THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

Equation (12.67) becomes(11D = λ+ +3λ + 20d 1 3λ + 20d 2[= 1.128= 0.05912.18 Approximations for Barrier Insertion Loss 315)13λ + 20d 313(1.128)+20(3.01) + 13(1.128)+20(2.59) + 13(1.128)+20(2.59)The insertion loss is then calculated:IL = 10 log(1/D) = 10 log(1/0.059) = 12 dB]12.18 Approximations for Barrier Insertion LossConsider the barrier of Figure 12.17. The Fresnel number N, given by Equation(12.57) can be restated asN =2(A + B − C)λ=2(A + B − C) fcA number of researchers in the field developed and verified analytic models,with a view to apply the results to highway barriers. For a point source locatedbehind an infinitely long solid wall or berm, the attenuation A ′ provided by abarrier are given by the following equations, where the arguments of tan and tanhare given in radians:A ′ = 0 for N < −0.1916 − 0.0635b( ′√ )−2π NA ′ = 5(1 + 0.6b ′ ) + 20 logtan √ for − 0.1916 − 0.0635b ′ ≤ N ≤ 0−2π N( √ )2π NA ′ = 5(1 + 0.6b ′ ) + 20 logtanh √ for 0 < N < 5.032π NFigure 12.17. The geometry of a barrier used in the calculation of the Fresnel number.