8.5 methods and means of noise control. Methods to combat noise at work

To combat noise in the premises, measures of both a technical and medical nature are taken. The main ones are:

eliminating the cause of noise, i.e. replacing noisy equipment and mechanisms with more modern, quiet equipment;

isolation of the noise source from the environment (use of silencers, screens, sound-absorbing building materials);

fencing noisy industries with green areas;

application of rational layout of premises;

use of remote control when operating noisy equipment and machines;

use of automation tools to manage and control technological production processes;

use of personal protective equipment (ear muffs, headphones, cotton swabs);

conducting periodic medical examinations with audiometry;

compliance with the work and rest regime;

carrying out preventive measures aimed at restoring health.

Sound intensity is determined using a logarithmic loudness scale. The scale is 140 dB. The zero point of the scale is taken to be the “threshold of hearing” (a weak sound sensation, barely perceived by the ear, equal to approximately 20 dB), and the extreme point of the scale is 140 dB - the maximum volume limit.

Volume below 80 dB usually does not affect the hearing organs, volume from 0 to 20 dB is very quiet; from 20 to 40 - quiet; from 40 to 60 - average; from 60 to 80 - noisy; above 80 dB - very noisy.

To measure the strength and intensity of noise, various instruments are used: sound level meters, frequency analyzers, correlation analyzers and correlometers, spectrometers, etc.

The principle of operation of the sound level meter is that the microphone converts sound vibrations into electrical voltage, which is supplied to a special amplifier and, after amplification, is rectified and measured by an indicator on a graduated scale in decibels.

The noise analyzer is designed to measure the noise spectra of equipment. It consists of an electronic bandpass filter with a bandwidth equal to 1/3 octave.

The main measures to combat noise are the rationalization of technological processes using modern equipment, sound insulation of noise sources, sound absorption, improved architectural and planning solutions, and personal protective equipment.

At particularly noisy production enterprises, individual noise protection devices are used: antiphons, anti-noise headphones (Fig. 1.6) and earplugs. These products must be hygienic and easy to use.

Russia has developed a system of health-improving and preventive measures to combat noise in industries, among which sanitary norms and rules occupy an important place. Compliance with established norms and rules is monitored by sanitary service and public control bodies.

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1. Sound and its characteristics

Mechanical vibrations of particles of an elastic medium in the frequency range 16 - 20000 Hz are perceived by the human ear and are called sound waves. Vibrations of the medium with frequencies below 16 Hz are called infrasound, and vibrations with frequencies above 20,000 Hz are called ultrasound. The sound wavelength is related to the frequency f and the speed of sound with the relationship = c/f.

The unsteady state of the medium during the propagation of a sound wave is characterized by sound pressure, which is understood as the root-mean-square value of the excess of pressure in the medium during the propagation of a sound wave above the pressure in an undisturbed medium, measured in pascals (Pa).

The transfer of energy by a plane sound wave through a unit surface perpendicular to the direction of propagation of the sound wave is characterized by sound intensity (sound power flux density),

W/m2: I = P2/(? c),

where P is sound pressure, Pa; - specific density of the medium, g/m 3 ;

c is the speed of propagation of a sound wave in a given medium, m/s.

The speed of energy transfer is equal to the speed of propagation of the sound wave.

The human hearing organs are capable of perceiving sound vibrations in very wide ranges of changes in intensities and sound pressures. For example, at a sound frequency of 1 kHz, the sensitivity threshold of the “average” human ear (hearing threshold) corresponds to the values P 0 = 2·10-5 Pa; I 0 = 10-12 W/m 2 , and the pain threshold (exceeding which can lead to physical damage to the hearing organs) corresponds to the values P b = 20 Pa and I b = 1 W/m 2 . In addition, in accordance with the Weber-Fechner law, the irritating effect of sound on the human ear is proportional to the logarithm of sound pressure. Therefore, in practice, instead of absolute values of intensity and sound pressure, their logarithmic levels, expressed in decibels (dB), are usually used:

L I = 10lg(I/I 0), L P = 20lg(P/P 0) ; (1)

where I 0 = 10-12 W/m2 and P 0 = 2·10-5 Pa are standard threshold values of intensity and sound pressure. For normal atmospheric conditions, we can assume that L I = L P = L.

If the sound at a given point consists of n components from several sources with sound pressure levels Li, then the resulting sound pressure level is determined by the formula:

(2)

where L i is the sound pressure level of the i-th component at the design point (dB).

In the case of n identical sound components L i = L, the total level is:

L = L + 10log(n). (3)

From formulas (2) and (3) it follows that if the level of one of the sound sources exceeds the level of another by more than 10 dB, then the sound of the weaker source can practically be neglected, since its contribution to the overall level will be less than 0.5 dB. Thus, when dealing with noise, it is first necessary to drown out the most intense sources of noise. In addition, when there are a large number of identical noise sources, eliminating one or two of them has very little effect on the overall noise reduction.

Characteristics of a noise source are sound power and its level. Sound power W, W, is the total amount of sound energy emitted by a noise source per unit time. If energy is radiated uniformly in all directions and the attenuation of sound in air is small, then at intensity I at a distance r from the noise source, its sound power can be determined by the formula

W = 4 r 2 I. By analogy with logarithmic levels of intensity and sound pressure, logarithmic sound power levels (dB) L W = 10 log(W/W 0), where W 0 = 10 -12 is the threshold value of sound power, W, are introduced.

The noise spectrum shows the distribution of noise energy in the audio frequency range and is characterized by sound pressure or intensity levels (for sound sources - sound power level) in the analyzed frequency bands, which, as a rule, are octave and one-third octave frequency bands characterized by lower f n and upper f in boundary frequencies and geometric mean frequency f сг = (f n f in) 1/2.

The octave band of sound frequencies is characterized by the ratio of its boundary frequencies satisfying the condition f in /f n = 2, and for the one-third octave band - the condition f in /f n = 2 1/3? 1.26.

Each octave frequency band includes three one-third octave bands, and the geometric mean frequency of the central one coincides with the geometric mean frequency of the octave band. Geometric mean frequencies f с octave bands are determined by a standard binary series, including 9 values: 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz.

2. Features of subjective perception of sound

The perception of sound by the human ear is very strong and non-linear. depends on its frequency. Features of the subjective perception of sound are most conveniently illustrated graphically using curves of equal loudness. Each of the family of curves in Fig. 1 characterizes sound pressure levels at various frequencies corresponding to the same loudness of sound perception and loudness level L N (background).

The volume level L N is numerically equal to the sound pressure level at a frequency of 1 kHz. At other frequencies, different sound pressure levels are required to achieve the same sound volume. From Fig. 1 it follows that the shape of the equal loudness curve and the corresponding characteristic of auditory sensitivity depend on the value of L N .

In calculations and measurements, the frequency response of the hearing organ is usually modeled by the frequency response of the correction filter A. Characteristic A is standard and is set by the correction system A i = ?(f сг i), where f сг i is the geometric mean frequency of the i-th octave band.

To correspond the objective results of sound pressure level measurements to the subjective perception of sound volume, the concept of sound level is introduced. Sound level L A (dBA) is the resulting sound pressure level of noise that has undergone mathematical or physical processing in a correction filter with characteristic A. The sound level value approximately corresponds to the subjective perception of noise loudness, regardless of its spectrum. The sound level is calculated taking into account the corrections A i using formula (2), into which (L i + A i) should be substituted instead of L i. Negative values of A i characterize the deterioration of auditory sensitivity compared to auditory sensitivity at a frequency of 1000 Hz.

2. Characteristics of noise and its regulation

Based on the nature of the spectrum, noise is divided into broadband (with a continuous spectrum more than one octave wide) and tonal, in the spectrum of which there are pronounced discrete tones, measured in one-third octave frequency bands with an excess of the sound pressure level over adjacent bands by at least 10 dB.

According to the time characteristics, noise is divided into constant, the sound level of which during an 8-hour working day changes by no more than 5 dBA when measured on the time characteristic of a “slow” sound level meter, and non-constant, which does not satisfy this condition.

Intermittent noises, in turn, are divided into the following types:

· time-fluctuating noises, the sound level of which continuously changes over time;

· intermittent noises, 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 at least 1 s;

· impulse noise, consisting of one or more sound signals, each lasting less than 1 s, while the sound levels in dBA and dBA(I), measured respectively on the “slow” and “impulse” time characteristics of the sound level meter, differ by at least 7 dBA.

To assess non-constant noise, the concept of equivalent sound level L A e (based on impact energy), expressed in dBA and determined by the formula L A e = 10log(I AC / I 0), where I AC is the average value of the intensity of non-constant noise, corrected by characteristic A, on the control time interval T.

Current values of sound level L A and intensity I A are related by the relation

L A (t) = 10lg(I A (t) /I 0), I AC /I 0 = (1/T)(I A (t) /I 0)dt, therefore

(4)

The values of L A e can be calculated either by automatically integrating sound level meters or manually based on the results of measurements of sound levels every 5 s during the noisiest 30 minutes.

The normalized noise parameters are:

· for constant noise - sound pressure levels L P (dB) in octave frequency bands with geometric mean frequencies 31.5; 63; 125; 250; 500; 1000; 2000; 4000 and 8000 Hz; in addition, for an approximate assessment of constant broadband noise in workplaces, it is permissible to use the sound level L A expressed in dBA;

· for non-constant noise (except for pulsed noise) - the equivalent sound level L A e (in terms of impact energy), expressed in dBA, is the sound level of such constant broadband noise that affects the ear with the same sound energy as the real one, changing during time noise over the same period of time;

· for impulse noise - the equivalent sound level L А e, expressed in dBA, and the maximum sound level L А max in dBA(I), measured on the time characteristic “impulse” of the sound level meter.

Permissible values of noise parameters are regulated by SN 2.2.4/2.1.8.562-96 “Noise in workplaces, in residential and public buildings and in residential areas.” Permissible values of noise parameters at workplaces are established depending on the type of work performed and the nature of the noise. For work related to creative, scientific activities, training, programming, the lowest noise levels are provided.

Below are the characteristic types of work distinguished during standardization, indicating the serial number:

1) creative, scientific work, training, design, construction, development, programming;

2) administrative and managerial work, work requiring concentration, measurement and analytical work in the laboratory;

3) dispatch work that requires voice communication by telephone, in computer information processing rooms, in precision assembly areas, in typing bureaus;

4) work in premises for the placement of noisy computer units, associated with the processes of observation and remote control without voice communication by telephone, in laboratories with noisy equipment;

5) all types of work except those listed in paragraphs. 1 - 4.

For broadband noise at workplaces in Table. 1 shows the permissible sound pressure levels L P in octave frequency bands with geometric mean frequencies f сг, sound levels L A (for subjective assessment of the loudness of constant noise) and equivalent sound levels L A e (for assessment of non-constant noise).

Table 1

Acceptable noise levels

type of work	Sound pressure levels L P (dB) in octave frequency bands with geometric mean frequencies, Hz	Sound levels L А, dBA

For tonal and impulse noise, as well as for noise generated indoors by air conditioning and ventilation installations, the permissible levels should be 5 dB lower than those indicated in Table 1 (when measured on the “slow” characteristic of a sound level meter).

For time-varying and intermittent noise, the maximum sound level should not exceed 110 dBA.

For impulse noise, the maximum sound level measured on the “impulse” characteristic of the sound level meter should not exceed 125 dBA (I).

In any case, even short-term stay of people in areas with sound pressure levels above 135 dB in any octave frequency band is prohibited. Areas with sound levels above 85 dBA must be marked with safety signs; Workers in such areas should be provided with personal protective equipment.

3. Methods and means of noise control

To reduce noise, the following main methods are used: eliminating the causes or weakening noise at the source, changing the direction of radiation and shielding noise, reducing noise along the path of its propagation, acoustic treatment of premises, architectural planning and construction acoustic methods.

To protect people from noise exposure, collective protective equipment (CPE) and personal protective equipment (PPE) are used. Prevention of the adverse effects of noise is also ensured by therapeutic, preventive and organizational measures, including, for example, medical examinations, correct choice of work and rest schedules, and reduction of time spent in industrial noise conditions.

Noise reduction directly at the source is carried out based on identifying specific causes of noise and analyzing their nature. The noise of technological equipment is often of mechanical and aerodynamic origin. To reduce mechanical noise, they carefully balance moving parts of units, replace rolling bearings with sliding bearings, ensure high precision in the manufacture of machine components and their assembly, enclose vibrating parts in oil baths, and replace metal parts with plastic ones. To reduce aerodynamic noise levels at the source, it is necessary, first of all, to reduce the speed of air and gas flows and jets flowing around parts, as well as vortex formation by using streamlined elements.

Most noise sources emit sound energy unevenly across space. Installations with directional radiation should be oriented so that the maximum emitted noise is directed in the direction opposite to the workplace or residential building.

Noise shielding consists of creating a sound shadow behind a screen located between the protected area and the noise source. Screens are most effective at reducing high- and mid-frequency noise and are poor at reducing low-frequency noise, which easily bends around screens due to the diffraction effect.

Solid metal or reinforced concrete shields lined with sound-absorbing material on the side of the noise source are used as screens that protect workplaces from the noise of serviced units. The linear dimensions of the screen must exceed the linear dimensions of the noise sources by at least 2 - 3 times. Acoustic screens are usually used in combination with sound-absorbing cladding of a room, since the screen only reduces direct sound, not reflected sound.

The method of sound insulation using fences is that most of the sound energy falling on it is reflected and only a small part of it penetrates through the fence. In the case of a massive soundproofing flat fence of infinite dimensions with a thickness much smaller than the longitudinal wavelength, the attenuation of the sound pressure level at a given frequency obeys the so-called law of mass and is found by the formula:

L P donkey = 20lg(mf) - 47.5, (5)

where f is the sound frequency, Hz; m is surface density, i.e. mass of one square meter of fencing, kg/m2. From formula (5) it follows that when the frequency or mass doubles, the sound insulation increases by 6 dB. In the case of real fences of finite dimensions, the mass law is valid only in a certain frequency range, usually from tens of Hz to several kHz.

The sound pressure level attenuation required for a given octave frequency band (with the corresponding geometric mean frequency f сг) is determined by the difference:

L P required (f сг) = L P measured (f сг) - L P norm (f сг), (6)

where L P meas (f сг) is the sound pressure level measured in the corresponding octave frequency band; L P norm (f сг) - standard sound pressure level.

Sheets of galvanized steel, aluminum and its alloys, fibreboards, plywood, etc. are used as soundproofing materials. The most effective are panels consisting of alternating layers of soundproofing and sound-absorbing materials.

Walls, partitions, windows, doors, and ceilings made of various building materials are also used as soundproofing barriers. For example, a door provides sound insulation of 20 dB, a window - 30 dB, an interior partition - 40 dB, an apartment partition - 50 dB.

To protect personnel from noise, soundproof observation and remote control cabins are installed, and the noisiest units are covered with soundproof casings. Casings are usually made of steel, their internal surfaces are lined with sound-absorbing material to absorb noise energy inside the casing. You can also reduce noise in a room by reducing reflected sound levels using sound absorption techniques. In this case, sound-absorbing linings and, if necessary, piece (volumetric) absorbers suspended from the ceiling are usually used.

Sound-absorbing materials include materials whose sound absorption coefficient (the ratio of the intensities of absorbed and incident sounds) at medium frequencies exceeds 0.2. The process of sound absorption occurs due to the transition of the mechanical energy of vibrating air particles into the thermal energy of the molecules of the sound-absorbing material, therefore, ultra-thin fiberglass, nylon fiber, mineral wool, and porous hard slabs are used as sound-absorbing materials.

The greatest efficiency is achieved when covering at least 60% of the total area of the walls and ceiling of the room. In this case, it is possible to ensure a noise reduction of 6 - 8 dB in the area of reflected sound (far from the source) and by 2 - 3 dB near the noise source.

During the construction of large objects, architectural planning and construction acoustic methods of noise control are used

If collective noise protection means do not provide the required protection or their use is impossible or impractical, then personal protective equipment (PPE) is used. These include ear muffs, earmuffs, and helmets and suits (used at sound levels above 120 dBA). Each PPE is characterized by a frequency response attenuation of sound pressure levels. High frequencies in the audio range are most effectively attenuated. The use of PPE should be considered a last resort measure for noise protection.

4 . Stand for measuring noise characteristics

source noise impact

The stand for measuring noise characteristics consists of an electronic noise source simulator and a sound level meter. In a sound level meter, sound vibrations are converted into electrical vibrations.

A simplified diagram of an analog sound level meter is shown in Fig. 2.

Rice. 2. Block diagram of a sound level meter

The sound level meter consists of a measuring microphone M, a switch D1 (“Range 1”), an amplifier U, a frequency response generator F1 with a switch S1 of their type (A, LIN, EXT), a second switch D2 (“Range 2”), a quadratic CD detector, time characteristics generator F2 with switch S2 of their type (S - “slow”, F - “fast”, I - “impulse”) and indicator I, graduated in decibels. Switches S1 and S2 are combined and form a common mode switch DR (“Mode”). In the EXT position of the DR switch, an octave bandpass filter is connected with a frequency value f сг selected by the DF switch.

In mode S (“slow”), the sound level meter readings are averaged. In mode F (“fast”), fairly rapid changes in noise are monitored, which is necessary to assess its nature. Mode I (“pulse”) allows you to estimate the maximum root mean square value of the noise. The results obtained from measurements in modes S, F, I (levels L S, L F, L I) may differ from each other depending on the nature of the measured noise.

When measuring noise at workplaces in industrial premises, the microphone is placed at a height of 1.5 m above the floor level or at the level of the person’s head if the work is done while sitting, and the microphone must be directed towards the noise source and removed at least 1 m from the sound level meter and the person taking the measurements. Noise should be measured when at least 2/3 of the units of technological equipment installed in a given room are operating under the most likely operating conditions.

The measurement of the resulting sound pressure level (dB) is carried out with a linear frequency response of the sound level meter - the DR (“Mode”) switch is in the “LIN” position. Sound levels (dBA) are measured by turning on a correction filter with a standard frequency response A (DR switch in position “A”).

To study the noise spectrum, the DR switch is set to the “EXT” position of mode S (“slow”). In this case, the frequency response is determined by the connected octave bandpass filter.

When measuring in mode S (“slow”), the count is made according to the average position of the instrument needle as it oscillates. For impulse noise, you should additionally measure the sound level on the time characteristic I (“impulse”) with a reading in dBA(I) of the maximum reading of the instrument needle.

Conclusion

Industrial noise is one of the unfavorable factors in the workplace.

An analysis of noise levels in industrial premises shows that the actual values at a number of workplaces exceed the permissible values according to sanitary standards. In designated production areas with high noise levels, noise protection measures are required.

The introduction of such measures, as well as the mandatory use of personal hearing protection, will reduce the harmful effects of noise on personnel, maintain their health, help reduce injuries and increase labor productivity.

Bibliography:

1. Combating noise at work: Directory /Under general. ed. E.Ya. Yudina. M.: Mechanical Engineering, 1985.

2. Life safety: Textbook for universities / Ed. S.V. Belova. M.: Higher School, 2004.

3. Life safety. Safety of technological processes and production: Textbook. manual for universities / P.P. Kukin et al. M.: Higher School, 2001.

4. SN 2.2.4 / 2.1.8.562-96 “Noise in workplaces, in residential and public buildings and in residential areas.”

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In 1959, the International Noise Abatement Organization was created. Combating noise is a complex, complex problem that requires a lot of effort and money.

Silence costs money and not little. Sources of noise are very diverse and there is no single way or method of dealing with them. However, acoustic science can offer effective solutions to noise. General ways to combat noise come down to the legislative, construction and planning, organizational, technical, technological, design and preventive world.

One of the areas in the fight against noise is the development of state standards for vehicles, engineering equipment, and household appliances, which are based on hygienic requirements to ensure acoustic comfort.

Hygienically acceptable noise levels for the population are based on fundamental physiological research to determine the effective and threshold noise levels.

Currently, noise for urban development conditions is standardized in accordance with the Sanitary Standards for Permissible Noise in Residential and Public Buildings and on Residential Development Territories (No. 3077-84) and Building Codes and Regulations II 12-77 “Protection from Noise.”

Sanitary standards are mandatory for all ministries, departments and organizations designing, constructing and operating housing and public buildings, developing planning and development projects for cities, microdistricts, residential buildings, neighborhoods, communications, etc.

Also for organizations that design, manufacture and operate vehicles, technological and engineering equipment for buildings and household appliances.

These organizations are obliged to provide and implement the necessary measures to reduce noise to the levels established by the standards.

GOST 19358-85 “External and internal noise of vehicles. Permissible levels and measurement methods" establishes noise characteristics, methods of their measurement and permissible noise levels of cars (motorcycles) of all samples accepted for state, interdepartmental, departmental and periodic control tests. The main characteristic of external noise is the sound level, which should not exceed 85-92 dB for cars and buses, and 80-86 dB for motorcycles.

For internal noise, the approximate values of permissible sound pressure levels in octave frequency bands are given: sound levels for passenger cars are 80 dB, cabins or workplaces of drivers of trucks, buses - 85 dB, passenger rooms of buses - 75-80 dB.

Sanitary standards for permissible noise necessitate the development of technical, architectural, planning and administrative measures aimed at creating a noise regime that meets hygienic requirements, both in urban areas and in buildings for various purposes, and helps preserve the health and working capacity of the population.

Reducing urban noise can be achieved primarily by reducing vehicle noise.

Urban planning measures to protect the population from noise include:

- increasing the distance between the noise source and the protected object;
- the use of acoustically opaque screens (slopes, walls and screen buildings), special noise protection strips for landscaping;
- use of various planning techniques, rational placement of microdistricts.

In addition, urban planning measures include rational development of main streets, maximum landscaping of microdistricts and dividing strips, use of terrain, etc.

A significant protective effect is achieved if residential buildings are located at a distance of at least 25-30 m from highways and the rupture zones are landscaped. With a closed type of development, only the spaces inside the block are protected, and the external facades of houses are exposed to unfavorable conditions, therefore such development of highways is undesirable. The most appropriate is free development, protected from the street side by green spaces and screening buildings for the temporary stay of people (shops, canteens, restaurants, studios, etc.).

The location of the main in the excavation also reduces noise in the surrounding area.

If the results of acoustic measurements indicate noise levels that are too high and exceed the permissible limits, all appropriate measures must be taken to reduce them. Although the methods and means of noise control are often complex, the relevant basic measures are briefly described below:

1. Reducing noise at its source, for example, by using special technological processes, modifying the design of equipment, additional acoustic treatment of parts, components and surfaces of equipment, or using new and less noisy equipment;
2. Blocking the paths of sound waves. This method, based on the use of additional technical means, consists of equipping the equipment with a soundproof coating or acoustic screens and suspending it on vibration absorbers. Noise in workplaces can be reduced by covering walls, ceilings and floors with materials that absorb sound and reduce the reflection of sound waves;
3. The use of personal protective equipment where other methods are not effective for one reason or another. However, the use of these means should be considered only a temporary solution to the problem;
4. Stopping the operation of noisy equipment is the most radical and last method, taken into account in special and serious cases. At this point, it is necessary to emphasize the possibility of reducing the operating time of noisy equipment, moving noisy equipment to another place, choosing a rational work and rest schedule and reducing the time spent in noisy conditions.

The assessment of working conditions in industrial premises and individual workplaces largely depends on the intensity of noise and its frequency characteristics.

Prevention of the formation of a significant level of sound pressure in production conditions should be carried out at the stages of designing technological equipment, design, construction and operation of enterprises, as well as the development of technological processes.

The fight against industrial noise is carried out using methods designated in four groups:

eliminating the causes of noise at the source of its formation;

soundproofing;

sound absorption;

application of organizational and technical measures.

The most effective way to combat noise is to reduce it at the source of its formation. by applying technological and design measures, organizing the correct setup and operation of equipment.

Structural and technological measures that make it possible to create mechanisms and units with low noise levels include improving kinematic schemes due to:

replacing gears with V-belt or chain drives; finding the best structural forms for shock-free interaction of parts and smooth air flow around them;

changes in the mass or rigidity of machine structural elements to reduce vibration amplitudes and eliminate resonance phenomena;

the use of materials that have the ability to absorb vibrational energy;

replacing the reciprocating motion of parts with rotational motion, and replacing rolling bearings with plain bearings;

the use of cushioning materials that impede the transfer of vibrations from one part to another.

An example of the latter is the introduction into practice of shock-absorbing gears.

A design feature of the shock-absorbing gear (Fig.) is the absence of a rigid connection between the hub and the crown.

Rice. Shock-absorbing gear: a - shock-absorbing gear; b - crown; c - hub; g - washer; 1 - crown; 2,3- washers; 4 - hub; 5 - bolt; 6.7 - liners

Torque is transmitted by rubber inserts, which are located between the internal teeth of the ring and hub. The elastic connection between the hub and the crown prevents the transmission of structural noise and vibration, improves engagement conditions and reduces aerodynamic noise.

Methods for reducing noise using some design, operational and adjustment measures are presented in Table.

Soundproofing- this is a set of measures to reduce the level of noise entering the premises from the outside.

Noise reduction using sound insulation is carried out by means based on the use of acoustic materials. The effectiveness of sound insulation is characterized by the reflection coefficient, which is numerically equal to the fraction of the sound wave energy reflected from the surface of the fence isolating the noise source.

The most common means of sound insulation include:

use of soundproof enclosures and cabins; increase in the mass of the obstacle;

separation of a light building structure by a continuous air gap into separate parts;

elimination or reduction of rigid connections between elements of a disconnected structure;

filling the air space in double lightweight partitions with sound-absorbing materials;

increasing the airtightness of the barrier.

Soundproofing casings cover the noisiest machines and mechanisms, thus localizing the source of noise. It is recommended to line the inner surface of the casing walls with sound-absorbing material.

For machines that generate heat, the casings are equipped with ventilation devices with mufflers (Fig. b).

Rice. Soundproof casing: a - diagram of the casing; b - design of the casing with a ventilation device; 1 - sound-absorbing material; 2, 6, 7 - channels with silencers for air inlet and outlet; 3, 5 - noise source; 4 - wall

The installed casing should not be rigidly connected to the mechanism. Otherwise, the casing becomes an additional source of noise.

Calculation of the soundproofing properties of a casing comes down to determining the required thickness of its walls to ensure the required noise reduction.

In table The mass of some building structures and materials is given.

Materials and designs	Thickness of structures, mm	Weight 1 m 2, kg
Steel sheet	2	16
Technical felt	25	8
Reinforced concrete	100	240
Hollow Pumice Blocks	190	190
Cinder concrete wall	140	140
Brick wall thickness:
0.5 bricks	120	250
1 brick	250	470
2 bricks	520	834
1.5 bricks	380	690
Partition made of boards 2 cm thick, plastered on both sides	60	70
Partition made of 10 cm thick posts, sheathed on both sides with 2.5 cm thick boards, plastered on both sides	180	95
Partition made of gypsum hollow stones	110	117
Glass	3	8

To lighten the enclosing structures without reducing the sound insulation ability, fences are used, consisting of two structures separated by an air gap. The air gap creates elastic resistance to the transmission of vibrations. The recommended width of the air gap is 3 ... 11 cm. This design has good sound insulation properties in the high frequency range.

With a mass of 1 m 3 of construction material up to 100 kg, sound-absorbing material is introduced into the gap between the separate panels. In this case, it should be placed in the middle of the gap, where the oscillatory speed of air particles, and therefore sound absorption, is greatest.

To increase the mass of a lightweight structure, it is recommended to fill the gap between double panels (made of boards, plywood, etc.) with clean river sand or fill it with glass wool. This type of design can provide sound insulation of up to 40 dB.

The need to fill the air space with soundproofing materials depends on the mass of the walls. For walls made of building materials weighing 1 m 3 more than 200 kg, it is advisable to leave air spaces 5 ... 10 cm wide unfilled. In walls with a mass of 1 m 3 100 ... 200 kg, a soft layer is attached to one side. In partitions weighing 1 m 3 to 30 kg, the entire air gap is filled with some kind of sound absorber.

Sound transmission from one room to another occurs not only through the barrier separating this room, but also through the adjacent side walls (longitudinal sound transmission).

Longitudinal sound transmission can be significant when a heavy building envelope with good sound insulation properties is adjacent to side walls made of lightweight building material.

Noise penetration into the room also occurs through cracks and leaks in doors and partitions. Even a small hole in a wall reduces its sound insulation capacity in the high frequency range by about 10 dB. The use of rubber seals increases the average sound insulation of doors and windows by 5 ... 8 dB.

Sound absorption- this is the weakening of the noise level spreading in the room due to the reflection of energy from the facing materials of fences and structural parts of equipment.

Sound absorption is characterized by the sound absorption coefficient, which is the ratio of the energy absorbed by 1 m 2 of surface to the energy incident on this surface.

It is advisable to use sound absorption if the sound absorption coefficient of the material is at least 0.2.

In terms of efficiency, the sound absorption method is much inferior to sound insulation.

Sound absorption, even with a very high absorption coefficient, can reduce the noise level by no more than 8 ... 10 dB. Effective noise protection requires the combined use of sound insulation and sound absorption methods.

In production shops of enterprises, various types of Akmigran slabs with a sound absorption coefficient of 0.6 can be used as acoustic treatment. This achieves high efficiency in absorbing high frequency sounds.

Akmigran slabs are used to cover the ceiling and the upper part of the walls, taking into account that its total area occupies at least 60% of the total area of the walls and ceiling of the room.

In addition, you can use sound absorbers, which are volumetric bodies filled with sound-absorbing material (Fig.). Sound absorbers are placed along the perimeter of the upper part of the walls or hung evenly to the ceiling at a certain height so as not to affect the lighting of workplaces.

Rice. Piece sound absorbers

You can reduce the noise level from the operation of production equipment using local screens. The screen is a soft sound-absorbing tape suspended from a horizontal gasket, which is attached to vertical posts. Racks can be made stationary or portable. The sound-absorbing tape consists of a tarpaulin material, a quilted fiberglass tape attached to it, covered with a layer of fiberglass with a total thickness of 40 ... 50 mm or super-thin fiberglass, covered with a polyamide film of the ATM-1 brand. The dimensions of the sound-absorbing tape are selected according to the size of the equipment.

At enterprises, when this is possible due to production conditions, as well as for lining protective chambers, the design of perforated linings with fabric developed by the Leningrad Institute of Occupational Safety and Health (LIOT) is used. The sound absorption efficiency of such cladding is about 10 dB, which corresponds to a reduction in sound volume by 30...50%.

The physical essence of the above sound absorption methods is that fibrous porous materials do not reflect sound well. When a sound wave falls on such a material, the air in the pores is set into oscillatory motion, which is sharply slowed down by the large resistance formed due to friction as it moves in small pores and channels. The energy of sound waves is consumed to overcome this resistance. As a result, the reflected wave is greatly weakened.

To reduce the spread of noise in the dining rooms of restaurants, cafes, and canteens, sound-absorbing materials of modern design are used.

The source of aerodynamic noise in public catering establishments is equipment that provides air conditioning for dining rooms, ventilation systems for industrial premises, refrigeration facilities and air heating (heat curtains for entrance doors).

Reducing the noise of ventilation units is achieved by well balancing the fan, installing it on the same axis with an electric motor or on an appropriate shock absorber in isolated rooms. The spread of sound through the air ducts is prevented by connecting the pipeline to the fan with elastic inserts.

Air ducts should be made without sharp turns and sudden changes in cross-section, which contribute to the formation of turbulence and the generation of aerodynamic noise.

To reduce the noise of various aerodynamic installations and devices, active and reactive mufflers are used. The action of active mufflers is based on the principle of absorption of sound energy by sound-absorbing material, while reactive mufflers reflect it back to the source.

The simplest active type muffler is a tubular muffler (Fig. a), which is a perforated steel air duct, the surface of which is covered with a layer of sound-absorbing material and a protective coating. The attenuation of noise by such a muffler is proportional to the absorption coefficient of the porous material, the length of the part lined with it, and inversely proportional to the cross-section of the channel. Since noise attenuation increases with decreasing channel cross-section, to reduce the length of the muffler, plate mufflers (Fig. b), which are assembled from separate sections filled with fibrous materials, are widely used in practice.

Rice. Aerodynamic noise silencers: a - tubular; b - lamellar; 1 - perforated steel air duct; 2 - sound-absorbing material; 3 - protective casing; 4 - sound-absorbing plate; 5 - plate frame; 6 - fibrous material; 7 - steel mesh

Reactive type mufflers are used to reduce noise with pronounced components.

The simplest reactive mufflers are expansion chamber type mufflers.

Organizational and technical measures to combat industrial noise include:

in the correct layout of workshops on the territory of the enterprise;

rational placement of equipment according to noise level;

landscaping indoors with broad-leaved plants, as they are able to absorb sounds well.

A good noise reduction effect is achieved by planting trees and shrubs on the territory of the enterprise. A multi-row planting of trees with breaks absorbs sound energy more intensely than a dense strip without breaks.

If engineering and technical means fail to reduce the sound pressure level to an acceptable value, personal protective equipment (headphones, antiphons, etc.) is used, when choosing which it is necessary to take into account such factors as the frequency spectrum of the noise, the requirements of sanitary standards for noise limitation, Comfortable to wear when performing specific work.

NOISE AND METHODS TO COMBAT IT

Purpose of the work : familiarization with the characteristics of noise and the features of its impact on the human body, with the features of measuring and normalizing noise parameters, as well as with methods of dealing with noise.

Theoretical part

1. Sound and its characteristics

Mechanical vibrations of particles of an elastic medium in the frequency range 16 20000 Hz are perceived by the human ear and are called sound waves. Vibrations of the medium with frequencies below 16 Hz are called infrasound, and vibrations with frequencies above 20,000 Hz are called ultrasound. Sound wavelength related to frequency f and the speed of sound with the dependence  = c / f.

The unsteady state of the medium during the propagation of a sound wave is characterized by sound pressure, which is understood as the root-mean-square value of the excess of pressure in the medium during the propagation of a sound wave above the pressure in an undisturbed medium, measured in pascals (Pa).

The transfer of energy by a plane sound wave through a unit surface perpendicular to the direction of propagation of the sound wave is characterized by sound intensity (sound power flux density), W/m 2: I = P 2 / (ρ ∙ c),

where P sound pressure, Pa; specific density of the medium, g/m 3 ;

c speed of propagation of a sound wave in a given medium, m/s.

The speed of energy transfer is equal to the speed of propagation of the sound wave.

The human hearing organs are capable of perceiving sound vibrations in very wide ranges of changes in intensities and sound pressures. For example, with a sound frequency of 1 kHz, the sensitivity threshold of the “average” human ear (hearing threshold) corresponds to the values P 0 = 2·10 5 Pa; I 0 = 10 12 W/m 2 , and the pain threshold (exceeding which can lead to physical damage to the hearing organs) corresponds to the values P b = 20 Pa and I b = 1 W/m 2 . In addition, in accordance with the Weber-Fechner law, the irritating effect of sound on the human ear is proportional to the logarithm of sound pressure. Therefore, in practice, instead of absolute values of intensity and sound pressure, their logarithmic levels, expressed in decibels (dB), are usually used:

L I = 10lg (I/I 0), L P = 20lg (P/P 0); (1)

where I 0 = 10 12 W/m 2 and P 0 = 2 10 5 Pa standard intensity and sound pressure thresholds. For normal atmospheric conditions it can be assumed that L I = L P = L .

If the sound at a given point consists of n components from several sources with sound pressure levels L i , then the resulting sound pressure level is determined by the formula:

where L i sound pressure level i - th component at the design point (dB).

In case n identical sound components L i = L the total level is:

L  = L + 10 log (n). (3)

Characteristics of a noise source are sound power and its level. Sound power W Watts, is the total amount of sound energy emitted by a noise source per unit time. If energy is radiated uniformly in all directions and sound attenuation in air is small, then at intensity I at distance r from a noise source, its sound power can be determined by the formula

W = 4  r 2 I . By analogy with logarithmic intensity and sound pressure levels, logarithmic sound power levels (dB) have been introduced L W = 10 lg (W / W 0), where W 0 = 10 -12 threshold value of sound power, W.

The noise spectrum shows the distribution of noise energy in the audio frequency range and is characterized by sound pressure or intensity levels (for sound sources sound power level) in the analyzed frequency bands, which, as a rule, are octave and one-third octave frequency bands characterized by lower f n and top f in boundary frequencies and geometric mean frequency f сг = (f n ∙ f in ) 1/2.

The octave band of sound frequencies is characterized by the ratio of its boundary frequencies satisfying the condition f in / f n = 2, and for one-third octave condition f in / f n = 2 1/3 ≈ 1.26.

Each octave frequency band includes three one-third octave bands, and the geometric mean frequency of the central one coincides with the geometric mean frequency of the octave band. Geometric mean frequencies f сг octave bands are determined by a standard binary series, including 9 values: 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz.

2. Features of subjective perception of sound ka

The perception of sound by the human ear depends very strongly and nonlinearly on its frequency. Features of subjective perception of sound are most conveniently illustrated graphically using curves of equal loudness (Fig. 1). Each of the family of curves in Fig. 1 characterizes sound pressure levels at various frequencies corresponding to the same loudness of sound perception and loudness level L N (background).

Rice. 1. Equal Loudness Curves

Volume level L N numerically equal to the sound pressure level at a frequency of 1 kHz. At other frequencies, different sound pressure levels are required to achieve the same sound volume. From Fig. 1 it follows that the type of the equal loudness curve and the corresponding characteristic of auditory sensitivity depend on the value L N .

When calculating and measuring the frequency response of the hearing organ, it is customary to model the frequency response of a correction filter A . Characteristic A is standard and is set by the correction system A i = φ(f сг i), where f сг i geometric mean frequency i th octave band.

To correspond the objective results of sound pressure level measurements to the subjective perception of sound volume, the concept of sound level is introduced. Sound level L A (dBA) the resulting sound pressure level of noise that has undergone mathematical or physical processing in a correction filter with characteristic A . The sound level value approximately corresponds to the subjective perception of noise loudness, regardless of its spectrum. Sound level is calculated taking into account corrections A i according to formula (2), in which instead L i should be substituted ( L i + A i ). Negative values A i characterize the deterioration of auditory sensitivity compared to auditory sensitivity at a frequency of 1000 Hz.

3. Characteristics of noise and its regulation

Based on the nature of the spectrum, noise is divided into broadband (with a continuous spectrum more than one octave wide) and tonal , in the spectrum of which there are pronounced discrete tones, measured in one-third octave frequency bands with an excess of sound pressure level over adjacent bands by at least 10 dB.

Based on their time characteristics, noise is divided into permanent , the sound level of which during an 8-hour working day changes by no more than 5 dBA when measured on the time characteristic of a “slow” sound level meter, and fickle , not satisfying this condition.

Intermittent noises, in turn, are divided into the following types:

time-varying noises, the sound level of which continuously changes over time;
intermittent noises, 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 at least 1 s;
impulse noise , consisting of one or more sound signals, each lasting less than 1 s, with sound levels in dBA and dBA( I ), measured respectively on the “slow” and “impulse” time characteristics of the sound level meter, differ by at least 7 dBA.

To assess non-constant noise, the concept equivalent sound level L Ae (by impact energy), expressed in dBAand determined by the formula L Ae = 10 lg (I AC / I 0), where I AC average value of the intensity of non-constant noise, corrected according to the characteristic A , on the control time interval T .

Current sound levels L A and intensity I A related by the relation L A (t) = 10 lg (I A (t) / I 0), I AC / I 0 = (1/T)(I A (t) / I 0) dt, therefore

(4)

L Ae values can be calculated either by automatically integrating sound level meters or manually based on the results of measurements of sound levels every 5 s during the noisiest 30 min.

The normalized noise parameters are:

For constant noisesound pressure levels L P (dB) in octave frequency bands with geometric mean frequencies 31.5; 63; 125; 250; 500; 1000; 2000; 4000 and 8000 Hz; In addition, for an approximate assessment of constant broadband noise in workplaces, it is permissible to use the sound level L A , expressed in dBA;
For intermittent noise(except pulse) equivalent sound level L Ae (by exposure energy), expressed in dBA, represents the sound level of such a constant broadband noise that affects the ear with the same sound energy as real, time-varying noise over the same period of time;
For impulse noiseequivalent sound level L Ae , expressed in dBA, and the maximum sound level L A max in dBA(I ), measured on the time characteristic of the “impulse” of the sound level meter.

Acceptable values of noise parameters are regulated CH 2.2.4 / 2.1.8.562-96 " Noise in workplaces, in residential and public buildings and in residential areas" Permissible values of noise parameters at workplaces are established depending on the type of work performed and the nature of the noise. For work related to creative, scientific activities, training, programming, the lowest noise levels are provided.

Below are the characteristic types of work distinguished during standardization, indicating the serial number:

1) creative, scientific work, training, design, construction, development, programming;

2) administrative and managerial work, work requiring concentration, measurement and analytical work in the laboratory;

3) dispatch work that requires voice communication by telephone, in computer information processing rooms, in precision assembly areas, in typing bureaus;

5) all types of work except those listed in paragraphs. 1 4.

For broadband noiseat workplaces in table. 1 shows permissible sound pressure levels L P in octave frequency bands with geometric mean frequencies f сг, sound levels L A (for a subjective assessment of the volume of constant noise) and equivalent sound levels L Ae (to evaluate intermittent noise).

Table 1

Acceptable noise levels

type of work	Sound pressure levels L P (dB) in octave frequency bands with geometric mean frequencies, Hz					Sound levels L А, dBA
type of work		31,5	1000	2000	4000	Sound levels L А, dBA	8000

For fluctuating in time and intermittent noisethe maximum sound level should not exceed 110 dBA.

For impulse noisethe maximum sound level measured on the “impulse” characteristic of the sound level meter should not exceed 125 dBA ( I).

4. Methods and means of dealing with noise

Solid metal or reinforced concrete shields lined with sound-absorbing material on the side of the noise source are used as screens that protect workplaces from the noise of serviced units. The linear dimensions of the screen must exceed the linear dimensions of the noise sources by at least 2 3 times. Acoustic screens are usually used in combination with sound-absorbing cladding of a room, since the screen only reduces direct sound, not reflected sound.

The method of sound insulation using fences is that most of the sound energy falling on it is reflected T and only a small part of it penetrates the fence. In the next at tea of massive soundproofing flat fencing h size, thickness, much less than the length of the longitudinal wave, donkey b The change in sound pressure level at a given frequency obeys the so-called law of mass and is found in the form u le:

L P donkey = 20 lg (mf) 47.5, (5)

where f sound frequency, Hz; m surface density, i.e. weight of one square meter of fencing, kg/m 2 . From formula (5) it follows that when frequency or mass doubles, sound insulation increases by 6dB. In the case of real fences of finite dimensions, the mass law is valid only in a certain frequency range, usually from tens of Hz to several kHz.

Required for a given octave frequency band (with corresponding geometric mean frequency f сг ) the attenuation of the sound pressure level is determined by the difference:

L P required (f сг) = L P measured (f сг) L P norm (f сг), (6)

where L P meas (f сг ) sound pressure level measured in the corresponding octave frequency band; L P norms (f сг ) standard sound pressure level.

The greatest efficiency is achieved when covering at least 60% of the total area of the walls and ceiling of the room. In this case, it is possible to ensure a noise reduction of 6 8 dB in the area of reflected sound (far from the source) and by 2 3 dB near the noise source.

During the construction of large objects, architectural planning and construction acoustic methods of noise control are used

Experimental part

1. Stand for measuring noise characteristics

A simplified diagram of an analog sound level meter is shown in Fig. 2.

Rice. 2. Block diagram of a sound level meter

The sound level meter consists of a measuring microphone M, switch D 1 (“Band 1”), amplifier U, shaper F 1 frequency response with switch S 1 of their types (A, LIN, EXT ), second switch D 2 (“Range 2”), quadratic detector KD , time characteristics generator F 2 with switch S 2 types of them (S “slow”, F “fast”, I “impulse”) and indicator AND , graduated in decibels. Switches S 1 and S 2 combined and form a common mode switch D.R. ("Mode"). In position DR switch EXT an octave bandpass filter with a frequency value is connected f сг , selectable by switch D.F.

In S mode (“slowly”) the sound level meter readings are averaged. In mode F (“fast”) fairly rapid changes in noise are monitored, which is necessary to assess its nature. Mode I (“impulse”) allows you to estimate the maximum root mean square value of the noise. Results obtained from measurements in modes S, F, I (levels L S, L F, L I ), may differ from each other depending on the nature of the measured noise.

The resulting sound pressure level (dB) is measured with a linear frequency response of the sound level meter switch D.R. (“Mode”) in the “ position LIN " Sound levels (dBA) are measured by turning on a correction filter with a standard frequency response A (DR switch in position “A”).

To study the noise spectrum, switch D.R. is set to “ EXT” mode S ("slowly"). In this case, the frequency response is determined by the connected octave bandpass filter.

When measuring in mode S (“slowly”) the count is made according to the average position of the instrument needle as it oscillates. For impulse noise, you should additionally measure the sound level on the time characteristic I (“impulse”) with a countdown in dBA( I ) maximum reading of the instrument needle.

How to use a sound level meter And The execution of the work is given in the materials of the laboratory stand.

The report must contain the measurement results, the results of the required calculations and graphical dependencies illustrating the calculation results.

1. Based on the measurement results, classify the noise under study (determine its nature).

2. Results of measurements of the spectrum of the noise under study according to point 5 of the work procedure L P meas (f сг ) and standard levels corresponding to the specification option (Table 1) in octave frequency bands L P norms (f сг ) enter into the table 2. For all values f сг enter into the table 2 results of calculations using formula (6) of the required attenuation of sound pressure levels L P required

Table 2

Results of measurements and calculations

f сг, Hz	31.5	1000	2000	4000	8000
L P meas., dB
L P norm, dB
L P required, dB
m, kg/m 2
L P osl, dB
L P sound from , dB

3. Based on the found values L P REQ (f сг ) and formulas (5) calculate and enter into the table. 2 surface density m soundproofing material, which ensured attenuation of the octave sound pressure levels of the noise under study to levels not exceeding the standard:

m = f SG ·10 0.05 L P required + 2.375, kg/m 2.

4. For the maximum found value of the parameter m calculate according to formula (5) and enter into the table. 2 levels of sound pressure attenuation per octave frequency band L P donkey (f сг ) provided by a soundproofing fence with a given parameter value m.

5. For each value f сг determine the noise sound pressure levels after using soundproofing fencing:

L P sv.iz = L P meas - L P os .

6. Graphically plot frequency dependencies in the plane of one drawing L P measured (f сг), L P norm (f сг), L P required (f сг) and L P values from (f сг) . In this case, for the frequency axis, select a binary logarithmic scale in accordance with the frequency series of values f сг . Ensure that noise spectrum levels after soundproofing L P star from (f сг ) in all octave bands do not exceed the levels of the standard spectrum L P norms (f сг).

Security questions

Sound and its characteristics.
Features of subjective perception of sound by humans.
Characteristics of noise and their classification.
Principles of noise regulation.
Methods and means of noise control and their comparative assessment.
Methodology for measuring noise parameters and sound level meter modes.
What noise parameters are measured using a sound level meter in modes “A”, “ LIN" and "EXT" "? What are the differences between these options?

Bibliography

Fighting noise at work: Directory /Under general. ed.E. Ya. Yudina. M.: Mechanical Engineering, 1985.
Life safety: Textbook for universities / Ed.S. V. BeloVA. M.: Higher School, 2004.
Life safety. Safety of technological processes and production: Textbook. manual for universities / P.P. Kukin et al. M.: Higher School, 2001.
CH 2.2.4/ 2.1.8.562-96 “Noise in workplaces, in residential and public buildings and in residential areas.”

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8.5 methods and means of noise control. Methods to combat noise at work

Submitting your good work to the knowledge base is easy. Use the form below

1. Sound and its characteristics

The transfer of energy by a plane sound wave through a unit surface perpendicular to the direction of propagation of the sound wave is characterized by sound intensity (sound power flux density),

W/m2: I = P2/(? c),

where P is sound pressure, Pa; - specific density of the medium, g/m 3 ;

c is the speed of propagation of a sound wave in a given medium, m/s.

The speed of energy transfer is equal to the speed of propagation of the sound wave.

L I = 10lg(I/I 0), L P = 20lg(P/P 0) ; (1)

where I 0 = 10-12 W/m2 and P 0 = 2·10-5 Pa are standard threshold values ​​of intensity and sound pressure. For normal atmospheric conditions, we can assume that L I = L P = L.

If the sound at a given point consists of n components from several sources with sound pressure levels Li, then the resulting sound pressure level is determined by the formula:

(2)

where L i is the sound pressure level of the i-th component at the design point (dB).

In the case of n identical sound components L i = L, the total level is:

L = L + 10log(n). (3)

W = 4 r 2 I. By analogy with logarithmic levels of intensity and sound pressure, logarithmic sound power levels (dB) L W = 10 log(W/W 0), where W 0 = 10 -12 is the threshold value of sound power, W, are introduced.

The octave band of sound frequencies is characterized by the ratio of its boundary frequencies satisfying the condition f in /f n = 2, and for the one-third octave band - the condition f in /f n = 2 1/3? 1.26.

2. Characteristics of noise and its regulation

According to the time characteristics, noise is divided into constant, the sound level of which during an 8-hour working day changes by no more than 5 dBA when measured on the time characteristic of a “slow” sound level meter, and non-constant, which does not satisfy this condition.

Intermittent noises, in turn, are divided into the following types:

· time-fluctuating noises, the sound level of which continuously changes over time;

· intermittent noises, 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 at least 1 s;

· impulse noise, consisting of one or more sound signals, each lasting less than 1 s, while the sound levels in dBA and dBA(I), measured respectively on the “slow” and “impulse” time characteristics of the sound level meter, differ by at least 7 dBA.

Current values ​​of sound level L A and intensity I A are related by the relation

L A (t) = 10lg(I A (t) /I 0), I AC /I 0 = (1/T)(I A (t) /I 0)dt, therefore

(4)

The values ​​of L A e can be calculated either by automatically integrating sound level meters or manually based on the results of measurements of sound levels every 5 s during the noisiest 30 minutes.

The normalized noise parameters are:

· for impulse noise - the equivalent sound level L А e, expressed in dBA, and the maximum sound level L А max in dBA(I), measured on the time characteristic “impulse” of the sound level meter.

Below are the characteristic types of work distinguished during standardization, indicating the serial number:

3. Methods and means of noise control

Bibliography:

1. Combating noise at work: Directory /Under general. ed. E.Ya. Yudina. M.: Mechanical Engineering, 1985.

2. Life safety: Textbook for universities / Ed. S.V. Belova. M.: Higher School, 2004.

3. Life safety. Safety of technological processes and production: Textbook. manual for universities / P.P. Kukin et al. M.: Higher School, 2001.

4. SN 2.2.4 / 2.1.8.562-96 “Noise in workplaces, in residential and public buildings and in residential areas.”

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Similar documents

NOISE AND METHODS TO COMBAT IT

1. Sound and its characteristics

2. Features of subjective perception of sound ka

3. Characteristics of noise and its regulation

4. Methods and means of dealing with noise

Experimental part

1. Stand for measuring noise characteristics

Rice. 2. Block diagram of a sound level meter

Security questions

Bibliography

where I 0 = 10-12 W/m2 and P 0 = 2·10-5 Pa are standard threshold values of intensity and sound pressure. For normal atmospheric conditions, we can assume that L I = L P = L.

Current values of sound level L A and intensity I A are related by the relation

The values of L A e can be calculated either by automatically integrating sound level meters or manually based on the results of measurements of sound levels every 5 s during the noisiest 30 minutes.