You have your microphone located at a bass null for 65Hz. Wavelength is 5.3m, iirc you're looking at wave peaks and troughs every 1/4 wavelength (I can't remember basic physics) so every 1.3 metres.
Opening a door has changed the null locations slightly, but just moving your head or moving the speakers would result in similar shifts, and it would probably mean you get messed up bass in other locations.
If anyone has a decent set of speakers, finding bass nulls is pretty interesting- go to a site that generates pure sine waves, generate a low tone (40-80Hz) and then walk around the room. Your head will go in and out of bass nulls and peaks, it is incredibly easy to hear- sometimes the tone simply vanishes.
Edit- hard to tell what that graph means as it's missing the Y axis labels.