Just saw the pics of flagship McIntosh floorstander. The measurement for JBL CBT speaker, still can't wrap my head around the super narrow vertical dispersion. Does the graph only represent far field? If you're sitting and standing somewhere within the speaker height, does these tweeters beam and change the treble response? Looks like a recipe for severe comb filtering.
Would like some help for my understanding of this. Thanks!
There is a big difference between narrow vertical directivity in a conventional multiway and that which you get from a line array.
In a line array there are drivers above and below the usual tweeter height, so the narrow window of directivity moves up and down to a certain extent meaning the tonality does not change anywhere near as much as it does in a conventional multiway. You can listen lying down seated or standing and the sound is remarkably similar.
If shading has been applied then there will be more variation with height as not all the drivers are receiving the same signal.
The horizontal positioning of the mid and tweeter line can present something of an issue as far as horizontal directivity is concerned, in much the same way as it is for all speakers using horizontally split drivers.
My personal initial position, is that comb filtering is a concern of objective evalutation and that subjectively the story may be different.
Edit - I've not yet researched for any publications studying this, so this is an opinion purely out of my own ass.
Your ass is spot on. Comb filtering in arrays does not sound anything like it looks in a measurement. It would be better to be avoided if possible but by keeping the drivers as close as possible it pushes the effect to higher frequencies as noted above. As listening distance increases the effect also diminishes. At 1m listening with a tall array you can hear the sound change as you move your head up and down. By the time you get to 2 to 3m the effect has disappeared. The treble balance is harder to set by looking at measurements and usually needs some experimentation.