Is this the Altec Duplex in reference here?

http://www.voiceofthetheatre.com/images/604E.SuperD.1.jpg

I'm thinkin' Altec made quite a few coaxial speakers.....

http://alteclansingunofficial.nlenet.net/proloudspeakers/duplex/index.html

"Either way they are all coaxial, because their acoustic centers are on the same axis... You'll here words like "duplex" and "compound" and "coincident", these are really all the same thing, they are just different ways manufacturers descride thier way of tackling a coax."

Makes sense to me.
Don't forget "Dual Concentric".

Those are almost identical to the Eminence layout, and they are a straight forward coax.

I never owned them, I built them for a guy at work.  They sounded surprisingly good, really.  Considering I used almost a stock crossover and a fairly cheap tweeter driver ($20 each, IIRC).  Dan Wiggins designed a crossover for the Beta 10 and 12 that sounded real good, the HE10 and HE12 Adire kits.  I never thought they sounded as good as some of the better speakers I have used/built, BUT, for the price and the efficiency you get out of them, they are pretty tough to beat with low powered amplifiers....  And I don't really think you could come up with a better crossover than what Dan designed, if you want to play with a big coax, I would copy the best I could the Adire design.  Black00 has a pair of the HE10s, I built the cabinets for him.  Talnlanky has a pair of the HE12s also.  I really like the soundstage they threw, honestly....  But you really have to be in the sweet spot with them.....  Oh yeah, they get loud as hell also....