Eminent Technology ET-2 Tonearm Owners

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.

Chris, thanks for Bruce's comments. It all makes complete sense, however my question is still not answered. I suppose its academic, but as a point of interest, I fail to see how air would NOT escape regardless of pressure. Air (like water) under any amount of pressue will choose the path of least resistance, so even though the air delivered at the "ideal" pressure will "surround the spindle 360 degrees", some air will still escape out of either end of the spindle; there is no gasket or blockage to stop it.

Re Dave's comment about air bearing stiffness: with my HP 2.0 bearing and Wisa pump, if I push on the spindle sideways, it takes very little force to cause the spindle to rub inside the manifold. With the Medo delivering 17-19 psi at the arm (yes, it will do that), it takes a considerable amount of sideways force to cause it to rub. The bearing is MUCH stiffer with the Medo, with a resulting major improvement in sound; particularly in the areas of dynamics, bass tautness and speed, and soundstage detail and stability.

Hi guys,

I talked with Bruce yesterday. My 2.0 HP manifold is two weeks off. There are no 2.5 manifolds nor setup jigs available right now, but there are tentative plans to make a production run of both in the next 6 months or so. Bruce confirmed that the 2.0 HP manifold is a better match for medium/high compliance cartridges and the 2.5 is a better match for low compliance carts (difference in horizontal effective mass with the 2.5 being heavier as noted previously in this thread).

We discussed the topic of air pressure and air escape. My interpretation of the conversation is that it is normal to be able to hear some amount of air escaping from the bearing and also to be able to hear a low-level air noise at high volume with your ear to the speaker (Chris's pump test). The amount of air escaping and thus the audibility will increase with higher air pressure for a given bearing clearance, consistent with my experience.

After extended listening comparisons, some including my golden eared wife, I have decided that changes in air pressure are audible (similar in scale to VTA changes) and our preference changed with the recording. Keep in mind that this is with the stock 2.0 manifold. Some instruments within the soundstage move forward at higher pressures, creating a better delineated front-to-back separation, but the overall sound is less relaxed and natural, with a change for the worse in tonal balance, particularly on piano. Ended up back at 3.6 psi (at the arm) for best overall performance with the stock manifold. Bruce has said this to me consistently over the years and, being the hard-head that I am, I had to prove it for myself and finally have the proper quality and control of the air system to feel confident in this conclusion.

As always, this is MY preference in MY system and YMMV. I feel certain that all this will change with the introduction of the HP manifold, where the smaller orifices and tighter bearing/spindle clearance will eliminate the downsides described above at higher pressures and further enhance dynamics, bass performance and soundstaging as Frogman describes.

Dave