What happened to my room acoustics

Thank you all for the advice. It appears that the consensus here is that I am sitting too far from the speakers. I've adjusted the seating position, bringing it closer to the speaker plane (11 ft), with the speakers now placed 9 ft apart. My room has a 10 ft high ceiling. At the new MLP, I measured the spectrogram again on both channels, both together and separately. The FFT results are as follows: The high-frequency dip has shifted to a slightly lower frequency and appears to be more pronounced. The left and right channels exhibit similar profiles.  On paper, it appears that sitting closer is not resulting in improved sonic performance in my room.  Basically, I agree with @audiokinesis who commented on the in-room energy below crossover frequency (=1.8khz).  I probably need a lot of panels on the sides, which may not receive WAF certification.

As I look at your latest graph readings, and I do not know how your unit operates, my initial concern is not so much about the rise of the upper bass thru the mid range, as a unevenness of the ’curve’ which shows alternating +/- readings of up to 10 db’s (between 100hz and 200hz and 1khz and 2khz. This suggests to me, and seems to support your conclusions re needing to tame your room with acoustic materials of some sort. But, before you go there, if you do, try running your tests with your speakers axis in different positions. FWIW, one of the benefits (and to others detriments’) of minimal to no toe in is that the 1st reflection points to the sides of the speakers can give a sense of greater width, however in reality in a recording an in-phase sound can only appear between the speakers. What you hear on the outside of your speakers is out of phase sound put there in the recording process or reflections off the side walls. I think you have pretty much identified the differences in set up and realize it’s a choice that affects what you want to hear.

I’m almost out of wind now, but FWIW, you might try measuring the FR of each speaker separately with your mic about 6ft from your speaker and see how flat the speakers FR really is and determine how much its unevenness, or lack thereof is contributing to your in-room response at your listening position. Just for kicks you might try measuring the FR from your listening position with it in an equilateral triangle and your speakers on axis. Probably won’t resolve anything but it might just be interesting. It will/should give you results which reduce the effect of the room in your sound. Hope this helps a bit.

Thank you, @newbee.  I did experiment with varying toe-in angles, ranging from straight to pointing towards my shoulder, to find a trade-off between the width of the soundstage and imaging. I ultimately settled on a slight toe-in that points slightly outside my shoulder without realizing that what I perceived as an 'augmented' soundstage was, in fact, the out-of-phase reflective wave. Surprisingly, I found that I actually prefer a wider and more three-dimensional soundstage, even though it doesn't come with the benefit of deepening the soundstage that I've always wanted. Dr. Toole has asserted that these reflections, including the first lateral reflection, should not necessarily be absorbed.

I did measure the right channel at 3 ft but didn't post it. The response appears flatter, but it has more humps and dips. I'm beginning to doubt the accuracy of the measurement tool I was using...

A suggestion, I start with math for positioning my woofers (Cardas formula) which in your case will be approximately 6.25' from front wall and 3.8' from side walls.

I would then start sitting (on a chair on casters) at a perfect equilateral triangle and roll back (away) from the speakers slowly which will help you find several "semi sweet" spots which you can focus on later on when fine tuning.

Of interest is that you mapped out the "golden triangle" and then didn’t adhere to it.

Thanks @aewarren & @ervikingo. I experimented with that a while ago. If you take a look at my second sketch, you’ll notice the ’golden ratio triangle’ where 0.448W and 0.276W align exactly with your numbers. Unfortunately, I’m not fond of this arrangement. Firstly, it utilizes only 6% (17 square feet) of my entire room space (280 square feet) for the listening area within the equilateral triangle. If I place my Poang chair with an ottoman in that listening position, my feet would almost touch the speaker plane. It feels quite cramped. Secondly, I found the speakers and stands to be extremely intimidating. I didn’t enjoy the setup at all, and I couldn’t sense a spacious soundstage in such a small space. I must admit it’s a setup that I find rather impractical. I apologize for the strong language, but that’s my honest feeling about it.