[JohnM]

Ron, the mistake the author is making is not thinking about the frequencies involved - it may be that the original discussion was about full range responses? At low frequencies the wavelengths compared to the room dimensions are large enough that behaviour is minimum phase (a 50Hz tone has a wavelength of about 22 feet, primary reflections from the walls, floor and ceilings of the room arrive at the listening position with a phase shift of much less than a cycle). At modal frequencies in particular the low frequency behaviour is dominated by the room's modal response. The modal response of the room acts like a 2nd order biquad, the room is giving the same effect you would achieve if you fed the sub signal through a 2nd order eq filter whose gain matched the mode's gain at your listening position and whose bandwidth matches the mode's Q. By applying an EQ filter with the same Q and the opposite gain you counter the effect of the mode at the listening position. Outside the low frequency range the behaviour is no longer minimum phase and this doesn't work, which is what the author's post details, but that is not a range in which we are suggesting EQ should be applied.