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

The concept of a wave is useful in describing many different phenomena in nature. water waves, sound waves, radiation and blast waves have a significant effect on their respective environments, however, they all have general properties. One of the fundamental concepts in chemistry and physics is the energy of a system. Recall from your basic physics that if a small rock is held at a certain height and can be dropped, it will strike with a certain force. The stone's energy transforms into several possible forms upon impact, such as heat and sound.

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.

If the ground is soft, the energy can be used in compression. Similarly, if a nail is struck with a hammer, the nail heats up, indicating that not all of the energy has gone into motion with the nail, but some has been lost as a result of heat caused by friction. The term "system" is used to refer to objects and the environment. Glass beaker containing chemically reacting chemical substances, is an example of a system that releases energy in environment as heat. Energy is a property that can be measured and is given a unit called joules.

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.

The heat of matter is a specific form of energy, measured in calories. All compressed gases have a property called "energy". If one of the reactants reacts with the acetylene gas and oxygen in the welder's torch, then a huge amount of energy is released in the form of heat. The energy contained in acetylene and oxygen is released into the environment. The burner gradually releases energy, as we all know that acetylene explosions can occur if explosive limits are reached.

An explosion occurs when there is an instantaneous release of energy from a system into the environment. Let's look at the case where our stone falls into a pool of water. The energy of the stone causes disturbance in the water and waves. These waves appear as a series of crests and troughs. The energy transferred to the water suddenly “pushes” it, is transferred. If you look at the water waves from a side view, you can see an image similar to the one below.

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

The crest of a wave or its height is called the amplitude of the wave. The wavelength is equal to the wavelength as shown. The wavelength is the distance for the total full positive and negative phases, i.e. cycle. The stone generates many cycles and the number of cycles generated per second is the frequency. Throwing a rock into a pool of water will cause many circular waves rather than one big wave. The amplitude of the waves will eventually decrease to zero as energy is lost to the water. The larger the amplitude of the wave, the more powerful or intense.

If a wave with a large amplitude travels to the wall barrier, it will be reflected back or if it is powerful enough, it will simply hit the wall. Water is the medium through which energy is transported, and this medium has certain mechanical properties such as viscosity and elasticity that determine how waves travel through it; the water particles themselves move up and down, perpendicular to the direction of the wave. You can see this by placing a cork on the water in the path of the waves.

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

The plug will move up and down, but will not move in the direction of the wave. Sound is another type of wave. When we speak our vocal chords vibrate and energize the air. Waves are generated and transmitted through the medium. Sound waves are a series of compression and rarefaction of air. These areas of high and low pressure discovered by our tympanic membrane like sound. Sound waves differ from water waves in that the wavelengths involved are much shorter. As mentioned earlier, the medium involved affects the propagation of the waves.

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

Sound energy can be transmitted through other media and result in different wave speeds. The rigidity of the iron seems to aid in the propagation of sound and illustrates that the nature of the medium certainly influences the propagation of waves. Sound cannot be transmitted in the absence of a medium, that is, a vacuum. Waves can also bounce off objects.

An explosion in the air will also release energy into the environment. Just as a rock falls into water, the explosion will provide a boost to the surrounding air. This push is provided by the hot expanding gases generated by the explosives. The amplitude of the wave is actually called overpressure in the air when we are talking about explosions. What might be the wave profile in this case?

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.

High explosive, such as dynamite, instantly releases its energy. This instantaneous release will result in a shock wave of large amplitude and short duration. In addition, supersonic wave velocities in detonation have been demonstrated. Indeed, we usually use the word "detonation" to refer to cases where the wave speed is supersonic. Being supersonic, an overpressure wave can hit a person before the sound from the explosion had a chance to arrive. There is also a zone of low negative pressure that follows the detonation and is caused by a direct air pulse.

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, the sound wave is reflected.

Many explosions involving compressed gases are not detonations but rather extremely rapid deflagrations, i.e. shock waves travel at subsonic speeds and overpressure peaks are lower. Although the overpressure is lower, deflagrations can still cause damage as they are usually longer. It has been shown that since the environment involved is important, we can assume that an explosion in the vacuum of space would be less destructive than a similar explosion on earth.

The waves considered so far belong to a broad class that are best described as mechanical waves. What about radio waves, light waves and other types of radiation? These waves are electromagnetic in nature, meaning they are associated with fields of energy. These waves travel at the speed of light. Wave energy is best viewed not as a series of compressions or excess pressures, but as small bundles of energy that have both partial and wave character. Light passes through many media without affecting the media, but is easily stopped by an opaque object.

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.

X-rays are high-energy waves that travel through many materials and are useful in medicine. Radio waves and microwaves travel very long distances and through many materials without being attenuated or disturbed. These waves are used to communicate with satellites and deep space probes many kilometers away. radiation from nuclear explosion dangerous because it produces a wide spectrum of radiation that strikes and passes through the body, causing great damage to human cells.

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,

Electromagnetic waves need to be considered a little differently because they have an extremely short wavelength and travel at the speed of light. They don't need a medium to transmit, they can bounce just like other types of waves. Sound waves are excited on lipid monolayers using a set of flat electrodes aligned parallel to the excitable medium. By measuring the frequency-dependent change in transverse pressure, we can extract the speed of sound for the entire monolayer phase diagram. We demonstrate that this rate can also be directly derived from the compressibility of the lipid monolayer and therefore displays a minimum in the phase transition mode.

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.

No significant attenuation can be detected confirming an adiabatic phenomenon. Therefore, orders of magnitude estimates from static couplings predict propagation of surface potential changes of 1-50 mV, 1 u. At pH and 01 K in temperature and fall in the same order of magnitude as the physical changes measured during the propagation of nerve impulses.

The lipid monolayer is ubiquitous in biology as half of a cell, organelle, or vesicle membrane. Therefore, full understanding physical properties lipid monolayers is of fundamental interest for understanding its role in biological bilayer systems.

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 salinity.

sound absorption

If, however, two-dimensional adiabatic excitations are present in simple lipid monolayer systems, their absence in complex biological lipid membranes seems unlikely. Here we present experimental and theoretical studies propagation of an adiabatic sound wave in lipid monolayers. Experimentally, lipid monolayers are excited by a variable electric field in a plane arising from a set of laterally patterned electrodes.

A thermodynamic analysis of the problem shows that both the transverse pressure change and the speed of sound for different thermodynamic states can be directly obtained from the phase diagram of the lipid monolayer and provide clear evidence for the existence of a propagating adiabatic sound wave. Order-of-magnitude estimates suggest that the origin of uncoupled propagation may be due to different sound speeds in two and three dimensions, as well as increased thermal conductivity of the water boundary layer.

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 . She got her name from 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 equal to 1. That is, such a surface must absorb absolutely all the energy of the sound wave.

Standard isotherms can be recorded, and the film balance control circuit allowed him to hold a certain monolayer pressure to measure the region expansion coefficient α. The inter-row gold electrodes were connected to an RF amplifier, which was controlled by a signal generator. Such chips are commonly used in our laboratory for surface acoustic wave research, including microfluidic and sensor applications.

To obtain lipid mixtures, lipids dissolved in chloroform were mixed in the desired proportions. Before spreading the lipid monolayers at the air-water interface, the chip and Wilhelmy plate were placed on the surface of the trough, as described below in FIG. 2.

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 concluded that there was a relationship between the size of the auditorium, the acoustic conditions, the type and area of ​​sound-absorbing materials, and reverberation time .

Fundamental thermodynamic relations

Corresponding thermodynamic force. This is the lateral isothermal compressibility of the lipid monolayer, which can be directly obtained from the pressure domain isotherm. Therefore, the mechanical properties of the lipid monolayer are a measure of susceptibility, i.e. inverse curvature of the entropy potential.

Coefficient of isobaric expansion. Therefore, side waves excited inside the lipid monolayer will be completely reflected. However, these oscillations do not provide significant dissipation, since their exponential penetration into the volume only resembles the energy distribution of an oscillating propagating sound wave around the interface and should not be mistaken as an actual energy transfer from the system, but are inseparable from the wave.

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 the results of his calculations, Sabin arranged 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.

The speed of sound propagation in air c \u003d 331.45 root T / 273

331m/s at 0˚s

Sound Wave Interference - imposing vibrations. from multiple sources

The sound field is the region of the space in the cat. sound waves.

Sound pressure - P-difference between the instantaneous value of the total pressure and the average pressure observed in the medium in the absence of a sound field

р=Pm sin (wt+ φ) ˂p˃=Pa= n/m²

R eff=Рm root2 Рm- pressure amplitude

Interference - physical phenomenon, observed when several wave processes are superimposed and consisting in local deviations of the total intensity from the sum of the intensities of the incoming waves.

The propagation of sounds in the atmosphere is influenced by many factors: temperature at different heights, air currents. Echo is 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 neighboring layers.

sound diffraction(lat. diffractus - literally broken, broken) - a phenomenon that can be considered as a deviation from the laws of geometric optics during the propagation of waves. Initially, the concept of diffraction referred only to the rounding of obstacles by waves, but in the modern, broader interpretation, a very wide range of phenomena that occur during the propagation of waves in inhomogeneous media, as well as during the propagation of waves limited in space, are associated with diffraction.

Sound speed- speed of propagation of sound waves in the medium.

As a rule, the speed of sound in gases is less than in liquids, and in liquids the speed of sound is less than in solids.

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

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

For gases, this formula looks like this:

where γ is the adiabatic index: 5/3 for monatomic gases, 7/5 for diatomic gases (and for air), 4/3 for polyatomic gases; k- Boltzmann's constant; R- universal gas constant; T- absolute temperature in kelvins; t- temperature in degrees Celsius; m- molecular mass; M - molar mass. In order of magnitude, the speed of sound in gases is close to average speed thermal motion of molecules and, in the approximation of constant adiabatic exponent, is proportional to square root from absolute temperature.



For solids, the speed of sound can be calculated as:

Where K- all-round compression module; E- Young's modulus; ν - Poisson's ratio.

In air, under normal conditions, the speed of sound is 331.46 m/s (1193 km/h).

In water, the speed of sound is 1485 m/s. (see Colladon-Sturm Experience)

In solids, the speed of sound is 2000-6500 m/s.

23. Sound field and main physical quantities characterizing it. (Sound pressure, sound field density). Sound power, sound intensity.

The density of the sound field, D is the sound energy contained in a unit volume of the medium D \u003d p² / pc² p is the density of the medium kg / m³; c is the speed of sound in the medium

Power sound and p is the amount of sound energy emitted by a sound source per unit time

Character. source of sound or noise the amount of sound energy passing in 1s through the area S surrounding the sound source ˂p˃=Vm

Sound intensity, I - the amount of sound energy propagated in the sound field per unit time through a unit area (if the waves in the sound field go in only one direction)

I=r²/rs ˂I˃=W/m²; p-density of the medium rs-acoustic resistance of the medium (impedance) kg/m²s

Sound field, a region of space in which sound waves propagate, i.e., acoustic vibrations of particles of an elastic medium (solid, liquid or gaseous) that fill this region occur. The sound wave is completely determined if, for each of its points, the change in time and space of any of the quantities characterizing a sound wave is known: the displacement of an oscillating particle from an equilibrium position, the oscillatory velocity of the particle, or the sound pressure in the medium; in individual cases, changes in the density or temperature of a medium in the presence of a sound wave are of interest.

On the energetic side, sound energy is characterized by the density of sound energy (the energy of the oscillatory process per unit volume); in those cases when energy transfer occurs in the sound wave, it is characterized by the intensity of sound, i.e., the time-averaged energy transferred per unit time through a unit surface perpendicular to the direction of wave propagation.

The pattern of sound waves in the general case depends not only on the acoustic power and directivity characteristics of the emitter—the source of sound—but also on the position and properties of the interfaces between different elastic media, if such surfaces exist. In an unbounded homogeneous medium, the static field is the field of a traveling wave. Far from a source in the sound pressure zone of almost any emitter, the sound pressure decreases according to the law 1/ r(where r- distance from the source.

Sound intensity (absolute) - a value equal to the ratio of the flow of sound energy dP through a surface perpendicular to the direction of sound propagation to the area dS this surface:

For quantitative comparisons of loudness, it is necessary to introduce the concept of sound intensity. The intensity of a sound wave is defined as the average energy flux through a unit area of ​​the wave front per unit time. In other words, if we take a single area (for example, 1 cm 2), which would completely absorb sound, and place it perpendicular to the direction of wave propagation, then the sound intensity is equal to the acoustic energy absorbed in one second. The intensity is usually expressed in W/cm2 (or W/m2).

Sound pressure - the difference between the pressure existing in the environment p wed at this moment, and atmospheric pressure p atm.

It is measured in pascals (a force of 1 N applied to an area of ​​1 sq. M.). Atmospheric pressure ~10 5 Pa. The sound pressures of speech and music are up to 100 Pa.

Like any force, sound pressure has a direction. However, pressure refers to a force perpendicular to the surface.

Sound Wave Speed (sound speed) with stars in the medium depends on the mass of molecules or atoms and the distance between them. And they, in turn, depend on chemical composition substance, its temperature, and for gases and pressure. For technical calculations, it is enough to consider

,

where T - temperature, K. At normal atmospheric pressure and T=290 K (17 0 С) sound speed 340 m/s.

The sound energy density e is the energy contained in a unit volume of the propagation medium.

The travel time of a wave of unit length along the beam 1/s sv => e =I/s sv; [e]=[W/m2]/[m/s]=[W*s/m3]=[J/m3].

Energy density through pressure:

.

The energy density, unlike the intensity, is a scalar value, and therefore it can also be used in cases where it is difficult or impossible to determine rays and wave fronts, for example, when sound waves propagate in rooms.

25. Sound intensity level and sound pressure level. Sound power level. Equivalent sound pressure level and equivalent sound level.

Sound level units The sound intensity level is measured in tenths of Bell (B) - decibel (dB)

For different sound pressure levels – various conditions sound perception:

124-pneumatic hammer

94- inside the subway car

85-inside the bus

25-bedroom at night

Adding sound intensity levels

Let there be n sound sources, each of which at a given point of the field has the same sound intensity I(first), with an intensity level L(first) L=lg·I(first). Total sound intensity I=I(first) n; Total sound intensity level:

Meaning of 10lgn:

24. Law of Weber - Fechner and its interpretation in acoustics. Units of sound intensity level. Addition of sound intensity levels.

For all human senses, sensation is proportional to the logarithm of the stimulus, harnessed in units of the sensation threshold.

Properties of logarithms log6a is the exponent of b that the number b must be raised to get the number a.

Sound intensity level and sound pressure level. Sound pressure range

Sound intensity level

Sound intensity level expressed in terms of sound pressure

Lp=20 lg (p/pₒ)

The sound pressure threshold pₒ corresponds to the sound intensity threshold Iₒ

рₒ=2 10(*in (-5) degrees)* Pa; I0 \u003d 10 (* in - 12 degrees *) W / m²; pₒ = 10 (* in - 12 degrees) W;

corresponding to the threshold of hearing at a frequency of 1000 Hz

At threshold values, sound intensity level and pressure level = 0

Sound power level Lp=10 lg(p/pₒ) pain threshold: p=2 10²Pa I=10² W/m² L=140 dB

Normal conversation - 50-60 dB

Virtually silent - 10 dB

Threshold of audibility dead silence - 0dB

BUT: less than 20db is hard to get

The intensity of the wave I is the value numerically equal to the time-averaged energy E, carried by the wave per unit time through the unit area of ​​the surface, located perpendicular to the direction of wave propagation:

where S is the area of ​​the surface through which the wave passes, t is the time of its passage through this surface. Wave intensity unit: J / (m 2 s) \u003d W / m 2.

Sound is an object of auditory sensations, therefore it is also subjectively evaluated by a person. The subjective characteristics of sound are: height - determined by the frequency of the tone, timbre - determined by the spectral composition of the sound, loudness - the level of auditory sensation, depending primarily on the intensity of the sound. Therefore, the objective characteristics of sound are: frequency, intensity, acoustic spectrum. The human ear perceives sounds at a frequency of 1 kHz with an intensity of at least I 0 =10 -12 W / m 2 and is called the intensity at the threshold of hearing. The maximum sound intensity at a frequency of 1 kHz, perceived by a person I b \u003d 10 W / m 2, is called the pain threshold, since it causes pain. The difference between I 0 and I b is very large (I b / I 0 \u003d 10 13), so it is convenient to use a logarithmic scale for measurements. In this regard, the magnitude of the sound intensity level is introduced, equal to the decimal logarithm of the ratio of the intensity of the studied sound I to the intensity I 0 at the threshold of hearing

Sound intensity level is measured in bels. bel - there is a unit of the scale of sound intensity levels, corresponding to a change in intensity by 10 times. Usually, a unit 10 times smaller is used, called the decibel (dB). Then formula (4.11) takes the form .

If L=1 dB, then , a . Thus, a decibel corresponds to such two levels, the intensities of which differ by a factor of 1.26.

According to the Weber-Fechner law, the increase in the strength of sensation is proportional to the logarithm of the ratio of the intensities of two comparable stimuli.

The Weber-Fechner law underlies the creation of the loudness level scale, as well as the intensity level scale. As a result, the hearing area is limited both above and below by curves. These curves are based on measurements taken with people who have the most sensitive organs of hearing. For most people, the hearing area is smaller; for many, the frequency boundary occurs at 18, 15 and even at 10 kHz. An intensity of 10 -12 W / m 2 is also not felt by every person. With age, the area of ​​hearing narrows. If the ear is damaged, it can become quite small, and with deafness it shrinks to a point.

In order to find a correspondence between loudness and intensity of sound at different frequencies, curves of equal loudness are used. It can be seen that the average human ear is most sensitive to frequencies of 2500 - 3000 Hz. Each intermediate curve corresponds to the same loudness, but different sound intensity for different frequencies. Using a set of curves of equal loudness, it is possible to find loudnesses for different frequencies corresponding to a certain intensity. For example, let the intensity of a sound with a frequency of 100 Hz be 60 dB

26. Frequency spectrum of sound. Frequency bands. A number of octave frequency bands. A number of one-third octave frequency bands.

Sound- fluctuations movement in any elastic material medium is called. any source, manifested. in period form. pressure changes.

Frequency spectrum of sound- representation of the amplitudes of sinusoidal oscillations or other quantities, character. sound energy as a function of frequency.

Periodic oscillations - the sum of sinusoids with different amplitudes.

Amplitude versus frequency. At continuous spectrum sound pressure spectrum level B - sound intensity level in the frequency band of 1 Hz.

White noise is a sound with a constant spectrum level B at all frequencies.

Frequency bands

Cut-off frequencies: f 1 - lower, f 2 - upper width Δ f \u003d f 2 - f 1

Avg. geometric frequencies

f cf =
Accepted range of octave frequency bands

Cutoff frequencies 45-90 90-150 150-355 355-710 710-1400 1400-2500
Avg. geometric frequency

Low frequencies: up to 355; average: 500-1000 (in men, low frequencies are present in a larger number than in women)

The frequency band, the upper limit of which is twice the lower limit, i.e. f 2 = 2 f 1 is called an octave.

For a more detailed study of noise, third-octave frequency bands are sometimes used, for which

f 2 \u003d 2 1/3 f 1 \u003d 1.26 f 1

The octave or third octave band is usually given by the geometric mean frequency:

27. Human hearing organ. Subjective perception of sound by a person. Volume level, background and sleep scales.

(Human hearing organs are capable of perceiving vibrations with a frequency of 15-20 hertz to 16-20 thousand hertz. Mechanical vibrations with the indicated frequencies are called sound or acoustic. Sound- these are mechanical vibrations that propagate in elastic media - gases, liquids and solids, perceived by the hearing organs. The main physical characteristics of sound are the frequency and intensity of vibrations. They also affect the auditory perception of people.)

Volume level in backgrounds: L f = 20 lg(p|/p0)

p | - sound pressure of a tone with a frequency of 1000 Hz is equal to loud with the one under consideration. (Our ear does not directly correspond to physical laws)

Equal Loudness Curve-geom. Place points of equal volume. They show comparative loudness.

Volume level, background and sleep scales.

backgrounds
sona 0,5

Sound impact comparison

Volume in 1 dream names sound with volume level in 40 phon

S=2 =2 2 =4son

sound diffraction- the ability of sound waves to bend around an obstacle when propagating.

Sound propagates from the source of the sound

Reverberation is the process of gradually reducing the intensity of sound as it is reflected multiple times. (after the sound stops)

(The conventionally accepted reverberation time is the time during which the sound level decreases by 60 dB. To calculate the reverberation time, use the formula:

, where V is the volume of the room A- total fund of sound absorption, , a i- sound absorption coefficient (depends on the material, its dispersed or frictional characteristics), Si is the area of ​​each surface.

28. Reflection and absorption of sound in rooms. Coefficients of absorption, reflection and sound transmission. The total sound absorption of the room.

Falling on the surface, the sound wave is partially reflected from it, partially absorbed by the surface material, turning into thermal energy, may partially go beyond the surface. The energy remaining in the room after reflection of the sound wave is characterized by the reflection coefficient , the energy lost in the room after reflection,  - by the sound absorption coefficient, the energy of the sound wave that has passed through the surface, τ - by the sound conductivity of the room. E pad - sound energy incident on the surface; E neg - the energy of sound reflected from the surface; E pr - the energy of the sound wave that passed through the surface into the adjacent room; E absorb - the energy of the sound wave lost in the room upon reflection. The values ​​of the coefficients ,  and  depend on the material and design features of the surface, frequency and angle  of the sound wave incidence on the obstacles.


Equivalent sound absorption area


Surface area with coefficient sound absorbing =1 (totally absorbing sound), which absorbs. the same number of energy sounds as the given surface or object.

29. Features of the wave approach in the analysis of the sound field of the room.

Reverberation is the process of a gradual decrease in the sound pressure level in the air. storage volume after the sound stops. (reverb time is the time it takes for the sound pressure level to drop by 60 dB)


(Sabin Wallace basic theories inferred form experimentally)

Due to interference (imposed vibrations from several sources), the reverberation process is not monotonous.

From the position wave theory air the volume of the room considered. how linear system with a definition range of properties. oscillation frequencies. When exposed to a signal emitted by a sound source, natural oscillations are excited in the air volume of the room. The spectrum of natural frequencies is quite simple to calculate only for rooms of simple geometric shapes. For example, for rooms in the form cuboid(with ideally rigid reflective surfaces) length l, width b and height h natural frequencies:

g, q, r-integers(0,1,2…)

At small values ​​of l, b h , in small rooms, the frequency of own. fluctuations are significantly different. from each other. In the region of high frequencies, the eigenfrequencies are close, and the larger the frequency range will be the resonance.

(for small spaces)

30.Geometric approach in the analysis of the sound field of the room.

Sound field is a region of space in which sound waves are observed (coming from a source along the shortest path to this point)

Main methods (approaches) for analyzing the sound field of a room:

1.wave 2.static 3.geometric

Reverberation is the process of a gradual decrease in the sound pressure level in the air. volume after the sound stops. (reverb time is the time it takes for the sound pressure level to drop by 60 dB)

Instead of sound waves, consider. sound beams in direction which the sounds propagate. waves .

The admissibility of the use of geometric. method depends on the wavelength, the size of the reflection. surface and its location in relation to to the sound source and receiving point.

The wavelength must be superior. smallest reflection size surface by at least 1.5 times. For reflection, possess. curvature naim. the radius of curvature must exceed in 2r.


The construction of the reflection front. Waves from the plane.


Distribution analysis. First reflections.


Geometric theory is more applicable to the analysis of acoustic processes in rooms large sizes- concert and theater halls, large studios. The optimal dimensions of the hall (studio) are determined based on the analysis of the initial reflections.

(The geometric (beam) theory of acoustic processes in rooms is based on the laws of geometric optics. The movement of sound waves is considered like the movement of light rays. In accordance with the laws of geometric optics, when reflected from mirror surfaces, the angle of reflection b is equal to the angle of incidence a, and the incident and reflected rays lie in the same plane.)

The sound field in the room is close to diffuse.

The sound field is called diffuse if the time-averaged sound energy density is the same at any point in the field D (x, y, z) = const

All directions of arrival of sound energy flows at any point are equally probable and the time-averaged flow of sound energy is the same in any direction (it is impossible to understand where the sound comes from).

Mean free path L=l/n(l1+l2+....ln)

L=4V/Stot; V-room volume


Wed free run time

r = l/c =4 V (c Stotal)

Аtot = ΣαiSi+ΣA

Average sound absorption coefficient αav=ΣαiSi/Stot=Atot/Stotal

T=0.161 V/ - ln(1- αav) Stotal definition of reverberation time

T=0.161 V/ αav* Stot

α – small value α≤0.2

Influence of humidity

The greater the humidity, the greater the sound absorption T=0.161 V/ - ln(1- αav) Stot+4mV

Difficulties in Calculating Reverb Time

one). Disproportionate premises

2). With sealed floor and ceiling

3). Sound absorption is concentrated on the ceiling or on opposite walls

four). At the bottom of the room

from neta: Sound field, a region of space in which sound waves propagate, i.e., acoustic vibrations of particles of an elastic medium (solid, liquid or gaseous) occur that fill this region reverberation research. Eyring's formula has the form:

To experimentally determine the reverberation time, Sabin used the simplest devices: organ pipes as a sound source and a stopwatch. He found that the reverberation time T is directly proportional to the volume of the room V and inversely proportional to the product of the average absorption coefficient a av and the area of ​​all obstacles S:

Average Absorption Rate:

where a 1 , a 2 ,... - absorption coefficients various materials;

S \u003d S 1 + S 2 + ... - total area of ​​​​obstacles; n is the number of different obstacles.

From this expression, we can conclude that the average absorption coefficient corresponds to a single material that could cover all the surfaces of the barriers of the room while maintaining the total sound absorption A = a cf S. The absorption unit is considered to be 1 m 2 of an open opening that completely absorbs all the energy incident on it ( excluding diffraction). This unit was called sabin (Sat).

ticket 32 ​​Sound-absorbing materials and structures.

Porous sound absorbers; - porous sound absorbers with perforated and other screens; - low-frequency absorbing structures; - piece (volumetric) sound absorbers (from the net: In cases where sound-absorbing material cannot be used on enclosing structures (for example, if they are translucent) or their area is insufficient to achieve the desired effect, suspended piece (volume) sound absorbers are used. Most often they are flat slabs of fibrous materials coated with porous paint, covered with fabrics or encased in perforated metal sheets.Such structures are acoustically very effective, since, suspended vertically, they absorb sound from both surfaces.If these absorbers are suspended so that they form closed shapes in plan (squares , triangles, etc.), then the sound absorption increases due to resonant absorption in the air between the verticals of the panels.); - rocker-type sound absorbers; - resonant and layered sound absorbers

porous

When a sound wave falls on a porous material, the air in the pores begins to oscillate and the energy of the oscillations is converted into heat.

A porous layer on a hard reflective surface. Frequency response drops at low frequencies

A porous layer away from rigid surfaces is an air gap instead of increasing the thickness of the porous layer. (from net: they are made in the form of plates that are attached to the enclosing surfaces directly or at a distance, from light and porous mineral piece materials - pumice, vermiculite, kaolin, slag, etc. with cement or other binder. Such materials are strong enough and can be used to reduce noise in corridors, foyers, flights of stairs of public and industrial buildings.)

porous e with perforated screens

Types: - film coating; - fabric screens

(increases) cfp at low frequencies and (falls) at high frequencies (increases) the growth of the effective mass. Low-frequency absorbers: - perforated materials in the form of thin panels with varying degrees of perforation, which can be made of gypsum boards, MDF, wood, etc.;

resonant


jamming certain frequencies (from the net: To obtain a high value of the sound absorption coefficient (0.7 ... 0.9) in a wide frequency range, multilayer resonant structures are used, consisting of 2-3 parallel screens with different perforations with an air gap of different thicknesses); - resonant structures made of porous/fibrous materials, perforated/fabric screens and an air gap. The absorption coefficient of these materials is in the range of 0.3 - 1.0 in the low frequency range (63 - 500 Hz).

Combined from resonators

different frequencies are attenuated on different layers

Absorbers in a wide frequency range:
- multilayer resonant structures, consisting of several parallel screens with different degrees of perforation and an air gap of different thickness;

Low frequency

The plate, behind which there is an air gap, the greater the mass, the lower the frequency at which sound absorption occurs

For (up) efficiently

Rocker sound absorbers


From the net: Sound absorbers of the rocker type provide more absorption than flat claddings that occupy the same area of ​​​​the interior surface of the hall.

Sound-absorbing materials - acoustic materials that are used in sound-absorbing linings: - to reduce the noise level of industrial premises and technical devices; and also - to create optimal conditions for hearing and improve the acoustic properties of the premises of public buildings.
The sound-absorbing ability of materials is due to their porous structure and the presence of a large number open interconnected pores. Sound-absorbing materials are divided according to different criteria. More often than other signs, they take on the nature of sound absorption, the type and technology of manufacture, and the nature of the surface of the products. All these materials are usually also finishing, as they contribute to the creation of external architectural expressiveness of the premises.


Noise propagation in the building

structure-borne noise protection - floors


type of "floating floor" on a solid elastic gasket

suspended ceiling on springs - shock absorbers

from the net: Noise protection by building acoustic methods should be provided by:

in residential and public buildings:

rational architectural and planning solution of the building; the use of enclosing structures that provide standard sound insulation; the use of sound-absorbing linings (in the premises of public buildings); the use of noise silencers in forced ventilation and air conditioning systems;

vibration isolation of engineering and sanitary equipment of buildings;

the use of sound amplification, warning and information transmission systems.

Noise protection measures should be provided in the projects:

« Noise Protection» at the stage of the project of a detailed planning of the city area - noise maps on the territory, calculations of the expected noise at the facades of buildings (residential, administrative, children's preschool institutions, schools, hospitals), recreation areas; types and location of noise-protective buildings on main streets; installation of noise screens on sections of high-speed roads; installation of noise protection strips of green spaces; the use of noise-protective windows on the facades of buildings facing the main streets.

Acoustic calculation must be done in the following order:

identification of noise sources and determination of their noise characteristics; selection of points in the premises and on the territories for which it is necessary to carry out the calculation (calculated points); determination of noise propagation paths from the source (sources) to the calculated points and sound energy losses along each of the paths (reduction due to distance, shielding, sound insulation of enclosing structures, sound absorption, etc.); determination of expected noise levels at design points; determining the required reduction in noise levels based on a comparison of the expected noise levels with acceptable values; development of measures to ensure the required noise reduction; verification calculation of expected noise levels at design points, taking into account the implementation of construction and acoustic measures.

question 34.

Necessary conditions for creating a comfortable acoustic environment in the halls.

Intense direct sound; - correct distribution and acceptable delay of sound reflection; - sufficient diffuseness of the sound field; - optimal reverberation time; - normative noise mode; - requirements for soundproofing of halls; + providing visibility

Correct distribution and allowable delay

⌂l=logr-lpr

⌂l =(⌂l/c)*1000 ms

For speech: ⌂t=20ms, but no more than 30ms

For music: ⌂t=25ms, but no more than 35ms

The first reflections should cover the entire zone of listening places, starting from dist. rpr

Rpr is the range of direct sound, i.e. distance, beyond which direct sound is required to be supported by the first reflection.

speech: . rr = 8-9 m

music. rpr=10-12m

Checking the admissibility of using geometrics. Reflect.

Overlapping fences

Violation of the correct distribution of the reflected sound, in the presence of large concave surfaces in the hall

Relaxation methods:

Breakdown of fencing elements

Sound absorbing finish

Combined

the most efficient divisions

reflector suspension

scattering effect of the high dome


The acoustic properties of the room significantly affect the nature of the sound reproduction in it. That is why rooms intended, for example, for lectures or concerts, must have different acoustic properties.
One of the main criteria for evaluating the acoustic quality of a room is the reverberation time. With a large value, the perception of music is distorted, the intelligibility of speech decreases, with a very small value, the effect of the “lifelessness” of the room appears, the “dryness” of the reproduced works. To ensure the optimal reverberation time (or adjust it) in most cases, modern acoustic materials and constructions allow, with the help of which additional sound absorption is created in the room.

To ensure the necessary sound absorption, the greatest attention is paid to the ceiling space. Therefore, "acoustic" ceilings that absorb sound have been produced for quite a long time. In large rooms, where only ceiling space is not enough to improve acoustics, it is also recommended to use sound-absorbing wall panels.

The choice of acoustic material for the ceiling or walls depends on various parameters: the purpose of the room, its volume, the price of the material, interior features, etc., as well as on which particular area of ​​the frequency range needs to be corrected.

The conditions for the occurrence of a “fluttering” echo are the presence of large flat parallel surfaces or a dome on a flat surface.

Theatrical echo– adjoining the back wall of the hall to the ceiling at an angle of 90º or less.

Ensuring sufficient diffuseness of the sound field

No parallel or concave surfaces

Compliance with the proportions of the hall

Division of surfaces (if necessary).

Maximum length of halls

Conference halls (audiences) -24-25m

Opera and Ballet Theater 30-32

Concert hall, chamber music 20-22

Symphonic music, choirs and organ concerts 42-46

Contemporary pop music 48-50

Multi-purpose halls with a capacity of more than 1000 seats 30-34

L≤Ladd; B=S/L; H=V/S; one

Division of the hall (effect in frequencies 200-600Hz.)