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# Online calculation of noise attenuation: free space and semi-free space

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### Application area

Environmental impact assessment calculation

### Description

Calculation of noise attenuation: free space and semi-free space.

Under the condition of free sound field (free space), the sound wave of the point source follows the spherical divergence law, and the sound power level is used as the point source evaluation quantity. The attenuation formula is:

$$△L=10 lg (1/4πr^2)$$

In the formula:

△ L - the increase in distance produces an attenuation value, dB;

R——the distance from the source to the sound point, m.

The attenuation value at the distance from the point source, r1 to r2:

$$△L=20 lg (r1/r2)$$

When r2=2r1, ΔL=-6dB, that is, the point source propagation distance is doubled, and the attenuation value is 6dB.

In semi-free space conditions, the formula is:

$$LA=(r)=LWA-20 lgr-8$$

• "National Environmental Protection Standards of the People's Republic of China" HJ2.4-2009
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