@jasonbourne52 You are correct. Stacked Advents were the bomb back in college. Henry Kloss was a great guy as well.
Years later we found out that the speakers were pretty bad--there are MANY that are much worse, they they are pretty bad. You have to actually LISTEN to them with good hardware to figure it out, but like most box speakers, they are pretty bad ("bad" meaning "inaccurate reproduction" of the music).
Still, back then they were considered quite a breakthrough, and if you could afford the better walnut cabs, they even looked nice.
Regarding stacked, yes, there were many discussions back then of how tweeters should be aligned, etc., how far away, etc., etc.
As for various comments on "tall" speakers, gee, wonder where they got that idea? Was not from Jim WIney, I am sure.
Finally, regarding stacked Quads in the HQD system, we made some of the stands for quads for Levinson (VERY slow payer) and some of the 24" Hartley woofer cabs. We listened to them next to Maggies. Even back then we could easily identify listening fatigue from the Quads, which are shrill and have a number of other issues regarding delay, etc., that you can easily hear. The Decca ribbon tweeter in the middle of the stacked Quads was interesting. Running them with Levinson gear back then (when it actually worked) made the sound so bad we had to turn them off.
REALLY bad!
Side by side with the Magges...NO contest.
Cheers!