# Commission Directive (EU) 2015/996 of 19 May 2015 establishing common noise assessment methods according to Directive 2002/49/EC of the European Parliament and of the Council (Text with EEA relevance), Division: Pure diffraction

Extent: E+W+S+N.I.

For pure diffraction, with no ground effects, the attenuation is given by:
Δdif =
10 C h × lg 3 + 40 λ C″δ
if 40 λ C″δ ≥ − 2
(2.5.21)
0
otherwise
where
Ch = 1
(2.5.22)
λ is the wavelength at the nominal centre frequency of the frequency band considered;
δ is the path difference between the diffracted path and the direct path (see next subsection on calculation of the path difference);
C″ is a coefficient used to take into account multiple diffractions:
C″ = 1 for a single diffraction.
For a multiple diffraction, if e is the total distance along the path, O1 to O2 + O2 to O3 + O3 to O4 from the ‘rubber band method’, (see Figures 2.5.d and 2.5.f) and if e exceeds 0,3 m (otherwise C″ = 1), this coefficient is defined by:
(2.5.23)
The values of Δdif shall be bound:
if Δ dif < 0: Δ dif = 0 dB
if Δ dif > 25: Δ dif = 25 dB for a diffraction on a horizontal edge and only on the term Δdif which figures in the calculation of Adif . This upper bound shall not be applied in the Δdif terms that intervene in the calculation of Δ ground , or for a diffraction on a vertical edge (lateral diffraction) in the case of industrial noise mapping.

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Source: https://www.legislation.gov.uk/eudr/2015/996/annex/division/ASSESSMENT/division/2/division/2.5/division/2.5.6/division/9 (the official version)
Page: https://openlegislation.uk/eu-directive-2015-996/annex/division-ASSESSMENT/division-2/division-2.5/division-2.5.6/division-9
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.