Control of noise at the entrance or exit of parking garages

The low-frequency broadband noise generated by vehicles may be disturbing for the neighboring residents when vehicles enter or leave underground (or semi-underground) parking garages. A special structural ramp was designed to reduce noise emissions at the entrance or exit of garages. Two-layer steel grilles with rectangular slots evenly distributed, on which the tires of vehicles run, were installed on the original cement ramp. Damping perforated plates sandwiched between the upper and under grille layers fixed on the original cement ramp, formed a resonance sound absorption structure together with the cavity in the layer under the grille. In addition, aluminum foams were embedded in the upper grille layer, and waterproof porous sound absorption materials filled the cavity of the under layer. Field tests using light cars with less than 8 seats were performed to evaluate the effect of the special structural ramp on noise reduction compared to the original concrete ramp. Results show that, when all seats were taken, noise reduction in the A-weighted level of 8 dB on the uphill ramp and 6 dB at the downhill ramp were achieved at the distance of 0.5 m away from the tires outside the vehicle, and a 13 dB and a 8 dB reduction at ears of the passenger respectively. Meanwhile, only a reduction of 2 dB or less could be achieved with further treatment of sound absorption on the middle of the pavement.