Agree with Ojgalli - your only viable option is to get a subwoofer and position it a little way forward into the room and then EQ it with notch filters so it does not add to the speakers peaks.
You need an enormous amount of acoustic treatments or a specific designed helmholtz resonator to have any effect at 40 Hz.
You need an enormous amount of acoustic treatments or a specific designed helmholtz resonator to have any effect at 40 Hz.