I've owned all three versions of the SR17 short of the newest, the SR17.5's.
There is a significant improvement from the very first version to my ears, in
both the second and third. I believe Alan changed both drivers from one to
two, though I'm not sure. The version III's I own now use two Dyanaudio
drivers which I'm pretty sure are the same in the 17.5. The one thing I hated
in the vII was the choice of oversized terminals that made using spades a real
PITA. Sensibly Alan changed that in the vIII. Someone correct me if I'm
wrong, but I think the differences in the 17.5 are a revised
("improved") crossover, and a thicker MDF used for the cabinet
(going from 3/4" to 1" thick), thus making the cabinet slightly
larger and more heavy. Alan changed cabinet makers entirely from what I
heard. I believe the two Dyanaudio drivers remain the same, but should
sound different given the different crossover and heavier cabinet. I've
enjoyed all three versions of the SR17, and the current vIII I own is certainly
my favorite. They are outstanding monitors, and put out prodigious bass for
such a small monitor. Alan's claims of 38hz are slightly exaggerated IMO and
having measured the bass response in my rooms with two different amps and
two different measuring tools. I'd say it's capable of around 45hz before it
dips pretty far down. I noticed in the specs Alan has dropped the range down
to 32hz for the 17.5. I'd have to hear that to believe it, but I must say they do
go low, and are very detailed and musical speakers. No experience with the
Dynaudio 1.3SE to speak of.
Marco