Found the bass dip. Ran per channel log chirps (full band sweep) and found the left channel is the culprit. Its close proximity to a sofa about 1.5ft outside of it is causing the issue I think. It is only noticable with a measurement though.
My room RT60 time is between 0.5 and 0.3 seconds depending on octave. Generally, the low frequencies had a shorter decay time.
The measurement delay time from L/R channel was 12.01ms and 12.04ms respectively at peak impulse. Pretty darn close. This is directly related to distance from the mlp.
I have come to the conclusion that even "high end" reviews often dont take the care to do all demonsrated in this thread. My takeaway from this entire process is as follows:
Speaker position is incredibly dynamic. As Matt pointed out, all variables are interwoven.
System symmetry is imperative for the full performance of imaging and transparency.
Spaciousness and bass response are somehow interrelated. Distance from room boundaries are directly involved.
Acoustical measuring tools speed the process up, but reveal issues that arent neccessarily real issues.
My recommendations are: (nothing new here)
Experiment with width first from room center line (equadistant from side walls.) No toe in.
Experiment with distance from rear wall behind speakers after width is tentatively set. No toe in.
Once width and back wall distance are set try toeing speakers in. Go slowly and be as exact as possible. A difference of 1/4" at the speaker is several inches where you sit.
Match distances between speakers and boundaries as closely as possible. Make sure your mlp is exactly centered in room. This ensures refections arriving are at least in time with one another. Incredible difference in drum synergy.
Doing these things will result in a larger sweet spot. Better resolution of fine detail. Improved spaciousness. Better bass response. Improved transparency and imaging. Better envelopment.
If you just plonked your speakers down, it will likely sound like a several thousand $ upgrade to you. But likely for most of us, steps like this are the leap from good to great. Or from great to hoping for poor weather.
