Sound field study of a building near a roadway via the boundary element method

Abstract

A two-dimensional boundary element method with a constant element type was adopted to study the sound field of a building near a roadway. First, a factor analysis of the computed results has been done, which include the element length, the Hankel functions’ calculation accuracy, and numerical integration accuracy. Then, boundary element method is applied to calculate building attenuation with different building aspect ratios and different frequencies with balconies, followed by drawing of the sound field distribution diagram. The calculation results revealed the following: (1) a wider building results in a more severe sound attenuation; (2) balconies on different floors produce a reduction of approximately 15 dB for broadband spectral characteristics of A-weight road traffic noise, and the maximum values appear at the bottoms of balconies; (3) for the points in the balconies, higher sound frequencies are correlated to larger insertion loss, with the insertion loss increasing from 3 dB to >10 dB when the sound frequency increases from 20 to 4000 Hz; (4) calculations of three typical frequencies indicate that the insertion loss of 500 Hz (main frequency of heavy vehicles) is 6 dB less than that of 800 Hz (main frequency of light vehicles), i.e. the flow control of heavy vehicles could conspicuously improve the ambient acoustic environment of buildings near a roadway.

Approaches for Noise Barrier Effectiveness Evaluation Based on In Situ “Insertion Loss” Determination

“…Mathematical methods have been widely used to determine the diffraction properties of the barriers. These methods can be based on the boundary element method [19,20], the finite element method [21,22], and the finite difference method [23].…”

“…The use of artificial noise sources is infrequent and is used only when it is not possible to use traffic noise in equivalent conditions. This artificial point source may be based on a loudspeaker that reproduces traffic noise [20] or a regulated artificial signal such as pink noise [43].…”

“…In most studies, microphones are placed at regular distances from the barrier (5, 10, 15 m), or corresponding to incremental doublings of the distance (e.g., 7.5, 15, 30 m) [42,44]. Some studies determine IL levels by placing a single microphone in the near field behind the barrier, at distances of 1-5 m [20,43,45,46]. The most common height for the microphone is 1.5 m, although there are studies that consider additional heights, which are similar to or higher than the barrier height (e.g., 2, 4, 6 m).…”

“…The results obtained in the different research studies conducted revealed moderate Insertion Loss values of the noise barriers. Attenuation values obtained in the near field, at distances from the barrier of 5-7 m, and heights above ground of 1.2-1.5 m, range between 7 and 10 dB(A) [20,42,[44][45][46]50]. Insertion Loss levels are higher at shorter distances from the barrier, such as 1 m [43].…”

Calculation of Noise Barrier Insertion Loss Based on Varied Vehicle Frequencies

“…The mathematical formula was first developed by Sommerfeld in 1896 [16] and has been subsequently developed by many other scholars. As such, rigorous diffraction results can be calculated in mathematical methods, e.g., the Boundary Element Method [17], the Finite Element Method (FEM) [18], and the Finite Difference Method (FDM) [19]. In many cases, the typical procedure for the mathematical computation is too complicated to be applicable to the engineering application.…”