Eminent Technology ET-2 Tonearm Owners

It's funny how that little styrene I-beam I bought at the hobby shop 10 years ago works pretty well. I tried using less weight on the I-beam further out, but when I moved the arm in or out, the I-beam waved back and forth like a dog wagging its tail! I can't place the weight out the same length as the arm wand for sure.
Am I missing something?
-John

John,
While my longer beam with weight almost at end does seem to flex a little more than the shorter one, it is not excessive on my rig.  Two thoughts.   Are you using a double or triple spring on your beam?   If not, that may solve the problem.  Secondly, perhaps your hobby shop beam is just more flexible than Bruce's.   

Chris,
Interesting observations.   My first setup with new plank was the same as yours.  With only the molded weight I could only get out to an inch from the end.  With only my diy smaller weight I got out to within 1/4 inch from the end with further improvement.

Harry

Am I missing something?

What Harry said. +1

You are not using Bruce’ Long I Beam designed for the tonearm.
Getting one would allow us to do an apples to apples comparison.
Remember, I did try to get a hobby shop I Beam. The ones I found were not fit - too flexible, cheap, mass produced.

Bruce’ long I Beam is 3d printed. V2 should be ready in a few weeks.

Also
If your end cap is the original one, take it apart, and make sure it is still fit to take the extra stress the longer beam brings.

imo -
This is a cheap upgrade that affects the heart of the arms performance. The I Beam/weights. The most misunderstood aspect of this tonearm’s setup. Bruce has built the Long I Beam for the ideal length based on his testing.

All ET2 owners should be contacting Bruce and getting one.

thoughts on two or three open questions & i-beam
@richardkrebs:
- I'm looking forward seeing pictures of your bearing tower!
- I did not yet try the elevated bearing position with the original ET bearing tower, as there will be drawbacks stiffness-wise because of the (practical but) rel. narrow tripod feet of the design.
- I think a 20 degree angled piece of good wood (with a slit / hole for the cartridge nuts) would do the major part of adaptation.
- arm lift adaptation could be tricky.

- magnetic damping: "My" magnets are kitchen magnets. They are round and have a simple collar-shaped pole piece which focusses and intensifies the flux around it. This will make a considerable difference in efficiency regarding damping compared to a normal "open" magnetic structure.
The magnets need to be placed really close, not more than 1mm on the closest place. The flat magnet shape vs round bearing tube  is obviously not ideal. My feeling is that it kind of cuts the peak of the resonance. It sounds and feels a step more stable - i don't like the sound of too much damping anyway.
It's difficult to extrapolate Bruces experiences & comment to different implementations without exact descriptions.

- i-beam: I checked the rotation pendulum formulas to be correct about this: If one doubles the length of the i-beam one halfs the needed weight, because of double the leverage. But the inertia grows with a square factor: 0.5 of the mass x 2^2.This results in double the inertia and 0.7 of the resonance frequency. 
The whole double mass double spring system of the ET is very ingenious but also quite complex. It is a 4th order resonant system instead of the usual 2nd order one. With one short attempt :-) i did not yet successfully find the correct CLCL model for simulation.In the most simple view there is an i-beam resonance and a bearing tube/cartridge resonance, with a zone where the i-beams spring and the cartridges compliance work in series (the i-beam springs damping can control the cartridge/bearing resonance, if the i-beam  resonance is well chosen... ;-).Problem is seeing / knowing what each one does. Simulation? Empirism?... :-)
My techno-intuitive thought on this is:
- The lower the resonance of the i-beam, the wider the frequency range over which the bearing/cartridge resonance can be controlled by it.
- the higher the resonance, the closer together both resonances and the more resonant interaction instead of control.

Does Bruce have the model? Or should I ask my more MATLAB-experienced son?

Chris,
When you get a chance, I sent an off topic question to you by pm a few days ago.
Harry