Features of sound propagation in the environment. Sound in Various Environments - Knowledge Hypermarket. Sound propagation in a confined space

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

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

From a depth of approx. 1200 m, where the water temperature remains practically constant, the change in the speed of sound occurs due to the change in pressure. "At a depth of approximately 1200 m (for the Atlantic), there is a minimum value for the speed of sound; at great depths, due to the increase in pressure, the speed of sound increases again. Since sound beams always bend towards the areas of the medium where their speed is lowest, they are concentrated in the layer with the minimum speed of sound ”(Krasilnikov, 1954). This layer, discovered by Soviet physicists L.D. Rosenberg and L.M. Brekhovskikh, is called "underwater sound channel". Sound trapped in the sound channel can propagate without attenuation over great distances. This feature must be borne in mind when considering the acoustic signaling of deep-sea fish.

Sound absorption in water is 1000 times less than in air. Sound source in the air with a power of 100 kW in the water is heard at a distance of up to 15 km; sound source in water at 1 kW heard at a distance of 30-40 km. Sounds of different frequencies are absorbed unequally: the high-frequency sounds are absorbed most of all, and the low-frequency sounds are absorbed most of all. Low absorption of sound in water made it possible to use it for sonar and signaling. Water spaces are filled with many different sounds. The sounds of reservoirs of the World Ocean, as shown by the American hydroacoustician Wenz (Wenz, 1962), arise in connection with the following factors: ebb and flow, currents, wind, earthquakes and tsunamis, industrial human activity and biological life. The nature of the noise generated by various factors differs both in the set of sound frequencies and in their intensity. In fig. 2 shows the dependence of the spectrum and pressure level of the sounds of the World Ocean on the factors causing them.

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

Thus, the composition and intensity of noise in different parts of the World Ocean are extremely diverse. There are empirical formulas showing the dependence of the intensity of sea noise on the intensity of the factors causing them. For practical purposes, however, ocean noise is usually measured empirically.

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

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

Meeting an obstacle on its way, sound waves can be reflected from it in the event that their wavelength (lambda) less than the size of the obstacle, or to go around (diffract) it in the case when their wavelength is greater than the obstacle. In this case, you can hear what is happening behind the obstacle without seeing the source directly. Falling on an obstacle, sound waves in one case can be reflected, in the other - to penetrate into it (be absorbed by it). The magnitude of the energy of the reflected wave depends on how strongly the so-called acoustic impedances of the "p1c1" and "p2c2" media differ, at the interface of which the sound waves fall. The acoustic resistance of a medium means the product of the density of a given medium p and the speed of sound propagation With in it. The greater the difference in the acoustic impedances of the media, the more energy will be reflected from the separation of the two media, and vice versa. If, for example, sound falls from the air, pc which is 41, into the water, pc which is 150,000, it is reflected according to the formula:

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

In connection with the reflection of sound from obstacles and its wave nature, addition or subtraction of the amplitudes of sound pressures of the same frequencies arriving at a given point in space can occur. An important consequence of this addition (interference) is the formation of standing waves during reflection. If, for example, you set a tuning fork in vibration, bringing it closer and away from the wall, you can hear the amplification and attenuation of the sound volume due to the appearance of antinodes and nodes in the sound field. Usually, standing waves are formed in closed containers: in aquariums, swimming pools, etc. with a relatively long sounding source.

In real conditions of the sea or other natural body of water, during the propagation of sound, numerous complex phenomena are observed that arise in connection with the inhomogeneity of the aquatic environment. The bottom and interfaces (water - air), temperature and salt inhomogeneity, hydrostatic pressure, air bubbles and planktonic organisms have a huge impact on the propagation of sound in natural water bodies. The water-air and bottom interfaces, as well as the inhomogeneity of the water, lead to the phenomena of refraction (bending of sound beams), or reverberation (multiple reflection of sound beams).

Water bubbles, plankton and other suspended solids help absorb sound in the water. A quantitative assessment of these many factors has not yet been developed. It is necessary to take them into account when staging acoustic experiments.

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

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

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

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

In the far acoustic field, the pressure is attenuated in inverse proportion to the distance from the sound source. In this case, in the far acoustic field, the displacement amplitudes are directly proportional to the pressure amplitudes and are related to each other by the formula:

where R - acoustic pressure in dyne / cm 2;

d- the magnitude of the displacement of particles in cm.

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

where R- acoustic pressure in dyne / cm 2;

d - the magnitude of the displacement of water particles in cm;

f - vibration frequency in hz;

pc- acoustic resistance of water equal to 150,000 g / cm 2 sec 2;

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

i= SQR i

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

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

where A - radius of the pulsating sphere;

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

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

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

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

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

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

The intensity of sound in absolute units is measured or by number erg / sec-cm 2, or w / cm 2. Moreover, 1 erg / sec = 10 -7 Tue

Sound pressure is measured in bars.

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

using which you can translate these values ​​one into another.

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

At the same time, most researchers take the threshold value of human hearing equal to 0.0002 for the zero reading of sound pressure P about bar for frequency 1000 hz.

The advantage of such a system is the ability to directly compare the hearing of humans and fish, the disadvantage is the difficulty of comparing the results obtained for the sound and hearing of fish.

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

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

The sound pressure of 1 is taken as the zero reference level. bar, which is 74 db higher than previously accepted.

Below is an approximate relationship between both systems.

Actual values ​​in US reference are marked with an asterisk in the text.

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 dog in the neighborhood, while in others it is possible to trace the route of movement of even a small cat through the apartment.

A sound wave is a vibration of particles in which energy is transferred. That is, the 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 air molecules vibrate at a certain frequency, which our hearing organ registers. Due to the disordered movement of molecules, they are faster than their "counterparts" in a solid, "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 over the 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, its average propagation speed 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.

The vibrations of air molecules are rather weak, so they can be absorbed by a thick wall, for example, a concrete wall. Of course, the thicker it is, the better it isolates the inhabitants of the apartment from acquaintance with the secrets of neighbors.

But if the movement of air molecules is stopped by a wall, then sound will rush through it without obstacles. The vibrations of molecules of solids are much more "energetic", therefore they easily transfer energy to air. 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 impact noise. But its neighbors a couple of floors above hear only the impact noise arising from the propagation of a sound wave along the structure of the building.

Let's say the neighbors from above are stomping, jumping, banging the ball until the middle of the night, and their big cat also likes to jump from the shelf of the closet to the floor just above your head. In this case, people are usually advised to soundproof the ceiling. But more often than not, it does not help or helps very little. Why? It is 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 walls of the room. Of course, damping the sound wave at the very beginning is much easier and more effective. Indeed, in the event of a fire, a towel that was unsuccessfully placed next to the burner, we extinguish the towel immediately, and do not wait until the whole kitchen is on fire. Therefore, it is better to immediately choose neighbors from above with a soundproofed floor. Or, when renovating, 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 structures according to construction technology are divided into panel, monolithic and prefabricated monolithic.

When a panel house is being built, the slabs are made in factories and delivered to the construction site, where the workers only have to assemble the required structure from them. At the slightest discrepancy between the plates, gaps appear between the apartments, 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 frame is built, and concrete is poured into a form already assembled with the help of strong shields. The thickness of the walls of such houses is on average 20-40 centimeters, so the conversations of neighbors are practically inaudible, but the impact noise easily spreads over 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 is very time-consuming. Although for the construction of monolithic houses, bricks are sometimes also used, 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.

"Sound insulation is highly dependent on both the material and the technology. Various porous materials must be used to absorb sound. For example, in old panel houses, where there was no sound insulation at all, they often hung carpets on the wall and laid them on the floor. Now the need for this is less and carpets have gone out of fashion, as they collect dust strongly. There are additives in concrete that can significantly reduce the noise transmitted along the walls. However, GOSTs and regulations do not oblige construction companies to add sound-absorbing additives to concrete, "says Ivan Zavyalov, a researcher at the Department of Applied mechanics of MIPT.

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

In the process of propagation of sound waves in the medium, their attenuation occurs. The vibration amplitude of the particles of the medium gradually decreases with increasing distance from the sound source. One of the main reasons for the damping of waves is the action of internal friction forces on the particles of the medium. To overcome these forces, the mechanical energy of vibrational motion is continuously used, which is carried by the wave. This energy is converted into the energy of chaotic thermal motion of molecules and atoms of the medium. Since the wave energy is proportional to the square of the vibration amplitude, then when waves propagate from the sound source, along with a decrease in the energy reserve of the vibrational motion, the vibration amplitude also decreases.

The propagation of sounds in the atmosphere is influenced by many factors: temperature at different altitudes, air currents. An echo is a sound reflected from a surface. Sound waves can be reflected from solid surfaces, from layers of air in which the temperature differs from the temperature of adjacent layers.

intensity of various natural and man-made sounds

Longitudinal and transverse waves

Each wave propagates with a certain speed, the speed of wave propagation is the speed of propagation of the disturbance. The speed of wave propagation is determined by the properties of the medium in which it propagates.

The speed of propagation of longitudinal waves in solids is greater than the speed of propagation of transverse waves. This circumstance is used to determine the distance from the source of the earthquake to the seismic station. First, a longitudinal wave is recorded at the station, and after a while - a transverse wave, which arises during an earthquake simultaneously with a longitudinal one. Knowing the velocities of the longitudinal and transverse waves in the earth's crust and the delay time of the transverse waves, it is possible to determine the distance to the earthquake source. In addition to these waves, a surface wave also propagates, its speed is lower, but it carries the greatest energy.

SPHERICAL WAVE - a wave radially diverging from a certain point (source) or converging to it (to a sink) and having spherical wave fronts (surfaces of equal phases).

Intensity andvisibility atka

Sound intensity, sound strength, the time-average energy transferred by a sound wave through a unit area perpendicular to the direction of wave propagation per unit time. For periodic sound, averaging is performed either over a period of time that is larger than the period, or over an integer number of periods.

Timbre

Timbre (fr. timbre- "bell", "mark", "distinguishing mark") - coloristic (overtone) coloration of the sound; one of the specific characteristics of a musical sound (along with its pitch, volume and duration).

By timbres, sounds of the same pitch and loudness are differentiated (distinguished from each other), but performed on different instruments, in different voices, or on the same instrument, but in different ways, strokes, etc.

The timbre of a musical instrument is determined by the material, shape, design and vibration conditions of its vibrator, various properties of its resonator, as well as the acoustics of the room in which this instrument sounds. In shaping the timbre of each specific sound, its overtones and their ratio in pitch and loudness, noise overtones, attack parameters (initial impulse of sound production), formants, vibrato characteristics and other factors are of key importance.

When perceiving timbres, various associations usually arise: the timbre specificity of the sound is compared with the organoleptic sensations from certain objects and phenomena, for example, sounds are called bright, shiny, frosted, warm, cold,deep, complete, sharp, saturated, juicy, metal, glass; the actual auditory definitions also apply (for example, voiced, deaf, noisy).

A scientifically based typology of timbre has not yet taken shape. It has been established that timbre hearing has a zonal nature.

Timbre is used as an important means of musical expression: with the help of timbre, one or another component of the musical whole can be emphasized, contrasts can be enhanced or weakened; changing timbres is one of the elements of musical drama.

In the music of the 20th century, a tendency arose to strengthen, emphasize the timbre side of sounding (parallelisms, clusters) by means of harmony and texture. Sonorics and spectral music are special areas for using the artistic properties and expressive possibilities of the timbre palette.

Reverberation

Reverb is the process of gradually decreasing the intensity of sound when it is reflected multiple times.

An echo represents a sound wave reflected from an obstacle. Reverberation is the superposition of different echoes from a single sound source. The reverberation effect can be observed in closed rooms after switching off the sound source. The artistic and aesthetic impression created by reverberation depends on the context of the sound work and is determined in the higher parts of the brain. Usually, an excessive duration of reverberation leads to an unpleasant boominess, "emptiness" of the room, and insufficient - to a sharp abrupt sound, devoid of musical "juiciness". Artificially generated reverberation within certain limits improves the sound quality, creating a pleasant "resonance" feeling in the room.

When recording speech, singing, music, as well as creating various noise effects, the use of artificial reverberation is an integral part of the overall audio signal processing. This type of processing is determined both by the technical conditions of the recording and artistic and aesthetic tasks. Reverb is used to improve and emphasize the artistic expressiveness of speech, singing, and the sound of individual musical instruments. So, for example, when recording music programs in a room with unsatisfactory acoustics or a volume small for a given composition of performers, usually it is not possible to obtain the necessary ratio between the boomy and clarity of the sound. In this case, the use of artificial reverberation can improve the sound quality of the music program. Likewise, reverb helps to create the necessary acoustic coloration of a voice or instrument when recording a vocalist or solo instrument, when he “drowns” in the sound of the accompanying ensemble.

With the help of reverb, you can create the effect of moving closer and closer to the sound source. For this, the level of reverberation is gradually changed, creating the illusion of a change in the acoustic ratio, and hence the impression of a change in the sound plan. When dubbing a video film or sounding a presentation, there is often a need to emphasize the acoustic setting of a particular scene. For this, a reverb effect is also used.

The reverberation effect can not only carry the character of the external design, but also be used as a means of enhancing the dramatic action. It is known, for example, what effect a whisper produces when recorded with a long reverberation time. It should also be remembered that there is better speech intelligibility in the background of music recorded with reverberation than when overdubbed with music recorded without reverberation. However, excessive reverberation should be avoided, as this can affect the clarity of the sound.

Sound propagates through sound waves. These waves pass not only through gases and liquids, but also through solids. The action of any waves is mainly in the transfer of energy. In the case of sound, transport takes the form of minute movements at the molecular level.

In gases and liquids, a sound wave shifts molecules in the direction of its motion, that is, in the direction of the wavelength. In solids, sound vibrations of molecules can also occur in the direction perpendicular to the wave.

Sound waves travel from their sources in all directions, as shown in the figure to the right, which shows a metal bell periodically colliding with its tongue. These mechanical collisions cause the bell to vibrate. The vibration energy is communicated to the molecules of the surrounding air, and they are pushed back from the bell. As a result, the pressure in the air layer adjacent to the bell increases, which then propagates in waves in all directions from the source.

The speed of sound is independent of volume or tone. All sounds from the radio in the room, be they loud or quiet, high-pitched or low, reach the listener at the same time.

The speed of sound depends on the type of medium in which it propagates and on its temperature. In gases, sound waves travel slowly because their rarefied molecular structure weakly inhibits compression. In liquids, the speed of sound increases, and in solids it becomes even faster, as shown in the diagram below in meters per second (m / s).

Wave path

Sound waves propagate through the air in the same way as shown in the diagrams to the right. Wave fronts move from the source at a certain distance from each other, determined by the frequency of the bell vibrations. The frequency of a sound wave is determined by counting the number of wavefronts that have passed through a given point per unit of time.

The front of the sound wave moves away from the vibrating bell.

In uniformly heated air, sound propagates at a constant speed.

The second front follows the first at a distance equal to the wavelength.

The sound is strongest near the source.

Graphic representation of an invisible wave

Sound sounding of the depths

A sonar beam of sound waves easily passes through ocean water. Sonar is based on the fact that sound waves bounce off the ocean floor; this instrument is usually used to determine the features of the underwater relief.

Elastic solids

The sound propagates in a wooden plate. The molecules of most solids are bound into an elastic spatial lattice, which is poorly compressed and at the same time accelerates the passage of sound waves.