Preliminary study on active control of double-glazing with pressure compensation using an in-cavity microphone

Enhancing the sound insulation in double-glazed units involves actively controlling inter-glazing cavity pressure to decouple each glass. The optimal strategy to maximize transmission loss requires loudspeakers in the cavity to generate anti-noise and error microphones in the reception room, outside of the cavity. However, this configuration is not suitable for a standalone product where out-of-cavity microphones are not allowed. This study presents an original method to experimentally learn the control of one loudspeaker with one error microphone, both inside the cavity, in order to maximize acoustic isolation in a low-frequency band. The method requires a compensation FIR filter, experimentally identified during a learning phase when an optimal command is applied. Experiments were conducted using an active symmetrical double-glazed unit (30.4 x 30.6 cm, 6 mm thick, 60 mm apart cavities) in a "waveguide" setup. Results show an average transmission loss gain from 50 to 550 Hz of 10 dB with in-cavity microphone compensation. It nearly reaches optimal performance, 11 dB reduction in transmitted waves, compared to 7 dB for the uncompensated in-cavity microphone. This encouraging preliminary result leads to further developments to extend the method to multiple loudspeakers and multiple microphones.