Frank Kuzma is releasing a new arm!

Frank Kuzma is no dummy, I totally agree.  I greatly admire his turntables, and based on the kudos accorded to them, I also admire his tonearms, until now, possibly. But sometimes even smart guys over reach.  We shall see. You wrote,  "no, you can't entirely divorce inertia from mass but it does matter where the mass is."  But in fact the equation for "effective mass" (not mass alone) already takes into account the distribution of mass in a tonearm, as I am sure you realize. Ergo "effective mass" is closely related to inertia. Perhaps Kuzma ameliorates the problem by using a variable damper counterweight, a la the Technics EPA100.

I also was wondering before this discussion ever came up, after having read Fremer's reveal of the sapphire tonearm, is sapphire really so much stiffer than other stiff but not so dense materials of which tonearms are conventionally made? For example, the Technics EPA100 arm wand, titanium nitride. And the Mk2 version which was made of boron something. Or even steel?

Here is what I found about the stiffness of Sapphire, albeit on a website for a company that sells things made of sapphire for industrial use:

"Sapphire is one of the hardest materials on earth. Mechanical hardness is typically measured using the Mohs scale: glass generally has a Mohs score between 6 and 7, and hardened steel which comes in at 8 Mohs. Sapphire has a Mohs hardness value of 9, placing it just below diamond which has a hardness of 10 Mohs.

Furthermore, sapphire is very stiff. Its Young’s modulus is 435 GPa, making it 6 times stiffer than quartz, so it can’t be stretched or deformed easily.

These properties make sapphire one of the strongest and most durable materials on the planet."

@mijostyn

@dover, You have your tonearm geometry mixed up. 

The 4 Point is a neutral balance arm. It will stay in whatever position you put it in. VTF stays constant regardless of position.

Wrong.

Here’s Michael Fremer in hs review of the 4Point9.

Because the 4Point’s two vertical bearing points and the cups they pivot in are well below the arm and thus its mass, the arm’s center of gravity is above the vertical pivot point—the opposite of stable balance. This produces what’s called negative balance, in which the VTF decreases as the arm is raised from the record surface.

Clearly you have no idea what you are talking about.

Specs & details aside, it still looks Playskool to my eyes....pardon.

And Lambo or Edsel, one can be dead in either.

@lewm , given the performance of Soundsmith's sapphire cantilevers I can believe that opinion or fact if you will. It is the thinnest cantilever I have ever seen and looks like it would snap with the slightest misstep but, I have already had one that would have definitely snapped a boron cantilever and the Soundsmith survived in perfect condition. Weight is another factor. Carbon fiber has become a popular arm tube material because it is stiff and light. The sapphire does not appear to be so light. Perhaps Kuzma designed it specifically for his cartridges?

@dover  well, that makes perfect sense. Sounds like a REALLY stable arm doesn't it? What happens when an arm designed to lower tracking force as it elevates hits a warp? Why do you think the counter balance weight of the 4 points is so low?

You are right, I have no idea what I am talking about. I did not have your post deleted because I want everyone to know what kind of f-up I am.