Tonearm Geometry and Setup

Dear Nandric, "we" (... we, the people ...) do indeed have a choice which of several options we do choose.
It does depend on personal preferences, stereo or mono, vintage of the majority of the records one owns/plays ( how close cut to inner label ), effective length of tonearm and expectation in sound reproduction/ability of a given audio set-up to recreate soundstage dimensions and acoustical positioning.
Most will fare well with Baerwald/Loefgren A IEC, owners of mostly modern pressings with large wax will do great with Loefgren B IEC, collectors of early vintage stereo records of the 1950ies to mid 1960ies will prefer Baerwald DIN or UNI DIN.
There is no absolute - and there is NO mathematical "best".
It is - as long as this was about mono reproduction only ( and mono only it was when Baerwald / Loefgren A was postulated ) and when one assumes that the music engraved is VERY homogenous without huge climax' towards the end of a piece/movement.
But since music is anything but homogenous in volume or structure nor are all records cut following IEC, we have do address our needs individually.
Cheers,
D.

Nandric, you said:

why are we not free to choose the zero points on the record radius independant of the tonearm used?

You are, of course, as Dertonarm says, free to choose whatever null points you wish. The origin of the null points for the geometries used are based on the inner and outer radii of a record which give a constant, the linear offset, which in turn gives an offset angle and effective length. To be strictly correct, any calculation is only accurate for one record, and is, to a greater or lesser extent, a compromise for all others.

So, a designer of tonearms has to decide first and foremost what are these inner and outer radii. Are they IEC or DIN, or the median of his own collection, or of a surmised potential buyer? In the past, 7" singles had to be considered so the range of possible radii was extended if they had to be accommodated as well as LPs.

In my case, the Odyssey arm used nulls similar to Lofgren A/Baerwald DIN. That was a design choice, as was the nominal effective length of around 230mm. If I was designing an arm today, I would make it have an adjustable offset angle in addition to an adjustable base, thereby allowing the user to choose the alignment. Also, the effective length used to be governed by the space available on turntables. This is less so now, so longer arms are more common, and they have advantages in reducing tracking error and skating forces.

(Though, as an aside, an 8" arm plays a 7" single with less distortion than a 12" arm playing an LP)

All these features in an arm are merely for facilitating setup, they do not define the arm except in the single case of the hypothetical standard LP, whatever it may have been.

Some corollaries of this are:
1. Some LPs may be more useful than others at showing the effects of particular alignments.
2. When evaluating an alignment choose a track at a distortion maximum not a null.
3. When comparing alignments you shouldn't use the same LP, as it will probably suit one alignment better than another unless you wish to use that LP as your standard.
4. You will have LPs with loud passages at the beginning of a side which may sound worse with certain alignments which favour end of side.
5. The cartridge offset angle need not be the same as the tonearm headshell offset, nor the mounting distance be the same as the specified tonearm alignment should another be used.

In all this it is illustrative to play with the fantastic calculators on Vinyl Engine which allow a reverse engineering of the geometry to try non-Lofgren alignments and look at how small are the variations in distortion with small changes in nulls. And how quickly the distortion rises on the inner grooves with LofgrenB. All a lot easier than calculating in the old way...

John
.

I got it. I have to do alignment/arm adjustment each time and somewhat differently before I play a record because they are all in one or more ways different. That's, of course, if I want the best results. And the better I can hear things the worse it is for me. Now that's a big fun and true joy.
Welcome to the audiophile madness club, everyone!

Dear John, If the designer is free to choose between Lofgren and non-Lofgren geometry than he obviously will do this according to his own preference or assumptions regarding the (potential) customer.But this way he already preselected the 'optimal adjustment' for the customer?
Kessler&Pisha stated in the context of 'Overhang' that many
Japanese designers 'overlooked' the dependance from or correlation with the eff. lenght. So, for exapmle, Dyna 505 has 15mm overhang while 17.164 should be optimal. Ie
the eff. lenght corresponding with 15mm overhang is 274mm
(10.787 in.). This lenght will not fit the turntables disigned for 9" tonearm ( Tonearm geometry and setup; Audio, January 1980). My 'intuition' is : you can't have
it both ways; the choice for the designer as well as the choice for the user. Ie the choice of the designer limits the choice of the user. As far as I know our choice for
Bearwald means the least distortion for the whole record
radius (aka 'avarage') while Stevenson means the least distortion near the lead out 'part'.
This means to me 'one way or the other' and this precludes
our 'free choice' or at least limits our choice. Otherwise
I am not able to make any sense of 'different tonearm geometry'.

Regards,


.

For those who think to be good in math but also think to
have good nerve there is an article from Stereophile by
Keith Howard on the net: ARC ANGELS; Optimizing Tonearm Geometry. Look for : tonearm geometry.
I myself should keep my promisse to myself made after
my high school : 'never ever mess with math '.

Regards,