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In Reply to: RE: it is a Stevenson if... posted by flood2 on February 15, 2017 at 14:45:49
I guess I ignored your table when I wrote my response. I'm sorry!
> Stevenson is a generalized method not an alignment that enables a design such that the weighted tracking error at the min and maximum radii
> (and intermediate radius corresponding to the maximum angular error between null points) of a record is the same.Your description of Stevenson is actually the description of Lofgren A. In fact, all the numbers in your table are Lofgren A numbers---not Stevenson numbers. Here is a graph of the numbers in Line 1A:
.> Let's not split hairs with hundredths of a mm on the defined radii. SME have rounded the numbers.
I'm not splitting hairs. Rounding numbers is perfectly acceptable. What is unacceptable is when the number are different. Although the number in Line 1A of Stevenson's table are very close to the alignment parameters for the SME 309, they are different. The followwing parameters are published on the SME website for the SME 309:
Effective Length = 232.32-mm
Pivot-to-Spindle = 215.35-mm
Offset Angle = 23.204-degreesThese numbers define the geometry of the SME 309. The null-points are:
Inner null-point = 63.575 ..... Rounded to 63.6-mm
Outer null-point = 119.496 ..... Rounded to 119.5-mm
Linear Offset = 91.535-mm ..... Rounded to 91.54-mmThese are different from the numbers in Line 1A of Stevenson's table. They are not rounding errors; they are different numbers.
> You should be looking at the calculated linear offset.
> The Linear Offset of the SME309 corresponds "extremely closely" to Stevenson Design 1AThey might be close but they are different.
Linear Offset of SME 309 = 91.535-mm.
Linear Offset of Line 1A = (63.50 + 118.97)/2 = 91.235.The geometry of the SME 309 is based on Lofgren A with a modulated groove envelope in-between groove radii of 58.00-mm and 146.00-mm.
.
The definition most commonly accepted for Stevenson's alignment includes the inner null-point being coincident with the innermost modulated groove. Perhaps Stevenson used Lofgren A for other alignments, but I'm pretty sure that Stevenson's main alignment had the inner null-point coincident with the innermost modulated groove.Best regards,
John Elison
Edits: 02/15/17Follow Ups:
Perhaps this 1966 paper from the man himself might shed some light on what is and isn't Stevenson: http://www.helices.org/auDio/turnTable/stevenson.pdf
Thanks, Garven!
After reading as much of that as I could, I'm inclined to agree with Anthony ( flood2 ) in that Stevenson developed a methodology nearly identical to Lofgren and Baerwald in order to minimize distortion within his chosen innermost and outermost groove radii for developing a set of null-points he believes will provide the best performance for modern LPs. Stevenson developed the table that Anthony reproduced in one of his posts. It contains his recommended alignments. Apparently, the alignment Stevenson believes to be optimal has its maximum distortion at an inner groove radius of 2.158" (54.132-mm) and an outer groove radius of 5.719" (145.2626-mm). He apparently applied equations equivalent to Lofgren's equations to minimize tracking error distortion within these limits thereby coming up with alignment null-points of 2.375" (60.325-mm) and 4.606" (116.9924-mm). Anyway, that's basically what I deduced from the article you referenced. Is that your understanding, too?
Thanks,
John Elison
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