I just wandered onto Kuzma's web site to check on the specs of one turntable only to be confronted with a $25,000 9 " sapphire tubed sorta 4 point arm. Looks like a winner to me. I think it is a better design than the SAT arms but then I thought the 4 Point 9 was a better design than the SAT arms. Next will be a diamond arm tube:-)
@dover, You have your tonearm geometry mixed up. The SAT arm is a stable balance arm. In other words it will always return to the same balance point after a period of oscillation. VTF changes with elevation. The 4 Point is a neutral balance arm. It will stay in whatever position you put it in. VTF stays constant regardless of position. Yes, the new arm is a heavier arm which means it is limited to cartridges that are on the stiff side. There are plenty of those. As it is very short, shorter than a Rega arm it's moment of inertia is low in spite of the mass which is more important than EF. It's major failure is it's price. Would I buy one? Certainly not for a Lyra Atlas.
Let’s spare ourselves the obvious jokes about its cost. The elephant in the room is that this tonearm is an elephant. At 60g effective mass, not many if any cartridges will qualify, if you base tonearm matching upon the equation for resonant frequency or even bring it into the buying decision? And yet its mass will be ignored by the well healed cognoscenti, because it is so expensive. In the minds of many with big bucks, cost can overcome the constraints of the physical universe. Even Fremer, who mentioned this product, its cost and its effective mass, in his most recent newsletter, didn’t bat an eyelash over that last specification. We shall see how it is ultimately viewed.
Just read Mijostyn’s last post after having posted this. I don’t see how you can divorce effective mass from inertia.
Aesthetics are important for some. Me included. To me it looks like an Orca whale (fitting giving it’s mass) and I would not want it if it were free. My Reed 3P’s not only sound great but to my eyes are beautiful. Same with my decks. I want both performance and beauty. If an Edsel could outrun a Lambo, would you want to be caught dead in it?
@lewm, no, you can't entirely divorce inertia from mass but it does matter where the mass is.
@fsonicsmith, stiffness of the arm tube is a very important characteristic for a tonearm and many of the best arms use wider diameter arm tubes. Certainly, the days of arms like the Infinity Black Widow are over. It does seem to me that if you are using a very stiff substance like sapphire you should be able to get away with a thinner lighter arm tube but there may be a problem manufacturing a smaller tapered sapphire tube. Frank Kuzma is no dummy. If he could have made it lighter he would have. He obviously had to compromise by making the arm a bit shorter. I think it is a good looking arm for what it is worth. Does it offer any advantages over arms like the regular 4 points or the Reed 2G, Schroder CB and Tri Planar? Set up correctly I would probably not be able to tell the difference and I would have to notice a difference to spend that kind of money. But, nobody has made a sapphire tonearm before so, this is another Kuzma first.
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."
The 4 Point is a neutral balance arm. It will stay in whatever position you put it in. VTF stays constant regardless of position.
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.
@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.