Eminent Technology ET-2 Tonearm Owners

Dover.
- The error you repeat, is saying that my arm exhibits a rise in bass response of 6-12db. I'm pretty sure that most of the readers here would not call 5Hz bass. I can't hear that frequency and my system certainly cannot reproduce it. The arm has always had some method of damping. This reduces the amplitude of resonance at Fr. If you ask BT, he will say that the amplitude falls away to be benign at 3x Fr. Just over 15hz in my case. A frequency which some may call Bass, but one which I doubt my system can reach down to either.
-The change in shape of the resonance curve I refer to is clearly shown in the graph BT published with the oil trough manual. It is not a smooth standard deviation type curve. There are bumps and hollows on the slopes. This is caused by other structures resonating at frequencies near the fundamental.
-BT does not increase the horiz effective mass by 18gm when he adds his oil trough and nor do I with mine. He adds 18gm to the total weight of the arm. The effective mass is increased by the weight of the paddle. Well under 1 gram on mine. This makes my arm around 96 gm when carrying the Shelter, not 114 as you state.
You repeatedly try to paint the weight of my arm as being an outlier in linear arms and that my arm is singular in being so heavy. It is not, as we have seen in this thread. Some fellow posters own these heavier arms. Criticize my arm and you simultaenously criticize theirs.
-BT uses a very elegant method to reduce the FM and AM interfearance in the audio band caused by a high ampltude Fr. He decouples the counterweight which reduces the amplitude at Fr. Other designers use another method, they damp the arms horizontal movement which also significantly reduces the amplitude at Fr. This by using an oil trough, the lead out wires, the air line or a combination of these. It is simply another method of dealing with the problem. Both are valid, both have their advocates and detractors. This is the nature of our hobby.
-Chris has clearly enunciated the improvemmets in the bass articulation when he applied my goose neck design. Could it be that the problems you hear in the bass region when you locked the counterweight were simply due to the compliance of the gooseneck being laid bare, combined with maybe insufficient damping?

TEST FOR STRUCTURE FEEDBACK ……. Start jumping up and down right beside your TT…….

Hi Ct,

The most extremely test of this sort that I have seen was that, while following your initial settings, instead of jumping around the TT, you kick on its stand! :-) 

It was performed on a Rockport Sirius III at the agent, and yes, it was pretty much silent from the speakers! That stand was actually an OEM pneumatic table by TMC, and I am using a similar one under my Capella II. Unless you kick it hard enough that the whole stand / TT assembly (roughly 400-500 lbs.) moves over the floor, you can hardly hear any thumping from the speaker indeed!

Hi Dover,

You have mentioned that too high a horizontal effective mass would result in a raised bass response by 6-12db. So, in what frequency range are we talking about (the Fr at below 12Hz?)?

I just wonder if the high horizontal effective mass is the only consideration here, and whether other factors, such as the design of the air-bearing, would make a considerable difference in the outcome. In short, does that only apply to the ET design, or also to the Rockport and Kuzma etc?

I asked because my Rockport 6000, already has a high horizontal effective mass of 80g (with the lightest counterweight, and excluding the cartridge), but yet MF found it lacking in the bass! The upgraded 7000 and Sirius III arms added even more mass to “cure” this problem!

Not meant to be argumentative, just want to learn more! Thanks!

The most extremely test of this sort that I have seen was that, while following your initial settings, instead of jumping around the TT, you kick on its stand!

This is not a test for Structure-Borne Feedback.
It merely places a Dynamic (hitting) sound source into a structure.
I have never seen a scientic correlation between 'Impact' sound sources and Air or Structure Borne sound sources?
It is like the ubiquitous "Boink Test" that some audio reviewers used to do........tapping on the plinths of their turntables to see how 'immune' the turntable is feedback?
Chris' test of jumping on the floor around the turntable is a little more viable as it transfers the impact-induced source into Structure-Borne feedback within the floor........ however the form of that feedback is quite different to that which our systems are normally subjected.
Any suspended floor system (timber or steel-framed or reinforced concrete) will be subjected to Structure-Borne Feedback because of the stresses and deflections caused by the structural spans.....as well as the materials used in the floor construction.
These stresses result in subsonic low-frequency Structure-Borne feedback which passes easily into equipment racks, support stands and into the turntable plinths sitting upon these racks/stands.
That's why a wall-mounted turntable shelf is the best way to minimise this.

These stresses result in subsonic low-frequency Structure-Borne feedback which passes easily into equipment racks, support stands and into the turntable plinths sitting upon these racks/stands.

Hi Halcro,

Thanks for the information! So, any idea what is the frequency range of these structure-borne feedback?

Thanks!

Hi Thekong,
In a suspended reinforced concrete slab......there can be frequencies from 5-10Hz and higher.
In a suspended timber-framed floor they could get up to 10-16 Hz but would not normally get as low as the concrete.
Of course....the 'creaking' we can often hear in suspended floor structures as they 'move' whilst we are in bed at nights......are of a far higher frequency.
It's really the very low frequencies doing the damage as Structure-Borne Feedback as they are indicative of 'movement' within the floor structure.