Low-frequency noise reduction through open ventilation windows using resonator arrays

Natural room ventilation provides fresh air circulation and thermal comfort but comes at the cost of unwanted noise in urban areas; the primary source is traffic, with noise levels being nearly 85 dB during the daytime. The dominant frequency range is usually from 200–800 Hz. The primary objective of this research is to develop a resonator array that can be retrofitted on a window to reduce sound levels transmitted through the window while keeping the open ventilation area to 85%–90% of the original. The initial target is to have three to four different resonator frequencies in the 400–600 Hz range. Suitable resonators are designed and numerically analyzed using MATLAB and COMSOL. The resonators are then fabricated for testing in an impedance tube to verify the results. Once the verification is completed, a resonator array tuned to the chosen multiple frequencies is made; different orientations (grazing and normal incidence) of the resonator array are tested in a small twin-room reverberation chamber using a 465 × 465 mm opening. The tests show an 8–12 dB drop in the intended frequency range when larger volume resonators are used.