Eminent Technology ET-2 Tonearm Owners
Dover has repetitiously stated richardkrebs ADVOCATES adding lead mass to ETs This is incorrect. Mr Krebs openly told the forum how he sets up HIS arm for his LOW compliance cartridge, and the reasoning behind it. He (RK) suggested others could try it to educate/inform themslves, adding to the collective knowledge of posters, because IT IS EASILY REVERSED. RK has not tried to CONVINCE others to follow his setup. |
Dover wrote:Sorry Dover, with respect, I hear what you are saying but I don't think that this is what a cartr stylus really "sees". Static Mass is one thing but Effective Mass is something slightly different... the latter is the "inertia" or the reluctance of the tonearm (pivoted or sliding) to move, as seen by the stylus. ie. At frequencies above Res Freq, the tonearm is effectively an immobile/stationary object or load, as seen by the stylus...which is a good thing, because you want a stable platform to trace the groove, right? Referring to your analogy, for example, the tonearm should not be "walking around", it should be standing absolutely still... & having 3 adults sitting on your shoulder ;) ...is going to help hold the cartridge steady. (The only potential problem with ultra low Res Freqs is the danger of coinciding with TT suspension/support/floor modes.) |
Thekong, hi there, Hi Dover, Just to clarify there are 2 separate issues with the Krebs set up - 1. Removing the decoupling of the counterweight This is where Bruce has tested extensively and posted his results on his website. The removal of the decoupling increases the amplitude of the fundamental resonance by 6-12db. Now if you read the Audio review posted by John47, bottom of page 5, you will see that with the Talisman they measured 2 resonances at 4hz & 9hz. This illustrates how the decoupling system works, by splitting the resonance it actually reduces the peak of the fundamental resonance and results in a flat response in the bottom end. Now Richard is saying that doesn't matter because the resonance is outside the audio band. That statement is not correct because a large resonance at the fundamental frequency will generate signal out of phase that imposes itself on the audible range, negatively impacting timing accuracy, imaging etc. A bass note for example will have harmonics that carry right through to the high frequencies. The preservation of phase at all frequencies is critical to presenting an accurate soundstage, harmonics etc. This is precisely why Frogman, Ct0517, Slaw and myself hear better timing with the counterweight decoupling tuned properly. Frogman has described hearing more bass notes. The other problem generated by the resonance is tracking and tracking distortion - if you have instability at very low frequencies there will be a negative impact on tracking, whether you hear it or not. 2. The other issue is adding significant mass. Now Richard is partially correct when he says that damping with oil, wire, air hoses etc will also help to control resonant peaks at FR. But the real issue is that there are 2 downsides to this approach of high mass - Firstly by carrying this additional mass the cantilever is now pushing a much higher weight. This means that on eccentric records the cantilever deflection will be much higher, and there is increased distortion from the coils moving into a non linear phase. This is one of the primary design considerations Bruce has endeavoured to address by keeping the mass as low as possible. It is wrong to think of this particular issue as a bass problem. The biggest negative is the phase distortion and tracking distortion which impacts the whole range. Secondly in my experience damping tends to slug the sound, as you heard at your friends place. There is a logical explanation for this - by loading up the cantilever it becomes less responsive, less nimble. By loading up the horizontal mass, you are increasing the inertia of the arm, it resists movement, the cartridge cant follow the groove, the cantilever flexes more, more distortion. In a nutshell you might get a more solid bottom end with more mass, but in my experience it comes at a cost - loss of speed and the preservation of accurate phase and time throughout the whole frequency range is compromised. Sometimes in audio less is more. Bottom end extension is not much good if it is muddy and out of phase. High frequency extension can tell you more about how hard a drum is hit than the actual fundamental. From this you can see that having the fundamental in phase with the upper harmonics is critical. In my early days of audio I reckon my Proac Tablettes, which rolled of from 70hz could tell you more about whats happening at 30hz simply because they were very quick compared to many full range speakers - and before the naysayers here get in - I had Proac Studio 3 EBS monitors at the same time. Bearings of course play a role, not just the pressure but the design and airflow etc. An air bearing can be stiffer than one at much higher pressure due to bearing surface area, etc. In the TAS review of the Kuzma/Walker clearly to the arms have different strengths and weaknesses. The Kuzma supposedly is very strong in the bottom end, the Walker appears to be more nimble presents timing better. Pretty hard to work out why these differences occur, because we dont have enough information. In my view given that you have both the Rockport and ET you should enjoy the benefits of both approaches - why anyone would try and convert the ET2 into something that it was never intended to be - a high mass arm - is beyond comprehension. I know at least one reviewer who considers the Kuzma is not as good as the ET2. With regard to Fremers comments on bass response, I dont take much notice. The chances of him getting the ET2 set up correctly are pretty remote, simply because he is time constricted. About the only reviewer that I would trust to ensure that the ET2 is set up correctly would be Martin Colloms due to his technical knowledge and insght, and in the early days of audio reviewers spent many months with gear, not days/weeks. |
Thekong. The answer to your question regarding frequencies impacted by horizontal Fr is shown in the attached graph. From memory your Horiziontal Fr was around 5hz with the A-90. So substitute 5 for 1 on the x axis and scale up from there. At 15 Hz (3) the rise in response is almost zero. This is what BT was talking about when he mentions 3xFr. It could be that the perceived improvement in bass performance of subsequent Rockport arms has more to do with the wand, gooseneck and counterweight arm stiffness, rather than total weight. Different bearings make virtually no difference to this graph since it is the mass that the cartridge has to push sideways that counts. The flavour of different arm bearings, however, is another matter entirely. The various curves are showing different values of Q (damping) Note the level of damping makes virtually no difference at frequencies of 3x Fr and above. This does not mean that we can ignore the amplitude at resonance, since it is shaking the arm and this has an impact in the audio spectrum. FM and AM modulation. Bruce reduces this amplitude by decoupling the counterweight. It is an elegant, brilliant solution. Others damp the resonance as I have done. The oil trough, way less elegant, is also a very effective way of doing this. Both methods reduce FM and AM artefacts. http://s1173.photobucket.com/user/CT-993/media/ResonanceGraph_zpsdd78e0f4.png.html?sort=2&o=7 What this means, as Spock15 says, at 3xFr and above the arm appears to be solid to the cartridge. We want the cantilever to move not the arm. Now look at frequencies below Fr. At say 0.25 Fr we get transmissibility of 1. What this means is that, with the compliance of the cartridge used, the whole arm moves sideways. The cantilever does not deflect. This is important for eccentric record issues. In other words stay above a horizontal Fr of 3hz. (4x 0.75hz) ) 0.75 Hz being the frequency seen with an eccentric record ay 45rpm. Putting this another way. BT uses at 30cu cartridge in his manual to calculate horizontal Fr. The arm weight he uses is 30gm plus 7gm for the cartridge. We have to assume that he is ok with this combination and that he is not worried about cantilever deflection on eccentric records. When using a 10cu cartridge we can increase the horizontal mass of the arm to 111 gm and have the same peace of mind about cantilever deflection with eccentric records. The cartridge is 3x stiffer so we can push around 3x the weight. It is that simple. Forces on the record groove wall are another thing. We use a stiff cartridge this is the price we pay. Don't play heavily eccentric records. Ha_ha_he_man. What I hear with a heavy linear arm is this... The music takes on mass. Individual notes are solid. This is not to be confused with "heavy" in the derogatory sense. A live struck triangle has this mass. One can imagine walking up to the sound of it and holding it. It would have mass and a textured surface. This is very hard to reproduce and I do not hear this effect with light linear arms when carrying low compliance cartridges. |
