Ron
You've heard Apogees, I know
Just why would you want dynamic woofers w ribbons as here?
The Graz Duettas I heard were so complete, of a whole, and apparently fully extended measured down to 21Hz w such solidity and texture, just why would you want to create any discontinuity w drivers?
I simply am reporting on a new speaker development.
Measured down to 21 Hz with what drop-off? I have trouble believing they are flat down to 21 Hz.
I had Martin-Logan Monoliths and Monolith IIIs for many years. I don't think I am particularly sensitive to the crossover discontinuity if it is implemented carefully.
To answer your question regardless of full-range driver design I like large cones brought in low, around 25 to 30 Hz. I would add REL No. 25s or JL Audio Gothams or 18" Velodynes or Seaton subwoofers or Wilson Thors, etc., to Apogees, Analysis Audios, Magnepans, Martin-Logans, Wilson XLFs, Rockport Altair IIs, etc.
(The surface area of the cones in the Pendragon equates to about 2 1/2 15" drivers per side.)
I agree, I don't believe even Graz’s Duetta Sig. can reach anywhere close to 21Hz, if we are talking about -3db.
The stock Duetta Sig. had a quoted spec. of 30Hz (-3db), and the Fullrange was 25Hz.
I had the Fullrange and Duetta Sig. placed at the exact same location of my room, driven by the same exact electronics. Some of the low bass information I heard from the Fullrange was not even hinted at by the Duetta Sig. I was so amazed at what a difference that last 5Hz made!