Interesting thread, indeed.
In
my multichannel multi-driver multi-amplifier active stereo system, I could establish 0.1 msec precision time alignment over all the SP drivers including tweeters and super-tweeters; my very
unique (eccentric?) physical alignment (positioning) of super-tweeters described
here would be of your interest and reference, I assume.
Edit:
Our ears are located left and right of our head, and hence we are rather sensitive for left-right sound image/allocation. On the other hand, our ears and brain would be relatively gullible with up-and-down sound staging, I assume. I think that
my unique physical alignment (positioning) of super-tweeters at under the main SPs, together with the upper tweeters, would give pseud-coaxial sound staging if complete time alignment has been achieved like in my setup, where tweeter and super-tweeter sing together higher than about 8 kHz.
In any way, I would like to suggest those who using super-tweeters to
at least try/test the positioning so that super-tweeter and tweeter would sandwich the woofer and squawker from up and down.