Sound is the physical and physiological characteristics of sound. Hearing sensation characteristics

Control and measuring devices.

Facilities personal protection from vibration.

Organizational measures to protect against vibration exposure.

They involve the use of special work and rest regimes for workers in vibration-hazardous professions. In accordance with GOST 12.1.012-90, an increase in the vibration level is allowed, provided that the time of exposure to workers is reduced, which should be

t \u003d 480 (V 480 / V f) 2,

where V 480- normative value of vibration velocity for an 8-hour working day,

V f- actual value of vibration velocity.

In all cases, the operating time with general vibration should not be more than 10 minutes and local - 30 minutes.

Mittens, gloves and liners are used as personal protective equipment against vibration when working with hand-held power tools in accordance with GOST 12.4 002-74.

Mittens are made from cotton and linen fabrics. The palmar part is doubled with foam rubber from the inside. To protect against general vibrations, special footwear is used in accordance with GOST 12.4.024-76 (semi-boots for men and women, anti-vibration, which have a multilayer rubber sole).

Vibration measuring set IVSH-1 includes: vibration measuring transducer (sensor), measuring amplifier, bandpass filters, registering device. Measurement of vibrational speed is carried out on the surfaces of the workplace or on the surface of a manual machine. Measurement of general vibrations is carried out according to GOST 12.1.043-84, and local - according to OST 12.1.042-84.

Sound- these are elastic oscillations in a solid, liquid or gaseous medium, arising as a result of the impact on these media of a perturbing force and perceived by the hearing organs of a living organism.

Noise- this is random fluctuations of various physical nature, characterized by the complexity of the temporal and spectral structure. In everyday life, noise is understood as various kinds of unwanted acoustic vibrations that occur in the process of performing various kinds of work, and interfere with the reproduction or perception of speech, disrupt the process of rest, etc.

The human auditory organ (receiver of sound stimuli) consists of three parts: the outer ear, the middle ear and the inner ear.

Sound vibrations entering the outer ear canal and reaching eardrum, cause its synchronous oscillations, which are perceived by the end of the auditory nerve. The excitations arising in the cells then spread along the nerves and enter the central nervous system. The intensity of sensations (Ln o) when receiving sound or noise (sensitivity) depends on the intensity of the stimulus (Ln. p).

Ln o = 10 Ln. R

So, for example, in conditions of complete silence, hearing sensitivity is maximum, but it decreases in the presence of additional noise exposure. A moderate decrease in auditory sensitivity allows the body to adapt to conditions external environment and plays a protective role against strong and long-lasting noises.

Muting one sound with another is called disguise, which is often used in practice to isolate a useful signal or suppress unwanted noise (masking a sent signal on high-frequency lines, receiving signals from artificial satellites.)

To the physical characteristics of sound include: frequency, intensity (strength of sound) and sound pressure.

Oscillation frequency (f=1/T=w/2p) where T is the oscillation period, w is the circular frequency. Unit of measurement (Hz).

The human ear perceives the oscillatory movements of an elastic medium as audible in the frequency range from 20 to 20,000 Hz.

The entire audible frequency range is divided into 8 octave bands. An octave is a band in which the value of the upper cutoff frequency (f1) is twice the value of the lower cutoff frequency (f2) i.e. f1/f2 = 2. The one-third octave band is the frequency band in which this ratio is f1/f2 = 1.26. For each octave band the value of the mean geometric frequency is set:

A number of geometric mean frequencies in octave bands has the form:

63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz.

Distinguish:

Low-frequency spectrum - up to 300 Hz;

Mid-frequency - 300-800Hz;

High frequency over 800Hz.

According to GOST 12.1.003-83 "SSBT. Noise. General safety requirements" noise is usually classified according to spectral and temporal characteristics.

According to the nature of the spectrum, noise is divided into:

- broadband, with a continuous spectrum with a width of more than one octave;

Tonal, in the spectrum of which there are audible discrete tones.

According to temporal characteristics, noise is divided into:

Constants, the levels of which change over time by no more than 5 dBA (pumping, ventilation units, production equipment);

- non-constant, the levels of which during an eight-hour working day change over time by more than 5 dBA.

Intermittent noises are divided into:

Time fluctuating noises whose levels change continuously over time;

Discontinuous, noise whose levels drop sharply to the level of background noise, and the duration of the intervals. during which the level remains constant and exceeds the background level, is 1 second or more;

Pulse, consisting of one or more sound signals, each lasting less than 1 second. (signal of an artificial satellite).

Sound– fluctuations in the frequency range of human hearing, propagating in the form of waves in elastic media. Noise - a random combination of sounds of different strength and frequency. The source of noise is any process that causes a local change in pressure or mechanical vibrations in solid, liquid and gaseous media.

Sound sensations are perceived by the human hearing organs when exposed to sound waves with a frequency in the range from 16 Hz to 20 thousand Hz. Vibrations below 16 Hz are called infrasound, and those above 20,000 Hz are called ultrasound.

The origin of the noise may be mechanical, aerohydrodynamic and electromagnetic.

mechanical noise occurs as a result of shocks in the articulating parts of machines, their vibration, during the machining of parts, in gears in rolling bearings, etc. The power of the sound radiation of a vibrating surface depends on the intensity of vibrations of the vibrating surfaces, their sizes, shapes, methods of fastening, etc.

Aerohydrodynamic noise appears as a result of pressure pulsation in gases and liquids during their movement in pipelines and channels (turbo machines, pumping units, ventilation systems etc.).

electromagnetic noise is the result of stretching and bending of ferromagnetic materials when exposed to alternating electromagnetic fields (electric machines, transformers, chokes, etc.).

The impact of noise on humans is manifested from subjective irritation to objective pathological changes functions of the hearing organs, the central nervous system, of cardio-vascular system, internal organs.

The nature of the noise impact is due its physical characteristics (level, spectral composition, etc.), the duration of exposure and the psycho-physiological state of a person.

Reduced by noise attention, performance. Noise disturbs people's sleep and rest.

All the variety of neurotic and cardiological disorders, disorders of the gastrointestinal tract, hearing, etc. that occur under the influence of noise, combined into a symptom complex of "noise disease" .

From a physical point of view, sound is characterized vibration frequency, sound pressure, intensity or strength of sound. In accordance with the Sanitary Rules and Norms 2.2.4/2.1.8.10-32-2002 "Noise at Workplaces, in the Premises of Residential, Public Buildings and on the Territory of Residential Buildings", the main noise characteristics are vibration frequency, sound pressure and sound level.

Sound pressure R(Pa) - the variable component of air or gas pressure resulting from sound vibrations, Pa.

When a sound wave propagates, energy is transferred. The energy carried by a sound wave per unit time through a surface perpendicular to the direction of wave propagation is called sound intensity I(W/m2) :

,

where R– sound pressure, Pa; ρ – density of sound propagation medium, kg/m 3 ; C is the speed of sound in air, m/s.

The human hearing aid has an unequal sensitivity to sounds of different frequencies. The human auditory organ is able to perceive sound vibrations in a certain range of intensities, limited by upper and lower thresholds, depending on the sound frequency (Fig. 1).

hearing threshold has a minimum value at about 1000 Hz. Intensity or strength of sound I o it is equal to 10 -12 W / m 2, and in terms of sound pressure P o– 2x10 -5 Pa. Threshold of pain at a frequency of 1000 Hz in intensity I max equal to 10 W / m 2, and in terms of sound pressure - R max\u003d 2x10 -5 Pa. Therefore, for reference a sound with a frequency of 1000 Hz is received. Between the hearing threshold and the pain threshold lies hearing area .

The human ear reacts not to an absolute, but to a relative change in sound. According to the Weber-Fechner law, the irritating effect of noise on a person is proportional to the decimal logarithm of the square of the sound pressure. Therefore, logarithmic levels are used to characterize noise:

sound intensity level L I and sound pressure level L P . They are measured in decibels and are determined accordingly by the formulas:

, dB,

, dB,

where I And Io- actual and threshold sound intensity, respectively, W/m 2 ; R And R o- actual and threshold sound pressure respectively, Pa.

unit of measurement white named after Alexandra Graham Bell- a scientist, inventor and businessman of Scottish origin, one of the founders of telephony (Eng. Alexander Graham Bell; March 3, 1847 (18470303), Edinburgh, Scotland - August 2, 1922, Baddeck, Nova Scotia, Canada).

Fig 1. Area of ​​human auditory perception

One bel is an extremely small value, a barely noticeable change in volume corresponds to 1 dB (corresponding to a change in sound intensity by 26% or sound pressure by 12%).

The logarithmic scale in dB (0…140) allows a purely physical characteristic of the noise to be determined, independent of frequency. However, the highest sensitivity of the human hearing aid occurs at frequencies of 800...1000 Hz, and the lowest at 20...100 Hz. Therefore, in order to approximate the results of subjective measurements to subjective perception, the concept corrected sound pressure level. The essence of the correction is the introduction of amendments to the measured value of the sound pressure level depending on the frequency. Most used correction BUT. Corrected sound pressure level L A \u003d L P - ΔL A called sound level.

The physical characteristics of acoustic and, in particular, sound waves are of an objective nature and can be measured by appropriate instruments in standard units. The auditory sensation arising under the action of sound waves is subjective, but its features are largely determined by the parameters of the physical impact.

• 7. Acoustics

Acoustic wave speed v determined by the properties of the medium in which they propagate - its modulus of elasticity E and density p:

Sound speed in air is about 340 m/s and depends on temperature (air density changes with temperature change). in liquid media and soft tissues In an organism this speed is about 1500 m/s, in solids it is 3000-6000 m/s.

Formula (7.1), which determines the speed of propagation of acoustic waves, does not include their frequency, so sound waves of different frequencies in the same medium have almost the same speed. The exception is waves of such frequencies, which are characterized by strong absorption in a given medium. Usually these frequencies lie outside the audio range (ultrasound).

If sound vibrations represent a periodic

Rice. 7.1.

process, such sounds are called tones or musical sounds. They have a discrete harmonic spectrum, representing a set of harmonics with specific frequencies and amplitudes. The first harmonic of the frequency w is called basic tone, and harmonics of higher orders (with frequencies 2co, 3co, 4co, etc.) - overtones. Clean(or simple) tone corresponds to sound vibrations having only one frequency. On fig. Figure 7.1 shows the spectrum of a complex tone, in which four harmonic components are represented: 100, 200, 300 and 400 Hz. The amplitude value of the fundamental tone is taken as 100 %.

Non-periodic sounds called noises have a continuous acoustic spectrum (Fig. 7.2). They are caused by processes in which the amplitude and frequency of sound vibrations change over time (vibration of machine parts, rustling, etc.).

Rice. 7.2.

Sound intensity I, as noted earlier, is the energy of a sound wave per site of a unit area per unit time, and is measured in W / m 2.

This physical characteristic determines the level of auditory sensation, which is called volume and is a subjective physiological parameter. The relationship between intensity and loudness is not directly proportional. For now, we only note that with increasing intensity, the sensation of loudness also increases. Loudness can be quantified by comparing the auditory sensations caused by sound waves from sources of different intensities.

When sound propagates in a medium, some additional pressure arises, moving from the sound source to the receiver. The magnitude of this sound pressure P also represents the physical characteristics of sound and its propagation medium. It is related to intensity. I ratio

where p is the density of the medium; And is the speed of sound propagation in the medium.

the value Z - ri called specific acoustic impedance or specific acoustic impedance.

The frequency of sound harmonic oscillations determines that side of the sound sensation, which is called sound height. If sound vibrations are periodic, but do not obey the harmonic law, then the pitch is estimated by the ear by the frequency of the fundamental tone (the first harmonic component in the Fourier series), the period of which coincides with the period of the complex sound effect.

Note that the possibility of assessing the pitch of the human hearing aid is related to the duration of the sound. If the exposure time is less than 1/20 s, then the ear is not able to assess the pitch.

Sound vibrations close in frequency with simultaneous sounding are perceived as sounds of different heights if the relative frequency difference exceeds 2-3%. With a smaller frequency difference, there is a feeling of a continuous sound of medium height.

The spectral composition of sound vibrations (see Fig. 7.1) is determined by the number of harmonic components and the ratio of their amplitudes and characterizes timbre sound. Timbre, as a physiological characteristic of the auditory sensation, to some extent also depends on the rate of rise and variability of the sound.

Sound as a physical phenomenon is characterized by sound pressure P(Pa), intensity I(W / m 2) and frequency f(Hz).

Sound as a physiological phenomenon is characterized by the level of sound (phones) and loudness (sleeps).

The propagation of sound waves is accompanied by the transfer of vibrational energy in space. Its amount passing through the area
1 m 2, located perpendicular to the direction of propagation of the sound wave, determines the intensity or strength of the sound I,

W / m 2, (7.1)

where E is the sound energy flux, W; S- Area, m2 .

The human ear is not sensitive to sound intensity, but to pressure. R, rendered by a sound wave, which is determined by the formula

where F is the normal force with which the sound wave acts on the surface, N; S is the surface area on which the sound wave falls, m 2 .

The sound intensities and sound pressure levels that have to be dealt with in practice vary widely. Oscillations of sound frequencies can be perceived by the human ear only at a certain intensity or sound pressure. The threshold values ​​of sound pressure at which sound is not perceived or the sound sensation turns into pain are called the hearing threshold and the pain threshold, respectively.

The threshold of hearing at a frequency of 1000 Hz corresponds to a sound intensity of 10 -12 W/m 2 and a sound pressure of 2·10 -5 Pa. At a sound intensity of 1 W/m 2 and a sound pressure of 2·10 1 Pa (at a frequency of 1000 Hz), a feeling of pain in the ears is created. These levels are called the threshold of pain and exceed the threshold of hearing by 10 12 and 10 6 times, respectively.

To assess the noise, it is convenient to measure not the absolute value of the intensity and pressure, but their relative level in logarithmic units, characterized by the ratio of the actually created intensity and pressure to their values ​​corresponding to the hearing threshold. On a logarithmic scale, an increase in the intensity and pressure of sound by 10 times corresponds to an increase in sensation by 1 unit, called white (B):

, Bel, (7.3)

(9.3)

where I o and R o - initial values ​​of intensity and sound pressure (intensity and pressure of sound at the threshold of hearing).

For the initial figure 0 (zero) Bel adopted threshold for hearing the value of sound pressure 2·10 -5 Pa (threshold of hearing or perception). The entire range of energy perceived by the ear as sound fits under these conditions in 13-14 B. For convenience, they use not white, but a unit 10 times smaller - decibel (dB), which corresponds to the minimum increase in sound strength distinguishable by the ear.

At present, it is generally accepted to characterize the noise intensity in terms of sound pressure levels, determined by the formula

, dB, (7.4)

where R- RMS value of sound pressure, Pa; R o - initial value of sound pressure (in air Р o = 2·10 -5 Pa).

The third important characteristic of sound, which determines its height, is the frequency of vibrations, measured by the number of complete vibrations made during 1 s (Hz). The oscillation frequency determines the pitch of the sound: the higher the oscillation frequency, the higher the sound. However, in real life, including in production conditions, we most often meet with sounds with a frequency of 50 to 5000 Hz. The human hearing organ reacts not to an absolute, but to a relative increase in frequencies: a doubling of the oscillation frequency is perceived as an increase in tone by a certain amount, called an octave. Thus, an octave is a range in which the upper limit frequency is equal to twice the lower frequency.

This assumption is due to the fact that when the frequency is doubled, the pitch changes by the same amount, regardless of the frequency interval in which this change occurs. Each octave band is characterized by a geometric mean frequency, determined by the formula

where f 1 – lower limiting frequency, Hz; f 2 – upper limiting frequency, Hz.

The entire frequency range of sounds heard by a person is divided into octaves with geometric mean frequencies of 31.5; 63; 125; 250; 500; 1000; 2000; 4000 and 8000 Hz.

The distribution of energy over noise frequencies is its spectral composition. In the hygienic assessment of noise, both its intensity (strength) and the spectral composition in terms of frequencies are measured.

The perception of sounds depends on the frequency of vibrations. Sounds that are the same in intensity, but different in frequency, are perceived by the ear as unequally loud. When the frequency changes, the sound intensity levels that determine the threshold of hearing change significantly. The dependence of the perception of sounds of different intensity levels on frequency is illustrated by the so-called curves of equal loudness (Fig. 7.1). To assess the level of perception of sounds of different frequencies, the concept of the sound volume level is introduced, i.e. conditional reduction of sounds of different frequencies, but the same volume to the same level at a frequency of 1000 Hz.

Rice. 7.1. Equal Loudness Curves

The sound volume level is the intensity level (sound pressure) of a given sound with a frequency of 1000 Hz, which is equally loud with it to the ear. This means that each equal loudness curve corresponds to one loudness level (from loudness level 0, corresponding to the threshold of hearing, to loudness equal to 120, corresponding to the threshold of pain). The loudness level is measured in an off-system dimensionless unit - phon.

Evaluation of sound perception using loudness level, measured in phons, does not give a complete physiological picture of the effect of sound on the hearing aid, because. A 10 dB increase in sound level creates the sensation of doubling the volume.

A quantitative relationship between the physiological sensation of loudness and loudness level can be obtained from the loudness scale. The loudness scale is easily formed taking into account the ratio that the loudness value of one son corresponds to the loudness level of 40 phon (Fig. . 7.2).

Rice. 7.2. Volume scale

Prolonged exposure to noise at high intensity levels can cause desensitization auditory analyzer, as well as cause disorders of the nervous system and affect other functions of the body (disturbs sleep, interferes with performing strenuous mental work), so for different rooms and various kinds works, various permissible noise levels are established.

Noise below 30-35 dB does not feel tiresome or noticeable. This noise level is acceptable for reading rooms, hospital wards, living rooms at night. For design bureaus, office premises, a noise level of 50-60 dB is allowed.

Noise classification

Industrial noise can be classified according to various criteria.

By origin - aerodynamic, hydrodynamic, metallic, etc.

According to the frequency response - low-frequency (1-350 Hz), mid-frequency (350-800 Hz), high-frequency (more than 800 Hz).

According to the spectrum - broadband (noise with a continuous spectrum with a width of more than 1 octave), tonal (noise in the spectrum of which there are pronounced tones). Broadband noise with the same sound intensity at all frequencies is conventionally referred to as "white". The tonal nature of the noise for practical purposes is established by measuring in 1/3 octave frequency bands by exceeding the level in one band over the neighboring ones by at least 10 dB.

According to the temporal characteristics, the noise is divided into permanent or stable and non-permanent. Constant noise is the noise, the sound level of which during an 8-hour working day or during the measurement in the premises of residential and public buildings, on the territory of residential development changes in time by no more than 5 dBA when measured on the time characteristic of the sound level meter "slowly".

Intermittent noise is noise whose sound level during an 8-hour working day, during a work shift or during measurements in the premises of residential and public buildings, on the territory of residential development changes over time by more than 5 dBA when measured on the time characteristic of the sound level meter "slowly ".

Intermittent noise can be fluctuating, intermittent and impulsive:

time-varying noise is noise whose sound level changes continuously over time;

intermittent noise - this is noise, the sound level of which changes stepwise (by 5 dBA or more), and the duration of the intervals during which the level remains constant is 1 s or more;

impulse noise is noise consisting of one or more audio signals, each less than 1 s long, with sound levels in dBA I and dBA, measured respectively on the time characteristics "impulse" and "slow", differ by at least 7 dB.

The last two types of noise (intermittent and impulse) are characterized by a sharp change in sound energy over time (whistles, beeps, blows of a blacksmith's hammer, shots, etc.).

Characteristics of constant noise at workplaces are sound pressure levels in dB in octave bands with geometric mean frequencies of 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz, determined by formula (7.4).

It is allowed to take as a characteristic of constant broadband noise at workplaces the sound level in dBA, measured on the “slow” time characteristic of the sound level meter, determined by the formula:

, dBA, (7.6)

where P (A) is the root mean square value of the sound pressure, taking into account the correction "A" of the sound level meter, Pa

A characteristic of intermittent noise at workplaces is the equivalent (in terms of energy) sound level in dBA.

Equivalent (energy) sound level, L A(eq), in dBA of a given intermittent noise, is the sound level of continuous broadband noise that has the same RMS sound pressure as the given intermittent noise over a specified time interval and is determined by the formula

, dBA, (7.7)

where p A(t) is the current value of the root-mean-square sound pressure, taking into account the correction " BUT"Sound level meter, Pa; p 0 - the initial value of sound pressure (in air p 0 = 2 10 -5 Pa); T– duration of the noise, h.

Noise- this is a set of sounds of different intensity and height, randomly changing in time and causing unpleasant subjective sensations in workers. From a physiological point of view, noise is any unwanted sound that interferes with the perception of useful sounds in the form of production signals and speech.

Noise as a physical factor is a wave-like mechanical oscillatory motion of an elastic medium (air), which, as a rule, has a random random character. In this case, its source is any oscillating body, brought out of a stable state by an external force.

The nature of the propagation of oscillatory motion in a medium is called sound wave, and the area of ​​the environment in which it spreads - sound field.

Sound represents an oscillatory movement of an elastic medium, perceived by our organ of hearing. The movement of a sound wave in air is accompanied by a periodic increase and decrease in pressure. The periodic increase in air pressure compared to atmospheric pressure in an undisturbed medium is called sound pressure. The greater the pressure, the stronger the irritation of the organ of hearing and the sensation of loudness of the sound. In acoustics, sound pressure is measured in N/m2, or Pa. The sound wave is characterized by frequency f, Hz, sound intensity I W/m 2 sound power W, Tue The speed of propagation of sound waves in the atmosphere at 20 °C and normal atmospheric pressure is 344 m/s. The speed of sound does not depend on the frequency of sound vibrations and is a constant value at constant parameters of the medium. With an increase in air temperature by 1 °C, the speed of sound increases by approximately 0.71 m/s.

Human hearing organs perceive sound vibrations in the frequency range from 16 to 20,000 Hz, the zone of greatest hearing sensitivity is in the region of 50-5000 Hz. Vibrations with a frequency of up to 16 Hz (infrasound) and above 20,000 Hz (ultrasound) are not perceived by the human ear.

The intensity of noise (sound) is measured both in the entire frequency range (total sound energy), and in a certain range of the frequency band - within octaves.

Octave- this is the frequency range in which the upper frequency limit is twice the lower one (for example, 40-80, 80-160 Hz). However, to designate an octave, it is usually not the frequency range that is indicated, but the so-called geometric mean frequencies, which characterize the strip as a whole and are determined by the formula

where f 1 and f 2 - respectively, the lowest and highest frequencies, Hz.

So, for an octave of 40-80 Hz, the geometric mean frequency is 62.5 Hz; for octave 80-160 Hz - 125 Hz, etc.

In acoustic measurements, the intensity is determined within frequency bands equal to an octave, half an octave and a third of an octave.

The geometric mean frequencies of the octave bands are standardized and for the sanitary and hygienic assessment of noise are 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz.

The minimum amount of sound that can be heard by the ear is called hearing threshold(I 0 \u003d 10 -12 W / m 2), it corresponds to sound pressure P 0 = 2-Yu "5 Pa.

Threshold of pain occurs at a sound strength equal to 10 2 W / m 2, and the corresponding sound pressure is 2 * 10 2 Pa. As you can see, the changes in the sound pressure of audible sounds are huge and amount to about 10 7 times. Therefore, for the convenience of measurement and sanitary-hygienic regulation of sound intensity and sound pressure, not absolute physical, but relative units are taken, which are the logarithms of the ratios of these quantities to the conditional zero level corresponding to the hearing threshold of a standard tone with a frequency of 1000 Hz.

Sound intensity level L, dB, determined by the formula

where I- sound intensity, W/m 2 ; I 0 - sound intensity taken as the threshold of hearing, equal to 10 -12 W/m 2 . Since the sound intensity is proportional to the square of the sound pressure, this formula can be written as

These logarithms of the ratios are called respectively sound intensity levels or more often sound pressure levels they are expressed in belah(B).

In addition, for a sanitary and hygienic assessment of the impact of noise on the human body, such an indicator as the sound level is used, determined on the A scale of a sound level meter with a dimension in dBA.

Since the human hearing organ is capable of distinguishing a change in the sound intensity level by 0.1 B, it is more convenient for practical use to have a unit 10 times less - decibel(dB).

Using the decibel scale is very convenient, since the entire huge range of audible sounds fits in less than 140 dB. When exposed to sound over 140 dB, pain and rupture of the eardrum are possible.

In production conditions, as a rule, there are noises of varying intensity and frequency, which are created as a result of the operation of various mechanisms, units and other devices.

Production noise, which is a complex sound, can be decomposed into simple components, the graphic representation of which is called spectrum(Fig. 2.4). It is a combination of eight levels of sound pressure at all geometric mean frequencies. The character may be different depending on the prevailing frequencies.

Rice. 2.4. Main types of noise spectra: but - discrete (linear); b- solid; in - mixed

If in this set the normative values ​​​​of sound pressure levels are presented, then it is called limit spectrum(PS). Each of the limiting spectra has its own index, for example, PS-80, where 80 is the standard sound pressure level (dB) in the octave band with f = 1000 Hz.

According to GOST 12.1.003, noise is classified according to the following features:

♦ by the nature of the spectrum: broadband, with a continuous spectrum more than an octave wide; tonal, in the spectrum of which there are audible tones. The tonal character is determined by the excess of the noise level in one band over adjacent one-third octave bands by at least 10 dB;

♦ by time characteristics: constant And fickle;

♦ noise is distinguished by frequency response low, medium And high frequency, having, respectively, the boundaries of 16-350, 350-800 and above 800 Hz.

Intermittent noises, in turn, are divided into:

♦ on fluctuating in time the sound level of which changes continuously over time;

♦ intermittent, the sound level of which changes in steps (by 5 dBA or more), and the duration of the intervals during which the level remains constant is 1 s or more;

♦ impulse, consisting of one or more sound signals, each lasting less than 1 s, while the sound levels differ by at least 7 dB.

Noise characterization in decibels within frequencies is not always sufficient. It is known that sounds having the same intensity but different frequencies are perceived by ear as unequally loud. Sounds that have a low or very high frequency (near upper bound perceived frequencies) are perceived as quieter compared to sounds in the middle zone. Therefore, to compare sounds of different frequency composition with respect to their loudness, loudness units are used - backgrounds And sleep.

The unit of comparison is conventionally taken as a sound with a frequency of 1000 Hz. IN international recommendations in recent years, sound with a frequency of 2000 Hz has been adopted as the standard.

Noise volume level(sound) is the level of strength of a sound equal to this noise with an oscillation frequency of 1000 Hz, for which the sound strength level in decibels is conditionally taken as the loudness level in phons. One background is the loudness of sound at 1000 Hz and 1 dB intensity level. At 1000 Hz, the volume levels are equal to the sound pressure levels. For example, a sound with an oscillation frequency of 100 Hz and a strength of 50 dB is perceived as equal to a sound with an oscillation frequency of 1000 Hz and a strength of 20 dB (20 phons). At low volume levels and low frequencies, the discrepancies between the sound intensity in decibels and the loudness level in phons are greatest. As the volume and frequency increase, this difference smoothes out.

Rice. 2.5. Curves of equal loudness of sounds

On fig. 2.5 shows equal loudness curves characterizing the loudness levels within earshot. It can be seen that the human hearing organ has the highest sensitivity at 800-4000 Hz, and the lowest - at 20-100 Hz.

Along with assessing the loudness of noise in the backgrounds, another unit of loudness is also used - sleep, which more clearly reflects the change in subjectively perceived loudness and allows you to determine how many times one sound is louder than another. With an increase in volume by 10 backgrounds, the volume level in sons increases by 2 times.

The loudness scale in dreams allows you to determine how many times the noise volume has decreased after the introduction of certain measures to combat it, or how many times the noise at one workplace is louder than the noise at another.

With the simultaneous propagation of several sound waves, it is possible to increase or decrease the volume of noise as a result of interference phenomena.

Vibration- these are mechanical oscillations and waves in solids, or more specifically, these are mechanical, most often sinusoidal, oscillations that occur in machines and apparatuses.

According to the method of impact on a person, vibrations are divided into general, transmitted through the supporting surfaces to the body of a seated or standing person, and local transmitted through human hands.

General vibration, depending on the source of its occurrence, is divided into three categories:

♦ transport: affects operators of mobile machines and Vehicle during their movement (1st category);

♦ transport and technological: with limited movement only on specially prepared surfaces of industrial premises (2nd category);

♦ technological: affects the operators of stationary machines or is transmitted to workplaces that do not have sources of vibration (category 3).

♦ at permanent workplaces of industrial premises;

♦ at workplaces in warehouses, canteens, amenity, duty and other auxiliary production facilities, where there are no machines and mechanisms that generate vibration;

♦ at workplaces in the administrative and service premises of the plant management, design bureaus, laboratories, training centers, computer centers, health centers, office premises, work rooms and other premises for mental workers.

General vibration is most often exposed to transport workers, operators of powerful dies, punching presses, etc.

Basic physical parameters of vibration: frequency f, Hz; oscillation amplitude A, m; oscillation speed V, m/s; oscillatory acceleration but, m/s 2 .

According to the nature of the spectrum, vibration is divided into:

♦ to narrowband with a frequency spectrum located
in a narrow band. At the same time, the level of controlled steam
meters in the octave frequency band by more than 15 dB above
no values ​​in adjacent one-third octave bands;

♦ broadband with a frequency spectrum, located
wide band (more than one octave wide).

According to the temporal characteristics, the vibration is divided into:

♦ on permanent, for which the spectral or frequency-corrected normalized parameter during the observation time (at least 10 minutes or the time of the technological cycle) changes by no more than 2 times (6 dB) when measured with a time constant of 1 s;

♦ fickle, for which the spectral or frequency-corrected normalized parameter during the observation time (at least 10 min or the time of the technological cycle) changes by more than 2 times (6 dB) when measured with a time constant of 1 s.

Intermittent vibration is:

♦ wavering in time, for which the value of the normalized parameter changes continuously in time;

♦ intermittent when the impact of vibration on a person is interrupted, and the duration of the intervals during which the vibration is affected is more than 1 s;

♦ impulse, consisting of one or more vibration impacts (shocks), each lasting less than 1 s.

Local vibration is mainly exposed to persons working with hand-held mechanized electric or pneumatic tools.

As well as for noise, the entire spectrum of vibration frequencies perceived by a person can be divided into octave and one-third octave frequency bands with geometric mean frequencies of octave bands 1; 2; 4; 8; 16; 32; 63; 125; 250; 500; 1000 and 2000 Hz.

The value V0\u003d 510 -8 m / s, corresponding to the root-mean-square vibrational velocity at a standard sound pressure threshold of 2 10 -5 Pa, although the vibration perception threshold for a person is much higher and equal to 10 -4 m / s. The zero level of oscillatory acceleration is taken as the value a = 3-10 -4 m/s 2 . At an oscillatory speed of 1 m/s, a person experiences pain.

Since the absolute values ​​of the parameters characterizing vibration vary over a very wide range, it is more convenient to measure non-real values

of these parameters, and the logarithms of their ratios to the threshold ones.

Vibration velocity level L v , dB, determined by the formula

where V- actual value of vibration velocity, m/s; V0- threshold value of vibration velocity (510 -8 m/s).

Spectra of vibrational velocity levels are the main characteristics of vibrations; they can be, just as for noise, discrete, continuous, and mixed.

SanPiN 2.2.4/2.1.8.10-33-2002 gives the relationship between the levels of vibration velocity in decibels and its values ​​in meters per second, as well as between the logarithmic levels of vibration acceleration in decibels and its values ​​in meters per second squared.

2.4.2. Impact noise, vibration and other fluctuations on the human body

Noise and vibration can, to a greater or lesser extent, temporarily activate or permanently suppress certain mental processes in the human body. Physiopathological consequences can manifest themselves in the form of a violation of the functions of hearing and other analyzers, for example, the vestibular apparatus, coordinating the functions of the cerebral cortex, nervous or digestive system, circulatory system. In addition, noise affects carbohydrate, fat and protein metabolism in the body.

Sounds of different frequencies, even with the same intensity, are perceived differently. Low-frequency sounds are perceived as relatively quiet, but as their frequency increases, the volume of perception increases, and as they approach the upper high-frequency border of the audio spectrum, the volume of perception falls again.

The area of ​​​​auditory perception available to the human ear is limited by the thresholds of hearing and pain sensation (Fig. 2.6). The boundaries of these thresholds, depending on

Rice. 2.6. Area of ​​auditory perception: P - speech; M - music; C - threshold of hearing; B - pain threshold

ti change significantly with frequency. This explains that high-frequency sounds are more unpleasant for a person than low-frequency ones (at the same sound pressure levels).

Occupational noise of varying intensity and spectrum, which affects workers for a long time, can eventually lead to a decrease in hearing acuity in the latter, and sometimes to the development of occupational deafness. It has been established that hearing loss usually occurs when exposed to noise in the frequency range of 3000-6000 Hz, and speech intelligibility is impaired at a frequency of 1000-2000 Hz. The greatest hearing loss of workers is observed in the first ten years of work, and this danger increases with age.

Vibration affects the central nervous system (CNS), gastrointestinal tract, balance organs ( vestibular apparatus), causes dizziness, numbness of the limbs, joint diseases. Prolonged exposure to vibration leads to occupational disease- vibration disease, effective treatment

Rice. 2.7. Types of effects of vibration on the human body

which is possible only for early stages, and the restoration of impaired functions proceeds extremely slowly, and under certain conditions, irreversible processes can occur in the body, accompanied by a complete loss of ability to work.

On fig. 2.7 summarizes the impact of vibration on the human body.

except harmful effects on the human body, vibration leads to the destruction of buildings, structures, communications, equipment breakdown. Its negative impact also lies in reducing the efficiency of operating machines and mechanisms, premature wear of rotating parts due to their imbalance, lowering the accuracy of control and measuring instruments (CIP), disruption of the functioning of automatic control systems, etc.

by infrasound It is customary to call vibrations propagating in the air with a frequency below 16 Hz. The low frequency of the infrasonic vibration determines a number of features of its propagation in environment. Due to the large wavelength, infrasonic vibrations are less absorbed in the atmosphere and more easily go around obstacles than vibrations with a higher frequency. This explains the ability of infrasound to propagate over considerable distances with little loss of energy. That is why standard measures to combat noise in this case are ineffective.

Under the influence of infrasound, vibration of large elements of building structures occurs, and due to resonance effects and excitation of secondary induced noise in the sound range, infrasound amplification may occur in some rooms.

The sources of infrasound can be means of land, air and water transport, pressure pulsation in gas-air mixtures (large-diameter nozzles), etc.

Compressors are the most characteristic and widespread source of low-acoustic vibrations. It is noted that the noise of compressor shops is low-frequency with a predominance of infrasound, and in the cabins of operators, infrasound becomes more pronounced due to the attenuation of higher-frequency noises.

Powerful ventilation systems and air conditioning systems are also sources of infrasonic vibrations. The maximum levels of their sound pressure respectively reach 106 dB at 20 Hz, 98 dB at 4 Hz, 85 dB at 2 and 8 Hz.

In the frequency range of 16-30 Hz, the threshold for the perception of infrasonic vibrations for the auditory analyzer is 80-120 dBA, and pain threshold- 130-140 dBA.

The effect of infrasound on a person is perceived as a physical load: spatial orientation is disturbed, seasickness, digestive disorders, visual disturbances, dizziness, and peripheral circulation change. The degree of exposure depends on the frequency range, sound pressure level and duration of exposure. Oscillations at a frequency of 7 Hz interfere with concentration and cause a feeling of fatigue, headache and nausea. The most dangerous oscillations with a frequency of 8 Hz. They can cause the phenomenon of resonance of the circulatory system, leading to an overload of the heart muscle, heart attack or even rupture of some blood vessels. Infrasound of low intensity can cause increased nervousness, cause depression.

Ultrasonic equipment and technologies are widely used in various branches of human activity for the purpose of active influence on substances (soldering,

welding, tinning, machining, degreasing parts, etc.); structural analysis and control of physical and mechanical properties of matter and materials (defectoscopy); for processing and transmission of radar and computer signals; in medicine - for diagnostics and therapy various diseases using sound imaging, cutting and joining biological tissues, sterilizing instruments, hands, etc.

Ultrasonic devices with operating frequencies of 20-30 kHz are widely used in industry. The most common levels of sound and ultrasonic pressure at workplaces in production are 90-120 dB.

ultrasound it is customary to consider oscillations above 20 kHz, propagating both in air and in liquid and solid media. In industrial sanitation, contact and air types of ultrasound are distinguished (San-PiN 9-87-98 and SanPiN 9-88-98).

contact ultrasound- this is ultrasound transmitted when hands or other parts of the human body come into contact with its source, workpieces, devices for holding them, sounded liquids, scanners of medical ultrasonic equipment, search heads of ultrasonic flaw detectors, etc.

air ultrasound are ultrasonic vibrations in air.

From these definitions, it follows that ultrasound is transmitted to a person through contact with air, water, or directly from a vibrating surface (tools, machines, apparatus, and other possible sources).

The thresholds for auditory perception of high-frequency sounds and ultrasounds are at a frequency of 20 kHz - 110 dB, 30 kHz - up to 115 dB and 40 kHz - up to 130 dB. Conventionally, the ultrasonic range is divided into low-frequency - 1.1210 4 -1.0 10 5 Hz, propagating by air and contact, and high-frequency - 1.0 10 5 -1.0 10 9, propagating only by contact.

High-frequency ultrasound practically does not propagate in the air and can affect workers mainly when the ultrasound source comes into contact with the open surface of the body.

Low-frequency ultrasound, on the contrary, has a general effect on workers through the air and a local one due to the contact of hands with the workpieces in which ultrasonic vibrations are excited.

Ultrasonic vibrations directly at the source of their formation propagate in a direction, but already at a small distance from the source (25-50 cm) they turn into concentric waves, filling the entire working room with ultrasound and high-frequency noise.

Ultrasound has a significant effect on the human body. As already noted, ultrasound can propagate in all media: gaseous, liquid and solid. Therefore, in the human body, it affects not only the actual organs and tissues, but also the cellular and other fluids. When propagating in a liquid medium, ultrasound causes cavitation of this liquid, i.e., the formation in it of the smallest void bubbles filled with vapors of this liquid and substances dissolved in it, and their compression (collapse). This process is accompanied by the formation of noise.

When working on powerful ultrasonic units, operators complain of headaches, which, as a rule, disappear when work is stopped; fast fatigue; night sleep disturbance; feeling of irresistible drowsiness during the day; blurred vision, feeling of pressure on eyeballs; poor appetite; constant dryness in the mouth and stiffness of the tongue; pain in the abdomen, etc.