## 3 Remarks and Current Challenges
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Device** & **Indicative References** & **Noise Reduction** & **Comments and Remarks** \\ \hline \hline \multirow{7}{*}{Fine, Intels, screens and similar protrusions} & [PERSON] et al. [24] & 3 dB max. & Not suitable for use in high-rise buildings unless significant sound absorption and/or effectiveness cuts for installed at appropriate locations, information loss to be higher than 4 dB & performance can be affected by sound incidence angle and relative orientations of the windows to noise sources. \\ \cline{2-3}  & [PERSON] et al. [29] & Prade sound insulation index (window closed): 20 to \(\sim\)40 dB from 100 to 53 Hz / 13 octave bands & City reverberation will reduce noise reduction capacities. \\ \hline \multirow{7}{*}{Resonant devices} & [PERSON] [32] & \(R_{p}=2\) dB & \\ \cline{2-3}  & [PERSON] et al. [54] & Noise level difference between two sides of the associated window- & Study device. \\ \cline{2-3}  & [PERSON] et al. [55] & 2- dB dB & \\ \cline{2-3}  & [PERSON] and [PERSON] [57] & \(\sim\)5 dB traffic noise insertion loss on average for a closed form balocry & \\ \hline \multirow{7}{*}{Balocories} & [PERSON] and [PERSON] [9] & Traffic noise reduction – 5 dB– 14 dB for recessed building & Massive structures, but relatively weak noise reduction. \\ \cline{2-3}  & [PERSON] and [PERSON] [41] & Courtyard with transducer: 8-28 dGCurrently with splitter: 10-27 dB & Not suitable for use in high-rise buildings unless significant sound absorption and/or effectiveness on be installed at appropriate locations. \\ \cline{2-3}  & [PERSON] [65] & Closed form balocry: 0.4–5 dB & Prior flight limits the use of reflectors in many cases. \\ \cline{2-3}  & [PERSON] et al. [6] & Insertion loss: 5-10 dB (2D simulation) & Performance is affected by sound incidence angle and relative orientation of the windows to noise sources. \\ \cline{2-3}  & [PERSON] and [PERSON] [67] & Insertion loss: 4-7 dB & City reverberation will reduce noise reduction capacities. \\ \cline{2-3}  & [PERSON] et al. [48] & Insertion loss: 7- dB max. & Use of sound absorption will lower down speech intelligibility \\ \cline{2-3}  & [PERSON] and [PERSON] [49,50] & Insertion loss: 0.5–6 dB & Courtyard/ recessed building design could result in poor natural ventilation. Less number of residential units can be built. \\ \cline{2-3}  & [PERSON] et al. [52] & Insertion loss: 4-5-dB & \\ \cline{2-3}  & [PERSON] and [PERSON] [53] & 7-10 dB higher noise reduction than conventional balocories & \\ \hline \multirow{7}{*}{Active noise control} & [PERSON] and [PERSON] [57] & 10 dB max. & Active control installation usually results in bulky systems, \\ \cline{2-3}  & [PERSON] et al. [58] & 400 Hz to 1 kHz & Tends to block air ventilation passage in some cases. \\ \cline{2-3}  & [PERSON] et al. [58] & 10 dB max. & Isefficiences affected by parameters which cannot be controlled. \\ \cline{2-3}  & [PERSON] and [PERSON] [60] & Average sound level differences across window: \(\sim\)29–33 dB & Not reliable for building scale application. \\ \cline{2-3}  & [PERSON] and [PERSON] [61] & Traffic noise insertion loss: 5-15 dB & \\ \cline{2-3}  & [PERSON] and [PERSON] [62] & \(R_{p}\sim\)C\({}_{V}\): 16-24 dB & \multicolumn{1}{c}{Can be used together with the above devices or other measures for enhanced noise screening performance} \\ \cline{2-3}  & [PERSON] et al. [63] & \(R_{p}\sim\)18–26 dB & Performance can be affected by sound incidence angle and relative orientation of the windows to noise sources. \\ \cline{2-3}  & [PERSON] et al. [46] & Traffic noise insertion loss: 7-9 dB & Performance is not much affected by city reverberation. \\ \cline{2-3}  & [PERSON] [64] & Traffic noise level differences across window: 19–23 dB & \multicolumn{1}{c}{\multirow{2}{*}{
\begin{tabular}{} \end{tabular} } } \\ \cline{2-3}  & [PERSON] [[66]] & Preams with fin: STC 30–40 & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Acoustical Performances of Natural Ventilation-enabling Noise Control Devices.