Why will no other turntable beat the EMT 927?

Raul and Lewm are both correct. The longer 12 inch arm can reduce tracking error but adds new design challenges by being longer. And as Lewm states, if the setup of the 12 inch arm is off a bit, the tracking error becomes worse than a 9 inch arm. And the articles that I read showed the tracking error is worse for the 12 inch arm vs. the 9 inch for the same amount of mis-setting. Effective mass is actually the inertia of the tonearm and inertia is mass times the radius squared plus 1/3 the length squared. So the 12 inch arm has to have a higher effective mass. The arm tube rigidity to avoid resonance response becomes a bigger challenge too for the longer arm. It is a mechanical engineering problem that was solved decades ago. The 9 inch arm, in general, provides the optimum solution for all conditions. Sure, new materials can justify a revisit of old ideas. Just watch out for new designs where the hype outweighs the engineering.

Rauliruegas, "From this point of view a long tonearm against a shortest one is in clear disadvantage because can't " respond " to the cartridge tracking movements as fast as the shortest one." I think you are referring to the great mass of the long tonearms. So this is a wrong statement. If you had a short arm with greater mass than a long arm, it would be untrue.

I still maintain that in my experience the same cartridge on the 407 sounds better than on the 345. Since I buy based on what I hear that was enough.

I heard a clearly better and more believable presentation with the SME V-12 than I did with the SME V using the same cartridge and cable on the same turntable during a direct comparison over a two week period. In fact, it was not really close.

The effective mass of the V-12 is only 1g more than the V. Inertia may even be less because the counterweight ended up being considerably closer to the pivot on the V-12. The weight of the arm tube and counterweight is greater on the longer arm, so there is more weight on the knife edge bearing, so that may also help drain energy away from the cartridge and into the arm base.

The headshell angle is less on the longer arm, so there is less need for antiskate and I used two Mint LP custom arc protractors for each alignment, so I presume one was not better set up than the other. So it is reasonable to presume some of the better sonics I hear are a result of the lower tracking distortion of the longer arm. To Tony's point, SME did spend two years developing the longer version of the V arm. It is not simply a 3" longer arm tube like some other designs.

My only experience with arms in my system is with three different SME arms, so I can not make a general argument for 12" arms over 9" arms, but the points raised above by both Raul and Lewm do make sense.

But, Peter, Raul and I were at odds on the subject. Whilst out for my evening constitutional, I thought of an additional advantage of 12-inch arms vs 9-inch: The former makes it easier for the cantilever to work against bearing friction at the pivot, because the longer arm affords greater mechanical advantage in overcoming that force. Of course, the possible negative trade-off is the additional inertia associated with heavier tonearms.

Well, I think Raul points out potential problems with the longer arms and if they are not addressed, then the disadvantages are outweighed by a correctly implemented 9" arm. However, if the effective mass is low enough and the arm and cartridge are properly aligned, then the advantages of the lower tracking distortion of the longer arms can be realized.

Though I'm not sure, I think that longer arms can have the same or lower inertia than shorter arms. It is a function of where the counterweight is located in relation to the pivot. In my specific case, though the effective mass of the V-12 is 1g greater than that of the 9" V, the inertia may be less because the counterweight is considerably closer to the pivot allowing the arm to react quicker.

People who have compared the V to the V-12 have commented that the V is more dynamic and "quicker" sounding. I did not notice this. I did hear a clearer, more detailed and smoother sound with the V-12 though.

Perhaps John Gordon can add some comments about effective mass and inertia.