A mechanism study of sound wave-trapping barriers

Abstract

The performance of a sound barrier is usually degraded if a large reflecting surface is placed on the source side. A wave-trapping barrier (WTB), with its inner surface covered by wedge-shaped structures, has been proposed to confine waves within the area between the barrier and the reflecting surface, and thus improve the performance. In this paper, the deterioration in performance of a conventional sound barrier due to the reflecting surface is first explained in terms of the resonance effect of the trapped modes. At each resonance frequency, a strong and mode-controlled sound field is generated by the noise source both within and in the vicinity outside the region bounded by the sound barrier and the reflecting surface. It is found that the peak sound pressures in the barrier's shadow zone, which correspond to the minimum values in the barrier's insertion loss, are largely determined by the resonance frequencies and by the shapes and losses of the trapped modes. These peak pressures usually result in high sound intensity component impinging normal to the barrier surface near the top. The WTB can alter the sound wave diffraction at the top of the barrier if the wavelengths of the sound wave are comparable or smaller than the dimensions of the wedge. In this case, the modified barrier profile is capable of re-organizing the pressure distribution within the bounded domain and altering the acoustic properties near the top of the sound barrier.

Sound barriers from materials of inhomogeneous impedance

“…To verify the accuracy of the finite element modeling adopt in this paper, the performance of the parallel barrier model investigated in the work of Yang et al 7 is predicted by the current finite element modeling, and then it is compared with those results presented in the work of Yang et al by BEM. The geometrical configuration investigated in the work of Yang et al is very similar to that used in this paper, except that the source in Ref.…”

“…Another solution is to use novel barrier arrangements such as inclined barriers 15 and multiple wedges. 7,11 Such barriers reduce sound diffraction at the edges of parallel barriers, but their profiles are usually complex.…”

“…Based on extensive experimental data, Maekawa 4 derived an empirical method to describe the sound attenuation of a screen, and this has become an established technique in noise reduction engineering for estimating the shielding effect of barriers. For numerical analyses, the boundary element method (BEM) [5][6][7] and the finite element method (FEM) 7 have been widely adopted; these numerical methods are superior for dealing with barriers that have complex profiles.…”

“…Various types of barriers, such as T-profiled, inclined, and multi-wedge barriers have been designed. [7][8][9][10][11] Moreover, active noise control has been used to reduce the amount of sound diffracted at the edge of barriers. 12 Of particular interest, a degradation in performance has been reported when barriers are placed on opposite sides of a source.…”

Forced acoustical response of a cavity coupled with a semi-infinite space using coupled mode theory

“…For example, when the radiated sound pressure by a point source within a pair of noise barriers was expanded by eigenmodes solved numerically using perfectly matched layers (PML), the correct response could only be found at the resonance frequencies. 6 The difficultymight be owing to the non-orthogonality and incompleteness of the frequency-independent eigenmodes (the resonance modes) associated with the acoustic resonance frequencies and modal damping ratio. [6][7][8] As a result, the sound pressure expanded by the frequency-independent eigenmodes of the open cavity may have a convergence issue, which inevitably gives rise to an ambiguity in the selection of basis functions, i.e., if the resonance modes do not work for modal expansion, then what are the suitable basis functions?…”