Eminent Technology ET-2 Tonearm Owners

My thinking on why pressure irregularities have such a large effect is this. It is to do with the way the air enters the bearing manifold. This thru a small single hole. It then circulates around the sleeve and enters the 14, from memory, threaded and loosely plugged holes exiting around the spindle. Each bleed hole will see a slightly different inlet pressure because their is a dynamic flow around the manifold with associated pressure drops. If there are pulsations in the air stream this will be manifest as slightly different flow rates into the manifold and thus pressures seen by each of these holes and the flow rate thru them. This would cause the spindle to chatter. When I built the replacement manifold, I planned to interpose a finely sintered metal tube between the air inlet and the sleeve. The idea being to force the air to more approximately enter the sleeve area at all points simultaneously. I didn't do this because it made the diameter of the manifold too large and it would have fouled with the platter and I didn't think that it was a big deal. I do now.
The walker arm manifold has 4 air inlet points. Maybe they have looked at this issue and used multiple inlets to help reduce its effect.

Richardkrebs,
On the one hand you say that the air bearing is rigid at audio frequencies, but now you speculate that the arm is prone to chatter due to "pressure irregularities". You also claim that the pressure irregularities are audible.
The two theories are mutually exclusive - they cannot both be true.

06-06-14: Richardkrebs
If there are pulsations in the air stream this will be manifest as slightly different flow rates into the manifold and thus pressures seen by each of these holes and the flow rate thru them. This would cause the spindle to chatter.

You do Bruce Thigpen a disservice.

06-04-14: Richardkrebs
Below is a copy of a mail I received from Bruce T many months ago.

The resonance of the air cavity is over 500Khz and does not manifest itself on the surface of the bearing, it is a well damped liquid bearing.

I used three measurement methods when developing the tonearm, accelerometers, strain gages, and the simplest and most effective was the use of a second tonearm to play parts of the tonearm under test while playing a record.

Please advise what testing you have done that would confirm your theory. The ET2 manual clearly states that Bruce goes through a design process, supported by principles of physics and sound engineering, includes mathematical modeling, the production of prototypes and thorough documented testing before his products go to market. There is no speculation or guesswork involved.

The ET2 has evolved from the 1st incarnation that utilized low pressure low flow bearing, then with the advent of customers using higher pressure pumps ( the WISA300 for example) Bruce redesigned the bearing for high pressure low flow air supplies. Bruce will also custom build for specific air pumps and provide advice on cartridge compatibility with each of the options.

It is abundantly clear that each bearing has an intended set of parameters with regard to pressure and flow. You have discarded the original ET manifold housing, discarded the decoupled counterweight, discarded the horizontal moving mass targets that the ET design is predicated upon, and may well be running a pump that is not optimised with your particular bearing. Unless you can provide some documented testing as Bruce does on his website, your comments can only be described as speculative at best.

Dover wrote:

".... Bruce goes through a design process, supported by principles of physics and sound engineering, includes mathematical modeling, the production of prototypes and thorough documented testing before his products go to market. There is no speculation or guesswork involved."

You say "I agree with Bruce's observations."

Please advise what testing you have done to arrive at that conclusion.

It should be verifiable engineering: no speculation, guesswork, or internet regurgitation will suffice.

RK - If this is correct then it may be better to have the regulator remote from the arm. A long length of soft hose to the arm then helping to smooth out the regulator pressure irregularities. Obviously more testing is required. One test would be to fit a surge tank after the regulator in a rig with a regulator close to the arm. Or simply add another long length of soft tube which would be so easy to do....Chris.

Hi Richard - the extra in room regulator I use allows for AB testing of this at anytime. Long tube versus short going to the tonearm. All I have to do is open /disengage the in room regulator and it functions as a filter only, so in effect is a long tube to the pump. Let me explain something about my Timeter pump and it will make things more clear.

From my experiences most pumps push air and the user is at the mercy of the environment as far as the quality of the air output goes. Meaning if the air has any moisture and particles, filters are needed to trap them. The ET tonearm's maker resides in Florida where it can get really humid. The ET 2.0, 2.5 tonearms if they had a choice would probably choose to live in Arizona; or in a room where there is forced air heating. They like the air dry ....very, very dry.

My Timeter was designed for human use and has performance settings as far as how humid I choose to send air out at.
Example:
If you are in a room and want to be comfortable you would probably prefer air around 55-60 which is in the middle of the humidity scale to be really comfortable. The Timeter - with my T valve regulator at the pump (see pics on my virtual page) can be dialed down/tightened so that it exhales dry Arizona like air - even if the room it is in is at 80 % humidity. No other pump/compressor I am aware of does this and the ET 2.5 loves dry air. I have never seen a DROP of water in the in room regulator bulb other than the one time there was a blockage. Now the pump does need to work harder to produce moisture free air in a humid room. For three seasons late fall, winter, early spring the basement stays fairly dry with the natural gas heating. Once summer kicks in, it takes only 3 days for the basement to start feeling like a basement again - humid and damp. This is also the time when I make an adjustment to the Timeter by tightening down the regulator at pump's outlet so the performance gauge reads in the green zone. Green zone for this compressor/pump means the system is running efficiently and no moisture is being sent down the line. It expels the moisture like a car's AC at the bottom of the pump.
It used to do 50 psi when new. It probably does around 45 now and I bought it used many years ago. With the in room regulator in engaged mode - I send down 21-22 psi from the pump and I steal 19 psi with the in room's regulator. So pressure drops at the arms location on purpose (Dover alluded to this in one of his posts) The excess air goes into the atmosphere beside the pump. So in fact I bleed out 25 + psi.

I prefer to run with the in room regulator functioning as a regulator with the short run to the arm. It is I believe more precise and the long tubing just before it acts like a second, redundant surge tank in addition to the timeter's own built in surge tank . Redundancy is good. Remember I am in the business of contingency planning/risk mgmt - redundancy is ingrained in me. You can call this mad, or you can call this anal.

The in room regulator is set for 19 psi. Along with being more precise/consistent, its bulb area also stabilizes the air (temperature) so it is same as in my room. Your average listening room goes up in temp as time goes by. Its important for the air imo going into the manifold being same temp as your room - just really dry.
The in room regulator also gives me a visual of what is going on. Kind of like driving a car with real engine and radiator temperature gauges. I want to know what is going on. Sorry for the long post.

Cheers

You can call this mad, or you can call this anal.

So go ahead and call me mad or call me anal.......just pls don't call me Dorothy.....I am not worthy.