Geometry for pivot tonearms - calculation errors??


During several threads in Audiogon's Analog forum the question of pivot tonearm geometry was discussed widely and wildly the past weeks. There seems to be a great confusion about the interelation - and interaction - between overhang, offset, effective length, mounting distance and the position of the 2 zero-error points on the arc over the LP's grooved area.
However - the correct tonearm geometry is paramount for the performance of any analog sourced High-end system.

Do we need a new calculation of these parameters?
Is mounting distance a variable factor in a given pivot tonearms geometry?
Can overhang serve as the fixed parameter for a pivot tonearm?
Is effective length a variable or a fixed parameter in pivot tonearm geometry?
Is there anything like an optimum geometry for a given cartridge/pivot tonearm set-up?

I invite all interested in this complex and very important topic to contribute their thoughts. If possible please do include the geometrical derivation for any given theory and opinion.
This might be difficult in some examples, but please try.
By doing so, - this will keep this thread on terms and will make it more valueable for all.
dertonarm

Showing 4 responses by rauliruegas

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 Dertonarm: Could you share your " finds " /thoughts n that 1st geometry for we can understand and try to help about?, because both have an intimate relationship.

Regards and enjoy the music.
Raul.
Dear Axel: My experience on cartridges are that: experiences on cartridges, MC or MM. I don't now why I give the impresion that I'm or have a MM bias, I'm not.
I have several MC experiences with vintage and today cartridges ( I own and owned ) and like the MM ones the MC has its own advantages and dis-advantages, same with the MM.

+++++ " With the "right" cartridge, it is a VERY serious tonearm... " +++++

absolutely yes.

Btw, the non-perfect world on the cartridge building is more " delicate " because this audio item is not a " mass production " one but almost made each one by hand where we even find " differences " between cartridges on the same model. So what the " poor " V owners have to do is " wait " to be lucky with the cartridge we have. Of course that are some " things " that we can do but always this " things " are add-ons that ( one way or the other ) could compromise the performance.

Dertonarm, I have too some interesting subjects on the LP " standards ", we keep in touch very soon.

Regards and enjoy the music.
Raul.
Dear Axel: I mounted my 97Xe ( a small brother of the V15 ) in the IV and works fine so I don't see any trouble with your combination.

I don't like to speak about devices that already own a person but I can't stay " quiet " . This next thoughts/experiences are in the animus to help about:

I owned the V15MR that I try in different tonearms/headshells and with different load impedance values and in my system I never achieve " stellar " or near it quality performance even the 97Xe like me more and that's why I still have it.

If you or any other person wants to " introduce " in the MM high-end " stage " the V15 IMHO is not the right answer if we want to compare against a top LOMC like the one you own.
.
My advise is to go for one of the next cartridges ( either ): Nagaoka MP-50 or better yet the MP-50 Super, Ortofon M20FL Super, Audio technica ATML180 OCC and/or Signet TK 10MLII.

Anyone of you could be " shocked " with the quality performance on these MM cartridges. Can/could beat a top LOMC ones?, I know the answer but the best judge are you.

Those cartridges are only the tip of the MM iceberg.

Normaly these MM cartridges perform better with a load impedance over 70K and total capacitance below 200pf and are so " inexpensive " that we can own dozens.

No, I'm not saying or implying in anyway that instead of our beloved LOMC ones: no, the MM is another very good " flavored " source.

Regards and enjoy the music.
Raul.