Eminent Technology ET-2 Tonearm Owners

I have been researching possible bearings for a new Arm and I came across the Kuzma web site and the Airline Arm. This appears to be unique in using a porous material rather than multiple drilled holes like the ET. It also has a sliding sleeve instead of the sliding spindle of the ET

Wow this is a spectacular looking arm which is definately on my wish list.

This brings me to the subject of horizontal effective mass again. I asked them for this figure for the Airline. It is probably not appropriate for me to publish this here, since it was a private conversation and the number is not shown in their specs. But I can say that it is higher than my heavy modified ET2 arm. We went on to talk about potential problems with cantiliver flex. His response was the resonant frequency due to the combination of a typical low compliance cartridge and horizontal effective mass was in the region of 2.5 -3.5 hz.(this has been published by them elsewhere), this is well above the 0.55 or 0.75 hz for 33 or 45 rpm eccentric records. Therefore the cartridge does not "see" this movement.

He directed me to a video of the arm and cartridge tracking the lead out grooves with a oscillation amplitude of 12mm. See www.Kuzma.si ,tech support,tech info, Airline video.

This Video was posted by them to allay fears of cartridge damage due to high horizontal mass.

This arm is amongst the best currently available. It has a large differential between its vert and horizontal effective mass figures and does not appear to be a cartridge killer.

I'm sure you will agree that this motion is violent and way beyond what any record eccentricity would produce. He assures me that there is no problem with the cantilever under these extreme circumstances.

I want one.

Richardkrebs

I have queries regarding your claims re the Kuzma air bearing tonearm.

This appears to be unique in using a porous material rather than multiple drilled holes like the ET.

This is not correct. The ET has a captured air bearing with a continuous air gap between bearing spindle and manifold.

We went on to talk about potential problems with cantiliver flex. His response was the resonant frequency due to the combination of a typical low compliance cartridge and horizontal effective mass was in the region of 2.5 -3.5 hz.(this has been published by them elsewhere), this is well above the 0.55 or 0.75 hz for 33 or 45 rpm eccentric records. Therefore the cartridge does not "see" this movement.

This defies basic physics.
Any lateral force on the stylus forces the cantilever to flex laterally, until the resistance of the cantilever to movement meets or exceeds that of the arm, at which point the arm must follow.
More mass in the arm = more inertia in the arm = more flex in the cantilever.

This Video was posted by them to allay fears of cartridge damage due to high horizontal mass.

This arm is amongst the best currently available. It has a large differential between its vert and horizontal effective mass figures and does not appear to be a cartridge killer.

The video does not show the cantilever. Proof of the above assertions is not demonstrated.

As regards the best available, what other arms have you auditioned to draw this conclusion.
If you are talking air bearing arms - where have you considered the dynamic stiffness of the air bearing. Although the Kuzma runs 60psi into porous tube versus the ET2 at 19psi into captured air bearing, the psi alone does not determine the dynamic stiffness.

Some other factors you need to consider are :
The hole sizes
The flow of air
The surface area of the bearing
etc

The ET2 also has a wider manifold. If we assume for arguments sake the air bearings are of equal dynamic stiffness, the ET2 will be inherently more stable than the Kuzma.

He assures me that there is no problem with the cantilever under these extreme circumstances.

This is an inadequate response.

To support your contention that adding mass has no deleterious effect, which cartridge designers have you sought an opinion as to loading up the cantilever in the manner you continue to advocate in this thread ?

Bruce Thigpen's patents clearly outline the benefits of the decoupled counterweight and lower mass.

Dover.

You need to research the difference between the two air bearing types. The Kuzma is unusual in its choice of bearing construction. So how am I wrong in my statement that the use of porous material appears to be unique?

This in no way detracts from the ET2 bearing. I was just showing that other options are out there.

At frequencies below resonance the cantilever is free to push the mass of the arm sideways. This does not defy physics, it is physics. In other words the cartridge suspension is stiff enough to accelerate the arm mass sideways. Think of a tension spring with a weight suspended at one end. This combination will have a resonant frequency. If you hold the spring end opposite to the weight and move it up and down at a frequency below resonance the weight will move up and down in sync with your movement. The spring will NOT stretch as a result of this movememt.

No, the video does not show the cantilever, that is why I asked him if it was a problem. I have to take his word on this that it is not, and resonance formula back him up. Further this confirms what I see when my arm is tracking eccentric records. I repeat the video is shown specifically to allay fears of problems due to high horizontal mass.

The Kuzma is unusual in its choice of bearing construction………… the use of porous material appears to be unique?

In his review on the Kuzma Airline, Michael Fremer also mentioned that the Airline use porous material in the airbearing, while the older, but similar designed, Rockport 6000 utilized a groove-compensated bearing, which has lateral grooves in the bearing wall.

He went on to comment that due to the difference in the bearing design, the much higher air-pressure used in the Airline didn’t necessary mean its bearing was stiffer.

It is also interesting to note that the arm on the Walker Proscenium turntable shares a similar design with the ET2, but using a fixed counterweight and much higher pressure at 45psi.

I believe Lloyd Walker is well known as a fanatic tweaker, who would not stop to squeeze out the last bit of performance from his turntable. So, why would he not use the decouple counterweight design (if he sees any advantage in it), or is that patented by ET?

Thekong
I don't know how long patents last, but would suggest the reason that Lloyd does not decouple the counterweight is simple.

It sounds better.