Acoustic calculations
Among the problems of health improvement environment the fight against noise is one of the most pressing. In large cities, noise is one of the main physical factors shaping environmental conditions.
Growth of industrial and housing construction, rapid development various types transport, increasingly used in residential and public buildings plumbing and engineering equipment, household appliances led to noise levels in residential areas of the city becoming comparable to noise levels in production.
The noise regime of large cities is formed mainly by automobile and rail transport, accounting for 60-70% of all noise.
A noticeable impact on the noise level is exerted by the increase in the intensity of air traffic, the emergence of new powerful airplanes and helicopters, as well as railway transport, open metro lines and shallow metro.
At the same time, in some large cities where measures are being taken to improve the noise environment, a decrease in noise levels is observed.
There are acoustic and non-acoustic noises, what is their difference?
Acoustic noise is defined as a set of sounds of varying strength and frequency that arise as a result of the oscillatory motion of particles in elastic media (solid, liquid, gaseous).
Non-acoustic noise - Radio-electronic noise - random fluctuations of currents and voltages in radio-electronic devices, arise as a result of uneven emission of electrons in electric vacuum devices (shot noise, flicker noise), uneven processes of generation and recombination of charge carriers (conduction electrons and holes) in semiconductor devices, thermal movement of current carriers in conductors (thermal noise), thermal radiation The Earth and the Earth's atmosphere, as well as planets, the Sun, stars, the interstellar medium, etc. (space noise).
Acoustic calculation, noise level calculation.
During the construction and operation of various facilities, noise control problems are an integral part of occupational safety and public health protection. Machines can act as sources vehicles, mechanisms and other equipment. Noise, its impact and vibration on a person depends on the level sound pressure, frequency characteristics.
Standardization of noise characteristics is understood as the establishment of restrictions on the values of these characteristics, under which the noise affecting people should not exceed the permissible levels regulated by current regulations. sanitary standards and rules.
The objectives of the acoustic calculation are:
Identifying noise sources;
Determination of their noise characteristics;
Determination of the degree of influence of noise sources on standardized objects;
Calculation and construction of individual zones of acoustic discomfort of noise sources;
Development of special noise protection measures to ensure the required acoustic comfort.
Installation ventilation systems and air conditioning is already considered a natural need in any building (be it residential or administrative), acoustic calculations must be performed for premises of this type. So, if the noise level is not calculated, it may turn out that the room has a very low level of sound absorption, and this greatly complicates the process of communication between people in it.
Therefore, before installing ventilation systems in a room, it is necessary to carry out an acoustic calculation. If it turns out that a room has poor acoustic properties, it is necessary to propose a number of measures to improve the acoustic environment in the room. Therefore, acoustic calculations are also performed for the installation of household air conditioners.
Acoustic calculations are most often carried out for objects that have complex acoustics or have increased requirements for sound quality.
Sound sensations arise in the hearing organs when they are exposed to sound waves in the range from 16 Hz to 22 thousand Hz. Sound travels in air at a speed of 344 m/s in 3 seconds. 1 km.
The threshold of hearing depends on the frequency of the sounds felt and is equal to 10-12 W/m2 at frequencies close to 1000 Hz. The upper limit is the pain threshold, which is less dependent on frequency and lies in the range of 130 - 140 dB (at a frequency of 1000 Hz, intensity 10 W/m2, sound pressure).
The ratio of intensity level and frequency determines the sensation of sound volume, i.e. sounds of different frequencies and intensities can be assessed by a person as equally loud.
When perceiving sound signals against a certain acoustic background, a signal masking effect may be observed.
The masking effect can have a negative impact on acoustic indicators and can be used to improve the acoustic environment, i.e. in the case of masking a high-frequency tone with a low-frequency tone, which is less harmful to humans.
The procedure for performing acoustic calculations.
To perform an acoustic calculation, the following data will be required:
Dimensions of the room for which the noise level will be calculated;
Main characteristics of the room and its properties;
Noise spectrum from the source;
Characteristics of the obstacle;
Data on the distance from the center of the noise source to the acoustic calculation point.
When calculating, first, noise sources and their characteristic properties. Next, points on the object under study are selected at which calculations will be carried out. At selected points of the object, a preliminary sound pressure level is calculated. Based on the results obtained, a calculation is made to reduce noise to the required standards. Having received all the necessary data, a project is carried out to develop measures that will reduce noise levels.
Correctly performed acoustic calculations are the key to excellent acoustics and comfort in a room of any size and design.
Based on the performed acoustic calculation, the following measures can be proposed to reduce noise levels:
* installation of soundproofing structures;
* use of seals in windows, doors, gates;
* use of structures and screens that absorb sound;
*implementation of planning and development of residential areas in accordance with SNiP;
* use of noise suppressors in ventilation and air conditioning systems.
Carrying out acoustic calculations.
Work on calculating noise levels, assessing acoustic (noise) impact, as well as designing specialized noise protection measures must be carried out by a specialized organization with the relevant field.
noise acoustic calculation measurement
In the very simple definition The main task of acoustic calculation is to estimate the noise level created by a noise source at a given design point with an established quality of acoustic impact.
The acoustic calculation process consists of the following main stages:
1. Collection of necessary initial data:
The nature of noise sources, their mode of operation;
Acoustic characteristics of noise sources (in the range of geometric mean frequencies 63-8000 Hz);
Geometric parameters of the room in which the noise sources are located;
Analysis of weakened elements of enclosing structures through which noise will penetrate into the environment;
Geometric and soundproofing parameters of weakened elements of enclosing structures;
Analysis of nearby objects with established quality of acoustic impact, determination of permissible sound levels for each object;
Analysis of distances from external sources noise to standardized objects;
Analysis of possible shielding elements along the path of sound wave propagation (buildings, green spaces, etc.);
Analysis of weakened elements of enclosing structures (window openings, doors, etc.) through which noise will penetrate into regulated premises, identifying their soundproofing ability.
2. Acoustic calculations are made based on current methodological instructions and recommendations. Basically these are “Calculation methods, standards”.
At each calculation point, it is necessary to sum up all available noise sources.
The result of the acoustic calculation is certain values (dB) in octave bands with geometric mean frequencies of 63-8000 Hz and an equivalent sound level value (dBA) at the calculated point.
3. Analysis of calculation results.
Analysis of the results obtained is carried out by comparing the values obtained at the design point with the established Sanitary Standards.
If necessary, the next stage of the acoustic calculation may be the design of the necessary noise protection measures that will reduce the acoustic impact at the design points to an acceptable level.
Carrying out instrumental measurements.
In addition to acoustic calculations, it is possible to calculate instrumental measurements of noise levels of any complexity, including:
Noise Exposure Measurement existing systems ventilation and air conditioning for office buildings, private apartments, etc.;
Carrying out measurements of noise levels for certification of workplaces;
Carrying out work on instrumental measurement of noise levels within the project;
Carrying out work on instrumental measurement of noise levels as part of technical reports when approving the boundaries of the sanitary protection zone;
Carrying out any instrumental measurements of noise exposure.
Instrumental measurements of noise levels are carried out by a specialized mobile laboratory using modern equipment.
Acoustic calculation deadlines. The timing of the work depends on the volume of calculations and measurements. If it is necessary to carry out acoustic calculations for residential development projects or administrative facilities, then they are completed on average 1 - 3 weeks. Acoustic calculations for large or unique objects (theatres, organ halls) take longer, based on the provided source materials. In addition, the operating life is largely influenced by the number of noise sources studied, as well as external factors.
Ventilation calculation
Depending on the method of air movement, ventilation can be natural or forced.
The parameters of the air entering the intake openings and openings of local suction of technological and other devices located in the working area should be taken in accordance with GOST 12.1.005-76. With a room size of 3 by 5 meters and a height of 3 meters, its volume is 45 cubic meters. Therefore, ventilation should provide an air flow of 90 cubic meters per hour. In summer, it is necessary to install an air conditioner in order to avoid exceeding the temperature in the room for stable operation of the equipment. It is necessary to pay due attention to the amount of dust in the air, as this directly affects the reliability and service life of the computer.
The power (more precisely, the cooling power) of an air conditioner is its main characteristic; it determines the volume of the room it is designed for. For approximate calculations, take 1 kW per 10 m 2 with a ceiling height of 2.8 - 3 m (in accordance with SNiP 2.04.05-86 "Heating, ventilation and air conditioning").
To calculate the heat inflows of a given room, a simplified method was used:
where:Q - Heat inflow
S - Room area
h - Room height
q - Coefficient equal to 30-40 W/m 3 (in this case 35 W/m 3)
For a room of 15 m2 and a height of 3 m, the heat gain will be:
Q=15·3·35=1575 W
In addition, the heat emission from office equipment and people should be taken into account; it is believed (in accordance with SNiP 2.04.05-86 “Heating, ventilation and air conditioning”) that in a calm state a person emits 0.1 kW of heat, a computer or copy machine 0.3 kW, By adding these values to the total heat inflows, you can obtain the required cooling capacity.
Q additional =(H·S opera)+(С·S comp)+(P·S print) (4.9)
where: Q additional - Sum of additional heat inflows
C - Computer heat dissipation
H - Operator Heat Dissipation
D - Printer Heat Dissipation
S comp - Number of workstations
S print - Number of printers
S operators - Number of operators
Additional heat inflows in the room will be:
Q additional1 =(0.1 2)+(0.3 2)+(0.3 1)=1.1(kW)
The total sum of heat inflows is equal to:
Q total1 =1575+1100=2675 (W)
In accordance with these calculations, it is necessary to select the appropriate power and number of air conditioners.
For the room for which the calculation is being carried out, air conditioners with a rated power of 3.0 kW should be used.
Noise level calculation
One of the unfavorable factors of the production environment in the computer center is the high level of noise created by printing devices, air conditioning equipment, and fans of cooling systems in the computers themselves.
To address questions about the need and feasibility of noise reduction, it is necessary to know the noise levels at the operator’s workplace.
The noise level arising from several incoherent sources operating simultaneously is calculated based on the principle of energy summation of emissions from individual sources:
L = 10 lg (Li n), (4.10)
where Li is the sound pressure level of the i-th noise source;
n is the number of noise sources.
The obtained calculation results are compared with the permissible noise level for a given workplace. If the calculation results are higher than the permissible noise level, then special noise reduction measures are required. These include: covering the walls and ceiling of the hall with sound-absorbing materials, reducing noise at the source, proper layout of equipment and rational organization of the operator’s workplace.
The sound pressure levels of noise sources affecting the operator at his workplace are presented in table. 4.6.
Table 4.6 - Sound pressure levels of various sources
Typically, the operator's workplace is equipped with the following equipment: a hard drive in the system unit, fan(s) of PC cooling systems, a monitor, a keyboard, a printer and a scanner.
Substituting the sound pressure level values for each type of equipment into formula (4.4), we obtain:
L=10 lg(104+104.5+101.7+101+104.5+104.2)=49.5 dB
The obtained value does not exceed the permissible noise level for the operator’s workplace, equal to 65 dB (GOST 12.1.003-83). And if we take into account that it is unlikely that peripheral devices such as a scanner and printer will be used at the same time, then this figure will be even lower. In addition, when the printer is operating, the direct presence of the operator is not necessary, because The printer is equipped with an automatic sheet feed mechanism.
Description:
The rules and regulations in force in the country stipulate that projects must include measures to protect equipment used for human life support from noise. Such equipment includes ventilation and air conditioning systems.
Acoustic calculation as a basis for designing a low-noise ventilation (air conditioning) system
V. P. Gusev, Doctor of Technical Sciences sciences, head laboratory for noise protection of ventilation and engineering-technological equipment (NIISF)
The rules and regulations in force in the country stipulate that projects must include measures to protect equipment used for human life support from noise. Such equipment includes ventilation and air conditioning systems.
The basis for designing sound attenuation of ventilation and air conditioning systems is acoustic calculation - a mandatory application to the ventilation project of any facility. The main tasks of such a calculation are: determination of the octave spectrum of airborne, structural ventilation noise at design points and its required reduction by comparing this spectrum with the permissible spectrum according to hygienic standards. After selecting construction and acoustic measures to ensure the required noise reduction, a verification calculation of the expected sound pressure levels at the same design points is carried out, taking into account the effectiveness of these measures.
The materials given below do not claim to be a complete presentation of the methodology for acoustic calculation of ventilation systems (installations). They contain information that clarifies, complements or reveals in a new way various aspects of this technique using the example of the acoustic calculation of a fan as the main source of noise in a ventilation system. The materials will be used in the preparation of a set of rules for the calculation and design of noise attenuation ventilation units to the new SNiP.
The initial data for acoustic calculations are the noise characteristics of the equipment - sound power levels (SPL) in octave bands with geometric mean frequencies 63, 125, 250, 500, 1,000, 2,000, 4,000, 8,000 Hz. For approximate calculations, adjusted sound power levels of noise sources in dBA are sometimes used.
Calculation points are located in human habitats, in particular, at the installation site of the fan (in the ventilation chamber); in rooms or areas adjacent to the fan installation site; in rooms served by a ventilation system; in rooms where air ducts pass through in transit; in the area of the device for receiving or exhausting air, or only receiving air for recirculation.
The design point is in the room where the fan is installed
In general, sound pressure levels in a room depend on the sound power of the source and the directional factor of noise emission, the number of noise sources, the location of the design point relative to the source and enclosing building structures, the size and acoustic qualities of the room.
The octave sound pressure levels created by the fan(s) at the installation location (in the ventilation chamber) are equal to:
where Фi is the directivity factor of the noise source (dimensionless);
S is the area of an imaginary sphere or part of it surrounding the source and passing through the calculated point, m2;
B is the acoustic constant of the room, m2.
The design point is located in the room adjacent to the room where the fan is installed
Octave levels airborne noise penetrating through the fence into the insulated room adjacent to the room where the fan is installed are determined by the sound insulating ability of the fences of the noisy room and the acoustic qualities of the protected room, which is expressed by the formula:
| (3) |
where L w is the octave sound pressure level in the room with the noise source, dB;
R - insulation from airborne noise by the enclosing structure through which noise penetrates, dB;
S - area of the enclosing structure, m2;
B u - acoustic constant of the insulated room, m 2;
k is a coefficient that takes into account the violation of the diffuseness of the sound field in the room.
The design point is located in the room served by the system
The noise from the fan spreads through the air duct (air channel), is partially attenuated in its elements and penetrates into the serviced room through the air distribution and air intake grilles. Octave sound pressure levels in a room depend on the amount of noise reduction in the air duct and the acoustic qualities of that room:
| (4) |
where L Pi is the sound power level in the i-th octave emitted by the fan into the air duct;
D L networki - attenuation in the air channel (in the network) between the noise source and the room;
D L pomi - the same as in formula (1) - formula (2).
Attenuation in the network (in the air channel) D L P of the network is the sum of attenuation in its elements, sequentially located along the sound waves. The energy theory of sound propagation through pipes assumes that these elements do not influence each other. In fact, the sequence of shaped elements and straight sections form a single wave system, in which the principle of independence of attenuation in the general case cannot be justified in pure sinusoidal tones. At the same time, in octave (wide) frequency bands, standing waves created by individual sinusoidal components cancel each other out, and therefore an energy approach that does not take into account the wave pattern in air ducts and considers the flow of sound energy can be considered justified.
Attenuation in straight sections of air ducts made of sheet material is caused by losses due to wall deformation and sound radiation outward. The decrease in sound power level D L P per 1 m length of straight sections of metal air ducts depending on frequency can be judged from the data in Fig. 1.
As you can see, in the air ducts rectangular section attenuation (decrease in USM) decreases with increasing sound frequency, and the circular cross-section increases. If there is thermal insulation on metal air ducts, shown in Fig. 1 values should be increased approximately twice.
The concept of attenuation (decrease) in the level of sound energy flow cannot be identified with the concept of a change in the sound pressure level in the air channel. As a sound wave moves through a channel, the total amount of energy it carries decreases, but this is not necessarily associated with a decrease in sound pressure level. In a narrowing channel, despite the attenuation of the overall energy flow, the sound pressure level can increase due to an increase in the density of sound energy. In an expanding duct, on the other hand, the energy density (and sound pressure level) can decrease faster than the total sound power. The sound attenuation in a section with a variable cross-section is equal to:
 |
(5) |
where L 1 and L 2 are the average sound pressure levels in the initial and final sections of the channel section along the sound waves;
F 1 and F 2 are the cross-sectional areas at the beginning and end of the channel section, respectively.
Attenuation at turns (in elbows, bends) with smooth walls, the cross section of which is less than the wavelength, is determined by reactance such as additional mass and the occurrence of higher order modes. The kinetic energy of the flow at a turn without changing the channel cross-section increases due to the resulting unevenness of the velocity field. Square rotation acts like a low pass filter. The amount of noise reduction when turning in the plane wave range is given by an exact theoretical solution:
 |
(6) |
where K is the modulus of the sound transmission coefficient.
For a ≥ l /2, the value of K is zero and the incident plane sound wave is theoretically completely reflected by the rotation of the channel. Maximum noise reduction occurs when the turning depth is approximately half the wavelength. The value of the theoretical modulus of the sound transmission coefficient through rectangular turns can be judged from Fig. 2.
In real designs, according to the work, the maximum attenuation is 8-10 dB, when half the wavelength fits into the channel width. With increasing frequency, the attenuation decreases to 3-6 dB in the region of wavelengths close in magnitude to twice the channel width. Then it smoothly increases again at high frequencies, reaching 8-13 dB. In Fig. Figure 3 shows noise attenuation curves at channel turns for plane waves (curve 1) and for a random, diffuse sound incidence (curve 2). These curves are obtained based on theoretical and experimental data. The presence of a noise reduction maximum at a = l /2 can be used to reduce noise with low-frequency discrete components by adjusting the channel sizes at turns to the frequency of interest.
Noise reduction on turns less than 90° is approximately proportional to the angle of rotation. For example, the reduction in noise level at a 45° turn is equal to half the reduction at a 90° turn. On turns with angles less than 45°, noise reduction is not taken into account. For smooth turns and straight bends of air ducts with guide vanes, the noise reduction (sound power level) can be determined using the curves in Fig. 4.
In channel branches, the transverse dimensions of which are less than half the sound wavelength, the physical causes of attenuation are similar to the causes of attenuation in elbows and bends. This attenuation is determined as follows (Fig. 5).
Based on the continuity equation of the medium:
From the condition of pressure continuity (r p + r 0 = r pr) and equation (7), the transmitted sound power can be represented by the expression
and the reduction in sound power level with the cross-sectional area of the branch
 |
(11) |
 |
(12) |
(13) |
If there is a sudden change in the cross-section of a channel with transverse dimensions less than half-wavelengths (Fig. 6 a), a decrease in the sound power level can be determined in the same way as with branching.
The calculation formula for such a change in the channel cross-section has the form
 |
(14) |
where m is the ratio of the larger cross-sectional area of the channel to the smaller one.
The reduction in sound power levels when channel sizes are larger than the half-wavelength of out-of-plane waves due to a sudden narrowing of the channel is
If the channel expands or smoothly narrows (Fig. 6 b and 6 d), then the decrease in the sound power level is zero, since reflection of waves with a length less than the size of the channel does not occur.
In simple elements of ventilation systems, the following reduction values are accepted at all frequencies: heaters and air coolers 1.5 dB, central air conditioners 10 dB, mesh filters 0 dB, the place where the fan adjoins the air duct network 2 dB.
Sound reflection from the end of the air duct occurs if the transverse size of the air duct is less than the sound wavelength (Fig. 7).
If a plane wave propagates, then there is no reflection in a large duct, and we can assume that there are no reflection losses. However, if an opening connects a large room and an open space, then only diffuse sound waves directed towards the opening, the energy of which is equal to a quarter of the energy of the diffuse field, enter the opening. Therefore, in this case, the sound intensity level is weakened by 6 dB.
The directional characteristics of sound radiation from air distribution grilles are shown in Fig. 8.
When the noise source is located in space (for example, on a column in a large room) S = 4p r 2 (radiation into a full sphere); in the middle part of the wall, ceiling S = 2p r 2 (radiation into the hemisphere); in a dihedral angle (radiation into 1/4 sphere) S = p r 2 ; in a trihedral angle S = p r 2 /2.
The attenuation of the noise level in the room is determined by formula (2). The design point is selected in the place of permanent residence of people, closest to the noise source, at a distance of 1.5 m from the floor. If noise at the design point is created by several gratings, then the acoustic calculation is made taking into account their total impact.
When the noise source is a section of a transit air duct passing through a room, the initial data for calculation using formula (1) are the octave sound power levels of the noise emitted by it, determined by the approximate formula:
(16) |
where L pi is the sound power level of the source in the i-th octave frequency band, dB;
D L’ Рnetii - attenuation in the network between the source and the transit section under consideration, dB;
R Ti - sound insulation of the structure of the transit section of the air duct, dB;
S T - surface area of the transit section opening into the room, m 2 ;
F T - area cross section air duct section, m2.
Formula (16) does not take into account the increase in sound energy density in the air duct due to reflections; the conditions for the incidence and transmission of sound through the duct structure are significantly different from the transmission of diffuse sound through the enclosures of the room.
Calculation points are located in the area adjacent to the building
The fan noise travels through the air duct and is radiated into the surrounding space through a grille or shaft, directly through the walls of the fan housing or an open pipe when the fan is installed outside the building.
If the distance from the fan to the design point is much greater than its size, the noise source can be considered a point source.
In this case, octave sound pressure levels at design points are determined by the formula
(17) |
where L Pocti is the octave sound power level of the noise source, dB;
D L Pneti - total reduction in sound power level along the path of sound propagation in the air duct in the octave band under consideration, dB;
D L ni - sound radiation directivity indicator, dB;
r - distance from the noise source to the calculated point, m;
W is the spatial angle of sound radiation;
b a - sound attenuation in the atmosphere, dB/km.
If there is a row of several fans, grilles or other extended noise source of limited size, then the third term in formula (17) is taken equal to 15 lgr.
Structure-borne noise calculation
Structural noise in rooms adjacent to ventilation chambers arises as a result of the transfer of dynamic forces from the fan to the ceiling. The octave sound pressure level in an adjacent insulated room is determined by the formula
For fans located in a technical room outside the ceiling above the insulated room:
 |
(20) |
where L Pi is the octave sound power level of air noise emitted by the fan into the ventilation chamber, dB;
Z c is the total wave resistance of the vibration isolator elements on which the refrigeration machine is installed, N s/m;
Z per - input impedance of the floor - load-bearing slab, in the absence of a floor on an elastic foundation, floor slab - if present, N s/m;
S is the conventional floor area of the technical room above the insulated room, m 2 ;
S = S 1 for S 1 > S u /4; S = S u /4; when S 1 ≤ S u /4, or if the technical room is not located above the insulated room, but has one wall in common with it;
S 1 - area of the technical room above the insulated room, m 2 ;
S u - area of the insulated room, m 2 ;
S in - total area of the technical room, m 2 ;
R - own airborne noise insulation by the ceiling, dB.
Determining the required noise reduction
The required reduction in octave sound pressure levels is calculated separately for each noise source (fan, shaped elements, fittings), but the number of noise sources of the same type in the sound power spectrum and the magnitude of the sound pressure levels created by each of them at the design point are taken into account. In general, the required noise reduction for each source should be such that the total levels in all octave frequency bands from all noise sources do not exceed permissible levels sound pressure.
In the presence of one noise source, the required reduction in octave sound pressure levels is determined by the formula
where n is the total number of noise sources taken into account.
When determining D L three of the required reduction in octave sound pressure levels in urban areas, the total number of noise sources n should include all noise sources that create sound pressure levels at the design point that differ by less than 10 dB.
When determining D L three for design points in a room protected from noise from the ventilation system, the total number of noise sources should include:
When calculating the required reduction in fan noise - the number of systems serving the room; noise generated by air distribution devices and fittings is not taken into account;
When calculating the required noise reduction generated by the air distribution devices of the considered ventilation system, - the number of ventilation systems serving the room; the noise of the fan, air distribution devices and shaped elements is not taken into account;
When calculating the required noise reduction generated by the shaped elements and air distribution devices of the branch in question, - the number of shaped elements and chokes whose noise levels differ from one another by less than 10 dB; The noise of the fan and grilles is not taken into account.
At the same time, the total number of noise sources taken into account does not take into account noise sources that create a sound pressure level at the design point that is 10 dB less than permissible when their number is no more than 3 and 15 dB less than permissible when their number is no more than 10.
As you can see, the acoustic calculation is not simple task. Acoustics specialists provide the necessary accuracy of its solution. The effectiveness of noise reduction and the cost of its implementation depend on the accuracy of the acoustic calculation performed. If the calculated required noise reduction is underestimated, the measures will not be effective enough. In this case, it will be necessary to eliminate deficiencies at the existing facility, which is inevitably associated with significant material costs. If the required noise reduction is too high unjustified costs are included directly in the project. Thus, only due to the installation of mufflers, the length of which is 300-500 mm longer than required, additional costs at medium and large facilities can amount to 100-400 thousand rubles or more.
Literature
1. SNiP II-12-77. Noise protection. M.: Stroyizdat, 1978.
2. SNiP 23-03-2003. Noise protection. Gosstroy of Russia, 2004.
3. Gusev V.P. Acoustic requirements and design rules for low-noise ventilation systems // ABOK. 2004. No. 4.
4. Guidelines for the calculation and design of noise attenuation of ventilation units. M.: Stroyizdat, 1982.
5. Yudin E. Ya., Terekhin A. S. Combating noise from mine ventilation units. M.: Nedra, 1985.
6. Reducing noise in buildings and residential areas. Ed. G. L. Osipova, E. Ya. Yudina. M.: Stroyizdat, 1987.
7. Khoroshev S. A., Petrov Yu. I., Egorov P. F. Combating fan noise. M.: Energoizdat, 1981.
