Acoustics—Attenuation of sound during propagation outdoors--Part 2:General method of calculation
Some standard content:
GB/T17247.2—1998
This standard is equivalent to the international standard ISO9613-2:1996 "Acoustics Outdoor Sound Propagation Attenuation Part 2: General Calculation Method" to make the calculation method of outdoor sound propagation attenuation consistent with the international standards, which is conducive to international trade, technology and economic exchanges. This standard and GB/T17247.1 Acoustics Outdoor Sound Propagation Attenuation Part 1: Calculation of Atmospheric Sound Absorption constitute a series of standards.
The writing format and expression method of this standard shall comply with the provisions of GB/T1.11993. Appendix A and Appendix B of this standard are indicative and for reference only. This standard is proposed and coordinated by the National Technical Committee for Acoustics Standardization. The drafting units of this standard are: the Third Research Institute of the Ministry of Electronics Industry, the Institute of Acoustics of the Chinese Academy of Sciences, Peking University, Beijing Meteorological Bureau and Tianjin Hearing Aids.
The main drafters of this standard are: Yang Jingang, Li Peizi, Luan Guidong, Mi Jide, Zhang Ruwei, and Tang Huide. 323
GB/T 17247.2-1998
ISOForeword
The International Organization for Standardization (ISO) is a worldwide federation of national standardization committees (ISO member states). The development of international standards is usually carried out by ISO technical committees. Each member state has the right to participate in a technical committee when it is interested in a standard determined by the technical committee. Governmental and non-governmental international organizations in contact with ISO may also participate in the work. ISO maintains close cooperation with the International Electrotechnical Commission (IEC) in all aspects of electrotechnical standardization. Draft international standards adopted by each technical committee shall be circulated to member states for voting. At least 75% of the member states must vote in favor of the draft international standard before it can be published as an international standard. International Standard ISO9613 was developed by Technical Committee ISO/TC43 (Acoustics), Subcommittee SC1 "Noise". ISO 9613 includes the following parts under the general title "Acoustics--Attenuation of sound during propagation outdoors": Part 1: Calculation of atmospheric sound absorption
Part 2: General method of calculation
Part 1 is limited to calculations of atmospheric absorption processes. Part 2 is a more approximate and empirical method of calculation of attenuation by various physical mechanisms.
Appendices A and B to this part of ISO 9613 are informative appendices. 324
National Standard of the People's Republic of China
Acoustics--Attenuation of sound during propagation outdoors
Part 2: General method of calculation
GB/T_17247:2-1998
eqvIso 9613-2:1996
Acoustics--Attenuation of sound during propagation outdoors--Part 2: General method of calculation This standard specifies an engineering method for calculating the attenuation of outdoor sound propagation in order to predict the ambient noise level caused by various types of sound sources at a distance. This method predicts the equivalent continuous A sound level for a known noise emitting source under meteorological conditions favourable to propagation (described in ISO 1996 Parts 1 to 3).
These conditions are for downwind propagation as specified in 5.4.3.3 of ISO 1996-2:1987, or equivalently for propagation under stable, moderate ground-based temperature inversions, which usually occur at night. Temperature inversion conditions over water are not included, for which the sound pressure levels predicted by this standard may be higher. This method can also predict the long-term average A sound level specified in ISO 1996-1 and ISO 1996-2, which covers the sound levels for various meteorological conditions.
The method specified in this standard includes, in particular, a multiple band algorithm (with a nominal band centre frequency of 63 Hz to 8 kHz) to calculate the attenuation of sound originating from a point source or group of point sources, which may be mobile or fixed, with the following physical effects provided for in the algorithm:
Geometric divergence
Atmospheric absorption
—Ground effect
—Surface reflection
—Shielding caused by obstacles
Additional information on propagation through buildings, foliage and industrial sites can be found in Appendix A. In practice this method is applicable to a wide variety of noise sources and noise environments, and it can be applied directly or indirectly to most situations involving road surfaces, rail traffic, industrial noise sources, construction activities and many other ground-based noise sources, but it cannot be applied to aircraft in flight, or to shock waves from mining, military or similar operations. To apply this standard, several parameters must be known, corresponding to the geometry of the sound source and the environment, the characteristics of the ground surface and the intensity of the sound source consistent with the propagation direction expressed as octave band sound power level. Note: If only the A-weighted sound power level is known, the attenuation at 500 Hz can be used to estimate the final attenuation. The accuracy of the method and its limitations in practical application are described in Chapter 9. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. At the time of publication of this standard, the versions shown are valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB3241--82 1/1 and 1/3 octave filters for sound and vibration analysis Approved by the State Administration of Technical Supervision on March 18, 1998 and implemented on October 1, 1998
GB/T 17247.2—1998
GB3785—83 Electrical and acoustic properties and test methods of sound level meters ISO1996-1:1982 Description and measurement of acoustic environmental noise Part 1: Basic quantities and procedures ISO1996-2:1987 Description and measurement of acoustic environmental noise Part 2: Collection of data related to land use Description and measurement of acoustic environmental noise Part 3: Application of noise limits ISO 1996-3:1987
ISO 9613-1:1993
Acoustics Attenuation of outdoor sound propagation Part 1: Calculation of atmospheric sound absorption 3 Definitions
In addition to the definitions in ISO 1996-1, this standard also adopts the following definitions (see Table 1 for symbols and units). 3.1 Equivalent continuous A-weighted sound pressure level LAr equivalent continuous A-weighted sound pressure level LArLAT is defined by formula (1):
LAr = 10 lg [(), pA*(t)dt |/po*]dB Where: PA(t) - instantaneous A-weighted sound pressure, Pa; - reference sound pressure (20 μPa),
specified time interval, s.
A frequency weighting is specified in GB 3785.
(1)
Note: The time interval T should be long enough to average out the changing meteorological parameters. This standard takes into account two different situations, namely short-term tailwind and long-term total average. 3.2 Equivalent continuous downwind octave-band sound pressure level Lr (DW)
LiT (DW) is defined by formula (2):
Ln (DW) = 10 lg{[()
pr(t)dt
Where: pt(t) is the instantaneous downwind octave-band sound pressure of a sound source (Pa), and the subscript f represents the nominal band center frequency of the octave-band filter. Note: The electrical characteristics of the octave-band filter shall at least meet the requirements of Type 2 in GB3241. 3.3 Insertion loss (of a barrier).(2)
The difference in sound pressure level at the receiving point at a specified location with and without a barrier, while other conditions affecting sound propagation do not change significantly.
Table 1 Symbols and units
Octave band attenuation
Meteorological correction
Distance from point sound source to receiving point (see Figure 3) Definition
Distance from the sound source projected onto the ground plane to the receiving point (see Figure 1)Distance between the sound source and the reflection point of the obstacle (see Figure 8)Distance between the reflection point on the obstacle and the receiving point (see Figure 8)Distance from the sound source to the (first) diffraction edge (see Figures 6 and 7)Distance from the (second) diffraction edge to the receiving point (see Figures 6 and 7) Figure 7) Directivity index of point sound source
Shielding attenuation
Distance between the first and second diffraction edges (see Figure 7)Ground factor
Average height from sound source to receiving point
Height of point sound source above ground (see Figure 1)
Height of receiving point above ground (see Figure 1)
Average height of propagation path above ground (see Figure 3)Unit
4 Description of sound source
GB/T17247.2—1998
Table 1 (end)
Maximum size of sound source
Minimum size of reflecting surface (length and height) (see Figure 8)Sound pressure level
Atmospheric attenuation coefficient
Angle of incidence
Sound reflection coefficient
The formula in this standard is applicable to the sound attenuation of point sound sources. A generalized noise source such as road and rail traffic or an industrial area (which may include some equipment or facilities as well as traffic within the site) will be represented by a group of partitions, each of which has a certain sound power and directional characteristics, and the attenuation calculated from the sound of a representative point in each partition is used to represent the sound attenuation of this partition. A line source can be divided into a number of line partitions, and an area source can be divided into a number of area partitions, each of which is represented by a point source in the center. On the other hand, a point source group can be described by an equivalent point source in the middle of the group, in particular the sound sources have: a) approximately the same intensity and height from the ground; b) the same propagation conditions to the receiving point, and c) the distance d from the single equivalent point source to the receiving point exceeds twice the maximum size Hmx of the sound source (d>2Hmx). If the distance d is small (d≤2H), or the propagation conditions of the component point sources are different (for example, shielding is added), the total sound source must be divided into a number of component point sources.
Note: In addition to the real sound sources mentioned above, virtual sound sources may also be introduced to describe the sound reflections from the augmentation and canopy (not the ground) as described in 7.5. 5 Meteorological conditions
The downwind propagation conditions of this standard are specified in 5.4.3.3 of ISO 1996-2:1987, namely: - the wind direction is within an angle of ±45° from the center of the main sound source to the center of the designated receiving area, when the wind blows from the sound source to the receiving point, and the wind speed is approximately between (1 and 5) m/s, measured at a height of (3 to 11) m above the ground. In this standard, the formula for calculating the average downwind sound pressure level LAT (DW) includes the attenuation formula given in Chapter ?, which is the average value of meteorological conditions within these limits, where "average" means the average over a short time interval as defined in 3.1. These formulas are equivalently applicable to average propagation based on the ground under moderate temperature inversion conditions, such as often occur on clear and windless nights.
6 Basic formula
The equivalent continuous downwind octave band sound pressure level Lrr(DW) at the receiving point position is calculated using formula (3) for each point sound source and its virtual source, for the 8 octave bands with a nominal center frequency from 63Hz to 8kHz: Lr(DW) = Lw + Dc - A
（3）
Where: Lw-the octave band sound power level generated by the point sound source (dB), the reference sound power is 1pW; Dc-directivity correction (dB), which describes the degree of deviation from the equivalent continuous sound pressure level of the point sound source and the level of the omnidirectional point sound source that generates the sound power level Lw in the specified direction. The directivity correction Dc is equal to the directivity index DI of the point sound source plus the sound propagation index Da taken into account within a solid angle of less than 4 steradians (sr). For an omnidirectional point sound source radiating into free space, De = 0 dB;
A—Octave band attenuation when sound propagates from a point sound source to a receiving point. 327
GB/T 17247.2—1998
1The italic letter symbol A indicates the attenuation of this standard. Be careful not to confuse it with the frequency weighting represented by the regular letter A. 2The sound power level in formula (3) can be determined from measurements, for example, as described in GB/T 14367-93 series (for machinery) or ISO 8297 (for industrial plants).
The attenuation term A in equation (3) is given by equation (4):
A= Adiv + Aatn + Agr + Abar + Amis Where: Adiv—
Attenuation caused by geometric divergence (see 7.1); Attenuation caused by atmospheric absorption (see 7.2); Attenuation caused by ground effect (see 7.3); Attenuation caused by added barriers (see 7.4); Amisc Attenuation caused by other multi-effects (see Appendix A). · (4)
The general calculation method for the first four terms in equation (4) has been specified in this standard, and the three contributing data for the last term Amic (attenuation caused by propagation through foliage, industrial sites and housing clusters) are given in Appendix A. The equivalent continuous A-weighted downwind sound pressure level is obtained by adding the time mean square sound pressure of the contribution calculated for each point sound source, their virtual source and each octave band according to equations (3) and (4), as specified in equation (5): LAar(DW) = 10 lg(Z[Z100-1t/m(0)+()])dBj-1
where n-
contribution terms (sound source and distance),
j——the serial number of the center frequency of the 8 nominal octave bands from 63Hz to 8kHz, A:—refers to standard A weighting (see GB3785). The long-term average A-weighted sound pressure level LAr(LT) is calculated according to equation (6): LAr(LT) = LAr(DW) -- Cmet
where; Cmet -
meteorological correction value described in Chapter 8.
·（5）
The calculations and importance of the various items in equations (1) to (6) are explained in the following sections. For a more detailed discussion of the attenuation terms, see the references in Appendix B.
7 Calculation of attenuation terms
7.1 Geometric divergence (A)
The geometric divergence is the attenuation caused by the spherical expansion of a point sound source propagating in a free field and is calculated by equation (7): Adiv [20 lg(d/d.) + 11JdB
Where: d is the distance from the sound source to the receiving point, m; a reference distance, 1 m.
Note: The constant in equation (7) relates the sound power level to the sound pressure level of an omnidirectional point sound source at a reference distance d of 1 m. 7.2 Atmospheric absorption (Aam)
The attenuation due to atmospheric absorption over the propagation distance d (m) Aatm (dB) is given by equation (8): Aam = αd/1 000
(7)
Where: α - atmospheric attenuation coefficient, expressed in decibels per kilometer (see Table 2). For values of α for atmospheric conditions not included in Table 2, see ISO 9613-1.
Relative humidity
GB/T17247.2—1998
Table 2 Atmospheric attenuation coefficient α for octave band noise Atmospheric attenuation coefficient α, dB/km
Centre frequency of nominal frequency band, Hz
1 The atmospheric attenuation coefficient is closely related to the sound frequency, ambient temperature and relative humidity of the air, but has little to do with the ambient pressure. 2 For the calculation of the ambient noise level, the average atmospheric attenuation coefficient determined by the range of ambient climate changes relevant to the local area should be used. 7.3 Ground effect (Ag)
7.3.1 General calculation method
Ground attenuation A. is mainly caused by the interference between the direct sound and the ground reflected sound from the sound source to the receiving point. The downward curved propagation path (downwind) ensures that the attenuation is mainly determined by the ground close to the sound source and close to the receiving point. This method of calculating the ground effect can only be applied when the ground is approximately flat and horizontal or has a constant inclination. Three different areas are defined for ground attenuation (see Figure 1): dp
Sound source area
Intermediate area
Figure 1 Three different areas for determining ground attenuation 30h
Receiving area
a) The sound source area is the distance extending 30h from the sound source to the receiving point, with a maximum value of d (h. is the sound source height, d. is the distance between the sound source and the receiving point projected onto the ground plane), b) The receiving area is the distance extending 30h from the receiving point to the sound source, with a maximum value of d.(h is the height of the receiving point), c) the middle area is the distance from the sound source area to the middle of the receiving area. When d < (30h. + 30h.), the sound source area and the receiving area overlap, and there is no middle area.
According to this schematic diagram, the ground attenuation does not increase with the size of the middle area, which is mainly related to the properties of the sound source area and the receiving area. The acoustic properties of each ground area are calculated by the ground factor G. The three types of reflecting surfaces are defined as follows: a) Solid ground includes paved roads, water, ice, concrete and other low-porosity ground, such as compacted ground that often appears in industrial cities, which can be considered solid. Solid ground G=0. Note: Inversion conditions above water are not included in this standard. b) Loose ground includes ground covered with grass, trees or other plants, and other ground suitable for plant growth, such as farmland. Loose ground G=1.
c) Mixed ground If the ground is composed of solid ground and loose ground, G takes a value between 0 and 1, which is a fraction of the loose range.
In order to calculate the ground attenuation of a specified octave band, first use the formula in Table 3 to calculate the partial attenuation A. in the sound source area determined by the ground factor G. in the area, the partial attenuation A. in the receiving area determined by the ground factor G., and the partial attenuation Am in the intermediate area determined by the ground factor Gm. The functions α', b', c and d' in Table 3 can also be directly obtained from the curve in Figure 2. The total ground attenuation of the octave band is obtained by formula (9):
Ag=A+Ar+Am
Note: The influence of the ground on sound propagation may change in areas with buildings (see A3). a) 125Hz
c) 500Hz
distance d,,m
h≥10.0m
10002000
50010002000
distance dp,m
b) 250Hz
d) 1000Hz
distance tp.ma
h≥10.0m
10002000
50010002000
distance dm
The functions α, B, c and d of ground condensation A, respectively, are calculated by the formulas in Table 3. Figure 2 shows the distance between the sound source and the receiving point, and the height h of the sound source or receiving point Note:
GB/T 17247.2—1998
Table 3 Expressions for calculating ground attenuation A, A. and Am (octave band) Nominal band center frequency
-1. 5+GXa'(h)
1.5+GXb(h)
-1. 5+GXc'(h)
-1.5+GXd'(h)
-- 1. 5(1—G)
-1. 5(1-G)
1. 5(1—G)
a'(h)=1. 5+3. 0Xe-0.12(h-5)\(1-e-4,/50)+5, 7Xe-0 0h (1-e-2.8x10-6x4,')b'(h)=1. 5+8. 6Xe-0. 0gh2(1—e-4,/50)c (h)= 1. 5+14. 0Xe-0.4h2 (1-ed,/50)d'(h)=1. 5+5. 0Xe-0..(1-e-4,/50)1) To calculate A, take G=G. and h=h. To calculate A, take G=G, and h=hr. The G values for various ground surfaces are shown in 7.3.1. 2) q-0 When d,≤30(h.+h)
When d>30(h.+h.)
Where d. 7.3.2 Another method for calculating Ag for the distance between the sound source and the receiving point projected onto the ground plane
Under the following specific conditions:
Only the A sound level is calculated at the receiving point
-The sound wave propagates over loose ground, or a mixed ground with mostly loose ground (see 7.3.1) The sound is not a pure tone
For any shape of ground, the ground attenuation can be calculated by formula (10): Ag 4.8 -- (2hm/d)[17+(300/d)]≥0 dB Where: d——The distance from the sound source to the receiving point, m, the average height above the ground for a propagation path, m. hm-
—3g(1 -Gm)
The average height above the ground hm can be calculated by the method shown in Figure 3. If the Ag obtained from formula (10) is a negative value, it is replaced by zero. Note: Formula (10) expects no attenuation for short distances, and formula (9) can be more accurate. Receiving point
ground section
ha=area F/d
Method for estimating average height hm
GB/T 17247.2—1998
Because the ground reflection near the sound source causes a significant increase in the sound source power level, when using formula (10) to calculate the ground attenuation, the directivity correction Dc in formula (3) will be included in the item Dn.
Da= 10 Ig{1 +[d2 + (h,- h.)°]/[d,+(hs+h)\])dB In the formula, h.-
height of the sound source from the ground, m;bzxz.net
height of the receiving point from the ground, m;
d-—the distance between the sound source and the receiving point projected on the ground plane, m. 7.4 Shielding (Abar)
An object is considered a shielding obstacle (often called a barrier) when it meets the following conditions: the surface density is at least 10 kg/m;
the object has a closed surface without large cracks or gaps (thus, the influence of engineering equipment such as in chemical plants is ignored); the projection of the object in the direction perpendicular to the line connecting the sound source to the receiving point is greater than the wavelength of the sound wave at the nominal band center frequency of the frequency band to be studied, in other words (+1.)> (see Figure 4).
Note: An object is considered a shielding obstacle only when the projection of the object in the direction perpendicular to the line connecting the sound source to the receiving point is greater than the wavelength mountain + 1.> insertion. Figure 4 Plan view of two obstacles between the sound source (S) and the receiving point (R) Any object that meets these conditions will be represented by a barrier with vertical boundaries. The upper boundary of the barrier can be an inclined straight line. For this standard, the attenuation represented by the shielding Ab is given as the insertion loss. Both diffraction across the upper boundary of the barrier and around the vertical boundary may be important (see Figure 5). The effect of diffraction over the upper boundary on downwind sound propagation (dB) is calculated as A = D, - Ag > 0
and the effect of diffraction around the vertical boundary is calculated as A = D, > 0
where D
is the shielding attenuation of each color band (see equation (14)), Ag is the ground attenuation when the barrier does not exist (i.e. the barrier is removed) (see clause 7.3). 332
(12)
(13))
GB/T 17247.2—1998
Figure 5 Different sound propagation paths over the barrier
1 When Ar determined by equation (12) is substituted into equation (4) to calculate the total attenuation A, the two A terms in equation (4) will cancel. The shielding attenuation D in equation (12) has taken into account the ground effect when the barrier exists.
2 For long distances and high barriers, the insertion loss calculated by equation (12) has not been fully verified experimentally. 3 For factories with high buildings (more than 10 m above the ground) nearby, in the case of multiple sound sources and high transient sound sources, the insertion loss is calculated by equation (13) for the long-term average sound pressure level (using equation (6)).
4 If the sound is emitted from a road with a surface below the ground surface, there may be an additional attenuation expressed by equation (12) due to the influence of the ground surface. In order to calculate the shielding attenuation D,, it is assumed that there is only one effective sound propagation path from the sound source to the receiving point. If this assumption is not true, the other propagation paths should be calculated separately (as shown in Figure 5), and the contributions of each path to the squared sound pressure should be added at the receiving point. The shielding attenuation D,, in dB for this path is calculated by equation (14). D, = 10 Ig[3 + (C,/^)C,zKmet]dB (14)
Where: C, equals 20, including the influence of ground reflection; in special cases, the ground reflection can be considered as a virtual sound source separately, then take Cz 40,
For single diffraction (see Figure 6),Cs is equal to 1
for double diffraction (see Figure 7):
Cg=[1+(5^/e)?]/[(1/3)+(5/e)\]-the wavelength of the sound wave at the center frequency of the nominal frequency band, m; the path difference between the diffracted sound and the direct sound, calculated using equations (16) and (17), m, Kme
the correction factor for meteorological influence, given by equation (18); the distance between the two diffraction boundaries in the case of double diffraction (see Figure 7). Figure 6 Determine the geometric quantity of the single diffraction path difference
(15)
GB/T 17247.2—1998
Figure 7 Determine the geometric quantity of the double diffraction path difference
For the single diffraction shown in Figure 6, the path difference is calculated with the help of formula (16): =[(d+d)2+ a\12 -
Where: d. The distance from the sound source to the (first) diffraction edge, m; dr—The distance from the (second) diffraction edge to the receiving point, m; The component of the distance between the sound source and the receiving point parallel to the upper boundary of the barrier, m. If the observation line between the sound source S and the receiving point R passes above the upper boundary of the barrier, it is negative. For the double diffraction shown in Figure 7, the path difference is calculated by formula (17). z = [(d + d.r + e)2 + aj1/2 d
The meteorological correction factor Km in equation (14) is calculated by equation (18). Kmet expE- (1/2 000) ddrd/(2z)]JKmet 1 When z ≤ 0
For lateral diffraction around the barrier, Ket = 1 is taken (see Figure 5). Note
1 When the distance from the sound source to the receiving point is less than 100 m, Kmt1 can be taken and calculated using equation (14) to achieve an accuracy of 1 dB. 2 Equation (15) provides a continuous change from single diffraction (e = 0) case C-1 to fully separated double diffraction (e>^) case C: = 3. (16)
(17)
3Due to reflections from other hard surfaces in the vicinity of the sound propagation path from the sound source to the receiving point or due to multiple reflections between the hard barrier and the sound source, the effect of the sound barrier may be less than the results calculated by equations (12) to (18). In any frequency band, the shielding attenuation D does not take a value greater than 20 dB in the case of single diffraction (i.e., thin barrier) and does not take a value greater than 25 dB in the case of double diffraction (i.e., thick barrier).
For the shielding attenuation of two barriers, as shown in the lower part of Figure 7, the double diffraction formula of equation (14) is used for calculation. For the shielding attenuation of more than two barriers, equation (14) can also be used for approximate calculation by selecting the two most influential barriers and ignoring the effects of other barriers. 7.5 Reflection
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