[Anthony]

Followup info:
30 Hz corresponds with the 1/2 wavelength of the long axis of the room (18.8 ft)

105 Hz corrensponds with the full wavelength of the width of the listening area of the L, or 10.75' So that may just be a microphone null in the listening position. I'll verify that tomorrow with another location.

I have no idea what the 260 Hz (4.3') is about, although that is about the height of the magnepans

Also the peak at 130 Hz corresponds to 8.6', which isn't anything special in this room, except that it's double the frequency of the 260Hz dip. Might be related to the magnepan size.