# Suitability of Active Noise Barriers for Construction Sites
## 1 Introduction  
Construction noise is a topic of recognized importance in terms of its impact on workers due to the high noise level generated [1, 2]. The issue has gained added significance given the ever-increasing environmental sensitivity of the general public and the corporate sector alike in recent years as construction noise can cause annoyance [3, 4, 5] and have adverse behavioral effects [6] on the neighborhood. Among others, the ubiquity of noise sources, the variability of the noise itself, the existence of the flows of materials, people and vehicles, the size of the whole plant, the limited efficiency of most solutions in the low frequency range, and even the difficulty of assessing the effect of mitigating measures [7] all contribute to on-site noise control. Noise control in this complex scenario generally calls for joint action on the transmitter, using low acoustic emission equipment [8] or managing the schedule and simultaneity of the performances [9], and on the transmission channel [10]. Alternatively, if all else fails, an action can be taken on the receiver [11]. A measure that is gradually being taken is the use of mobile noise barriers that adapt to the construction process [12, 13, 14, 15], despite their limited efficiency in the low-frequency range, which predominates in construction noise. The recent study [16] defined the difficulties of the application of active noise barriers inopen space. It is known, however, that active noise control is especially efficient in the low-frequency range, and that is why recent research has focused on applying this strategy to construction noise control, with promising results [9; 17]. A natural outgrowth of these recent studies consists of the investigation of the applicability of active noise barriers (ANBs) in construction, which combines portability with maximum efficiency. Many prior studies also are conducted to predict the behavior of the active noise barrier. [PERSON] et al. [18] investigated the noise reduction mechanisms of active noise barriers. This study shows that at low frequencies, transferred acoustics energy in space is the dominant mechanism when the noise source and control source are well separated. However, the noise reduction mechanism changes to sound absorption and/or radiated energy suppression by the control sources when they are close to the noise source. At high frequencies, the mechanism for noise reduction can be the sound absorption by the control sources. Other studies [19; 20; 21; 22; 23] investigated different approaches to control surrounding noise by the active noise barriers. [PERSON] and [PERSON] [24] evaluated the efficiency of an active noise barrier when error microphones are located on the edge to suppress the diffracted pressure. Their results revealed that reasonable attenuation is achieved when the distance between error microphones on the edge is shorter than half the wavelength of the noise generated by the primary source and when control sources are located to the primary source as close as possible. [PERSON] et al. [25] carried out an investigation on finding the best position for error microphones near the edge of a noise barrier when 16 control sources were fixed on the top edge. The noise reduction was computed at 6 observational points placed at the shadow zone of the barrier. They conducted theoretical and experimental measurements for three different error microphone placements and their results showed that there is an optimum value between the distance of control sources and error microphones. Their observations showed that when the control sources are located on the top edge of the barrier the best position for the error microphones were placed above the secondary sources. [PERSON] et al. [26] proposed a new arrangement for control sources and error microphones presented in a previously studied case [25]. Their arrangement included two rows with eight units of control sources and corresponded error microphones on the top edge of the barrier.