Eminent Technology ET-2 Tonearm Owners

The kong,
I am on a project at the moment and cant get back to the article but I believe it was a direct quote..I can confirm later if you like.
Meanwhile I see in the stereophile review of the Sirius arm: August 2000

The Sirius tonearm tube should be virtually inert, made of a constrained-layer-damped, 8-ply sandwich of carbon fiber and epoxy composite: four layers on each side of the damping material. Inside is a second tapered carbon-fiber tube, the space between the two filled with yet another damping material. The materials, construction, and aerospace pressure-laminating techniques create an armtube said to have the stiffness of steel, yet weighing only half as much as a comparable aluminum tube.

Another single billet of aluminum alloy is machined to make the bearing mount, tonearm clamp, and counterweight assembly. This is a big improvement over the design of the Series 6000 arm: the structure is said to be 20 times stiffer than before, yet no heavier.

This suggests the armtube is more rigid in the later models but lighter.
Fremer also paraphrases Payors comments on the ET as follows:

The air-bearing scheme—comprising a stationary bearing and a moving rail—invented by Eminent Technology's Bruce Thigpen and used on his tonearm as well as on the Maplenoll and Walker Audio turntables, comes closer to being truly "linear" because the bearing can be more highly pressurized. But the rail's large horizontal moving mass creates another set of problems. And a true linear tracker completely eliminates a pivoted arm's inherent tracking error and skating-force vectors.
All of which, to Payor, means that his arm is the best currently available, and the true state of the art.This is extremely important, as low moving mass is critical to the performance of a linear-tracking arm.

The use of English can be deceptive - large, heavy, higher mass. We see that Thigpens "heavy" armtube is only 2 gm higher. Payor may be referring to the physically large area of the arm/bearing tube or he may be referring to the actual mass, but it seems clear to me that he favours minimising the horizontal mass.

Furthermore, if you read the full article you will see that the bearing design and parameters and moving masses involved are mutually dependent as they are on all airbearing tonearms. I dont believe you can convert a Kuzma to a low mass or an ET2 to a high mass arm without redesigning the air bearing.
The resonances of the bearing itself can end up in conflict with the resonances generated by the arm/cartridge compliance.

This is where Richardkrebs continues to get the maths and physics wrong; there are multiple resonances involved, and the multiple resonances can quickly accumulate when overlapping - they are not a single spike at one frequency. This is what is happening with the ET2 when Bruce measures a 6-12db lift in the bass when coupling the counterweight - which effectively doubles the horizontal effective mass.

Richard re: damping trough. Thanks for bringing this up. I have completed my game of musical turntables, so I will revisit the damping trough now. It can get messy when moving an ET2 from one TT to the next with a trough of oil attached !
My main TT is completely changed from the last time I used the fluid so will try it again.

The fluid that Bruce uses in the trough is 8000 centistoke silicone fluid. I ordered some today from him along with the adhesive. Will post impressions later.

Richardkrebs - My apologies in advance if this topic has already been covered in the thread. Too many posts to read thru.

Richard - This thread is unfolding like a book. Very relevant ET2 information was discussed early on and throughout. I encourage a read through. If for no other reason than to understand and gain insight into why some members made the decisions they did.

Cheers

http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1325551242&openflup&67&4#67

Thekong - In the later, upgraded, models of the Rockport 6000, i.e. the 7000 and the arm on the Sirius III, AP chose to use heavier armtubes. I believe all 3 arms used the same air-bearing, and their armtube clamping systems are of the same (or very similar) total weight, but the clamping system on the Sirius III are said to be 20 times stiffer due to the improved design.

....Granted, AP might have added the weight to help (add) more in the vertical, rather than the horizontal, moving mass, for better matching with mid/low compliance cartridges, but added weight he did! That may just be a matter of compromise!

Thekong - thanks for sharing this info. Are you able play high compliance cartridges on your Rockport arm ? We know the heavier ET2 armtube affects the horizontal mass as well.

but the clamping system on the Sirius III are said to be 20 times stiffer due to the improved design.

I am assuming that this would limit the type of cartridges the Rockport Sirius III tonearm can now play as far as compliance is concerned ?

Cheers

Ct0517 - We know the heavier ET2 armtube affects the horizontal mass as well.

this was worded badly. This thread is too old to allow for corrections. I wanted to say the arm wand weight lighter or heavier, affects both the vertical and horizontal inertia at the same time. This is really important.

The 6000's relatively low vertical effective mass put its resonant frequency above the ideal 8-12Hz region with moving-coil cartridges of average weight and typically low compliance, causing the bass to begin rolling off prematurely. Andy Payor solved the problem on the System III Sirius arm—see my analogsourcereviews/review in August 2000—by adjusting the mass so that the arm's fundamental resonant frequency would be compatible with a wider range of cartridges.

Hi Dover,

Thank you for taking the time to check!

The above is a quote of MF from his review of the Kuzma Airline. By “adjusting the mass”, I am sure he meant “adding the mass”! Both the 6000 and 7000 also used carbon-fiber armtubes, but not as sophisticated as the one on the Sirius III.

But then, I agree with you that the weight increase of the armtube would definitely be less than 10g, and most likely in the 3-5g range.

Actually, by looking at the photos alone, it is hard to believe the massive armtube clamping system on the Sirius III has the same weight as that on the 6000. But, I have no reason to doubt AP’s claim!

Sirius III

6000

Hi Ct,

While I don’t have any really high compliance MM cartridges, I have no problem, “sound wise”, matching the 6000 to the relatively high compliance VDH Colibri! Yes, the combo is relatively lean in the bass/mid bass, but I consider it the character of the cartridge.

Now, I say “sound wise”, because while the sound was fine, I (and also my friend who had the same combo) found the Colibri’s cantilever slightly off-centered after a period of time. This I took it as the fragile nature of the Colibri’s design.

MF repeatedly stated the 6000 was relatively bass shy compared to the Sirius III and Kuzma Airline; I believe a major reason was that the stock pump just couldn’t supply enough pressure. As I mentioned before, I believe the 6000, 7000 and Sirius III shared the same bearing, but the 6000’s stock pump (probably due to cost constrains) could only supply a max pressure of around 11 psi, and without any surge tank. Once I upgraded it to a June Air compressor with integral surge tank, plus additional pressure regulators, supplying 34psi to the 6000, its bass weight and definition improved considerably! As I understand from the Rockport agent, the Sirius III’s arm also uses around 32-35 psi!