For those wondering about Dertonarm's numbers...
Using the FR-64S as a base, and the original 245mm EL, the average/peak % tracking distortion between 57.5mm and 116mm (the inner 2/3 of the record assuming a 57.5mm innermost groove (DIN standard)) using an IEC inner groove standard (i.e., setting up a tonearm for modern usage, but playing a record with a slightly closer inner groove) sampled at 1mm intervals is as follows:
CURVE Average Peak
Mfr 0.54% 0.85% (same in IEC range)
Stevenson 0.45% 0.72% (same in IEC range)
Baerwald 0.47% 0.86% (0.67% in IEC range)
Lofgren B 0.36% 1.45% (1.02% in IEC range)
If I read through Dertonarm's proposal above, using a 246mm EL and 14.5mm OH, I can come up with a number of different solutions depending on where one sets the inner groove null point (i.e. how one sets offset angle). Based on his "distortion 5% lower than average Baerwald and 20% lower max distortion than Lofgren B", it is easy to get the "5% better than Baerwald" for the whole record, but getting both that and the 20% max distortion depends on the scope of your measurement (does one measure 57.5-146 or 60-146 to find the max - it matters as the Lofgren B tracking distortion can rise a full 0.5% in those last 3mm). I will assume a DIN record but IEC setup, and offer three 'Dert' measurements, depending on where one sets the inner nullpoint.
CURVE Average Peak
Dert66 0.36% 0.98%
Dert63 0.37% 0.89%
Peaks are on the outermost groove whereas for Baerwald/LofB they are on the innermost groove (so Dert's max distortion numbers don't change much if records are longer or shorter, whereas Baerwald, and to a much greater extent Lofgren B, are much more sensitive to how small the runout is).
Offset angle for Dert66 is 20.325 degrees. Offset for Dert63 is 20.574 degrees.
On the inner 2/3 of the record, the average tracking distortion is indeed about 40% below that of Baerwald and 20% less than Lofgren B. Average unweighted distortion is where Dertonarm says it is (right between Baerwald and Lofgren B). However, I cannot get a "45% lower tracking distortion than Lofgren B in the last 8-12mm of a record. I see that the distortion compared to Lofgren B is even lower unless one counts the 60-72mm section. If one does the 57-65mm section, the distortion is 70% lower than Lofgren B.
Note that on the innermost 3mm, Lofgren B is EXTREMELY sensitive as to whether one uses IEC or DIN setup with a record which has a DIN inner groove. The inner null point moves 3mm (to be same as Dert63) from IEC to DIN, in which case the last 12mm is about 50% better than Lofgren B, which is probably close enough to Dertonarm's figures for this exercise.
Disclaimers:
1) I have not discussed this alignment, calculation thereof, or anything related to this post with anyone.
2) I simply did this to put a stop to the months of questioning. The exercise took me all of 10mins to do (given a pre-existing spreadsheet), far less time than has been spent on questioning whether the numbers come out this way.
3) I have never used this setup, but given the above results, I will certainly try.
Note: this kind of alignment should work for any tonearm to a certain extent (assuming flexibility of headshell mounting), because it is really a matter of tailoring the tracking distortion curve to the records and listening preferences one has. If one has a lot of records with a small radius inner groove and significant dynamics or significantly quiet passages in the last 10mm, this kind of 'astuce' (trick) is one which should work on many/most 'universal' tonearms (universal in this case meaning flexible mounting so as to allow significant cart movement forwards, backwards, and by angle).
