Eminent Technology ET-2 Tonearm Owners

Been thinking about the "air escaping" issue. Seems to me that what has not been made clear enough is that there will be air escaping no matter what the pressure is. While it is obviously true that an air bearing will be optimized for a specific pressure range beyond which some of the mentioned issues concerning resonance may occur, we also know that dealing with resonance is a tricky issue and a bit of a black art which involves the rest of the system (specific cartridge and its resonance characteristics, and even things like how much torque one uses to tighten the adjustment bolts on the arm). Clearly, there will be a point when too much, or too little pressure, will be simply too much/little, but I believe that there is a fairly wide range beyond the "design ideal" which is "system" dependent and which, as always, is determined by what simply sounds best.

Someone explain to me how in a "captured air" bearing design air will NOT escape regardless of the pressure delivered to it. I think that when we talk about being able to hear it, it is simply that, the point at which it becomes audible; not that there is no air escaping prior to that point.

Dgarretson - The air pressure at this threshold depends on the weight of the selected wand and counterweights.

Dave G - thanks for that interesting info re: Trans Fi tonearm.

Would it be correct to assume an owner of a Transfi needs a pump that is variable in its PSI for the different arm wands and cartridges ?

With the ET2, ET 2.5 one psi is used it does not change as the Spindle/Manifold remains the same. Different armwands and I Beam adjustments - single, double, triple springs are made for the different cartridges.

yes two very different designs.

Frogman - Someone explain to me how in a "captured air" bearing design air will NOT escape regardless of the pressure delivered to it. I think that when we talk about being able to hear it, it is simply that, the point at which it becomes audible; not that there is no air escaping prior to that point.

Frogman - I remember talking to Bruce about this some years ago.
I sent him an email and also confirmed things in a call this morning.

The ET2, ET 2.5 is a captured air bearing system meaning

"Air surrounds the spindle in a circle 360 degrees"

I did ask him about the type of air bearing tonearm that uses a cup bearing which is floated.
We did not reference the Trans Fi or other tonearm just the type of design.

- his response to me on the phone-
the more air and it will become floppy. So just enough air to float is required - supporting what Dave G said.

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Some more information - this was from my actual email - his response in quotations.

Hello Bruce

I have two general questions.

If we use my ET 2.5 as an example that you set up for 19 psi. A continuous 19 psi air flow is sent in. Can we assume the spindle uses all 19 psi to work optimally (or is it a percentage of this amount)


"The manifold is optimized for the design pressure, the pressure at the surface of the spindle is a percentage of the inlet measurement, this is by design."

If someone has a 20 year old stock ET2 designed for about 3 psi and decides to pump in 15 psi. The extra air will just escape around the edges of the manifold and at a rate that can be heard ?

"The extra air will escape, but the rate of escape will not be that large from an operational point of view, but the escaping air is usually audible which causes one problem and the air can cause a push back at the extremes of travel. "

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Bruce really like the idea of the pump test.

I then asked him about all the ET2's on ebay and other sites that people are buying used - many come with no pumps. His advice was to start low with them 3 psi and go up. Whatever PSI it takes to float the spindle properly and work is the PSI that should be used.

A case in point my ET 2.5 is designed for 19 psi. I told him if I start lowering the PSI it will start mistracking a few PSI below that. He confirmed this and this is by design.

I would think that the favorable qualities of a captured air bearing in this application are maximum bearing stiffness(a function of air pressure) and minimal air turbulence(a function of air velocity through the bearing and surface friction.) The best one should have the tightest clearance in order to minimize air loss and turbulence attendant with velocity.

In contrast, the stability of the Trans-Fi bearing is not a function of stiffness, but rather of aerodynamic balance. It functions like a glider wing that requires only the minimal air pressure and flow to obtain lift. It operates in a horizontal plane, rather than in 360 degrees as with a captured air bearing. The air velocity through the bearing is higher than with captured air bearing, but as air pressure is low, turbulence is minimized. In this particular instance, the more pressure, the higher the lift, the sloppier the bearing.

Chris, Trans-Fi needs only a 4 psi aquarium pump, smoothing tank(s), and a good brass needle regulator. No need for an evaporator tank, given the small 2-3 psi differential between the pump and the tonearm. One may be tempted to think of it as a poor man's solution, however in my view its design has fewer problems to solve than a captured air bearing and illustrates the virtue of KISS.