I am disappointed that the thread degenerated and we lost track of the very interesting original post. The issues of moment of inertia, rigidity, and perhaps to a lesser extent, tracking error and anti skate forces are all worthy of discussion to better understand their relative effect on what is a complex system.
Mr. Fremer shared his view that he prefers 9" arms because they sound better to him. He supported this preference by mentioning technical reasons why a shorter arm might sound better and by referencing comments made by tonearm designers. I happen to agree with Davey that Fremer's own comment about manufacturer's telling him privately, "off the record", that they are only producing longer arms because of customer demand raises all sorts of questions. Would not some manufacturers want to design a product that might improve performance? Why is there customer demand for longer arms, if not for improved performance? Might they not sound better if properly designed? If the customers want the product, and the manufactures can make money selling it to them, everyone wins.
We do not actually know if the designers think the longer arms perform better or worse. We do know that the longer arms usually cost more. We also know that some customers prefer the longer arms for a variety of reasons, and they buy them. Once one manufacturer started to build londer arms, and people bought them, it seems that other manufacturers noticed a new market or trend and started to produce their own longer arms. DDK and I have actually done direct comparisons between arms of the same design and of different lengths. Our listening experience does not match Mr. Fremer's personal preference and what he tells us that the manufacturers tell him privately. I am left to wonder why this is the case.
I tried to make the point that the market will decide in the end because people will hear the longer arms and decide whether or not they want to buy them. I do not see why this issue led to such controversy. However, I do have some real questions for Mr. Fremer. I had hoped he would respond to some of my posts, specifically his own review of the SME 312S arm, in which he said that the 12" variant has all of the theoretical benefits of the longer arm, and none of the disadvantages (meaning less rigidity and greater moment of inertia). This seems at odds with his preference for 9" arms. I wish he had addressed this in the thread.
I presume he must have been thinking about the 9" SME arm when he wrote the review about the 12" arm. He did not do a direct comparison between the arms, which is also disappointing, and makes his position about arm length less convincing. It is obvious that there are technical differences between arms of the same design but of different lengths. A direct listening test would be the best way to know if the technical differences matter in the end. The reader would be better served with a report of a direct listening comparison. Mr. Fremer admits he is not an engineer, but a listener. His value as a reviewer is his sharing of his listening impressions. I enjoy reading them.
In the end, I think Mr. Fremer prefers the 9" SAT arm to all other arms he has heard. I understand that and would like to hear that arm one day. The controversy results from the idea that 9" arms are inherently better. He did not state that and he made this point repeatedly on this thread. His position would be much stronger, in my opinion, if it were supported by a series of direct listening comparisons between multiple 9" and 12' variants of the same arm design. This idea was notably absent from his many posts. I hope that some day he is able to directly compare the 9" and 12" SAT arms. He will then be able to share a new perspective based on broader experience. I also wish that he had not commented on what manufacturer's told him "off the record" because it can be interpreted as a support of his preference for 9" arms and it raises questions for those who happen to have directly compared the different arms and prefer the longer ones.
I think it is very difficult to design a longer arm that performs as well as a shorter arm, in terms of rigidity and moment of inertia. It requires added design time, new production challenges, and greater cost. Marc Gomez and hte engineers at SME (among others) have addressed these challenges. Simply adding 3" to the arm wand is a simple solution which probably results in poorer performance. Is this the simple truth that Mr. Fremer was writing about? Who knows? I wish he had stayed around and been willing to really get into this discussion and share his experience.