Active control of sound transmission through a floor-level slit

The floor-level slit between the door and the floor is one weak point in building noise insulation. In this paper, an active noise control system is proposed to reduce the sound transmission through a floor-level slit with evenly distributed secondary sources on its top boundary. The system performance is first investigated based on the analytical and numerical models, and simulation results indicate a decrease in active control performance with increasing frequency. The upper limit frequency of 10 dB effective control increases with a higher number of secondary sources, and the corresponding wavelength of the upper limit frequency is approximately the interval between the secondary sources when a plane wave is incident normally. Although the upper limit frequency decreases with the slit height, it approaches a constant when the slit height becomes significantly smaller than the wavelength in the incident sound. The experimental results based on a typical floor-level door slit support the findings in the numerical simulations. For a slit with a width of 0.9 m and a height of 0.005 m, the upper limit frequency of 10 dB noise reduction can reach up to 2830 Hz when ten secondary sources are employed in the experiments.