Just to add a bit to my post above, if moment of inertia were such a critical design criterion why not a 3", 5" or 7" arm? We all know the answer to that. The formula for moment of inertia is I=L/w where L is angular momentum. Guess what, angular momentum is determined in part my mass, L= mvr with the m being mass. So if it were so critical, why are we not back to the days of the Infinity Black Widow tonearm? Anybody remember them? Google it. The unchecked pursuit of low mass tonearms personified. The answer to that question is that low mass brings it’s own host of problems. So suddenly we are to believe that a stout 9" arm like SAT’s top of the line arm is the ideal (until next month when Marc Gomez comes out with the next best arm) is without compromise? This entire argument surfaced when Mike Fremer, always the worshipper of the most exclusive, started parroting-and when it comes to engineering, Fremer is 99% a parrot of things he has been told by others-statements made by Marc Gomez of Swedish Audio Technology aka SAT. Until recently SAT offered 12" arms though Gomez was quoted as saying he only offered them to accommodate the market. Again, I don’t dispute that with certain cartridges moment of inertia is an important factor and that a 9" arm may well be optimum, everything else remaining equal. But only with certain cartridges since compliance, suspension design, and even the stylus shape and cantilever material will all play a role. A Koetsu may very well benefit from the inherent virtues of a 12" arm-greater mass, different resonant frequency, less tracking error-whereas Mikey’s current favorite-the Lyra Atlas Lamda- may sound slightly better on an otherwise identical 9" arm. Compared to the thousands of other compromises made in an entire system, the 9" vs. 12" is in relative terms de minimus in degree.
