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9", 10" or 12" tonearm?

Can anyone explain why many analog aficionados like or dislike 12" tonearms? What is the main sonic difference between a 9 or 10" tonearm and a 12" one? Is the 12" dogma outdated? I must say that in the past there were more 12" designs (SME 3012, SAEC, Audiocraft) than nowardays. Is 12" for "audiophools" with strong nostalgic feelings (like me)? (Especially when combined with those old Denon 103 or Ortofon SPU).
dazzdax
bdp24's avatar
bdp24
10,289 posts
 

Geoffrey Owens of Helius Designs makes a 9", 10", and 12" version of his excellent Omega arm. It is his opinion that the 10" provides the best balance between the advantages and disadvantages of all lengths. 12" arms, while providing significantly smaller tangency error than do 9", have far greater moment-of-inertia mass, generally not a good thing. Geoffrey feels the 10" arm’s tangency error advantage over the 9" is worth the only-slightly greater m-o-i of the arm, a justifiable trade-off. But the m-o-i penalty of the 12" in relation to the 10" is greater than it’s lower tangency error advantage over the 10", an inadvisable compromise.

The introduction of the Trans-Fi Terminator air-bearing linear-tracking arm has changed the landscape of that design. Go to the T-F website for details. Perhaps the greatest tonearm value right now---just over $1000!

noromance's avatar
noromance
10,201 posts
 
I'll just throw in that my two Jelco 750 12" arms sound better with anti-skating off. (Think they look nicer over 9" too)

chakster's avatar
chakster
6,144 posts
 
@dazzdax i also use "9, "10 and "12 tonearms and all of them are great, but for some turntables like Technics SP-10mk2, SP-20 the "10 and "12 tonearms are much easy to use and to mount. Aesthetically "10 and "12 are better (imo). So you can't be wrong with "10 inch tonearms like Technics EPA-100mk2 for example. My reference is Reed 3p "12, it's had to find anything like that, because with Reed anyone could adjust absolutely everything (including azimuth) on the fly (the best engineering).  
melm
1,085 posts
 
Another advantage of a 12" arm is that once you set the correct VTA/SRA, it changes less with different weight records than does a shorter arm.
larryi
4,357 posts
 
Another advantage of the 12" arm that has not yet been mentioned is that VTA changes less with different record thicknesses.  Also, because the offset angle is lower on a 12" arm, skating forces should be reduced.  

As others have mentioned, the tradeoff on long arms is that, for any given effective mass, the arm will be less rigid and more prone to problems with resonance.  Not only are the arms themselves slightly heavier, having the heavy cartridge well out on the end of what is a cantilever means that the effective mass (inertial mass) of the cartridge is much higher.  If one were to try to reduce effective mass by reducing the mass of the arm itself, that means less material in the arm and less rigidity or damping capability.

Linear tracking arms come in a WIDE variety of designs.  Those that rely on very low friction to allow the arm to be pulled along by the forces on the stylus (like the air bearing arms), put more stress on the cartridge's cantilever than do pivoting arms (because of no mechanical advantage of a pivot and lever).  Some say that the requirement of such designs to yank the cantilever sideways enough to move the arm actually means the cantilever is almost always further out of tangent than on a conventional arm. 

Whatever the theory, I cannot say that I've heard differences in performance that are consistently attributable to one type of arm or to particular lengths of arms.  
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