Thanks for the suggestions.
I didn't move the speakers forward because I don't want to throw the distance calculations off from where they'll actually reside.
On NAD's suggestion, I plugged the test mic into the BluOS hub instead of into the computer.
NAD also revealed the existence of a calibration file for the included NAD mic... which isn't mentioned in the manual. I thought it was pretty questionable to have a calibration mic with no calibration file in the first place. Even now there's only one calibration file for all these NAD mics. In scrolling through a Web page to acquire it, I also happened to notice a target-curve file, which is also not mentioned in documentation. It seems to me that NAD's biggest weakness is poor UI design and documentation. Why am I only finding out about this stuff weeks later?
I also moved the table away and closed the blinds over my sliding door. I also made sure I was distinguishing the center point of the listening area from the center of the couch, which is not equal. I was probably pretty close before, but this time I put the mic against my ear on its stand and then slid away.
The results are a lot better. The temporal issue seems to be gone, so the imaging is not ruined. The target curve saves a lot of time in establishing a pleasant tonal balance. I wish there were an easy way to match levels between Dirac on & off, to make comparison easier.
One bug I found in the Dirac software (aside from not-infrequent crashes) is that it fails to reset the receiver's volume if you return to the measurement page to take more samples after doing some listening tests. This is dangerous to your speakers and very unpleasant for you and your neighbors.
The end result of Dirac in my case is primarily reduced shrillness in my listening area. I don't hear much if any difference between filters generated from a single measurement location and those with five sample locations (that's all I have the patience for); I wonder how Dirac uses the additional data in creating the final filter.
Anyway, thanks for the participation everybody.
Last edited by Stokestack; 11-18-2019 at 06:22 PM.