Kuzma 4Point vs Airline - is it worth the upgrade?

Jameswei: "Can you share with me your understanding of how the bearing is implemented? I am intrigued and itching with curiosity!"

2 points + 2 points = 4 points

Extra point: HiFi Plus review by Roy Gregory.

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Jfrech: "So Mikey kept saying chatterless...seems like there can be chatter in this bearing too...maybe he means less via the 3 points in a cup. 4th on a post..."

I think you got it confused. It should be 2 points for vertical and 2 points for horizontal movement.

The whole point (pun intended) of this design is not to use any ball racing bearings and/or gimbal bearings. The concept is derived from unipivot style bearing but using 4 of them. It's like 4 unipivot arms merged into one to combat unnecessary azimuth/torsional movement. 4 spikes in 4 cups, very simple and effective and cleverly arranged. Check pictures below.

The two spikes are for vertical movement so there are only two contact points, low friction and no ball bearings that can chatter. On the pivot post, the female part, one spike is on the top for horizontal movement and another spike for keeping it from swinging around. So the whole column can only rotate about 45° which is just enough for a pivot to swing from rest position to the spindle. It's an ingenious design that allows the lowest contact points (4) without resorting to a unipivot (1) that exhibits azimuth movement. On top of that, both vertical and horizontal motions have fluid damping troughs so each can be damped individually, whereas typical unipivot or gimbal arms damp both at the same time. Again, clever. Also notice the two cups are located not at the middle cross section of the column? It's intentionally off-centered so whole arm's mass is concentrated at the horizontal spike. Essentially all 4 points are preloaded with mass. Simple and clever. Oh, don't forget the two spikes for vertical bearings are positioned 19.50° off-centered (less than typical 9" arms at 23°) to match the headshell so VTA would not affect azimuth angle. Also nice. The bigger counterweight is on the same horizontal plane as the two vertical spikes so render the arm neutral balance without any pendulum effect, low inertia. Good.

Some more pictures:

4 point locations & Specifications

I am not surprised by the positive reviews as it clearly shows, to me at least, good engineering in many parameters of a good tonearm. The designer has done his homework. As for the negative reviews, it maybe is in the material and execution, over damping, wires, energy transfer, etc..., anything is possible. Since I don't have the arm to play with, I have no comment on the sound. The above is only my observation. From what I saw, Mr. Kuzma has earned my respect as a designer. Tonearm design is fun to look at and think about for me. As a student of the art, it's nice to see some clever thinking these days.

Have fun.

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Dover: "Unlike a true unipivot the whole arm tube will chatter with a low compliance cartridge.."

Conceptually similar to SME but I don't see how two needle points sitting on two cups with the entire mass of the arm preloading the bearings can chatter or chatter to the level of conventional gimbal bearings. I agree with Brian.

I did not say it is a unipivot but clearly and explicitly the designer had the concept of unipivot tonearm, which Kuzma also makes, in mind. Check specification page. (Sorry about the early post that I uploaded the wrong spec image.)

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Jameswei: "In other words, the distance between the tips of the spikes must be exactly equal to the distance between the centers of the cups. They must not be off by even a little bit. I see from the first "2point" pic that one spike tip position appears adjustable since there seems to be a set screw for the spike."

Very good point, Jameswei. I think as long as one spike/cup contact is secured, the other one may fall wherever it may be in the cup and still not chatter, though not as elegant. Another solution is on the female side to be one cup and the other a groove and this way the tolerance need not be so tight. The Morch DP6 tonearm is a two point bearing design and one spike/cup is height adjustable in order to change azimuth. Perhaps the set screw on the spike of the Kuzma 4Point is for that too.

The Origin Life Encounter tonearm is also a two point bearing design that does not allow azimuth change at the bearings and they are factory set to ensure perfect contact.

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Yes, Jameswei. That is the link. I was very sloppy with my links. Thanks.

Here's the jpeg link explaining the Origin Life tonearm.

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