Question on effective length and overhang

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sng
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Question on effective length and overhang

Post by sng » 05 Oct 2019 07:18

Hello everyone,

I am trying to understand what these terms mean. I’ve seen the diagrams showing all the relationship of overhang and effective length to the pivot to spindle (p2s) distance and from a measurements point of view are not difficult to understand. What really gets me is the fact that there are different targets for minimal distortion (Baerwald, Löfgren, Stevenson) and also recommendations for the inner radius which (please correct me if I am wrong), I believe gave rise to each of these targets.

The confusing thing is that each of these targets will have us setting the actual stylus location at different distances from the pivot centre. The final stylus location depending on which target is selected can vary by a substantial amount (between 3-5 mm). One thing I have not considered is how much the variation is for different tonearm lengths. I would not be surprised if there will be substantial differences in stylus location. As I understand it, the tonearm manufacturer specifies an exact p2s distance as well as an exact overhang. What each of these different targets and inner radii does is to basically ignore the overhang distance specified by the tonearm manufacturer. Doesn’t this make the overhang distance specification superfluous and in fact it’s unnecessary?

If anyone can help with my confusion it would be very much appreciated.

JaS
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Re: Question on effective length and overhang

Post by JaS » 05 Oct 2019 11:25

sng wrote:
05 Oct 2019 07:18
What really gets me is the fact that there are different targets for minimal distortion (Baerwald, Löfgren, Stevenson) and also recommendations for the inner radius which (please correct me if I am wrong), I believe gave rise to each of these targets.
Not quite, the choice of inner/outer radii has nothing to do with the choice of optimisation. You choose the inner/outer radii based on the records you intend to play, then apply the optimisation equation.

For example, if you only expect to play 7" records you would choose different radii than if you planned to play 16" transcription records. FWIW most tonearms are optimised for 12" records, although the exact inner/outer radii vary (as do the published standards for record manufacturers).

The choice of optimisation equation applied to these radii is a separate consideration. For example if you want the lowest peak distortion you would apply the Löfgren A/Baerwald equation to the chosen radii, or for the lowest average RMS distortion you would use the Löfgren B equation.

FWIW if you apply Baerwald optimisation to IEC 12" inner/outer groove radii you get null points of 66 and 120.9mm. These null points will give the lowest peak distortion for records with IEC 12" max/min groove radii for any length tonearm. This is why universal protractors work; the overhang/offset needed to hit the null points will change with tonearm mounting distance, but as long as you adjust the cartridge to hit both null points you will get low distortion across the record.
What each of these different targets and inner radii does is to basically ignore the overhang distance specified by the tonearm manufacturer. Doesn’t this make the overhang distance specification superfluous and in fact it’s unnecessary?
If you don't have the original manufacturer's alignment tool and are using a 3rd party protractor then yes, you should ignore the manufacturer's recommended overhang and offset angle.

Of course 99% of people don't need to know any of this stuff as using either the manufacturers tool or a decent universal protractor should give good results :wink:

sng
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Re: Question on effective length and overhang

Post by sng » 20 Nov 2019 00:19

Hello JaS,

Firstly, thanks for making the effort and taking the trouble to reply to my posting. Secondly, sorry it’s taken me so long to respond.

Since then, I’ve tried using various templates to see if I can make anything sensible out of the question of the sound I hear and the precision required in setting the overhang. I used the template from the tonearm manufacturer, 2 point protractors like that from dB, the ClearAudio protractor and a custom arc protractor from MintLP. If I am not mistaken most use the Baerwald recommendation. Some are more difficult to use than others. The ClearAudio protractor is doubly difficult to use because my tonearm (Reed 1X) does not have a pivot centre mark!

The thing that bothers me though is with these recommended settings the sound is dry, the frequency extremes are poor and dynamics poor. I eventually settled on a position where the stylus is about 2mm in front of the recommended arc.

I am not in a position to conclude anything from my experiments since the variables are many and who am I to refute the mathematics? It could be that I am not using these protractors correctly or that my eyesight is not as perfect as I hope it to be, and, it’s possible my tonearm is not mounted precisely with respect to the spindle to pivot dimension. It could also mean that my final setting is producing much more distortion than the recommended one, but to my ears and taste, it sounds much better🤔

I have noticed that with my final setting, 95% of recordings sound very good but there are a few that sound less than perfect compared to my experience listening to them on another system (much more expensive than mine). I can not explain this. It’s possible the cutting heads were aligned differently but I put this variance down to equipment capability rather than precision of setting the overhang. The lesson learnt personally, is that my ears and taste are the final arbiter in these matters. The tools get me close to what I need but some experimentation is needed from there on.

Thanks again.

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