Division 2.7.24: Weighted equivalent sound levels - 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)

Time-weighted equivalent sound levels, which account for all significant aircraft sound energy received, shall be expressed in a generic manner by the formula

L_{eq,W} = 10 \times \lg [\frac{t_{0}}{T_{0}} \times \sum_{i = 1}^{N} g_{i} \times 10^{L_{E,i} ∕ 10}] + C

(2.7.56)

The summation is performed over all N noise events during the time interval T ₀ to which the noise index applies. L_E,i is the single event noise exposure level of the i-th noise event. g_i is a time-of-day dependent weighting factor (usually defined for day, evening and night periods). Effectively g_i is a multiplier for the number of flights occurring during the specific periods. The constant C can have different meanings (normalising constant, seasonal adjustment etc.).

Using the relationship

g_{i} = 10^{Δ_{i} ∕ 10}

where Δ_i is the decibel weighting for the i-th period, equation (2.7.56) can be rewritten as

L_{eq,W} = 10 \times \lg [\frac{t_{0}}{T_{0}} \sum_{i = 1}^{N} 10^{(L_{E,i} + Δ_{i}) ∕ 10}] + C

(2.7.57)

i.e. the time-of-day weighting is expressed by an additive level offset.

Division 2.7.24 Weighted equivalent sound levels