From that speaker design article by JA, on time/phase coherence:
"Many loudspeakers are claimed by their manufacturers' marketing departments to be time-coherent. There are also a number of speakers that have sloped front baffles, implying that they are time-coherent. However, its step response immediately gives you an indication of whether or not a loudspeaker is time-coherent (on the chosen measurement axis).
And almost all loudspeakers are not. Along with false claims of high sensitivity, false claims of time coherence are among the commonest lies in high-end audio."
We're lookin' at you, Wilson Audio.
;-)
Read more at https://www.stereophile.com/content/measuring-loudspeakers-part-two-page-3#v9HvcSQGM5O3Ciq3.99