# Suitability of Active Noise Barriers for Construction Sites
## 3 Method  
Acoustic barriers are commonly used in cities to control the construction noises in the street area and neighboring buildings. These kinds of barriers are generally composed of several short length segments (Figure 2) so that they can be installed, moved, and adapted to the boundary of the construction sites. In this study, three zones are considered to model the construction site and its nearby areas: (I) the construction site (Figure 2a), where the activities are progressing and the noise sources are located; (II) the building area, representing close buildings; and (III) the street area, representing the sidewalk zone between neighborhood buildings and the construction site (Figure 2b). In the simulation, the barrier with rigid surfaces on both sides and a practical height of \(H_{b}\) = 2.5 m is considered between the construction site and the sidewalk and buildings area (Figure 3). The thickness of the barrier is considered negligible vis-a-vis the noise wavelength. In the calculations, the ground is also assumed to be hard and the reflected pressure at both sides of the barrier are computed based on the image method [42]. To address the movement of the noise source in the construction site, the simulation is conducted for different positions of the noise source. The distance of the noise source from the barrier, \(d_{pr}\), ranges from 1 to 7 m, and for simplicity, it is always located at plane \(Y\) = 0 and a height of 0.3 m. The frequency spectra throughout this work are formed by the center frequency of each third octave band from 63 Hz to 1 kHz and the power output of the noise source is 1 \(W\) at each considered frequency. Figure 3 schematically shows the construction site and the nearby areas. In this figure, the control zone is the region close to the barrier, reserved to place the transducers. This zone is intentionally selected near the barrier so that the transducers can be installed in real applications and also the active barrier remains as a unique, portable device. For this study, the control zone surrounds the barrier with a size of \(1\times 3\) m\({}^{2}\). The positions of the transducers are optimized through the control zone to minimize the sound level in the target areas (shaded areas in Figure 3). The street area with a size of \(10\times 8\) m\({}^{2}\) is recognized  
Figure 2: On-site noise control barriers. (**a**) Construction site area. (**b**) Sidewalk and neighboring buildings. as the first target area that is covered with 15 points for computing the pressure. These points are located at a height of 1.65 m.  
The second target area in this research is the shadow zone on the facade of the neighboring building. The whole building facade is \(20\times 8\) m\({}^{2}\), located on the plane \(X=15\) m (Figure 3) and placed symmetrically with respect to the \(Y\)-axis. The size of the shadow zone on the facade depends on the relative location of the noise source from the barrier. In the current work, the same density of points as the street area is always considered to compute the pressure on the facade. The set of control sources is defined by an array of \(N_{\rm s}=10\) control sources arranged linearly along the \(Y\)-direction and distributed symmetrically with respect to the \(X\)-axis. The space between the adjacent control sources in the \(Y\)-direction is \(d_{\rm s}=0.2\) m, which is close to half the shortest wavelength at 1 kHz, a distance that gives a better performance for an array of control sources [24; 43]. The suitable location for the control sources is found among 341 candidate positions in the control zone (Figure 3), defined by a grid of 0.1 \(m\) steps in both \(X\)- and \(Z\)-direction. For each candidate position, the strength of the control sources is calculated so that the acoustic pressure is minimized at the observational points in the target areas, calculated using Equation (9). The position that gives the maximum attenuation is considered as the best location for the control sources.