Eminent Technology ET-2 Tonearm Owners

Chaps...I'm not an ET user nor an Aro user, but I do use both a 12" unipivot + an air bearing linear tracker, so if I could be permitted to offer a humble opinion, hopefully useful to the topic ;)....

In this game, sometimes we tend to think about what we SHOULD hear, rather than what we DO hear...

In principle, the tolerance gap of a air bearing leads us to think that an air bearing will be therefore compromised sonically - ie. because it will never have solid bearing contact. However I hear no lack of 'leading edges' with a linear tracker. So what is going on?

On the topic of 'leading edges', I think a 'square wave' is an appropriate analogy. The leading edge of square wave (rise time/slope, overshoot control...) is determined primarily by the HF component of the signal/tone. In the same way, the perceived 'leading edges' of sound is poor, if the HF harmonic component of music signal is compromised.

A unipivot typically has excellent HFs, owing to absence of 'bearing rattle'. I also hear excellent HF tone & extension with an air bearing tonearm. Go figure...

The explanation I think is that, at groove modulation frequencies, it is not the rigidity of the bearing that is key, but rather the inertia of the tonearm, as 'seen' by the stylus, that is key. From this perspective, a pivoted tonearm rotates freely, ie. has very low (rotational) friction.... and a linear tracker also has low (linear) friction. Both are similar... but from the viewpoint of the stylus in groove, 'inertia' or Effective Mass (at groove modulation frequencies) must be high - adequately high to reproduce LF signals without resonance/loss of power delivery.

Contributes to the discussion I hope.

(Apologies if this is old ground, I haven't managed to read all 700 pgs ;) )

05-15-13: John47
Bruce Thigpen:
"The ET-2 with the
damping trough will exhibit almost perfect low frequency phase response."
You don't like the ET-2 set up to have near perfect low frequency phase response?
Thats fine, its a free world, but it means you accept/enjoy DISTORTION.

No I dont believe Bruce Thigpen does enjoy distortion. On the contrary Bruce Thigpen has cleverly designed an arm that tracks superbly and can be fine tuned via the adjustable VTA, Azimuth, and decoupled counterweight.
Bruce Thigpen does not add 60g+ of horizontal effective mass and remove the decoupling of the I Beam.
The perfect phase response that Bruce obtains with the damping is achieved by operating the arm within its design parameters. Keeping the horizontal mass as low as possible is part of the design. Adding 30g of lead to the arm and removing the counterweight decoupling will indeed create significant distortion, including an inflated bottom end and phase anomalies, but that is not how Bruce runs the arm.

Pseudo science from Dover:

"removed their fluid damping and replaced it with electromagnetic damping which has the benefit of not inhibiting movement until the movement happens."

Pseudo science: its identical with fluid damping - there is no damping unless there is movement (same with the dampers, so called shock absorbers, on your car. Drive slowly over a speed hump and the whole vehicle is raised, ie there is no movement, and no damping).

Dover.
Secondary resonance? You mentioned this twice in your post 05-15-13. The frequency numbers you used were 3x Fr for this. The 3x Fr figure is the multiplier used by BT where he considers the amplitiude and phase anomolies above Fr have fallen to a level that is benign. Think a normal distribution curve. In our industry, we use a 6x Fr multiplier since we operate in a much more conservative environment.

There is no 6-12db increase in amplitude at 3x Fr or even Fr. The arm is damped with an oil trough. See the graph and read the technical notes from BT, posted by Chris on 05-14-13. Note also, Bruce set up the arm with a "deliberately high Q" and low compliance cartridge.

You let slide and error in my calcs because other parts of the arm have their own resonance. Sorry No. See BT's own formula for calculating horizontal Fr. It does not take into account these other structural resonances.
That said these other resonances can have an effect on the shape of the resonance curve but the fundamental determinent is the horizontal mass.

There are 2 possibly 3 structures in a standard ET who's own resonance is low enough to have this impact. The decoupled counterweight, which is deliberate. The relatively compliant gooseneck and the o'rings in the manifold. The o'rings are a maybe since they typically allow movement towards and away from the record, not laterallly.
(Anyone interested in observing how compliant the goose neck is could try this test. Do it at your own risk!
Lift the arm with the lifter and put the stylus guard on. Travel the arm fully inwards and then lightly push the spindle where the wiring plug is against the bearing sleeve. Now lightly pull the cartridge end of the wand towards the outer edge of the record. You can clearly see deflection of the wand. The goose neck is flexing. If you are able to let it go quickly, you will see it momentarially oscillate. If chris did this with the aluminium goose neck he would need to literally bend the wand to get any deflection.)
All three of these structures have been altered (stiffened) or eliminated in my arm since in my opinion they all compromise "leading edge" and have other negative consequences.

The other compponents of the standard arm have, IMO less impact on leading edge performance with the airbearing having none at all. It's resonance is in the 100s of Khz, way outside the audio spectrum. Spock15's experience with his air bearing arm seems to support my view. However it is the cacophony of all of the individual resonances amongst many other factors that makes up the "sound" of the arm. On that front we agree.

Spock15
I currently own an ET2, Naim Aro & Hadcock unipivot and have just sold off my Bluenote Borromeo ( Titanium tubed unipivot ).
I hear a crisper articulation of the leading edge with all three unipivots. It's not large. The Aro is better in this regard than the Bluenote & Hadcock. I do agree with you that effective mass, both horizontal and vertical contribute to the "squarewave".
With regard to the high horizontal mass the standard ET2 has a very high horizontal effective mass as standard ( 25g plus the weight of the cartridge ) compared to a pivoted arm.
Richardkrebs has advocated adding 60+g of horizontal mass by adding lead to the bearing spindle and removing the decoupling mechanism of the counterweight. With the ET2 the decoupling of the counterweight is part of the strategy to keep horizontal mass not too high.
Bruce Thigpen has measured, not theorised, actually measured on the ET2 a 6-12db lift in bass response when increasing the horizontal effective mass by 30g ( removing the decoupling ). From what I have actually heard, in a real system, since I have owned an ET2 from the mid 80's, increasing the mass slugs the sound and robs the music of musical pace and timing. Most of the contributors on this thread ( Frogman, Slaw, Ct0517 & myself )have found big improvements when carefully tuning the decoupled counterweight, as predicted by Bruce's testing.
By the way I still own a Dynavector 501 which has a very high horizontal effective mass, and whilst the bass is quite punchy, the musical timing, soundstaging, and resolution is well down on both my Naim Aro and Fidelity Research FR64S ( yes I own 2 of these as well ).