Vuong
Yes my AF holds its tune quite well, and I'm sure the single stringing helps. It has a number of unique design characteristics. E.g., wippen-assist springs up to the upper treble (where the dampers stop). AF uses them instead of putting a lot of lead weights in the keys, which supposedly reduces key inertia. The sound board is "floating," i.e., the part of the sound board at the tail is not fitted into the frame, supposedly increasing resonance. The bridge pins are slightly on the shoulder of the bridge. Not sure what this does (downbearing?)
The sound board itself is bigger across than most grands, giving it more board to resonate.
The rim is not laminated wood bent into an S-shape by forms; rather it is a "soft" rim produced by stacking pieces of wood vertically next to each other. (Bösendorfer does something similar, I believe.)
The bass bridge is set well back from the edge of the piano, which supposedly also helps increase resonance.
Anyhow, it is a great and extraordinarily responsive instrument. Some complain that AFs are too bright. They can be, but I've found that with some judicious voicing, my AF can deliver anything from ppp to fff, and the "brightness" seems to have much more to do with my technique (or lack thereof). I'd say it is capable of much clarity, and it makes voicing a line of music easier than on many instruments. Finally, the scaling is superb...there is no discernable break between the bass and lower treble, and the tone is smooth to the last octave.
Sorry for going on...but I love my piano!