Eminent Technology ET-2 Tonearm Owners

Richard

The resonance frequency figures we have from BT that we have discussed here.

ET 2 (5 - 6 hz)
ET 2.5 (2 - 3 hz) due to the larger spindle plus weighing a little more - not sure what the actual gram number is.

So at 3x the resonant frequency we are loosing around 15% of the groove modulation, as the arm is still at this point moving back and forth sideways slightly.

This is not a problem provided this 3 x resonant frequency is not a valid audio signal. Actually you would need to extend the graph out to around 6x resonant frequency before the transmissibility was approaching 0. Until we reach that point, part of the low frequency groove modulation goes into moving the cartridge and arm sideways and not into generating an output voltage.

Based on what you are saying Richard - does this not then mean:

ET 2.5 = 6 x 2.5 hz (midpoint for the ET 2.5) places it at 15 hz

ET 2.0 = 6 x 5.5 (midpoint for the ET 2.0) = 33 hz

The number 6 that you multiplied the resonance frequency by. Would this number need to change for a really high compliance versus really low compliance cartridge to be more accurate ?

Chris.

The 6 x multiplier is a factor extrapolated from the graph I posted the link to. 6 x being a figure where the resonant structure would likely be still, with some safety margin. It would not change with cartridge compliance. But the system resonant frequency could change outside the published figures if you were to use an outlier cartridge.
A really stiff cart would push the resonant frequency up, moving further into the audio band. A really floppy cartridge would push the resonant frequency down, with a real risk of problems due to eccentricity.

Hi Ct,

During the testing phase, my ET2.5 will be set up with a ClearAudio Sigma. When the final comparison comes, I will be using the Ortofon A90 between the Rockport and the ET.

I am using 15psi for the moment with a compressor together with its integral surge tank, and 2 regulators before the air enters the arm. I can easily increase the pressure up to 34psi, which is what I am using for the Rockport, for testing.

About the counterweight, the aluminum square is tapped and the threaded rod just screwed into it. I “reinforced” it a bit with superglue !

Hi Richard, Dover,

I don't have the knowledge to even start participating in the discussion on the physics of moving mass, however I have some general observation.

It seems to me all the other arms that we have discussed recently (Airline, Rockport, Terminator, Walker) have much higher horizontal mass than the ET with the decoupled counterweight.

Take the Airline as an example, if its horizontal mass is 100g, then it is even higher than the 85g of Richard’s modified ET. While I don't have the Airline myself, 2 of my friends have it for a couple of years already and have no problem with cartridge damage. I have also never seen any actual negative report regarding this matter on the internet. The same applies to the other 3 arms.

Looking at the massive construction of the Airline, I couldn’t help but wonder whether Kuzma could reduce the size and weight somewhat without sacrificing rigidity. They didn’t do so appears to me that they have no concern on this high horizontal mass being detrimental to the performance, or worst yet, causing cartridge damage.

Could all these arm designers be wrong when their products are getting very positive comments from actual users, not just magazine reviews?

Of course, all these other arms, with the exception of the Terminator, are very expensive, so they most likely are being matched with highend MCs with medium to low compliance. Maybe the high horizontal mass is less of a problem in these conditions?

Thekong -

I would ask you to consider the looking at this the other way round. Just because everyone says something sounds the best, is it. Most people thought the world was flat at one time.

My experience with high end audio is that most audiophiles dont hear much and have no sense of timing. Products that produce "impressive" bottom end or top end sell well, and even get reviewed well. Of course it's like car reviews, the next one comes out and all the flaws of the last model get written up.

If we look at the wealthier clientele that Kuzma is targetting, most of them will have large multidriver speakers, eg Wilsons etc. Large full range speakers are incredibly difficult to get coherent in a domestic environment. Alternately we get the wealthy single ended group - these are just tone controls, pleasant, but usually at the expense of speed timing and coherence.

My experience of the higher mass is that it might have a "bigger" bottom end but at what cost in terms of speed and coherence.

Most folk who own these expensive arms are also likely to be changing cartridges regularly - are they really tested. I'm sure some cartridges may be fine, but it's not a given, and the additional forces on the cantilever and stress on the suspension are present, to argue otherwise defies physics.

My ran my ET in the manner it was designed ( decoupled counterweight, no added mass ) simply because it sounded better that way.

Richardkrebs

OK now I understand where you are going wrong in your thinking.

Shown here is a link to the Math on driven harmonic oscillators, a mathematical representation of an arm/ cartridge assembly.

The arm/cartridge/record interface has 2 fulcrum points -
The stylus point around which the cantilever pivots.
The cantilever suspension point, about which the cantilever also pivots, but which is partially constrained by the rubber suspension damping.

The forces involved are double ended - you have the groove applying a force to one end of the cantilever via the stylus. The other end of the cantilever has an restorative forces being applied from the arm motion.
The 2 forces are not in sync because there is a suspension joint between the cantilever and the arm.
Think of 2 people holding a pipe and each one trying to move it sideways out of sync with the other. That's what the cantilever experiences.

The model you are working with is irrelevant. It is too simplistic. If you had studied mechanical engineering you would understand this better.

if we take say 5 hz as the resonant frequency, we see that it will not be until we reach say 30hz before we have complete conversion into an output voltage. I dont think that this is desirable.

Making the arm lighter still will extend this frequency upwards.

This is the classic mistake made by an untrained ear. Let's add mass, lower the resonant frequency and we get more bottom end.
Dont worry about the increase in distortion through the upperbass, midrange and top end from the cantilever being forced to deflect further.

Richard, you have not answered the question posed in my earlier post..

Bruce Thigpen has confirmed that Richardkrebs assertion that ‘the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection’ is wrong.

The following are quoted from the correspondence with Bruce Thigpen:
the cartridge will "see" .55Hz mounted in any tonearm, more so in one with higher horizontal inertia

I don't think Kuzma means the stylus does not deflect at all at .55Hz, that would defy physics

The question I am still waiting for a response is:

Does the cantilever deflect below resonance ?

Just give me a straight answer - Yes or No