Eminent Technology ET-2 Tonearm Owners

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.

However the FR64 of course, has Eff Mass of 30-35gms (or more).

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.

I'm not sure if there is any (groove tracking) disadvantage in having Eff Mass too high, ie. Res Freq too low.

Sure, there may be issue with particular TT suspension or TT support resonances, but arguably not detrimental to good record tracking?

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.

I'm not sure if there is any (groove tracking) disadvantage in having Eff Mass too high, ie. Res Freq too low.

Sure, there may be issue with particular TT suspension or TT support resonances, but arguably not detrimental to good record tracking?

05-15-13: Richardkrebs
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.

05-16-13: Richardkrebs
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.

Richardkrebs, according to your own posts
05-15-13: Richardkrebs - There is a phase and amplitude problem at 3xFr
05-16-13: Richardkrebs - There isn't a problem at 3xFR
Of course I agree with your first statement. The second is wrong.

05-15-13: Richardkrebs
Note also, Bruce set up the arm with a "deliberately high Q" and low compliance cartridge.

Richardkrebs your statement is misleading.
Bruce added 18g of horizontal effective mass with the damping trough mechanism. You have added 62g of mass to your arm by adding lead and removing the decoupled counterweight.
Assuming your example of 9g cartridge and 32g of counterweight plus your added lead of 30g then;
The horizontal effective mass of the ET2 with damping trough is
Std ET2 - 25+9+18=52g
KREBS ET2 - 25+9+32+18+30=114g
If you believe that you can increase the horizontal mass of the ET2 from 52g to 114g and get the same results as Bruce Thigpen, then that is where you are wrong.

05-15-13: Richardkrebs
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.

Ok, so you disagree with me, then in the second sentence you agree with me.
I'll take the second view. If the fundamental determinant is horizontal effective mass, why do you expect the same results as Bruce Thigpen when you have more than doubled the horizontal mass with your changes to your ET2.

The other key issue with running high horizontal mass, far higher than recommended by Bruce Thigpen, is the increased tracking distortion that this causes.
I quote from Bruce Thigpen:

If the weight is coupled the system resonant frequency would be extremely low, a resonant frequency at 3Hz with a significant rise in response (6-12dB) results, which would affect tracking slightly because of the asymmetric position of the cantilever, we opt for splitting the horizontal resonance frequency into two points and lowering the "Q" which improves tracking.

More important than tracking, the intent was to reduce the modulation effects of low frequency energy (FM and AM) that increase distortion in the cartridge,

To reiterate, from my listening experience increasing the horizontal mass and removing the decoupling of the counterweight on the ET2 slugs the sound and the distortion can be clearly heard.

05-17-13: Ct0517
As I type this Ottawa to Toronto area of Ontario experienced a 4.8 earthquake – a little shakey.
Sort of like my JMW 12 unipivot. :^)

My local audio shop has been selling VPi’s for some years. In my experience if the arm is wobbling then it is either not set up correctly or perhaps the bearing needs checking.
As a matter of interest, the Aro is inherently more stable than the VPI and most unipivots as the bearing is a radius tip sitting in a cup with a defined radius. This provides damping of around 2db, is a true mechanical ground and is self centering. With the VPi the tip is upside down – the cup sits on top of the tip, so it is less stable, and is not a true mechanical ground.

Stereophile review ARO – June 1993
Unipivots have traditionally been only marginally stable, but much thought has evidently gone into the ARO's design. Lowering the counterweight to about record level has given the ARO excellent stability. This also lowers the center of gravity to below the pivot point, providing about 6dB of mechanical damping of the stylus. Another 2dB or 3dB seem to come from the bearing cup, which has a sapphire insert. The bearing is the ARO's stroke of genius. In other unipivots, a sharp pin is mounted to the turntable and the arm carries a cup which sits atop the pivot point. The ARO's arm carries the sharp tip, resting this atop a stationary cup: a true mechanical ground

I can run an extremely eccentric record or a warped record and the ARO remains incredibly stable – there is no wobble or change of azimuth when disturbed.