Control of diffracted sound by means of thnadners

Abstract

The diffraction of sound around barriers partially defeats efforts to control noise by interruption of line of sight. Recent legislation, which limits allowable highway noise in adjacent communities, has stimulated interest in this problem. Currently, solid walls are used to provide partial acoustical shadows. This approach is expensive, partly because of nonacoustical engineering requirements. A review of Fresnel diffraction theory suggests that either transparency gradients or phase velocity gradients or both may be used to provide deeper shadows. Elemental Fresnel theory is slightly modified to introduce transparency or phase gradients near the diffracting edge and parametric studies are reported which define configurations that deepen the shadows. Scale model tests are described which display the trends predicted by the theory. This agreement leads to the fascinating conclusion that the best way to improve the performance of a solid wall is to cut a substantial portion of it away. Structures are suggested for the practical implementation of the method into noise barriers. A literary analogy suggests that such structures be called Thnadners.

Design of a jagged-edge noise barrier: Numerical and experimental study

“…The studies range from semi-empirical models [1][2][3] * , to rigorous [4][5][6][7], to approximate analytical solutions [8][9][10], and numerical methods [11,12] to name a few from the vast literature on the subject. Furthermore, substantial effort has been devoted to improving the shielding effect of a barrier [13][14][15][16][17][18][19][20][21][22][23][24][25]. The work on improving the barrierʼs noise-reduction performance by introducing jaggedness is somewhat limited [26][27][28][29].…”

Noise reduction by a barrier having a random edge profile

“…Measurements with a rectangular barrier also showed degradation of the scattered signal when the barrier edge was made jagged. Wirt 17,18 has also considered deviating from the straight edge geometry of conventional barriers in order to improve barrier performance. However, his motivation was to vary barrier properties deterministically, not randomly.…”

A Review on Natural Ventilation-enabling Façade Noise Control Devices for Congested High-Rise Cities

“…Hammad and Gibbs [41,42] investigated the resultant acoustical protection when thnadners and splitters were applied to the courtyard wall, and the balcony front parapet facing the road traffic. A thnadner is a kind of shaped noise barrier [43]. For the courtyard cases, the use of a thnadner and splitter was shown to not significantly affect the acoustical protection, when compared to a solid wall, except at floor levels close to the ground/source.…”