[Seb]

too easy!!

best regards

Seb

[guest1632]

too easy!!

best regards

Seb

hi, lol, well, yes and no. On the Pmount cartridges and arm, then you need to see if they have the correct arcing of how the arm is going to swing. Then even if you know all that, you can't correct it. So Frank just might be right. So just get a pmount cartridge and arm and be done with it. Otherwise by not using a straightline tracking arm, you are just messing with compromises.

Ray

[vinylengine]

Just logically, I thought this would put the stylus on the same exact arc path over the record as had I used the recommended 212 and 18.  Why doesn't it?

It surprises  me that I should actually now be using a slightly greater overhang (per VINYLENGINE).

I guess logic does not work in these complex matters!

Very good point

An arm mounted 211mm away from the centre can never be made to trace the same arc as one mounted at 212mm. However, this isn't important as you are only interested in it aligning at the same radii - the important point to note is that the actual points of alignment shift around the disc a little with mounting distance. If you plotted the two arcs you would see they follow different paths across the record (as viewed from above) but using the figures I gave they would both achieve tangency with the groove at the same distances from the spindle, giving exactly the error characteristics Loefgren (and later Baerwald) intended for that mounting distance.

Regards,
JaS

[Wayner]

They are not exact.

[Wayner]

In fact, I've plugged in all the numbers for my 6 turntables using the Loefgren B curve and all the curves have different distortion outcomes, they all follow a different distortion path and assuming that many different combinations of overhang and offset angle will result in the same values, aligning on the 2 null points generated by any of the gentlemen discussed is geometrically impossible. They are all uniquely different. Period.

Wayner

[Wayner]

Another comment that is interseting is how 2 different overhangs with 2 different pivot to spindle distances can have the same same radii?

I think there is a bit of far reaching going on here and the fact is that every combination of overhang, offset angle and pivot to spindle ratio, regardless of which null points you conform to result in it's own individual, unique distortion curve. Not identical, different. Maybe by small amounts, but they are not the same, ever!

[doug s.]

Another comment that is interseting is how 2 different overhangs with 2 different pivot to spindle distances can have the same same radii?

I think there is a bit of far reaching going on here and the fact is that every combination of overhang, offset angle and pivot to spindle ratio, regardless of which null points you conform to result in it's own individual, unique distortion curve. Not identical, different. Maybe by small amounts, but they are not the same, ever!

i agree w/this.  the baerwald curve will only be exactly matched when the pivot-to-spindle distance is exactly the same as what baerwald used.  when using a different pivot-to-spindle length, you can achieve the same two null points by adjusting the overhang and offset angles, but the errors at other points will wary a bit.  while i don't know for sure, logic tells me that the longer the pivot-to-spindle distance is, the smaller the error, and wice wersa.  if the pivot-to-spindle distance is greater than what baerwald used, the errors will be smaller than what he got, and wice wersa...

doug s.

[vinylengine]

I think the confusion here is presuming that a universal protractor is designed to produce the same arc for different mounting distances. It isn't, it's designed to produce tangency at the same null points (albeit on a different arc) resulting in the calculated overhang/offset angle and error characteristics for that alignment.

In fact, I've plugged in all the numbers for my 6 turntables using the Loefgren B curve and all the curves have different distortion outcomes

Just to be clear, Loefgren never said it was possible to get the same tracking error and/or error curve from tonearms with different mounting distances, and neither did I 

What I meant by 'exact' is that by aligning perfectly to the null points you will achieve the correct overhang and offset angle for that (altered) mounting distance and therefore get the exact error characteristics Loefgren calculations predict for that combination of mounting distance and inner/outer groove radii.

In this case the Loefgren A (Baerwald) IEC null points will minimise and equalise the tracking error at the inner, centre and outer grooves.

Because the tonearm is mounted closer to the spindle the error at these points will be slightly higher (you can't cheat the effects of arm length) but the aim of minimising and equalising for those radii will still have been met.

In the case of a universal protractor with Loefgren B null points you will minimise average WTE between the inner and outer groove radii, also with any length arm.

they all follow a different distortion path and assuming that many different combinations of overhang and offset angle will result in the same values, aligning on the 2 null points generated by any of the gentlemen discussed is geometrically impossible

I believe your assumption is wrong.

For any fixed mounting distance there is one overhang distance and offset angle that will align the cantilever at both null points. Therefore if you align to both null points you have set the correct overhang/offset angle. This is why universal protractors work.

If you get a spare 5 minutes take a read of Graeme Dennes paper, which not only proves that the overhang and offset angle are unique, but also that no other alignment will produce the same levels of error:
Is the Loefgren A Solution Unique?

Another comment that is interseting is how 2 different overhangs with 2 different pivot to spindle distances can have the same same radii?

I don't see where that comment came from? I didn't make that statement.

However, aligning accurately to the universal protractor will result in tangency at the same two distances from the spindle.

The location of these points will be different when viewed from above as they are on a different arc, but they will result in the overhang/offset angle figures and distortion curve that Loefgren's equations predict.

If I get the time I'll plot the results to illustrate this.

Regards,
JaS

 

[Seb]

they all follow a different distortion path and assuming that many different combinations of overhang and offset angle will result in the same values, aligning on the 2 null points generated by any of the gentlemen discussed is geometrically impossible

I believe your assumption is wrong.

For any fixed mounting distance there is one overhang distance and offset angle that will align the cantilever at both null points. Therefore if you align to both null points you have set the correct overhang/offset angle. This is why universal protractors work.

This assumption is definitively wrong.

proven by this graph :


according to your effective length, there is only ONE pair of overhang/angular offset that will give you the pair of null points.

best regards

Seb

[vinylengine]

according to your effective length, there is only ONE pair of overhang/angular offset that will give you the pair of null points

Am I right in saying that this applies when using a universal protractor with a tonearm of fixed mounting distance? It seems obvious to me but it would be nice to have it confirmed 

Regards,
JaS

[Seb]

Jas, you're dissapointing me!

since mounting distance is effective length minus overhang,
since for a effective length, there is a unique pair of overhang/angular offset that will drive you to the choosen null points,

for every mounting distance, there is only one pair of overhang/angular offset that will give you the pair of null points you choosed (the lofgren A in my graph)

shame on you

best regards

Seb

[JackD201]

In fact, I've plugged in all the numbers for my 6 turntables using the Loefgren B curve and all the curves have different distortion outcomes, they all follow a different distortion path and assuming that many different combinations of overhang and offset angle will result in the same values, aligning on the 2 null points generated by any of the gentlemen discussed is geometrically impossible. They are all uniquely different. Period.

Wayner

Since we're talking fractions of mms here, I'm curious if multiple turntables of the same model from the same manufacturer will be identical. These are very tight tolerances after all. Even if the design plans are perfect, manufacturing and assembly is quite something else.

[vinylengine]

For every mounting distance, there is only one pair of overhang/angular offset that will give you the pair of null points you choosed (the lofgren A in my graph)

shame on you

That's just as I thought. It seemed a very simple deduction to make but it doesn't hurt to have it verified

Regards,
JaS

[Seb]

same graph but I indicated the mounting distance



the data presented on this graph are CALCULATED,
see this excel file

best regards

Seb

[vinylengine]

I'm curious if multiple turntables of the same model from the same manufacturer will be identical. These are very tight tolerances after all. Even if the design plans are perfect, manufacturing and assembly is quite something else.

The accuracy of arm mounting distance does vary from deck to deck. If in doubt you can use a universal two-point protractor as it will set the correct overhang/offset for that mounting distance - although it's worth repeating that they won't be the same as the manufacturers unless they used the same null points when calculating their data.

A bigger problem for me is visually aligning the stylus. Checking alignment at both null points is more accurate than just using an overhang gauge, and aligning to the cantilever is more accurate than aligning to the cartridge body, but you will only ever get close.

The best way of reducing tracing error is to choose the null points that produce the lowest theoretical amount (Loefgren A or B depending on your leanings) then align to them as closely as your eyes/patience allows

I reckon after you've done that any audible issues with distortion are more likely due to the quality/condition of your tonearm, stylus or record.

Regards,
JaS

[Wayner]

None of your graphs show the distortion curve. Doug s. has hit the nail on the head and that, my friends (we are still friends), even tho we disagree is the whole point to this thread.

Yes, we can align are cartridge to the null points (in most cases), however, the distortion curve for each particular arm/table will vary from instance to instance. Some, not by much others may be more significant.

Jeb, I believe your chart. but that is not the issue. We are talking about actual mechanical harmonic and tracking distortion.

You guys are somethin' else! 

Have a great day!

Wayner 

[vinylengine]

Wayner,
Here are my conclusions so far:

(1) Your plots show that most manufacturers use overhang distances and offset angles that aren't applicable to alternative alignment methodologies. As these are simply the result of the chosen null points, the original position of the cartridge in the headshell can be safely ignored when using another method

(2) By plotting Loefgren calculated arcs for different mounting distances and measuring the offset angle at the null points I've shown that any length tonearm can theoretically align to Loefgren calculated null points, given enough adjustment in the headshell to achieve the required overhang and offset angle. if your arm was designed for radically different null points or your cartridge has an odd mounting hole/stylus tip distance then this may be difficult to achieve

(3) The null points for Loefgren A or B are a result of the chosen inner and outer groove radii. For IEC grooves at 60.325 and 146.05mm, Loefgren A null points are at 65.998 and 120.891mm and Loefgren B at 70.285 and 116.604mm. These null points are applicable to all arm lengths.

(4) Graeme Dennes paper goes a step further to prove that there is only one overhang/offset angle at which this alignment will take place for a given mounting distance/effective length. Therefore if you can visually confirm alignment at both of these points (eg using a universal protractor) you have set the correct overhang/offset angle for your arm length

(5) Graeme Dennes paper also shows that Loefgren A (Baerwald) is a unique alignment and no other will produce the same effect - in this case minimising and equalising the error at three points on the record. Applying this alignment to tonearms of different mounting distances produces different arcs across the record and different calculated error curves, but the result is still the lowest equalised error at the three points for each mounting distance. Similarly, Loefgren B alignment will produce the lowest average WTE between any chosen inner and outer grooves for any length arm.

(6) As small changes in mounting distance/overhang/offset angle produce different arcs/error curves the accuracy with which you align to the grids/points on a protractor will affect the final result. Additionally, if using an arm specific arc protractor the mounting distance should be accurately measured as the arc is only applicable to one mounting distance.

(7) For any chosen alignment method a longer arm will always give lower tracing error/distortion. As shown in Seb's graphs, as effective length increases the overhang and offset angle decrease. From a purely theoretical viewpoint, the ideal length pivoted arm would have infinite length and zero overhang and offset angle, giving zero tracing error. In reality 12" seems to be the practical limit due to other factors.

I look forward to any comments/suggestions/corrections!

Regards,
JaS

PS I think your issues regarding tracing error and distortion are covered in Graeme Dennes paper

[Seb]

so, distortion curves for various mounting distance (lofgren A null points):



no problem here even if there is nothing you can really do since the mounting distance is a constant on a particular TT unless you're having a slidding base (and a headshell with slots).

they all follow a different distortion path and assuming that many different combinations of overhang and offset angle will result in the same values, aligning on the 2 null points generated by any of the gentlemen discussed is geometrically impossible

the bold part of this sentence is still problematic to me.

best regards

Seb

[vinylengine]

And here are some distortion figures for tonearms with common mounting distances aligned at Loefgren A and B null points with IEC groove diameters.

To my thinking, to justify a new alignment method would mean calculating null points that produce lower average RMS distortion than Loefgren B?


Comparison of % average RMS distortion

make / model	standard	loefgren A	loefgren B
alphason hr100	0.433050	0.429266	0.385381
rega rb300	0.493758	0.407711	0.365987
technics sl1210	0.534326	0.421167	0.378094

Typical figures for arms aligned to Loefgren A and B

md	max dis (A)	max dis (B)	av dis (A)	av dis (B)
211	0.643737	0.445638	0.429266	0.385381
215	0.631659	0.437298	0.421167	0.378094
222	0.611584	0.423432	0.407711	0.365987
225	0.603366	0.417754	0.402205	0.361034
230	0.590153	0.408627	0.393354	0.353074

md = mounting distance

max dis = % maximum distortion between null points

av dis = % average RMS distortion


Feel free to check my distortion figures!

Regards,
JaS

[BobM]

So, bottom line. Which template is the best to use for those of us who are using a paper template and eyeballs to align with (understanding that? L-A (Baerwold), L-B or something else? Or is the margin of error in these paper tools and out aging eyes too great that it really isn't going to make much of a difference?