Eminent Technology ET-2 Tonearm Owners

05-14-13: Richardkrebs
The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping.

The adding of lead mass will increase distortion due to the higher inertia of the arm. Basically you have added a peak resonance in the bass, then tried to tame it by adding damping. Both the added mass and fluid damping will increase inertia, and compromise the ability of the cartridge to track the grooves accurately. On an eccentric record this will be even worse. The Krebs arm has some 65g of horizontal effective mass added - an increase of inertia close to 300%. This increases cantilver flex and distortion as per Bruce Thigpens commentary.

05-14-13: Richardkrebs
With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz.

This is not true. Most tonearm designers target a FR of around 8-12hz. This is based on an assumption that most systems dont produce much response below 20hz and footfalls are in the zone of around 2-3hz, dangerously close to your 5hz.
Secondly, the increased distortion from the added inertia of the arm resulting from the increased horizontal effective mass certainly impacts the audio frequencies.
The phase anomalies from the increased distortion on the cantilever can be heard quite clearly in a system that is reasonably transparent and quick. Furthermore the peak resonance at 2-5hz that you quote can invoke instability in tracking, its the same as walking past a turntable on loose floorboards.

05-14-13: Richardkrebs
In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust.

Basically what you are saying here is that you like the sound of the ET2 with additional drag inhibiting the free movement of the arm to track the grooves. In my experience this slugs the sound. Other users have found improvements by removing this drag - they have removed their fluid damping and replaced it with electromagnetic damping which has the benefit of not inhibiting movement until the movement happens.

05-14-13: Richardkrebs
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams.

Your mathematics is incorrect :
The bearing spindle without arm/counterweight is 14g
The aluminium arm is 11g
The CF arm is 17g
The Magnesium arm is 19g

So the total horizontal effective mass of your 9gm cartridge on a standard ET2 arm with a 32gm decoupled counterweight is:
9g(cart)+11g(arm)+14g(bearing spindle)=34gm

The total horizontal effective mass of your 9gm cartridge on your altered ET2 "Krebs arm" with 30g of lead added and the 32gm counterweight coupled is:
9g(cart)+11g(arm)+14g(bearing spindle)+30g(lead that you added to the spindle)+32g(counterweight that the cartridge now sees because you removed the decoupling)=96g

Therefore you have increased the horizontal effective mass from 34gm to 96gm, an increase of 62g.

I cannot see how you get to 6gm in your maths.

Coupling the 32g counterweight adds 32g to the horizontal effective mass.
Adding 30g of lead to the spindle increases the horizontal mass by 30g, even when placed inside the bearing.

05-14-13: Richardkrebs
If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams.

This is another area where the underlying assumptions are misunderstood. Bruce's recommendations documented in the ET2 manual on low compliance cartridges is carry as little weight as possible as far out on the I Beam as possible. This keeps the horizontal effective mass low but increases the vertical effective mass. It is not recommended to load the I Beam with all the counterweights if one can shift the counterweights further out.

05-14-13: Richardkrebs
.. if my heavy ET has problems with cantilever flex, bass boost, phase shift and so on; so do the other heavy arms. Rockport, Walker, Kuzma. This because the horizontal effective mass is solely determined by the total weight that is moved sideways at the frequency of interest, since all of these designs are virtually frictionless.

Thats correct and thats why the lower mass ET2 has a big advantage over the heavy arms when kept in its standard format.

The level of damping of course changes all this.

This is not correct. The damping may ameliorate the amplitude of the resonant peak, and result in less bass boost, but the high mass still provides an inertia, a resistance that the cartridge has to work against to track the groove, particularly on eccentric records. It is this inertia that causes the cantilever to flex and increase distortion.

Dover.

My calculation of weight delta was based on how much weight the air bearing has to carry. Not the horizontal effective mass. You voiced concern that I had taken it outside its load carrying capability. My calculation is correct since the bearing is supporting the weight of the counterweight, it is designed to take the heavier magnesium wand, the full counterweight complement and heavier cartridges.

Re heavy arms. I assume you are saying that ANY heavy arm, and this includes the Rockports, Walker and Kuzma have serious problems with distortion. Further, by implication, you are saying that the owners of these arms are deaf to these distortions.

We will have to agree to disagree on where we should target the horizontal Fr. In Bruce's paper on the oil trough he talks about the effect of Fr being apparent at 3x its frequency. Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good.

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.

BTW, as you haven't run an ET2 for heading towards two decades, isn't your credibility suspect?

05-15-13: Richardkrebs
Dover.
My calculation of weight delta was based on how much weight the air bearing has to carry. Not the horizontal effective mass. You voiced concern that I had taken it outside its load carrying capability.

Optimum load capacity. You have added 30g of lead to the mass the bearing has to carry. This has 2 negative effects - it pushes to mass to the extreme and one would redesign the bearing if one were knowingly going to operate the arm at a higher mass level. Secondly the added mass will impact the shearing forces involved - the arm is not frictionless and the bearing is not absolutely rigid - these are some of the reasons why users are hearing different results with higher pressures.
As a point on your calculations on FR I led slide the error in your calculations - the bearing has a resonance, the bearing tube has a resonance and the total resonance will be a sum of the resonances inherent in the arm. One really needs to measure the resonances to see whats going on , thats why Bruce does extensive testing. The maths you are using for FR calculations is not the complete story.

05-15-13: Richardkrebs
Re heavy arms. I assume you are saying that ANY heavy arm, and this includes the Rockports, Walker and Kuzma have serious problems with distortion. Further, by implication, you are saying that the owners of these arms are deaf to these distortions.

I think you should use the word preferences, when making judgments on other folk, but certainly they may well be. Some folk like fat bottom ends others prefer speed and musical timing. For me music is about timing and nuance - I can certainly hear the slugging of the sound and loss of musical timing when adding too much horizontal effective mass to the ET2 as others in this thread have also found when they removed the decoupling from the I Beam.
You may also like to read the comparison of the Kuzma to the Walker in the Absolute Sound mag December 2006 where the reviewer articulates the differences - the Kuzma being dark and solid vs the Walker having more of "the "gestalt" of a live concert, more lifelike presence of instruments, their colors, their dynamics, and the space they play in" of the Walker "fuller, more realistic in tonal color, bigger, bloomier, wider, deeper, more layered in soundstaging, and a bit more authoritative dynamically".

05-15-13: Richardkrebs
Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good.

Depends how big the amplitude problems are. Some of the heavy arms you have mentioned have additional measured resonances at 100hz & 200hz.
In your case you you have reduced the theoretical resonance from 8.08hz to 5.17hz. so yes you have a small residual at 24hz in a standard unmodified arm - but this is outweighed by the amplitude of the resonance being much higher when you added 62g of horizontal effective mass. Furthermore that small secondary resonant peak at 24hz with the standard arm can be dialled down with careful tuning of the counterweight spring. I very much doubt whether many systems are truly flat to 20hz in a real home environment.
In your case you have shifted the secondary resonance from 24hz to 15hz, but have increased the amplitude of the 15hz resonance substantially - probably 6-12db higher in amplitude compared to the smaller resonance at 24hz with the arm as standard.