Adding a bit to what
@TLS Guy said about the MLP and a null – you haven’t mentioned much about your room, but generally speaking, perceived bass levels are strongest near a wall, and decrease as you move towards the center of the room. The dead center of the room ends up being a bass “dead zone” – i. e. the null you refer to.
In my experience, the effect is more pronounced the smaller the room is, as typically after you allow for a normal seating distance from the TV, you end up being in or near the center of the room, and thus in the middle of that null.
Since you’re in an apartment, I expect the room in question is on the small side.
Thus, a solution would be to put your seating against the back wall. This is typically thought to be a lousy location, as for as a good surround sound experience is concerned. But it’s a good one in your situation, as it would allow you to reduce the subwoofer level for your neighbor’s benefit, yet still adequately hear it, for your own benefit.
Regards,
Wayne A. Pflughaupt