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I think the arguments against 12" tonearms are greatly exaggerated...

Posted by John Elison (A) on February 22, 2009 at 23:48:58

In Reply to: RE: 12 inch tonearms ? posted by ASW27 on February 22, 2009 at 17:32:54:

I believe that AVID HiFi exaggerates the disadvantages while minimizing the advantages of 12" tonearms.

> Average distortion on 9" arms is 0.85%, whilst 12" arms are 0.67%. Some trying to impress will
> say this is 20% lower distortion, however this is incorrect as in real terms its only 0.18% lower.

Mathematically, the number 0.67 is 21% lower than the number 0.85 whereas the difference is only 0.18. However, let's compare alignment graphs of the two arms in question.

The numbers in turquoise represent tracking error distortion for a stylus tip velocity of 10-cm/s. RMS distortion as well as instantaneous distortion within the playing area are actually 28% lower for a 12" arm as opposed to a 9" arm. While the actual difference is not very large, the longer arm clearly delivers lower tracking error and lower distortion.

> Now add to this the downsides of higher moving mass, lower arm rigidity, higher
> counterweight inertia and worst of all higher distortion caused by misalignment.

This statement is misleading and somewhat exaggerated. Yes, longer tonearms have higher moving mass, but they are not necessarily significantly less rigid. We are talking about a mere three inches. Furthermore, comparing inertia for different length arms is deceiving. The honest way to compare the effects of inertia for different length tonearms is to divide their moments-of-inertia by the square of their effective lengths in order to compare effective mass. For example, the 12" SME 312 is very well designed for structural rigidity and yet has only 12-grams effective mass. While this is a little higher than the SME 309, it is comparable to many other makes of 9-inch tonearms.

> Yes...in the real world rarely are styli correctly fitted within the cartridge body and most fit their cartridge
> using a standard alignment gauge using the body as a guide. Therefore if your stylus is misaligned within the
> headshell the distortion will be greater using the 12" arm as the distance from pivot to stylus is greater.

I believe that for any reasonable alignment error, a 12" tonearm will still have lower distortion than a similarly misaligned 9" tonearm, although the longer arm's advantage will be lessened to some degree. For example, suppose you are aligning a cartridge body with a cantilever misalignment of 1-degree. Comparing the following graphs for 1-degree offset error, the 12-inch tonearm still has lower overall distortion than the 9" tonearm, but only by 11.5% instead of 28%. Furthermore, 1-degree would be a gross alignment error and very unlikely in my opinion.

> Record damage is greater due to counterweight inertia, warp tracking worse by
> higher moving mass and sonic degradation caused by unwanted structural resonance’s
> in longer arms, coupled to having oversized turntables causing more issues.

As I stated above, counterweight inertia and moving mass are deceptive parameters in that they cannot be compared directly for different length tonearms. It would be like comparing apples to oranges instead of apples to apples. The meaningful parameter for evaluating record damage from warp tracking is called tonearm effective mass. It makes direct comparisons of the effects of inertia for different length tonearms possible and applicable. As noted above, modern 12" tonearms have only slightly greater effective mass than 9" tonearms.

Sonic degradation caused by unwanted structural resonances in 12" arms may or may not be greater than sonic degradation in 9" tonearms. It really depends on the design of the specific tonearm.

Issues with oversize turntables necessary to accept 12" tonearms is a rather vague statement. What are the issues? Perhaps a larger turntable stand?

In conclusion, I feel the arguments presented by AVID HiFi against 12" tonearms are greatly exaggerated. Personally, I do not own a 12" tonearm, but I believe there are more advantages than disadvantages in favor of modern 12" tonearms like the SME 312.

Best regards,
John Elison

Edits: 02/23/09 02/24/09

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