Harbeth M40.1 measurement done by an REG forum member using a TacT 2.2XP.
M40.1s on 14" stands; tweeters 40" above floor; mike at 40" above floor
I would guess the huge lift below 100hz is due to the floor coupling from the low, 14" stands for the Harbeth's. My older 3-way AR 58's with a 12" woofer (acoustic suspended) seem to sound best on my heavy pedestals that are 24 1/2" off the floor. It may not be the optimum tweeter height, but the speakers are anything but reticent at this height. My old large Advents are too close to the floor at 14" and I need to get them higher as well to sound best in the bass. A project in waiting.
The Harbeth's trough at just above 100hz is troubling. At least to me. I will admit that my older Triangle Cometes probably measure better than the newer version that AD recently reviews and JA measured. That new version is certainly tipped up at both ends and would seem to sound bright to me, even with me being hearing impaired.