Why use a super accurate cartridge protractor

Cocoabaroque,

Are we not taking it on faith that the great masters of cartridge alignment(!)--Lofgren, Baerwald, Stephenson, etc knew what they were doing even though they disagree amongst themselves?

You don't have to take anything on faith, it is not a matter of "faith". The only reason we can all actually talk about alignments and geometry and use the words to describe them is because Loefgren, (and Wilson before him in the 20's) spent many hours (without calculators or computers) to figure out from first principles how to minimise tracking error and then tracking distortion.

Subsequently Baerwald, Bauer, Stephenson et al came up with variations based on those calculations, which have different perpectives, but in no way disagree. Rega doesn't use a "special" alignment. It is just not Loefgren A IEC. Stephenson IEC is simply a Loefgren A with inner radius around 54.8mm which places the inner null at 60.3mm, the IEC inner radius.

Dertonarm is correct in saying that conditions change as the radius decreases, but the calculations for minimising tracking error are the same as they always have been. It is the distortion caused by that error that is the issue...

Which is why he is advocating different alignments. But these alignments are still predicated on the Loefgren equations and merely reflect his preferences as to where the equations should be weighted. This can now be done by anyone and his brother, who (unlike Loefgren) has access to the excellent Vinyl Engine calculators. In the same way that Stephenson came up with his variation, we can enter minimum and maximum radii such that the shape of the distortion curve suits our purpose for the records we have.

However, as far as I know, no one has yet come up with a formula which has been designed to use different weightings (other than those for average distortion (Loefgren B), or for minimising/equalising distortion peaks (LoefgrenA))

Whatever our reasons, in coping with tracing distortions caused by using modern stereo (versus old mono) stylii, Dertonarm and the rest of us are basically still using Lofgren A, with variations in input parameters.

Although all this doesn't address the issue of how significant are errors in set up in relation to the distortions at particular radii.
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Moonglum,

After the first 60 tries (yes you read that correctly) I was still unhappy with the final cart position which often ended up with an estimated 0.2mm offset from target in any given direction(!!!). I finally got the perfect result (and was only truly happy) after 70 tries...

Interesting to hear your take - I would imagine that +/-0.2mm is pretty good and that 0.5mm is more typical. I have played around trying to estimate how accurately I could set the offset angle, as I think that is the real unknown when it comes to talking about accuracy, and reckon +/-0.25 degree is the variation.

However, no protractor manufacturer, as far as I know, actually says either how accurately their protractor is made, or how accurate, precise and repeatable are the setups typically achieved with their device. In particular, regarding offset angle. So, is a Mint more accurate than a Denessen, a DB, a Wally tractor, a Feickert? How to measure this?

Löfgren just used euclidean geometry - as does did everybody before/after him in the past 2260+ years in the western hemisphere - be it in tonearm geometry or any other geometrical topic related to mechanics and 3-dimensonal space on earth.
He was however unquestioned the first to muse and care about giving phono playback an optimized geometric solid basis.
And every analog audiophile should be grateful for his attempt.
I for one certainly am.
Viewed in the light of fact that there is a wide diversity of stereo records since 1958 with groove cut area varying by a wide margin, his preferences and weightings aren't as universal applicable as they were in 1934/38.

Dear John, When I stated in some thread that I am hardly
able to see 1mm I got an reprimand from Dertonarm. My compliments for your eye and capabilty to handle fractions of an 1 mm. But if the spindle variations are > 1mm (I forget what Yip from Mint tractor told me) then what is the sense of aiming at 0,2 mm elsewere? Ie some tractors must be more precise then other.

Regards,

Dear Nikola, spindle diameter variations are usually between 7,00 to 7,25 mm - so we are talking derivations between spindle diameters of maximum 0.25 mm.
As long as one tries to be as precise as possible in as many parameters as possible, it is at least a suitable way to get close to a precise alignment.
If the inaccuracy however builds up and adds ever more with the number of parameters "not cared that much about", one may (not need to - by dump luck) get not an alignment, but a "guess" which may be way off.

Why use a super accurate protractor?
Simply because it helps to get the best (read: best sonic performance) out of your cartridge/tonearm.
Would you use an expensive high performance Porsche or Mercedes (Audi, Jaguar - extend at wish ...) with old worn tires suitable for a 1955 beetle?
Not using an as precise as possible alignment ( = super precise protractor ) is simply giving away possible sonic quality and putting the whole performance of one's audio set-up at risk (sonic wise).
It is as easy as that.
If one doesn't really care about sound and possible wear of his/her records - fine, no problem (at least not mine).
But then the question arise why spending hundreds and thousands of dollars for analog playback at all?
CD-players are cheap to get and don't need a protractor (at least not a super precise one ...).
Cheers,
D