Efficiency of a noise barrier with an acoustically soft cylindrical edge for practical use

This paper examines the sound shielding efficiency of a noise barrier having an acoustically soft cylindrical edge, as it compares to that provided by the well-known absorptive cylindrical edge. It has been reported that the waterwheel-shaped cylinder (acoustic tubes in a radial arrangement) approximates a soft surface cylinder, and that the sound shielding efficiency of a noise barrier is improved by placing the cylinder on its edge. The efficiency of the waterwheel-shaped edge barrier is strongly frequency dependent, thus the improvement in overall sound pressure level is smaller than expected when the source is broadband noise. The present study investigates the use of varied tube depths to improve the efficiency of the waterwheel-shaped edge. It is shown that adding tubes of different depths can flatten the frequency dependence, and that such tubes are only needed in the upper half of the cylinder. These findings led to the design of a new edge device for controlling road traffic noise, whose numerical simulations suggest that it is twice as effective in overall sound pressure level as the original waterwheel with uniform-depth channels.