Why do tonearm specifications list null points?

Regarding a mirrored surface, I'm currently using the Dr. Feickert generation 2 protractor; while it doesn't have a mirrored surface, it has white etchings on a black matte aluminum surface are very precise and extremely easy to read (for me personally, this is easier to see than white etchings on a mirrored surface on protractors used in the past). I also have a very high intensity work light that I use from different angles (same height as stylus and shooting from the side or front as required) as well as magnification to ensure the diamond tip is in the cross-hairs. I'll admit I think I do have it easier than most because the Clearaudio Jubilee MC cart I'm using has the long cantilever extended out in front of the cartridge body making it very easy to confirm the cantilever's parallelity with the lines on the protractor.

With all this said, I'll be the first to admit that the improvement I think I'm hearing from switching back to to Lofgren A (Baerwald) from Lofgren B is a) either in my head because Clearaudio specified the Baerwald null points in their tonearm specs, or b) as @rauliruegas pointed out, most likely from tiny errors from my hand or sighting with the protractor.

Thanks all for your comments - always fun to discuss these things and learn from each other.  -cheers!

You need a mirrored surface with lines finely etched and magnification.  

and certainty that the diamond tracing faces (assuming advanced profile) are aligned precisely 90° to the cantilever.

dave

This happens all the time: we conflate tracking angle error with "distortion" without actual evidence that the two are perfectly correlated. And what sort of distortion might be correlated with TAE? Suffice to say it seems to be a good idea to minimize TAE, but whether that also minimizes "distortion" in a predictable or audible way is not established. Or if it is, where are the data?

@dover , right on. 

@rauliruegas exactly, overall distortion levels are lower with Lofgren B except at the very innermost part of the record. Modern records are not cut that far in. Som older records are but I do not notice significant problems with records cut all the way in and I Use Lofgren B religiously. It is tedious setting up a cartridge correctly especially if you are trying to change alignments. Any tonearm set up for Lofgren A can be made to do Lofgren B but to do it accurately and consistently you need a protractor like the WallyTractor or the SmarTractor. You need a mirrored surface with lines finely etched and magnification.  

Several years ago, I experienced the issue discussed by Dover and Larry with a Dynavector DV505 tonearm, probably because the DV uniquely places the vertical pivot so far forward from the horizontal pivot.  The DV was designed with headshell offset for Stevenson or something very close to it.  When I aligned a cartridge according to Baerwald, I of course had to twist the cartridge in the headshell so that its long axis was deviated toward the spindle. I was unhappy with the resulting SQ.  Reasoning that the problem was due to the necessary misalignment of the cantilever with the vertical bearing arc, I then straightened out the cartridge using Stevenson.  Whether this hypothesis for cause is valid or not, correcting the alignment of the cantilever to be in the same plane as the arc of the vertical bearing made for a big improvement in SQ.

Dear @jimmy_jet  : As a fact normally manufacturers did not write that spec because it's not really a tonearm spec and could makes ( as in your case. ) a " mix-up " for the owner.

Those null points means that one kind of alingment you can choice is the IEC standard Löfgren A and that's it.

" Soundstage returned ", well that's what you listen but not really a change by the Löfgren B because the overhang in between both alingments is lower than 0.5mm with the same offset angle.

Even the average distortions between both kind of alignment is around 0.04% lower in the LÖfgren B than in A.

What you listen is more a consequence of the tiny errors coming from the protractor and coming from our " hands " movements to the new set up. It's almost imposible to make a change in alingment making the same change 3-4 in a raw and achieve exactly the same grade of accuracy.

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

@larryi Thanks for even more clarification - I was struggling a bit about the azimuth being thrown off but also concluded that it would have to be very minute.

While the overhang for a different alignment scheme would result in a different angle of the cartridge that would not have the cantilever of the cartridge perpendicular to the axis of the vertical bearing of the arm

This really brought it home for me and now it's clear why the manufacturer would list the null points in the tonearm specs 💡

I don't know if it's just psycho-acoustics or reality, but when I switched back the alignment from Lofgren B  to use the manufacturer's null points (virtually Baerwald), the soundstage magic returned...

Dover, 

very good, and concise, explanation.  While the overhang for a different alignment scheme would result in a different angle of the cartridge that would not have the cantilever of the cartridge perpendicular to the axis of the vertical bearing of the arm, the difference in angle would be small, so that the imperfection would be more theoretical than practical.  There would be only a small variance in azimuth for different settings of VTA such that I would not worry much about it.  

Thanks for the explanation 

So, is the tonearm manufacturer trying to say that this particular tonearm is somehow optimized or was designed to utilize those null points they list in the spec?

Short answer is yes.

In theory you can run any alignment you want eg Stevenson, Baerwald or even create your own. The headshell has an offset, but due to the slots you can rotate the cartridge and move it back and forth.

However the pillar bearings for vertical motion are offset to match the headshell  and if you use another alignment that results in the cartridge offset being different to the pillar bearing offset then you introduce issues where if you adjust VTA then azimuth will change at the same time. Each time you change VTA you will need to recheck azimuth. This is not ideal.