements of the particles of the medium at some point in time during the propagation of longitudinal waves in the medium. The velocities of these particles at the considered moment of time will be represented by a cosine wave, or, which is the same, a sinusoid leading the displacement sinusoid by a quarter of the period (in Fig. 161 - a solid line). It is easy to see that thickening of the medium will be observed where at the given moment the particle displacement is zero or close to zero and where the velocity is directed in the direction of wave propagation. On the contrary, rarefaction of the medium will be observed where the particle displacement is also zero or close to zero, but where the particle velocity is directed in the direction opposite to the wave propagation. So, in condensations particles move forward, in rarefaction - backwards. But in

Rice. 161. In condensations of a passing sound wave, particles move forward,

There are more particles in dense layers than in rarefied ones. Thus, at any time in traveling longitudinal sound waves, the number of particles moving forward slightly exceeds the number of particles moving backward. As a result, a sound wave carries with it a certain amount of motion, which is manifested in the pressure that sound waves exert on the obstacles they encounter.

Sound pressure was experimentally investigated by Rayleigh and Petr Nikolaevich Lebedev.

Theoretically, the speed of sound is determined by the Laplace formula [§ 65, formula (5)]:

where K is the modulus of all-round elasticity (when compression is performed without the influx and release of heat), density.

If the compression of the body is carried out while maintaining the temperature of the body constant, then for the modulus of elasticity, values ​​\u200b\u200bare obtained that are smaller than in the case when the compression is performed without the inflow and release of heat. These two values ​​of the modulus of uniform elasticity, as proved in thermodynamics, are related as the heat capacity of a body at constant pressure to the heat capacity of a body at constant volume.

For gases (not too compressed), the isothermal modulus of uniform elasticity is simply equal to the pressure of the gas. If, without changing the temperature of the gas, we compress the gas (increase its density) by a factor, then the gas pressure will increase by a factor. Therefore, according to the Laplace formula, it turns out that the speed of sound in a gas does not depend on the density of the gas.

From gas laws and Laplace's formula it can be deduced (§ 134) that the speed of sound in gases is proportional to the square root of the absolute temperature of the gas:

where is the acceleration of gravity, the ratio of heat capacities is the universal gas constant.

At C, the speed of sound in dry air is equal to the speed of sound at medium temperatures and average humidity. In air, the speed of sound in hydrogen is equal to

The speed of sound in water is in glass and in iron.

It should be noted that the shock sound waves caused by a shot or an explosion, at the beginning of their path, have a speed

far exceeding the normal speed of sound in the medium. A shock sound wave in the air caused by a strong explosion can have a speed near the sound source that is several times higher than the normal speed of sound in air, but already at a distance of tens of meters from the place of the explosion, the wave propagation speed decreases to a normal value.

As already mentioned in § 65, sound waves of different lengths have almost the same speed. The exception is those frequency ranges, which are characterized by particularly rapid damping of elastic waves during their propagation in the medium under consideration. Usually these frequencies lie far beyond the limits of hearing (for gases at atmospheric pressure, these are frequencies of the order of vibrations per second). The theoretical analysis shows that the dispersion and absorption of sound waves are related to the fact that some, albeit short, time is required for the redistribution of energy between the translational and vibrational motions of molecules. This causes long waves (audio range) to travel somewhat slower than very short "inaudible" waves. So, in carbon dioxide vapor at and atmospheric pressure, sound has a speed, while very short, "inaudible", waves propagate at a speed

A sound wave propagating in a medium can have a different shape, depending on the size and shape of the sound source. In the most technically interesting cases, the sound source (emitter) is some oscillating surface, such as, for example, a telephone membrane or a loudspeaker diffuser. If such a sound source radiates sound waves into open space, then the shape of the wave depends essentially on the relative dimensions of the radiator; the radiator, whose dimensions are large compared with the length of the sound wave, radiates sound energy in only one direction, namely in the direction of its oscillatory movement. On the contrary, a radiator of small size compared to the wavelength radiates sound energy in all directions. The shape of the wave front in both cases will obviously be different.

Consider first the first case. Imagine a tough flat surface sufficiently large (compared to the wavelength) size, making oscillatory movements in the direction of its normal. Moving forward, such a surface creates a condensation in front of it, which, due to the elasticity of the medium, will propagate in the direction of the emitter displacement). Moving back, the emitter creates a rarefaction behind itself, which will move in the medium following the initial condensation. With a short oscillation of the emitter, we will observe a sound wave on both sides of it, characterized by the fact that all particles of the medium that are at an equal distance from the radiating surface of the average density of the medium and the speed of sound with:

The product of the average density of the medium and the speed of sound is called the acoustic impedance of the medium.

Acoustic impedance at 20°C

(see scan)

Let us now consider the case of spherical waves. When the dimensions of the radiating surface become small compared to the wavelength, the wavefront becomes noticeably curved. This is because the vibration energy propagates in all directions from the emitter.

The phenomenon can be best understood with the following simple example. Imagine that a long log has fallen on the surface of the water. The waves that have arisen due to this go in parallel rows on both sides of the log. The situation is different when a small stone is thrown into the water, and the waves propagate in concentric circles. The log is relatively large

with the wavelength on the surface of the water; the parallel rows of waves coming from it represent a clear model of plane waves. The stone is small in size; circles diverging from the place of its fall give us a model of spherical waves. When a spherical wave propagates, the surface of the wave front increases in proportion to the square of its radius. At a constant power of the sound source, the energy flowing through each square centimeter of the spherical surface of the radius is inversely proportional. Since the energy of vibrations is proportional to the square of the amplitude, it is clear that the amplitude of vibrations in a spherical wave must decrease as the reciprocal of the first power of the distance from the sound source. The spherical wave equation therefore has the following form:

MOSCOW, October 16 - RIA Novosti, Olga Kolentsova. Everyone knows that every house has its own audibility. In some houses, people are not even aware of the existence of a noisy child and a huge shepherd in the neighborhood, while in others you can trace the route of even a small cat moving around the apartment.

It happens that after many months of repair, you finally look around the finished version - and are disappointed. Because the result is real life does not look like the project. Repair specialists told the RIA Real Estate website how to quickly and inexpensively make changes to the interior.

A sound wave is a vibration of particles in which energy is transferred. That is, particles change their position relative to equilibrium, vibrating up and down or left and right. In the air, particles, in addition to vibrations, are in constant chaotic motion. When we speak, we make the air molecules vibrate at a certain frequency, which is registered by our hearing organ. Due to the random movement of molecules, they are faster than their "brothers" in a solid body, "lose" the frequency within which they moved earlier.

What about solids? If you hit the wall or floor of a house with a hammer, the sound wave will run through a solid structure, causing the atoms or molecules that make up it to vibrate. However, it should be remembered that in solids, the particles are "packed" more densely, since they are located closer to each other. And the speed of sound in dense media is several times higher than the speed of sound in air. At 25 degrees Celsius average speed its propagation is 346 meters per second. And in concrete, this value reaches 4250-5250 meters per second. The difference is more than 12 times! It is not surprising that a sound wave can be transmitted over long distances in solids, and not in air.

Vibrations of air molecules are rather weak, so they can be absorbed by a thick, for example, concrete wall. Of course, the thicker it is, the better it isolates the inhabitants of the apartment from getting to know the secrets of their neighbors.

But if the movement of air molecules is stopped by a wall, then inside it the sound will rush without barriers. Molecular vibrations of solids are much more "energetic", therefore, they easily transfer energy to air environments. Suppose a person on the fifth floor decides to nail a shelf to the wall. The movement of the drill bit causes the molecules that make up the entire solid surface to vibrate. The person himself hears both airborne noise and shock. But his neighbors a couple of floors above hear only impact noise resulting from the propagation of a sound wave through the building structure.

Let's say the upstairs neighbors stomp, jump, bang the ball until the middle of the night, and their big cat likes to jump from the closet shelf to the floor just above your head. In this case, people are usually advised to soundproof the ceiling. But most often it does not help or helps very little. Why? It's just that the sound wave propagates through the material upon impact. She will successfully run not only on the ceiling, but also on the walls and even on the floor. Therefore, to effectively combat noise, it is necessary to insulate all the walls of the room. Of course, it is much easier and more effective to dampen the sound wave at the very beginning. Indeed, in the event of a fire in a towel that was unsuccessfully placed next to the burner, we immediately extinguish the towel, and do not wait until the entire kitchen catches fire. Therefore, it is better to immediately choose neighbors from above with a soundproof floor. Or, during repairs, you will have to do complete insulation of the bedroom.

The series of apartment buildings can be divided into brick, block and reinforced concrete. But the latest constructions according to construction technology are divided into panel, monolithic and precast-monolithic.

When a prefabricated house is being built, the slabs are manufactured in factories and delivered to the construction site, where workers only have to assemble the desired structure from them. At the slightest discrepancy between the plates between the apartments, gaps appear through which sound passes. And the thickness of such panels is most often 10-12 centimeters, so these houses are considered one of the worst in terms of sound insulation.

For monolithic houses, a reinforcing cage is being built, and concrete is poured into a form already assembled with the help of durable shields. The thickness of the walls of such houses is on average 20-40 centimeters, so the conversations of neighbors are practically inaudible, but impact noise easily spreads through the ceilings due to their solidity.

Brick houses are traditionally considered the quietest and warmest. True, residents of large cities can say goodbye to the dream of purely brick houses, since the work on their construction requires a very large time investment. Although bricks are also sometimes used for the construction of monolithic houses, lining them with external walls and partitions. But this has little effect on the overall sound insulation, so any monolithic houses are considered quite noisy.

“Soundproofing is highly dependent on both the material and the technology. Various porous materials must be used to absorb sounds. For example, in old panel houses where there was no soundproofing at all, carpets were often hung on the wall and laid on the floor. Now there is less need for this and carpets are out of fashion, as they collect dust a lot. There are additives in concrete that can significantly reduce the noise transmitted through the walls. However, GOSTs and regulations do not oblige construction companies to add sound-absorbing additives to concrete, "says Ivan Zavyalov, Researcher Department of Applied Mechanics, Moscow Institute of Physics and Technology.

Modern buildings are far from the ideals of sound insulation. To be completely sure of round-the-clock peace and not depend on the neighbors' hobbies, perhaps, it remains only to purchase a private house.

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?

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

If, for example, a stone fell in the mountains, and there was no one nearby who could hear the sound of its fall, did the sound exist or not? The question can be answered both positively and negatively equally, since the word "sound" has a double meaning. Therefore, we need to agree. Therefore, we need to agree on what is considered sound - physical phenomenon in the form of propagation of sound vibrations in the air or sensation of the listener. The first is essentially a cause, the second is a consequence, 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. Such a sound can change the medium 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 is exposed to the brain through the hearing aid. Hearing a sound, a person can experience various feelings. The most diverse emotions are evoked in us by that complex complex of sounds that we call music. Sounds form the basis of speech, which serves as the main means of communication in human society. And 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 whistling of the wind, and 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 various environments, 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 the 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

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

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

The oscillation frequency is the number of complete oscillations (periods) in one second. This unit is called the hertz (Hz). The higher the oscillation frequency, the higher the sound we hear, that is, the sound has a higher tone. In accordance with the accepted international system 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 a qualitative characteristic of sound. The more overtones superimposed on the main tone, the more "juicy" the sound musically.

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

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

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

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

The effect of sound on the human ear

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

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

The effect of sound on the human body

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 modern man this function of hearing has lost such practical significance, "vegetative reactions of the struggle for existence" have been preserved. So, even a short-term noise of 60-90 dB causes an increase in the secretion of pituitary hormones that stimulate the production of many other hormones, in particular, catecholamines (adrenaline and norepinephrine), the work of the heart increases, blood vessels narrow, blood pressure (BP) rises. At the same time, it was noted that the most pronounced increase in blood pressure is observed in patients with hypertension and those 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 unpleasant consequences are caused not only by excessive noise in the audible range of oscillations: ultra- and infrasound in the ranges not perceived by human hearing (above 20 thousand Hz and below 16 Hz) also causes nervous strain, malaise, dizziness, changes in the activity of internal organs, especially the nervous and cardiovascular systems. It has been established that residents of areas located near major international airports have a distinctly higher incidence of hypertension than in a quieter area of ​​the same city. Excessive noise (above 80 dB) affects not only the hearing organs, but also other organs and systems (circulatory, digestive, nervous, etc.), vital processes are disturbed, energy metabolism begins to prevail over plastic, which leads to premature aging of the body .

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

Soundproofing

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

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

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

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

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

Noise. Music. Speech.

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

Noise is an unsystematic combination of a large number of sounds, that is, the merging 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 healing properties to it. With the help of music, you can normalize biorhythms, ensure the optimal level of activity of the cardiovascular system. But one has only to remember how the soldiers go into battle. From time immemorial, the song has been an indispensable attribute of a soldier's march.

Infrasound and ultrasound

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

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

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

Infrasonic waves propagate in 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 usually called hypersound. By frequency, ultrasound is conveniently divided into 3 ranges: low frequency ultrasound (1.5 (104 - 105 Hz), medium frequency ultrasound (105 - 107 Hz), high frequency ultrasound (107 - 109 Hz). Each of these ranges is characterized by its own specific features of generation, reception, distribution and application .

By 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 bats and dolphins have an amazing ability to both emit and receive ultrasound.

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

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

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

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

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

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

Bibliography

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

Kasyanov V. A. Physics Grade 10

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

Chapter 2. Acoustic noise and its impact on humans

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

Introduction

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

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

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

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

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

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

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

History reference

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

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

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

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

In 1700-1707. Joseph Saveur's memoirs on acoustics were published by the Paris Academy of Sciences. In these memoirs, Saver discusses a phenomenon well known to organ designers: if two pipes of an organ emit two sounds at the same time, only slightly different in pitch, then periodic amplifications of sound are heard, similar to a drum roll. Saver explained this phenomenon by the periodic coincidence of the vibrations of both sounds. If, for example, one of the two sounds corresponds to 32 vibrations per second, and the other to 40 vibrations, then the end of the fourth vibration of the first sound coincides with the end of the fifth vibration of the second sound, and thus the sound is amplified. From organ pipes, Saver moved on to an experimental study of string vibrations, observing the nodes and antinodes of vibrations (these names, which still exist in science, were introduced by him), and also noticed that when a string is excited, along with the main note, other notes sound, length whose waves are ½, 1/3, ¼,. from main. He called these notes the highest harmonic tones, and this name was destined to remain in science. Finally, Saver was the first to try to determine the limit of the perception of vibrations as sounds: for low sounds, he indicated a limit of 25 vibrations per second, and for high ones - 12,800. After that, Newton, based on these experimental 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 occur when the skin stretched over the drum moves, the waves of the sea surf, the branches swaying by the wind. All of them are different from each other. The "color" of each individual sound strictly depends on the movement due to which it arises. So if the oscillatory movement is extremely fast, the sound contains high frequency vibrations. A slower oscillatory motion creates a lower frequency sound. Various experiments show that any source of sound necessarily oscillates (although most often these oscillations are not noticeable to the eye). For example, the sounds of the voices of people and many animals arise as a result of the vibrations of their vocal cords, the sound of wind musical instruments, the sound of a siren, the whistling of the wind, and the peals of thunder are due to fluctuations in air masses.

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

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

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

If the speed of the oscillatory movement determines the frequency of the sound, then its magnitude (the size of the room) is the loudness. If such a wheel is rotated at a high speed, a high-frequency tone will occur, a slower rotation will generate a tone of a lower frequency. 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 blow. Therefore, sound also propagates in water. Fish hear footsteps and the voices of people on the shore, this is well known to anglers.

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

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

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

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

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

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

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

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

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

Noise measurement

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

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

The noise level is measured in units,

Expressing the degree of pressure sounds, - decibels. This pressure is not perceived indefinitely. The noise level of 20-30 dB is practically harmless to humans - this is a natural noise background. 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. operate with such big numbers uncomfortable. 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.

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

Noise levels

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

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

Permissible indoor noise

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

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

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

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

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

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

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

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

Acoustic neuroma is a benign tumor that causes hearing loss. Scientists examined 146 patients with acoustic neuroma and 564 healthy people. They were all asked questions about how often they had to deal with loud sounds no weaker than 80 decibels (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 listened to loud music had a 2.5-fold increased risk of acoustic neuroma.

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

Impact of acoustic noise on humans

The impact of acoustic noise on a person is different:

A. Harmful

Noise causes a benign tumor

Prolonged noise adversely affects the organ of hearing, stretching the eardrum, thereby reducing sensitivity to sound. It leads to a breakdown in the activity of the heart, liver, to exhaustion and overstrain 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 an aid. Psychotherapists also use the so-called "white noise". This is a kind of hiss, vaguely reminiscent of the sound of waves without splashing water. Doctors believe that "white noise" soothes and lulls.

The impact of noise on the human body

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

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

1. Noise causes premature aging. Thirty times out of a hundred noise reduces the life expectancy of people in major cities for 8-12 years.

2. Every third woman and every fourth man suffers from neurosis caused by increased level noise.

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

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

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

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

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

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

NOISE PROBLEM

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

And still automobile transport leading among the main sources of noise in the city. It is he who causes noise up to 95 dB on the sound level meter scale on the main streets of cities. 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 reasons: the brand of the car, its serviceability, speed, quality of the road surface, engine power, etc. The noise from the engine increases sharply at the time of its start and warming up. When the car is moving at the first speed (up to 40 km / h), the engine noise is 2 times higher than the noise generated by it at the second speed. When the car brakes hard, the noise also increases significantly.

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

Now it is believed that noise can reduce the life expectancy of a person by almost 10 years. There are more and 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. The natural noises of nature are becoming more and more rare, disappearing 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 sufficiently coordinate the work of various body systems. This results in disruption of their activities.

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

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

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

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

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

SOUNDPROOFING

Soundproofing greatly helps to avoid the harmful effects of noise.

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

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

FIGHTING ACOUSTIC NOISE

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 a space up to 10 m high, up to 20 m wide and up to 100 m long from car exhaust gases. At the same time, unlike many other trees, chestnut decomposes toxic gases with almost no damage to its “health”.

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

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

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

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

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

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

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

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 which medium the sound comes from. 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 is equal to the angle of incidence - the concept of echo is associated with this. If sound is reflected from several surfaces at different distances, multiple echoes occur. Sound propagates in the form of a diverging spherical wave that fills an ever larger volume. As the distance increases, the oscillations of the particles of the medium weaken, and the sound dissipates. It is known that in order to increase the transmission distance, sound must be concentrated in a given direction. When we want, for example, to be heard, we put our hands to our mouths or use a mouthpiece. Diffraction, that is, the bending of sound rays, has a great influence on the range of sound propagation. The more heterogeneous the medium, the more the sound beam is bent and, accordingly, the shorter the sound propagation distance.

sound propagation

Sound waves can propagate in air, gases, liquids and solids. Waves do not form in airless space. This can be easily seen from a simple experiment. If an electric bell is placed under an airtight cap from which the air is evacuated, we will not hear any sound. But as soon as the cap is filled with air, sound occurs.

The speed of propagation of oscillatory motions from particle to particle depends on the medium. In ancient times, warriors put their ears to the ground and thus discovered the enemy's cavalry much earlier than it appeared in sight. And the famous scientist Leonardo da Vinci wrote in the 15th century: “If you, being at sea, lower the hole of the pipe into the water, and put the other end to your ear, you will hear the noise of ships very distant from you.”

The speed of sound in air was first measured in the 17th century by the Milan Academy of Sciences. A cannon was installed on one of the hills, and an observation post was located on the other. The time was recorded both at the moment of the shot (by flash) and at the moment of sound reception. From the distance between the observation post and the gun and the time of origin of the signal, the speed of sound propagation was no longer difficult to calculate. It turned out to be equal to 330 meters per second.

In water, the speed of sound propagation was first measured in 1827 on Lake Geneva. Two boats were one from the other at a distance of 13847 meters. On the first, a bell was hung under the bottom, and on the second, a simple hydrophone (horn) was lowered into the water. On the first boat, at the same time as the bell was struck, gunpowder was set on fire, on the second observer, at the moment of the flash, he started the stopwatch and began to wait for the sound signal from the bell to arrive. It turned out that sound travels more than 4 times faster in water than in air, i.e. at a speed of 1450 meters per second.

echo- reflected sound. Usually, an echo is noticed if one also hears a direct sound from a source, when at one point in space one can hear sound from one source several times, which came along a direct path and is reflected (possibly several times) from surrounding objects. Since a sound wave loses energy when reflected, a sound wave from a stronger sound source can be reflected from surfaces (for example, houses or walls facing each other) many times, passing through one point, which will cause a multiple echo (such an echo can be observed from thunder ).

Echo is due to the fact that sound waves can be reflected by solid surfaces, this is due to the dynamic pattern of rarefaction and air compaction near the reflecting surface. If the sound source is located near such a surface, turned to it at a right angle (or at an angle close to a right angle), the sound, reflected from such a surface, as circles on the water are reflected from the shore, returns to the source. Thanks to the echo, the speaker can, along with other sounds, hear his own speech, as if delayed for a while. If the sound source is at a sufficient distance from the reflective surface, and there are no additional sound sources besides the sound source, then the echo becomes the most distinct. An echo becomes audible if the interval between the direct and reflected sound wave is 50-60 ms, which corresponds to 15-20 meters that the sound wave travels from the source and back, under normal conditions.

If a sound wave encounters no obstacles in its path, it propagates uniformly in all directions. But not every obstacle becomes an obstacle for her.

Having met an obstacle in its path, the sound can bend around it, be reflected, refracted or absorbed.

sound diffraction

We can talk to a person standing around the corner of a building, behind a tree, or behind a fence, although we cannot see him. We hear it because the sound is able to bend around these objects and penetrate into the area behind them.

The ability of a wave to go around an obstacle is called diffraction .

Diffraction is possible when the wavelength of the sound wave exceeds the size of the obstacle. Low frequency sound waves are quite long. For example, at a frequency of 100 Hz, it is 3.37 m. As the frequency decreases, the length becomes even longer. Therefore, a sound wave easily bends around objects commensurate with it. The trees in the park do not prevent us from hearing the sound at all, because the diameters of their trunks are much smaller than the wavelength of the sound wave.

Due to diffraction, sound waves penetrate through gaps and holes in an obstacle and propagate behind them.

Let us place a flat screen with a hole in the path of the sound wave.

When the sound wave length ƛ much larger than the hole diameter D , or these values ​​are approximately equal, then behind the hole the sound will reach all points of the area that is behind the screen (the area of ​​​​sound shadow). The outgoing wave front will look like a hemisphere.

If ƛ only slightly smaller than the slot diameter, then the main part of the wave propagates directly, and a small part diverges slightly to the sides. And in the case when ƛ much less D , the whole wave will go in the forward direction.

sound reflection

If a sound wave hits the interface between two media, it is possible different variants its further distribution. Sound can be reflected from the interface, it can go to another medium without changing direction, or it can be refracted, that is, go by changing its direction.

Let's suppose that an obstacle has appeared in the path of the sound wave, the size of which is much larger than the wavelength, for example, a sheer cliff. How will the sound behave? Since it cannot go around this obstacle, it will be reflected from it. Behind the obstacle is acoustic shadow zone .

Sound reflected from an obstacle is called echo .

The nature of the reflection of the sound wave can be different. It depends on the shape of the reflective surface.

reflection is called a change in the direction of a sound wave at the interface between two different environments. When reflected, the wave returns to the medium from which it came.

If the surface is flat, the sound is reflected from it in the same way as a ray of light is reflected in a mirror.

Sound rays reflected from a concave surface are focused at one point.

The convex surface dissipates sound.

The effect of dispersion is given by convex columns, large moldings, chandeliers, etc.

Sound does not pass from one medium to another, but is reflected from it if the densities of the media differ significantly. So, the sound that appeared in the water does not pass into the air. Reflected from the interface, it remains in the water. A person standing on the river bank will not hear this sound. This is due to the large difference in wave resistance of water and air. In acoustics, wave resistance is equal to the product of the density of the medium and the speed of sound in it. Since the wave resistance of gases is much less than the wave resistance of liquids and solids, when it hits the border of air and water, a sound wave is reflected.

Fish in the water do not hear the sound that appears above the surface of the water, but they clearly distinguish the sound, the source of which is a body vibrating in the water.

refraction of sound

Changing the direction of sound propagation is called refraction . This phenomenon occurs when sound passes from one medium to another, and the speed of its propagation in these media is different.

The ratio of the sine of the angle of incidence to the sine of the angle of reflection is equal to the ratio of the speeds of sound propagation in media.

where i - angle of incidence,

r is the angle of reflection,

v1 is the speed of sound propagation in the first medium,

v2 is the speed of sound propagation in the second medium,

n is the index of refraction.

The refraction of sound is called refraction .

If the sound wave does not fall perpendicular to the surface, but at an angle other than 90°, then the refracted wave will deviate from the direction of the incident wave.

Sound refraction can be observed not only at the interface between media. Sound waves can change their direction in an inhomogeneous medium - the atmosphere, the ocean.

In the atmosphere, refraction is caused by changes in air temperature, the speed and direction of movement of air masses. And in the ocean, it appears due to the heterogeneity of the properties of water - different hydrostatic pressure at different depths, different temperatures and different salinities.

sound absorption

When a sound wave hits a surface, some of its energy is absorbed. And how much energy a medium can absorb can be determined by knowing the sound absorption coefficient. This coefficient shows what part of the energy of sound vibrations is absorbed by 1 m 2 of the obstacle. It has a value from 0 to 1.

The unit of measure for sound absorption is called sabin . It got its name from the American physicist Wallace Clement Sabin, founder of architectural acoustics. 1 sabin is the energy that is absorbed by 1 m 2 of the surface, the absorption coefficient of which is 1. That is, such a surface must absorb absolutely all the energy of the sound wave.

Reverberation

Wallace Sabin

The property of materials to absorb sound is widely used in architecture. While researching the acoustics of the Lecture Hall, part of the Fogg Museum, Wallace Clement Sabin came to the conclusion that there is a relationship between the size of the hall, the acoustic conditions, the type and area of ​​sound-absorbing materials, and reverberation time .

Reverb called the process of reflection of a sound wave from obstacles and its gradual attenuation after turning off the sound source. In an enclosed space, sound can bounce off walls and objects multiple times. As a result, various echo signals appear, each of which sounds as if apart. This effect is called reverb effect .

The most important feature of a room is reverberation time , which was introduced and calculated by Sabin.

where V - the volume of the room,

BUT – general sound absorption.

where a i is the sound absorption coefficient of the material,

Si is the area of ​​each surface.

If the reverberation time is long, the sounds seem to "roam" around the room. They overlap each other, drown out the main source of sound, and the hall becomes booming. With a short reverberation time, the walls quickly absorb sounds, and they become deaf. Therefore, each room must have its own exact calculation.

Based on his calculations, Sabin positioned the sound-absorbing materials in such a way that the "echo effect" was reduced. And the Boston Symphony Hall, on which he was an acoustic consultant, is still considered one of the finest halls in the world.