Theory behind well tempered tonearm?

@dangcaonguyen - why not contact Well Tempered? Or a dealer within your locale that handles the table and provide further info?

Dang, You are right to wonder about the WT tonearm.  It is said to have no bearing and hence zero bearing friction.  But of course, it DOES have a bearing in the strict definition of the term; otherwise it could not pivot.  As you mentioned, the "bearing" is essentially a golf ball suspended in lots of goop.  In fairness, the well that confines the damping fluid affords only a very little tolerance for the golf ball to "wiggle", but without measuring it, I would guess that the tolerance exceeds that for any decent quality tonearm with captured bearings.  For me, the consequence of the design that irks me is my observation that the azimuth setting is not stable as the tonearm traverses the LP surface.  In addition, as you note, the headshell holes are not slotted, so the distance between the mounting holes in the cartridge body and the stylus tip had better be the standard value (which I don't recall), else the cartridge will be a bit out of line with whatever geometry WT had in mind. One reason why the tonearm can sound "good" to many people, in my opinion, is the heavy damping of tonearm motion in all directions, which may mask imperfect control of the cartridge body.  The extensive damping makes most LPs sound alike, in my experience.  All "good"; none "great" or exceptional.

All of the above observations are relevant to the WT Reference tonearm that was introduced in the 90s.  I heard it many times, mounted on a WT Reference TT, over a period of more than 10 years in the system of a close friend who owned a fine audio system.  The latest iterations of the WT tonearm, such as the one used on the Amadeus, may be free of most or all of the perceived issues. For sure, the Amadeus has many fans.

@whart 
Thanks, but it is not my turntable. I just curious about the Well Temperd tonearm geometry, but I will do some research.
@lewm 
Yes, I have been thinking the same thing. What my friend listening is not the best the cartridge can bring to the performance. Since the arm is heavy damp, it is masking both the good and bad. But I will do some more research.
Thank you all.