I recalibrated my room after upgrading my computer hardware and putting my monitors on some new iso acoustic stands.
 
My room now seems to have an almost infinite capacity to absorb at ~75 Hz!?
 

 
I was using v2.0 of the ARC 2 s/w though; I was having difficulties with the later version(s), but that was likely to be due to too small an ASIO buffer size being set; the measurement software went completely unresponsive at the stage after you select the microphone, i.e. when you select the audio driver.  Now I think that I know what the problem with the software was, I might try upgrading it and re-doing the calibration to see if that changes anything or not.

Oh, and I do use ARC2.
T