Geometry for pivot tonearms - calculation errors??

Wow-you need to spend more time at VA. This stuff has been widely discussed, and thanks to some kindly VA members virtually anyone willing to put in a little study can be an alignment expert. But here's a good start:

John Elison has an excel spread sheet that allows you to extrapolate null points for any pivot-to-spindle and effective tonearm length for both Lofgren A (Baerwald) and Lofgren B. The link below gives you instructions, and there is a link at the bottom of that page to the actual Excel file. (BTW, JE's on a crusade to call Baerwald 'Lofgren A', since his studies have shown that Lofgren published an identical geometry long before Baerwald)

http://www.avhub.com.au/Features.aspx?MagazineID=5&FeatureID=85

Conrad Hoffman (old nuff 2 no better) has produced an arc protractor calculator that allows you to input custom spindle-to-pivot lengths, null points, etc. to print out an arc protractor of your own design. A boon for those of us with several makes of tonearms, and it's fun exploring differing alignment configurations (it has inputs for Lofgren A (Baerwald), Lofgren B, and Stevenson) to determine which alignment you prefer. For you Mint, or other custom, protractor buyers, this will allow you to dictate to the custom builder the parameters that *you* enjoy, from actual experience.

http://www.conradhoffman.com/chsw.htm

Then, of course, there's the great Cartridge Data Base produced by 'EdAInWestOC' that has a wealth of data on specific cartridges, along with a calculator to allow you to match your cart's compliance and mass to an arm with the correct effective mass. Thanks again Ed for all your hard work.

http://www.cartridgedb.com/

Plus, the Vinyl Engine has several good articles exploring pivot tonearm geometry, and searching the archives at VA will provide a great deal of discussion and added knowledge. But the three links above make the whole deal so, so much easier.

Dear John: Good to see your links, by coincidence ( in other thread: http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1235522919&openflup&82&4#82 ) I posted your first link ( calculator ) that is very useful.

Well, this is an interesting one too:

http://www.vinylengine.com/phpBB2/viewtopic.php?t=4854

Through these links and many others almost all of us can/could make and try different " options " on the subject and decide which " distortions " likes more to each one of us or which " distortions " match our music/sound quality performance reproduction in our home audio systems. Even we can create " new " tonearm geometry equations.

Dertonarm, about your questions there are different answers depending on the approach you take, in my case I don't want to " invent " something new but to optimize what we have already in hand.
Something that I learn through the time ( experiences ) and through our self tonearm design is that each time you change the effective length ( by changing the overhang or changing the pivot to spindle distance, etc, etc ) we change the tracking distortions/tracking error.
In a pivot tonearm we can't to be at cero tracking error so IMHO what we have to look for is the best way ( best trade-offs for each one of us ) to put at minimum.

As you point out this is a very complex subject and where ( till today, at least I don't know it ) there is no perfect whole answer.
We have to take in count other very important subjects on the tonearm-cartridge set-up where any deviation on any of those set-up parameters degrade or invalidate our " perfect " efforts.

The analog medium is totally imperfect input to output and the best we can do is try to put at minimum every kind of distortions from " everywhere " source and certainly the tonearm audio item is a critical link in this analog audio chain.

Regards and enjoy the music.
Raul.

Dear Johnbrown, thanks for the input.
A good start for this thread.
And the above mentioned links are useful indeed.

However - this is all included in the G.F.Dennes Tonearm Analysis and Summary. These are all about the different options in calculating the arc and the position of the 2 zero-points (together with the maxima and minima of the derivation from the zero-track of course).

I nevertheless got the impression during several threads the past weeks that the BASIC tonearm geometry (all the mentioned links are dealing mostly NOT with the basic geometry, but with the alignment of the stylus) is indeed hardly discussed at all.

Otherwise there wouldn't be that much irritation and confusion about the basic geometry of the tonearm itself - mainly spindle - pivot mounting distance and its ealtions to effective length, offset and overhang.

Baerwald, Stevenson, Bauer, Loefgren - this is all about the aligment of the stylus and the different options of the tracking arc over the LP grooved area.

This is not dealing with the basic geometry of a given tonearm but with its geometrical interaction with the mounted cartridge.