CN104484564A - Method for calculating contact noise of workers under outdoor complicated sound field environment - Google Patents

Abstract

The invention provides a method for calculating contact noise of workers under an outdoor complicated sound field environment. The method comprises the following steps: (1) obtaining basic data of a working field; (2) constructing an actual scene physical model for predicating the noise; (3) setting sound source types; (4) calculating attenuation characteristics of the different sound source types in the actual scene physical model and attenuation characteristics of noise propagation under the action of obstacles so as to calculate noise values of the noise in contact with the workers by classes; (5) synthesizing the noise values of the noise in contact with the workers and synthesizing operation point contact equivalent sound grades. The method can be used for accurately calculating the contact noise of the workers at outdoor working fields. In a calculation process, sound field attributes can be considered and the influences on noise attenuation, caused by different sound source types, terrains, obstacles and the like, can be sufficiently considered; the calculation precision of the contact noise of the workers is remarkably improved, and technical references are provided for occupational health evaluation on the workers in a noisy working field.

Description

For calculating the method for operating personnel's contact noise under outdoor complex sound field environment

Technical field

The present invention relates to neighbourhood noise field, particularly a kind of method calculating noise under the environment of outdoor complicated field.

Background technology

Noise is along with the continuous progress of society, and the wish that people pursue comfortable operating environment is more and more stronger, and therefore, Occupational Health receives the extensive attention of people, and obtains in recent years and greatly develop.Noise evaluation of hygiene obtains equally as the important one side of Occupational Health and shows great attention to.For strengthening the occupational health evaluation to Noise Exposure place, accurately must calculate the contact noise of operating personnel.On the whole, the contact noise value of Noise Exposure place operating personnel is mainly subject to the impact of the following aspects:

1. noise is subject to the various decay that ground, Atmospheric Absorption, barrier etc. cause in communication process;

2. setting contact noise is by the impact of ground unrest;

3. by the impact of complicated landform (concave, convex, slope etc.) in noise transmission process

4. different sound source is to the contribution of setting contact noise;

5. the impact of sound field environment residing for setting;

6. the impact of type belonging to Work places: comprise office operation environment, outdoor work environment;

At present for problems, research is few both at home and abroad, its research mainly concentrate on different sound source decay is calculated theoretical analysis, the investigation and analysis work of Work places contact noise and the calculating aspect of setting noise exposure value.But setting contact noise value calculates mainly for the situation of ecotopia at present, lack the consideration to complex sound field environment, especially lack considering different sound source type, complicated sound source, sound field attribute etc., its computational accuracy receives certain impact.

Summary of the invention

Object of the present invention is just to provide a kind of method for calculating operating personnel's contact noise under outdoor complex sound field environment, and it accurately can calculate the contact noise of outdoor work place operating personnel.

The object of the invention is by such technical scheme realize, concrete steps are as follows:

1) Work places basic data is obtained;

2) according to step 1) basic data that obtains, build the actual scene physical model of noise prediction;

3) according to step 1) basic data that obtains, sound source type is set;

4) calculate the attenuation characteristic of different sound source types in actual scene physical model respectively, and barrier is to the attenuation characteristic of noise transmission, thus classified calculating goes out the noise figure of operating personnel's contact;

5) according to step 4) result that calculates, the noise figure of synthetic job human contact, synthetic job point cantact equivalent sound level.

Further, step 1) described in basic data include: environment space location parameter belonging to noise source characteristic and setting and periphery thereof;

Noise source characteristic includes: the self attributes of the octave band sound power level of noise source, sound pressure level, ground unrest sound power level, sound pressure level data, the space position parameter of sound source, the physical dimension parameter of sound source and sound source;

Belonging to setting and periphery thereof, environment space location parameter includes: setting space position parameter, sound source position parameter, setting periphery Obstacle Position geometric parameter, Work places terrain parameter and Work places size dimension parameter.

Further, step 3) described in the concrete grammar of setting of sound source type be: sound source type includes point sound source, line source and area source of sound, when the distance of operating personnel's distance sound source is greater than 2 times of sound source biggest size of element, this sound source is set to point sound source; When operating personnel's distance sound source is less than or equal to 2 times of biggest size of element, arrange according to the self attributes of sound source.

Further, step 4) described in the computing method of the attenuation characteristic of different sound source types in actual scene physical model be:

For point sound source:

When this sound source non-directive, setting contact noise value following formula calculates:

L _A(r)＝L _AW-20lg(r)-8

When this sound source has directive property, setting contact noise value following formula calculates:

L _P(r)＝L _W-20lg(r)-11+D _Iθ

Wherein: D _{i θ}the sensing factor at r place on a certain θ direction;

The correction Δ L that reflecting body causes:

When point sound source and setting are in reflecting body homonymy, the sound level at future position place is the result that direct sound wave superposes with reflected sound; Work as r _d/ r _rwhen approximating 1, Δ L=3dB; Work as r _d/ r _rwhen approximating 1.4, Δ L=2dB; Work as r _d/ r _rwhen approximating 2, Δ L=1dB; Work as r _d/ r _rwhen being about greater than 2.5, Δ L=0dB.

Further, step 4) described in the computing method of the attenuation characteristic of different sound source types in actual scene physical model be:

For line source: for sweep in irregular shape, its equivalence is become the line segment combination of multiple different length, calculate according to line source decay;

Work as r<L ₀during/π, this line source is set to finite length line sound source:

If wire sound source is long is L ₀, the power of unit length line source radiation is W watt/meter, and respective levels is L _w, make the vertical line of line source from future position P, intersection point is an O, and with O point for initial point, line source axis is X-axis, and two extreme coordinates of line source are respectively X ₁, X ₂.If OP length is r, then the overall sound pressure level that produces at setting of line source:

$L_P=L_W+10\lg \left(\frac{Q}{4\mathrm{\&pi;}}\right)+10\lg \left[\frac{1}{r}(\mathrm{arctg}\frac{X_2}{r}-\mathrm{arctg}\frac{X_1}{r})\right]$

In formula, complete free space Q=1, semi-free space Q=2,1/4 free space Q=4,1/8 free space Q=8;

As r " L/ π time, this line source is set to infinite line sound source, the overall sound pressure level that line source produces at setting:

L _P＝L _W+10lg[Q/(4r)]

In formula, directivity factor Q value is: free space Q=1, semi-free space Q=2,1/4 free space Q=4,1/8 free space Q=8 completely.

Further, step 4) described in the computing method of the attenuation characteristic of different sound source types in actual scene physical model be:

For area source of sound: area source of sound can be divided into gore sound source again, rounded face sound source, rectangular surfaces sound source, complicated area source of sound can be simplified to the combination of above three kinds of sound sources, carries out sound level calculating respectively;

Calculate according to area source of sound as r<a/ π:

For a uniform rectangle planar sound source, its unit area sound power level is W (W/m ²), respective levels is L _w.Calculate for simplifying, first needing sound source place plane definition is the plane of Z=0, and its four edges is parallel with coordinate axis, and the coordinate of four angle points is: (a ₁, b ₁, 0), (a ₁, b ₂, 0), (a ₂, b ₁, 0), (a ₂, b ₂, 0), and a ₁<a ₂, b ₁<b ₂(a=|a ₁-a ₂|, b=|b ₁-b ₂|, and a<b); For future position P (a, b, c), in sound source, a unit dimension dxdy at (x, y, 0) place can regard a point source as, and infinitesimal is R:R to the distance of future position ²=(x-a) ²+ (y-b) ²+ (c) ², then the sound pressure level of setting is according to following formulae discovery:

$L_P=10\lg \frac{\frac{\mathrm{QW}}{4\mathrm{\&pi;}}\underset{a_1}{\overset{a_2}{\&Integral;}}\left\{\underset{b_1}{\overset{b_2}{\&Integral;}}\frac{1}{{(x-a)}^2+{(y-b)}^2+{\left(c\right)}^2}\mathrm{dy}\right\}\mathrm{dx}}{I_0}$

Calculate according to line source as a/ π <r<b/ π;

As r≤b/ π, calculate according to point sound source.

Further, step 4) described in the computing formula of barrier to the attenuation characteristic of noise transmission as follows:

A _bar＝10lg[3+(C ₂/λ)×[1+(5λ/e ²)/[1/3+(5λ/e) ²]]×z×K _met]

In formula, C ₂the constant coefficient relevant with ground return, C ₂=40;

λ is the wave length of sound of nominal band centre frequency;

E is the distance that double wrap penetrates in situation between two diffraction borders;

Z is the path difference of diffraction sound and direct sound wave, z=[(d _ss+ d _sr+ e) ²+ a ²] ^1/2-d; Wherein: a is that distance between sound source and receiving station is in the projected length being parallel to barrier border; d _ssfor sound source is to the distance on the first diffraction limit; d _srbe the distance of the second diffraction limit to receiving station;

K _metit is the meteorological correction factor.

Owing to have employed technique scheme, the present invention has following advantage:

The present invention accurately can calculate the contact noise of outdoor work place operating personnel.In computation process, not only can consider sound field attribute, different sound source type can also be taken into full account, landform, barriers etc. are on the impact of noise attentuation, the computational accuracy of the contact noise of its operating personnel obtains and significantly improves, and can provide Technical Reference for the operating personnel's occupational health evaluation of Noise Exposure place.

Other advantages of the present invention, target and feature will be set forth to a certain extent in the following description, and to a certain extent, based on will be apparent to those skilled in the art to investigating hereafter, or can be instructed from the practice of the present invention.Target of the present invention and other advantages can be realized by instructions below and claims and be obtained.

Accompanying drawing explanation

Accompanying drawing of the present invention is described as follows.

Fig. 1 is structural representation of the present invention.

Fig. 2 is that reflecting body of the present invention affects schematic diagram;

Fig. 3 is that line source of the present invention decay calculates schematic diagram;

Fig. 4 is area source of sound schematic diagram;

Fig. 5 is that area source of sound decay calculates schematic diagram;

Fig. 6 is the double wrap schematic diagram of invention;

Fig. 7 is that the double wrap of invention penetrates decay calculating schematic diagram;

Fig. 8 is that on multi-obstacle avoidance, diffracted sound field calculates schematic diagram;

Fig. 9 is that multi-obstacle avoidance side diffracted sound field calculates schematic diagram.

Embodiment

Below in conjunction with drawings and Examples, the invention will be further described.

For calculating a method for operating personnel's contact noise under outdoor complex sound field environment, concrete steps as shown in Figure 1:

1) Work places basic data is obtained;

The first step obtains noise source characteristic, includes the self attributes of the octave band sound power level of noise source, sound pressure level, ground unrest sound power level, sound pressure level data, the space position parameter of sound source, the physical dimension parameter of sound source and sound source;

Second step obtains setting space position parameter, include setting space position parameter, sound source position parameter, setting periphery Obstacle Position geometric parameter, Work places size dimension parameter and Work places terrain parameter, i.e. landform convex-concave angle, if ideal plane landform, then need not consider;

2) according to step 1) basic data that obtains, build the actual scene physical model of noise prediction;

Obtain the physical model of actual scene by Rational Simplification, comprise Work places sound source attribute, noise source characteristic, environment space position, geometric shape parameters belonging to operating personnel and periphery thereof.

3) according to step 1) basic data that obtains, sound source type is set;

Sound source type comprises point sound source, line source, area source of sound.For line source and area source of sound, when the distance of operating personnel's distance sound source is greater than 2 times of sound source biggest size of element, this sound source is set to point sound source; When operating personnel's distance sound source is less than 2 times of biggest size of element, carry out the setting of sound source type respectively according to sound source self attributes.

4) calculate the attenuation characteristic of different sound source types in actual scene physical model respectively, and barrier is to the attenuation characteristic of noise transmission, thus classified calculating goes out the noise figure of operating personnel's contact;

The attenuation characteristic of dissimilar sound source comprises the attenuation characteristic of institute's sound source in Work places; Barrier specifically comprises on the impact of noise transmission the attenuation characteristic of sound in complicated landform that sound source sends.

For point sound source:

(1) when this sound source non-directive, setting contact noise value following formula calculates:

L _A(r)＝L _AW-20lg(r)-8

(2) when this sound source has directive property, setting contact noise value following formula calculates:

L _P(r)＝L _W-20lg(r)-11+D _Iθ

Wherein: D _{i θ}the sensing factor at r place on a certain θ direction.

(3) the correction Δ L that causes of reflecting body

When point sound source and setting are in reflecting body homonymy, the sound level at future position place is the result that direct sound wave superposes with reflected sound, when reflector surface is smooth, hard, reflecting body size be far longer than sound wave long and incident angle is less than 85 ° time, need to consider that the sound level that emitter causes raises.As shown in Figure 2, r is worked as _d/ r _rwhen approximating 1, Δ L=3dB; Work as r _d/ r _rwhen approximating 1.4, Δ L=2dB; Work as r _d/ r _rwhen approximating 2, Δ L=1dB; Work as r _d/ r _rwhen being about greater than 2.5, Δ L=0dB;

For line source: for sweep in irregular shape, its equivalence is become the line segment combination of multiple different length, calculate according to line source decay.

(1) r<L is worked as ₀during/π, this line source is set to finite length line sound source:

As shown in Figure 3, if wire sound source length is L ₀, the power of unit length line source radiation is W (watt/meter), and respective levels is L _w.Make the vertical line of line source from future position P, intersection point is an O.With O point for initial point, line source axis is X-axis, and two extreme coordinates of line source are respectively X ₁, X ₂.If OP length is r.The then overall sound pressure level that produces at setting of line source:

$L_P=L_W+10\lg \left(\frac{Q}{4\mathrm{\&pi;}}\right)+10\lg \left[\frac{1}{r}(\mathrm{arctg}\frac{X_2}{r}-\mathrm{arctg}\frac{X_1}{r})\right]$

In formula, complete free space Q=1, semi-free space Q=2,1/4 free space Q=4,1/8 free space Q=8.

(2) as r " L/ π time, this line source is set to infinite line sound source, the overall sound pressure level that line source produces at setting:

L _P＝L _W+10lg[Q/(4r)]

In formula, directivity factor Q value is the same.

For area source of sound: area source of sound can be divided into gore sound source again, rounded face sound source, rectangular surfaces sound source, complicated area source of sound can be simplified to the combination of above three kinds of sound sources, carries out sound level calculating respectively.For rounded face sound source and triangle sound source, when the distance of operating personnel's distance sound source is greater than 2 times of sound source biggest size of element, directly calculate according to point sound source, computing method are the same.When sound source is rectangle sound source:

(1) calculate according to area source of sound as r<a/ π

For a uniform rectangle planar sound source, its unit area sound power level is W (W/m ²), respective levels is L _w.Calculate for simplifying, first needing sound source place plane definition is the plane of Z=0, and its four edges is parallel with coordinate axis, and the coordinate of four angle points is: (a ₁, b ₁, 0), (a ₁, b ₂, 0), (a ₂, b ₁, 0), (a ₂, b ₂, 0), and a ₁<a ₂, b ₁<b ₂(a=|a ₁-a ₂|, b=|b ₁-b ₂|, and a<b), shown in following Fig. 4 and Fig. 5;

For future position P (a, b, c), in sound source, a unit dimension dxdy at (x, y, 0) place can regard a point source as, and infinitesimal is R:R to the distance of future position ²=(x-a) ²+ (y-b) ²+ (c) ², then the sound pressure level of setting is according to following formulae discovery:

$L_P=10\lg \frac{\frac{\mathrm{QW}}{4\mathrm{\&pi;}}\underset{a_1}{\overset{a_2}{\&Integral;}}\left\{\underset{b_1}{\overset{b_2}{\&Integral;}}\frac{1}{{(x-a)}^2+{(y-b)}^2+{\left(c\right)}^2}\mathrm{dy}\right\}\mathrm{dx}}{I_0}$

For gore sound source and rounded face sound source, computing method are the same, integral domain revised accordingly.

(2) calculate according to line source during a/ π <r<b/ π.

(3), during r≤b/ π, calculate according to point sound source.

The influence of fading of barrier;

In complex scene, can exist many arbitrarily, irregular barrier is put in position, comprises buildings, various equipment etc.At this moment sound source is by the decay of barrier, mainly comprises the side diffraction crossed barrier coboundary He walk around vertical boundary, calculates by the following method:

A _bar＝10lg[3+(C ₂/λ)×[1+(5λ/e ²)/[1/3+(5λ/e) ²]]×z×K _met]

Wherein: C ₂the constant coefficient relevant with ground return, C ₂=40;

λ is the wave length of sound of nominal band centre frequency;

E is the distance that double wrap penetrates in situation between two diffraction borders;

Z is the path difference of diffraction sound and direct sound wave, z=[(d _ss+ d _sr+ e) ²+ a ²] ^1/2-d; Wherein: a is that distance between sound source and receiving station is in the projected length being parallel to barrier border; d _ssfor sound source is to the distance on the first diffraction limit; d _srbe the distance of the second diffraction limit to receiving station, as shown in Figure 6 and Figure 7;

K _metit is the meteorological correction factor.

Upper diffracted sound field calculates: as Fig. 8, connects RS, finds out each barrier set [P] crossing with RS line; In [P], connect the summit of sound source S and each barrier, when other barrier in the line and set [P] on S and certain barrier summit is without intersection point, or have intersection point, but intersection point is just on the summit of other barrier, then the summit of this barrier is as E point; Use the same method and try to achieve F point; Utilize double wrap to penetrate calculating Shangrao and penetrate loss.

Side diffracted sound field calculates: as Fig. 9, generate straight line S1S2 and R1R2 (note: they be parallel to ground) vertical with RS; Send out by S, to S1 direction by certain spacing, this distance can arrange movement, obtains S ', connects R and S ': if 1. there is the intersection point with barrier, continue mobile S '; If 2. do not have intersection point, then movement completes, and last intersection point C tries to achieve; If 3. S ' moves to S1, the limit point arranged in advance, also has intersection point, illustrates that this side is without diffraction not by this side diffraction; Use the same method and try to achieve A, B, C, D 4 three-dimensional coordinates; Calculate S to be penetrated by the double wrap of A, B, C, D 4.Wherein, displacement can be arranged as an initial parameter.During calculation side diffraction Diffraction Point, what use is all barriers, and in calculating during diffraction, what use is the barrier set crossing with RS, if A and C point overlaps, adopts the distance of A and C to be less than certain value and is coincidence, adopt single diffraction to calculate during calculating.

5) according to step 4) result that calculates, the noise figure of synthetic job human contact, synthetic job point cantact equivalent sound level.

What finally illustrate is, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although with reference to preferred embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that, can modify to technical scheme of the present invention or equivalent replacement, and not departing from aim and the scope of the technical program, it all should be encompassed in the middle of right of the present invention.

Claims (7)

1., for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, concrete steps are as follows:

1) Work places basic data is obtained;

2) according to step 1) basic data that obtains, build the actual scene physical model of noise prediction;

3) according to step 1) basic data that obtains, sound source type is set;

4) calculate the attenuation characteristic of different sound source types in actual scene physical model respectively, and barrier is to the attenuation characteristic of noise transmission, thus classified calculating goes out the noise figure of operating personnel's contact;

5) according to step 4) result that calculates, the noise figure of synthetic job human contact, synthetic job point cantact equivalent sound level.

2. as claimed in claim 1 for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, step 1) described in basic data include: environment space location parameter belonging to noise source characteristic and setting and periphery thereof;

Noise source characteristic includes: the self attributes of the octave band sound power level of noise source, sound pressure level, ground unrest sound power level, sound pressure level data, the space position parameter of sound source, the physical dimension parameter of sound source and sound source;

Belonging to setting and periphery thereof, environment space location parameter includes: setting space position parameter, sound source position parameter, setting periphery Obstacle Position geometric parameter, Work places terrain parameter and Work places size dimension parameter.

3. as claimed in claim 2 for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, step 3) described in the concrete grammar of setting of sound source type be: sound source type includes point sound source, line source and area source of sound, when the distance of operating personnel's distance sound source is greater than 2 times of sound source biggest size of element, this sound source is set to point sound source; When operating personnel's distance sound source is less than or equal to 2 times of biggest size of element, arrange according to the self attributes of sound source.

4., as claimed in claim 3 for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, step 4) described in the computing method of the attenuation characteristic of different sound source types in actual scene physical model be:

For point sound source:

When this sound source non-directive, setting contact noise value following formula calculates:

L _A(r)＝L _AW-20lg(r)-8

When this sound source has directive property, setting contact noise value following formula calculates:

L _P(r)＝L _W-20lg(r)-11+D _Iθ

Wherein: D _{i θ}the sensing factor at r place on a certain θ direction;

The correction Δ L that reflecting body causes:

When point sound source and setting are in reflecting body homonymy, the sound level at future position place is the result that direct sound wave superposes with reflected sound; Work as r _d/ r _rwhen approximating 1, Δ L=3dB; Work as r _d/ r _rwhen approximating 1.4, Δ L=2dB; Work as r _d/ r _rwhen approximating 2, Δ L=1dB; Work as r _d/ r _rwhen being about greater than 2.5, Δ L=0dB.

5., as claimed in claim 4 for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, step 4) described in the computing method of the attenuation characteristic of different sound source types in actual scene physical model be:

For line source: for sweep in irregular shape, its equivalence is become the line segment combination of multiple different length, calculate according to line source decay;

Work as r<L ₀during/π, this line source is set to finite length line sound source:

If wire sound source is long is L ₀, the power of unit length line source radiation is W watt/meter, and respective levels is L _w, make the vertical line of line source from future position P, intersection point is an O, and with O point for initial point, line source axis is X-axis, and two extreme coordinates of line source are respectively X ₁, X ₂.If OP length is r, then the overall sound pressure level that produces at setting of line source:

$L_P=L_W+101g\left(\frac{Q}{4\mathrm{\&pi;}}\right)+101g\left[\frac{1}{r}(\mathrm{arctg}\frac{X_2}{r}-\mathrm{arctg}\frac{X_1}{r})\right]$

In formula, complete free space Q=1, semi-free space Q=2,1/4 free space Q=4,1/8 free space Q=8;

As r " L/ π time, this line source is set to infinite line sound source, the overall sound pressure level that line source produces at setting:

L _P＝L _W+10lg[Q/(4r)]

In formula, directivity factor Q value is: free space Q=1, semi-free space Q=2,1/4 free space Q=4,1/8 free space Q=8 completely.

6., as claimed in claim 5 for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, step 4) described in the computing method of the attenuation characteristic of different sound source types in actual scene physical model be:

For area source of sound: area source of sound can be divided into gore sound source again, rounded face sound source, rectangular surfaces sound source, complicated area source of sound can be simplified to the combination of above three kinds of sound sources, carries out sound level calculating respectively;

Calculate according to area source of sound as r<a/ π:

For a uniform rectangle planar sound source, its unit area sound power level is W (W/m ²), respective levels is L _w.Calculate for simplifying, first needing sound source place plane definition is the plane of Z=0, and its four edges is parallel with coordinate axis, and the coordinate of four angle points is: (a ₁, b ₁, 0), (a ₁, b ₂, 0), (a ₂, b ₁, 0), (a ₂, b ₂, 0), and a ₁<a ₂, b ₁<b ₂(a=|a ₁-a ₂|, b=|b ₁-b ₂|, and a<b); For future position P (a, b, c), in sound source, a unit dimension dxdy at (x, y, 0) place can regard a point source as, and infinitesimal is R:R to the distance of future position ²=(x-a) ²+ (y-b) ²+ (c) ², then the sound pressure level of setting is according to following formulae discovery:

$L_P=101g\frac{\frac{\mathrm{QW}}{4\mathrm{\&pi;}}\underset{a_1}{\overset{a_2}{\&Integral;}}\left\{\underset{b_1}{\overset{b_2}{\&Integral;}}\frac{1}{{(x-a)}^2+{(y-b)}^2+{\left(c\right)}^2}\mathrm{dy}\right\}\mathrm{dx}}{I_0}$

Calculate according to line source as a/ π <r<b/ π;

As r≤b/ π, calculate according to point sound source.

7., as claimed in claim 6 for calculating the method for operating personnel's contact noise under outdoor complex sound field environment, it is characterized in that, step 4) described in the computing formula of barrier to the attenuation characteristic of noise transmission as follows:

A _bar＝10lg[3+(C ₂/λ)×[1+(5λ/e ²)/[1/3+(5λ/e) ²]]×z×K _met]

In formula, C ₂the constant coefficient relevant with ground return, C ₂=40;

λ is the wave length of sound of nominal band centre frequency;

E is the distance that double wrap penetrates in situation between two diffraction borders;

Z is the path difference of diffraction sound and direct sound wave, z=[(d _ss+ d _sr+ e) ²+ a ²] ^1/2-d; Wherein: a is that distance between sound source and receiving station is in the projected length being parallel to barrier border; d _ssfor sound source is to the distance on the first diffraction limit; d _srbe the distance of the second diffraction limit to receiving station;

K _metit is the meteorological correction factor.