Chris,
Thanks.
The results concur with both my own testing and the correct application of the laws of physics and sound engineering practice when setting up the ET2. The use of decoupling is an essential element to optimize the performance. To remove the decoupling and add mass is an ill conceived notion not supported by the laws of physics and cannot be recommended.
The removal of the decoupling mechanism and adding mass will result in an unnatural hump in the low bass as explained in the ET2 manual.
|
Richardkrebs,
There was no personal attack. I simply addressed the anomalies and reasons for the errors in your post dated 03-14-13.
I will review your latest post tomorrow. |
Richardkrebs - You have now conceded after 4-5 weeks of obfuscation that there is cantilever deflection on eccentric records below the resonant frequency. It follows that adding mass increases deflection as I asserted back in February. On 02-16-13: By increasing the horizontal mass of the arm significantly, when you play an eccentric record the increased resistance to motion from the additional mass will result in increased cantilever flex. Your latest comparison of the deflection of a sprung cantilever with the elasticity of a silk thread is at odds with the application of scientific principles. Do we need to spend another 5 weeks going through the difference between the modulus of elasticity of a woven silk thread and the bending motion of a cantilevered suspension. Hasn't this discussion run its course. This is the third time that I'm aware of over the past weeks that you have requested a discussion be terminated. It is not obligatory for anyone to participate. Whilst you are keen to champion your Technics modifications and your own homebrew tonearm, this is not your personal thread. No confusion at all. In Engineering, the term absolute is.....absolute. This not correct. The discussion we are having is on the cantilever flex generated by an eccentric record. This is not absolute as there are variables involved, to wit - the mass and inertia of the arm, the compliance of the cartridge and the level of eccentricity in the record. The laws of physics are absolute. Correctly applied they enable us to develop mathematical models for scenarios that are not absolute. |
Richardkrebs Readers of this thread will now see that you are contradicting yourself. Adding additional weight to an ET2.5 would be inadvisable since it is already in the Goldilocks zone I mentioned. Namely its horizontal resonant frequency is in the range of 2-3hz, when using a decoupled counterweight and a low to med compliance cart. Richardkrebs - this comment is unbelievable. This completely contradicts your earlier posts. You encouraged Thekong to add horizontal mass to his ET2.5 and I quote; 03-12-13: Richardkrebs
Thekong
I don't know how long patents last, but would suggest the reason that Lloyd does not decouple the counterweight is simple.
It sounds better.
03-12-13: Richardkrebs
Thekong
We look forward to reading your comments.
03-13-13: Richardkrebs
Thekong.
Thanks for posting the photo of the counterweight arm. One suggestion is that you need to be very carefull with the stiffness of this. Any shake rattle and roll here is bad since it is no longer free to pivot about the leaf spring. I experimneted with the rod carrying the weight and finished up with an aluminium rod with a M10 thread for adjustment. Smaller diameters were quite flexable. I repeat, you have now opined that it is inadvisable to add mass to an ET2.5, whilst you have been encouraging Thekong to add mass to his ET2.5 by coupling his counterweight and furthermore, stiffening the counterweight assembly with an M10 bolt no less. Your advice on adding mass and coupling the counterweight has been wrong. Earlier I advised readers to be aware of the pitfalls and possible deleterious consequences. In a response you hysterically claimed that I was scaring people off from trying your suggested modifications and accused me of being a scaremonger. Richardkrebs - readers of this thread are quite capable of evaluating the arguments put forward for and against. I have a higher respect for the intelligence of the readers of this thread. Your refusal to acknowledge the recommendations outlined in the ET manual, your continual refusal to acknowledge the laws of physics, and now a complete reversal on the advice given Thekong on his ET2.5 suggest that readers should disregard your advice completely. |
Chris/Frogman -
Thanks for your feedback and comments. I was beginning tho think that analogue heaven consisted of only me and Bruce on a desert island.
I think the key point Chris as you have alluded to is that even if we assumed the Kuzma was the best arm in the world, adding substantive mass to the ET2 is wrong, it is taking it out of its design parameters. To accommodate the mass one would have to redesign the main air bearing and retune the Q of the total system. These factors are being completely ignored by the other folk.
Chris I note that you are also using the carbon fiber arm tube for high compliance cartridges and yet still finding the optimum is only 2 springs with the Benz. This does suggest to err on the more decoupled side of the ledger for LOMC's as well, the only downsides being possibly a fall off below 30hz.
I would be very surprised if many were getting below 30hz in a domestic environment, and if they were it would be unable to be controlled in that environment. To put it another way a roll off below 30hz I would see as an advantage in most domestic environments where room bass response is usually quite uneven and unpredictable. |
1986, June as I recall, my first ET.
In '78 whilst studying Engineering at University I learnt a fundamental law of physics.
Q : How do you titillate an ocelot.
A : You oscillate it's tit a lot.
We didn't have Wikipedia in those days.
|
Hi Slaw,
The arm wand and bearing tube are ungrounded. I tried grounding the aluminium arm wand but couldn't hear any difference. I had a major problem with RF when using van den hul monocrystal silver wire, and went back to a stranded copper litz ( same as used in the old Sumiko PBT tonearm interface ) and had no RF problems whatsoever after that. My arm cable went from the wand straight into the phono on the side of the TT rather than through the bearing tube. If you are using the aluminium arm tube, running an electrical signal along a piece of aluminium can induce hysteresis distortion in the signal and maintaining a litz configuration would be desirable. |
Further to the above post for those interested the weights of the arm options excluding the wire are: 13g ( Al) . 17g (Cf) & 19g for the heavy magnesium version. So Bruce has designed in only an additional 2-6g for MC's.
|
Thekong, hi there, 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! 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 - yes you are correct. That "rebound" as you call it has a resonance. The idea behind the variable spring rate and shifting the position of the lead counterweight is to place that resonance below the horizontal resonance of the arm so that the 2 resonances ( arm and beam ) do not couple together to produce a large peak at the arms resonant frequency.
All tonearms will have a lift or peak in response at their natural frequency. The tuning with the I beam ( decoupled ) is designed to reduce this natural bass peak at the resonant frequency of the arm to produce a flat bass response. This is illustrated in the graphs on Bruce Thigpen's website where he has published some of his test results.
The idea behind loosening the I beam that I outlined in my earlier posts is to lower this "rebound" resonance, by allowing the I beam to swing freely and also keep the horizontal arm mass low. Some wag above says you get no response below 30hz but that is not correct. You get a low fall off in bass below 30hz.
Rigidly coupling the I beam will increase the bass, adding more bass lift at the resonant frequency and beyond. If you run 30 year old Acoustat 2+2's in a room barely 10ft x12ft, listening position 5 feet from the panels and you like humpa humpa one note bass, then that is your ideal solution. |
Richardkrebs: Yet again I have to address your gross assumptions and misunderstanding of the principles of the ET. Richardkrebs
Frogman and Dover say that they prefer a loose connenction and one leaf spring. Chris says that triple springs produce a sound that is too lean.
Rockport, Walker, Kuzma and I say that there should be no spring at all.
I believe ALL of the above statements as I think that they are actually saying the same thing along a continuum.
It all depends upon the voicing of your system and our biases, and we all have biases. This is absolute rubbish. You are implying that the decoupling and non-decoupling are both valid, when they are not. With the ET2, the outcomes are entirely different and Bruce Thigpen has tested and measured these. The decoupled methodology employed by Bruce Thigpen is designed to minimize horizontal inertia and ensure the resonance of the I beam and counterweight remains below the horizontal resonance of the arm. The rigid coupling of the I beam and counterweight that you advocate is contrary to these stated design goals. Your comment about voicing the system to biases is as presumptuous as it is incorrect. An experienced listener can hear changes in transient speed and accuracy of timbre and timing irrespective of the system. That is how a system should be tuned. Richardkrebs
Double or triple springs push the resonant frequency above the core resonance which is also good. Your statement contradicts research and testing by Bruce Thigpen, and I quote the following email from Bruce Thigpen published above: Bruce Thigpen
Chris,
You always want the horizontal natural frequency of the counterweight to be less than the cartridge/arm resonance, this is the case 98% of the time.
The natural frequency of the I-beam/leaf spring depends on the thickness of the spring, the amount of weight, and where the weight is on the beam. The natural frequency goes down as the weight moves further out on the beam which is where we want it to be.
brucet Richard, clearly you have not done any testing to support your guesswork, otherwise you would have found that 98% of the time you are wrong. If you bothered to read the manual you would see that the double spring is for low compliance cartridges and should be used with the minimum counterweight pushed further out on the I beam to position the resonance of the I beam and counterweight BELOW the horizontal resonance of the arm. Richardkrebs
I have said that I don't think that it is a good idea to have a mass attached to two dissimilar springs who's resonances are in the same neighbourhood. Again, if you bothered to read the manual and Bruce Thigpen’s website, the decoupled counterweight is designed precisely to achieve this. Furthermore on Bruce’s website he has provided extensive test results proving this. Richardkrebs
The transmissibility graph I posted shows the potential nasty consequences of this. I have already explained to you in great length that the mathematical model you refer to, "harmonic oscillators", which you pulled out of wikipedia, does not apply. Let me help you. Read my post of 03-14-13, the first sentence begins Dover
Richardkrebs
OK now I understand where you are going wrong in your thinking. Richardkrebs
At least a 6 x seperation of the two resonant frequencies would a target. Where did you pluck this number from? Why 6 times? Please don't use an incorrect mathematical model again when you attempt to explain. Richardkrebs
We also have to be carefull that we do not go to low with lite springs since we get close to eccentricity frequencies again with possible nasty consequences. Bruce has completed extensive testing and provided clear guidelines on the use of the light spring. He has calculated the resonances and provided extensive guidance. What testing have you done, or is this purely speculative guesswork on your part yet again. Richardkrebs
My early fixed counterweight designs resonated somewhere in the midrange.
Increasing its rigidity more, pushed the resonance above the frequency of audibility. Have you tested this? What resonant frequency did you measure? More guesswork? Richardkrebs
This is desirable and is the final logical progression to the tests that have been listed in this thread. You persist in arguing your unfounded case for fixing the counterweight. Arrant nonsense. To remind readers I repeat: The decoupled methodology employed by Bruce Thigpen is designed to minimize horizontal inertia and ensure the resonance of the I beam and counterweight remains below the horizontal resonance of the arm. The rigid coupling of the I beam and counterweight that you advocate is contrary to these stated design goals. Once again, we go round the block for the umpteenth time. Bruce Thigpen has calculated, tested and measured precisely the resonances of the decoupled I beam and counterweight with a wide variety of cartridges from low to medium to high compliance to determine the level of decoupling required to optimize the cartridges performance. How many times before you get that decoupling is an integral part of the ET2 design and how the arm is engineered to optimize performance. You are clearly out of your depth. You persist in misapplying physics and just don’t seem to be able to comprehend the design. Do you run your car on 3 wheels? You have resorted to implying that readers who have tried removing the decoupling and found it to be detrimental are either fixing up defects in their system or have biases. That is an arrogant assumption, and reflects poorly of your estimation of the contributors to this thread. |
Chris, your diligent follow up with Bruce Thigpen is much appreciated: 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, Bruce Thigpen’s contribution affirm my statements over the past 7-8 weeks that Richardkrebs fixation with adding lead mass to the arm and coupling the I beam will increase distortion, affect tracking and produce an unnatural bass lift in response. My own analysis has long been based on a thorough understanding of the design principles and physics involved. It is disappointing that those who disagree, and clearly do not grasp the principles involved in this arm, have resorted to denial and personal attacks 03-04-13: Richardkrebs
Dover
Your scaremongering
03-17-13: Richardkrebs
Dover.
Hasn't this discussion run its course.
03-18-13: John47
Mr Dover’s bombastic contentions.
03-21-13: John47
Put on your knitwear cardy so don't catch a cold, your thick lensed glasses so you don't fall, then pop out and replenish your Prozac.
03-23-13: Gnnett
As a New Zealander I would like to apologies for the behavior of Dover. It is a narrow country and this breeds narrow mindedness. All too often denial and personal abuse is the last refuge of the desperate. Sadly those posters who are fixated with the idea of adding lead mass and removing the decoupling will continue to deny the science and exhaustive testing and measurements that underpin Bruce Thigpen’s design. If they prefer the sound of the arm set up incorrectly, there are clearly fundamental flaws in their system and they should look at the rest of their components and set up. This includes the environment in which they are listening. 03-04-13: Richardkrebs
Dover
I am the only person here who can speak with any authority on the subject. Richardkrebs, the ET2 is a brilliant design and deserves to be treated with respect. |
Chris - thanks - no war down here.
My motivation is to help people set their systems up correctly and learn more. We all learn from shared experiences. The debate over the past 7-8 weeks could have been much shorter had it not been inundated with junk science.
Richardkrebs, claims to be an authority, yet all the way through been belligerently dismissive of Bruce's recommended set up procedures and of the design principles that underpin this arm. Many of his arguments put forward were simply nonsense.
Everything I have said has since been verified by Bruce Thigpen's recent communications. The addition of lead mass and removal of the decoupling of the I beam will load the cantilever, increase distortion, and deliver a bloated bass response.
Would you have rather everyone who read this thread ignore Bruce's advice - add lead mass and bolt up their I beams as was suggested ad infinitum?
That, along with much uninformed comment, is an affront to the time and dedication that Bruce has put into this product. It is impossible not to have robust debate when basic scientific principles continue to be denied.
|
Richardkrebs - So predictable. Yes there may be other brilliant designs, but the discussion is about the ET2, in case you've forgotten.
Yet again you just dont understand the physics.
You are trying to turn the ET2 into a home brew Kuzma, Rockport, or other design which have started with a different set of design parameters and operating assumptions completely - different masses involved, different bearings required, different air pressures required, forces will be seen by the arms differently and completely different set of resonances involved, all of which are fundamental to the performance of any of these arms.
You are tinkering around trying to convert a low mass tangential arm into a high mass tangential arm but have failed to address most of the queries I raised. You have provided some home grown theories and analogies that bear no resemblance to engineering science. You have provided no measurements of your system to support your assertions.
Bruce Thigpens documented design brief and extensive testing show that your approach is wrong in the context of the ET2 ( this thread is about the ET2 ).
I remind you that if you go back to my very first post after you described your lead footed home modified ET2 that my comments on increased distortion, increased cantilever flex, possible record damage from mis-tracking were all preceded with the words "on eccentric records" and I stand by that statement.
In your self taught engineering school of fabulosity do you understand what an eccentric record is?
Do I need to remind you of the laborious weeks of denial on your part that the cantilever does not see the side loads generated from an eccentric record, accompanied by much junk science subsequently refuted by Bruce Thigpen.
Do I need to remind you of the incorrect advice you gave to Thekong and then retracted when I pointed out your own self conflicting arguments, which you then retracted.
In a nutshell Richard you are telling Porsche drivers they can improve their car by converting it to a Hummer. If you prefer the Hummer, I have no issue with that. If you try to tell me that there are no consequences arising from this conversion then you are wrong - yet again. |
Richardkrebs re your last post.
I believe we have something in common. In the contract work I specialise in I too am totally indispensable. Not only dozens but hundreds of employees world wide depend on my expertise. One mistake and a company could be bankrupted. Worse still, the New Zealand economy could collapse. Like you I also understand Q, and P that comes before it and R that comes after, and the other 22 letters of the alphabet too. Part time I moonlight as a neurosurgeon. My expertise in soldering gives me the manual dexterity to perform such delicate operations. It provides a diversion from responding to lunatics who post garbage on audio blogs. With your background in avionics, you would have become accomplished in soldering too. Perhaps you could apply one of your many talents to a part time career in neurosurgery. Just a thought. |
Chris/Slaw - At the time I tried the van den hul the arm was mounted on a Roksan Xerxes. I was using a Shure V15Vmr so that could have been a contributing factor for picking up RF due to the higher impedance than a MC. Having said that, with litz wire there was no RF in the same situation. This suggests that even if you cant hear RF a litz wire will provide a lower noise floor. |
Hi Richardkrebs
Had a very good Easter beak, very relaxing. Thank you for asking.
Was wondering, now that you know how the ET2 works, whether you had found time over the long Easter break to remove the lead from your arm, put the decoupling spring back in, dial in the vertical effective mass ( less lead further out for your cartridge ) and set the I Beam resonance below the arm resonance as prescribed in the manuals.
Frogman, Chris & Slaw have all found significant gains with the correct decoupling strategy employed. Frogman has reported significantly more bass information loosening off the end cap as per my suggestion some weeks ago.
I would be very interested to hear what sort of improvements you get when you get the arm back to standard configuration.
Looking forward to hearing how it goes. |
04-07-13: Richardkrebs
Double posts and thread ghosts of the past. How does that happen? Richardkrebs – Audiogon has advised that it looks like it was double posted by the original author – that’s you Richardkrebs. No ghosts involved. Is it possible that whilst sleepwalking, on the night of 07-04-2013, you reposted your earlier post of 03-30-2013? For the benefit of readers, Richardkrebs original post reads 03-30-13: Richardkrebs
Dover
" self taught engineering school of fabulosity."
You go too far....
I have a tertiary education in engineering. I hold an aircraft avionics qualification and a radio technicians certificate. I teach hydraulics and electronics to paying clients.
My company employs 52 people across two countries.
We specialize in the design and building of complex servo electro hydraulics.
Recent projects have been damper doors for jet engine power stations in Oman and Iraq.
These doors, 7 meters square, are required to swing thru a 90.degree arc and stop precisely in position. Fractions of a mm are possible. The doors need to do this at both high, emergency close speeds and normal slow rates. With the multi mega watt engine buffeting it with an air stream just below supersonic.
Get the Q wrong with something as massive as this and it either fails to reach the go to point in time or it shakes itself to destruction. We usually target just below critically damped to give added safety.
My public liability does not cover destroying a multi billion power station.
I understand resonance, Q, time constants, mass damping et el.
The survival of my company and potentially the power station workers and my staff depends upon it.
You cannot begin to imagine the pre qualification process a company has to go thru to be even considered to quote on projects like this.
Compared to design work like this, a tonearm is relatively mundane. Certainly a whole lot less stressful.
I know how the ET2 works.
Richardkrebs (Answers | This Thread) This was posted again on 07-04-2013 04-07-13: Richardkrebs
Dover
" self taught engineering school of fabulosity."
You go too far....
I have a tertiary education in engineering. I hold an aircraft avionics qualification and a radio technicians certificate. I teach hydraulics and electronics to paying clients…. ) If this is the case, what possessed you to repeat your qualifications and work experience yet again? Nevertheless, thank you, you have reminded me - I do have a few observations and suggestions. You seem to object to my observation regarding your self taught engineering. I note from your post and from your website that you encourage us to read that you have some electrical trade certificates. From your website you joined the company as a storeman, after attaining these electrical trade certificates. There is nothing on the website that suggests you have had any formal tertiary education in the fields of “engineering” applicable to the design of the ET2, specifically the physics and mathematics of this arm. This being the case, I understand more clearly now why you have difficulty comprehending the complexity of Bruce Thigpens design. I draw your attention to Bruce Thigpens background. After completing a business degree, Bruce commenced working for W.H.Coloney, an engineering company specializing in mechanical and civil engineering. Bruce project managed the development of the Coloney air bearing TT & tonearm ( now the Walker ). He was taught air bearing technology by qualified civil & mechanical engineers. Bruce returned to university as a post graduate student, to study Physics, Maths & Audiology to ensure that he had a comprehensive understanding of the physics and mathematics involved in developing air bearing TT’s and tangential air bearing tonearms and the outcomes. Bruce holds many patents pertaining to air bearing tonearms and others such as patents on vacuum hold-down on records. I studied Structural & Mechanical Engineering, Physics, Maths & Inorganic Chemistry at university in the late 70’s, before switching to Finance. Now to the issue at hand. For some months now you have argued that users of the ET2 tonearm should add lead mass and remove the decoupling from the I beam/counterweight assembly. This advice on your part is in direct conflict with the set up procedures in the manual. 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, Bruce Thigpen’s contribution affirms my statements over the past 2 months that your fixation with adding lead mass to the arm and coupling the I-beam will increase distortion, affect tracking and produce an unnatural bass lift in response. My own analysis has long been based on a thorough understanding of the design principles and physics involved. If you go to the Eminent Technology website and read the ET1 manual ( that’s the arm that precedes the ET2 ) you will discover that the ET2 was a design decision to move away from the high mass/fixed counterweight model utilized in the design of the ET1 to the low mass decoupled counterweight model utilized in the ET2. These new design considerations embodied in the ET2 resulted in substantive improvements in the quality of sound reproduction. The decoupled I-beam methodology employed by Bruce Thigpen in the ET2 is designed to minimize horizontal inertia and ensure the resonance of the I-beam and counterweight remains below the horizontal resonance of the arm so that the 2 resonances ( arm and beam ) do not couple together to produce a large peak at the arms resonant frequency in the bass. All tonearms will have a lift or peak in response at their natural frequency. The tuning with the I-beam (decoupled) is designed to reduce this natural bass peak at the resonant frequency of the arm to produce a flat bass response. This is illustrated in the graphs on Bruce Thigpen's website where he has published test results. The addition of lead mass that you continue to advocate goes directly against the design of this tonearm. The rigid coupling of the I-beam and counterweight that you advocate is contrary to these stated design principles. Furthermore you acknowledged in your posts dated 03-19-13 and 03-20-13 that you have only just worked out how the decoupled I-beam works after some 25+ years of ownership. 03-19-13: Richardkrebs
It could be that tuning here with springs and weights (and their position) is at least partly to do with sorting this possible frequency interaction rather than just the weight or stiffness employed.
03-20-13: Richardkrebs
The thought that there may be more going on with the decoupled counterweight was triggered by your post where you quoted BT where he said that the ibeam had a natural frequency of 2-5 hz. , In light of this newfound knowledge and your assertion that you now understand how the arm works, including the I-beam, I made a polite inquiry in my post dated 04-02-13 if you had had time over the Easter break to set up your ET2 correctly as per the manual.
Hi Richardkrebs
Was wondering, now that you know how the ET2 works, whether you had found time over the long Easter break to remove the lead from your arm, put the decoupling spring back in, dial in the vertical effective mass ( less lead further out for your cartridge ) and set the I Beam resonance below the arm resonance as prescribed in the manuals.
Frogman, Chris & Slaw have all found significant gains with the correct decoupling strategy employed. Frogman has reported significantly more bass information loosening off the end cap as per my suggestion some weeks ago.
I would be very interested to hear what sort of improvements you get when you get the arm back to standard configuration. ,
You have not responded. Can I assume that you have no interest in setting your ET2 tonearm up correctly? It is clear from your continued denial of fundamental physics and mathematics and your statements disagreeing with Bruce Thigpen and myself in the design and implementation (set up) of the ET2, your continued fixation with adding lead mass and removing the decoupling from the I beam/counterweight assembly, that you do not have sufficient understanding of the principles involved in the design of this arm. These are fundamental principles of physics, for which you would be better placed to debate if you had some formal education that is wider than what one would infer from your posts. Anyone who understands physics would not for one minute contemplate the homebrew mods you advocate. I quote direct from the ET2 Manual p29 ET2 Manual p29
It is desirable in most cases ( low to medium compliance cartridges 5x10 dynes/cm – 20x10 dynes/cm ) to use the minimum number of weights, far out on the cantilever stem. This decreases the horizontal inertia of the tonearm while increasing its vertical inertia. , Readers should be aware that this is the exact opposite of what Richardkrebs continues to advocate. Richardkrebs is advocating increasing the horizontal inertia for low compliance cartridges – the opposite of what Bruce Thigpen recommends. Richardkrebs, my recommendation for you, if you are serious about owning and operating an ET2, would be to enrol in some Physics and Mathematics papers at university. That may help you to comprehend the principles that make this an excellent arm when set up correctly. I would advise readers and ET2 owners to ignore Richardkrebs erroneous recommendations and follow the set up procedures outlined in the ET2 manuals that can be found here. http://www.eminent-tech.com/main.htmlFrogman, Chris(Ct0517), Slaw and myself have all found significant gains with the correct decoupling strategy employed. Furthermore Frogman has reported significantly more bass information loosening off the end cap as per my suggestion some weeks ago. My own experience with tuning the decoupled counterweight correctly and using a lower weight counterweight further out on the I-beam for low compliance cartridges as recommended in the manual yielded significant improvements in speed and articulation, transparency of soundstage and lower distortion, exactly as predicted by Bruce Thigpen’s substantive testing and published results. |
John47
The thread is about the ET2. Your facetious comments demonstrate that you have no respect for the designer of the tonearm and clearly do not understand and are not interested in how it works. Not for one second could anyone consider you to be an audiophile. |
Yes, John47, diatribe does indeed describe your contributions to this thread. However, please continue to waste more of our time posting your vitriol as this appears to be your preoccupation. |
Richardkrebs. If you prefer the sound of your ET2 loaded with lead and decoupled counterweight removed thats fine. A couple of technical points though. Paragraphs 1-3 : You miss the point here. Your quasi-mathematical arguments on resonant frequency are meaningless because the arm is more complex than what you appear to comprehend. You continually factor only one resonant frequency into your arguments to attempt to justify your opinion. The ET2 as designed has a multitude of resonances, which you appear to be oblivious to and ignore in your calculations. I use the word calculations loosely here, as I suspect your numbers are mostly guesswork. You have ignored horizontal/vertical resonance of the cartridge horizontal resonance of the sprung counterweight the horizontal/vertical resonance of the air bearing natural resonances of the bearing tube/rigid arm wand natural resonance of the counterweight assembly. Count them up. This is the fundamental flaw in your postulations. The arm is a precision instrument and is designed to have split resonances and variable vertical and horizontal mass in order to be tuned. The tuning is critical to optimizing the performance of any cartridge. For example
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.
Please note the comments from Bruce Thigpen "splitting the horizontal resonance frequency into two points". As I said there are multiple resonant frequencies to consider. Clearly you still don’t get that your home brew efforts to remove this tunability by rigidly coupling the counterweight assembly result in a bass lift of 6-12db and increased distortion. Your addition of lead mass will increase these distortions further. Believe me Richard I have heard it, you apparently cannot. Richardkrebs
Re my question re interaction between the two spring rates, …
I started thinking about this when Dover commented on the superior transient performance of his unipivot. The idea further coalessed when the tests were done with loosening the CW arm bolts. This would change the Q and possibly the res frequency of the CW assembly. Potentially reducing any interaction between the two springs, but not eliminating it. My comments on the Naim Aro unipivot were pertaining to the superior preservation of the leading edge of notes - this is quite different from “transient performance”. Unipivots are mechanically coupled, whereas an air bearing is not rigid and loses some of the leading edge. It has nothing to do with Q as you claim. The addition of lead mass will alter the dynamic stiffness and compromise the performance of the air bearing. Capturing the leading edge requires secure tracking and speed, both of which are compromised by your addition of lead mass. I do agree that it is possible that the spring could have some issues, and that is why I believe I got an improvement by using teflon rather than spring steel for decoupling. Contrary to what you hear, when I trialed increased mass and coupled the counterweight rigidly with a low compliance cartridge I got bass that lacked coherency and was out of tune as is predicted by the maths and verified by Bruce Thigpen’s extensive testing. As a matter of point I reached this conclusion in 1986, well before Bruce published his test results. The website did not exist then. Frogman, Slaw and Chris have also come to this conclusion with a variety of cartridges and systems. You choose to throw away two of the fundamental principles of the ET2 – maintaining a low horizontal mass and the ability to tune the horizontal and vertical resonances by using decoupled I-beams and variable effective mass for optimum performance. It is disappointing that you are so rigid in your fixation with mass as I think you are missing an opportunity to substantially improve your system. The preservation of low horizontal effective mass even with low compliance cartridges as prescribed in the manual and supported by Bruce's test results ensures the bass does NOT have a lift of 6-12db and improves tracking. By my calculation AND what I have heard and experienced you have a bass lift and increased tracking distortion from your removal of the decoupled I-beam and the lead mass that you added. If you prefer that, fine, but lets be clear, you can not call the misguided conversion of your ET2 into a high mass rigidly coupled arm an upgrade. |
Chris, 04-16-13: Richardkrebs
... Later on in the thread, 03/14/13, Chris published the actual weight of the ET2.5 being only 8gms heavier than the ET2. This means that ET did not use the same cart parameters when giving Chris the original info..
Bruce has confirmed same cart parameters were used. This is a good example of someone who doesn't have the physics and maths knowledge to apply it correctly. I usually dont bother to check Richardkrebs maths because the underlying assumptions that he uses are usually wrong to start with. Dover
The arm is a precision instrument and is designed to have split resonances and variable vertical and horizontal mass in order to be tuned. The tuning is critical to optimizing the performance of any cartridge.
Dover – I agree with you and the key for me is “any” No limitation on the cartridge –imo. So far anyway.
imo - Someone just getting into analog with an ET2 doesn’t have this tuning knowledge to start with. It is gear and room specific so takes time to acquire. Looking back now I think I got to about - 6 out of 10 in the beginning; years ago and thought it sounded great. I thought I had it running good – but I didn't understand. The rest comes with experience; Experience comes with time, time in listening to it in your own room and tuning it with your own gear. I believe if had this thread 10 years ago I could have fast-tracked. But then I would have missed out on some fun. Chris - I agree with your last post and that is why it is vitally important that new owners get correct advice on how to set the arm up correctly. People very seldom read the manual until something doesn't work as expected - sound familiar. We should be encouraging ET2 owners to explore the opportunites afforded by the tunability of the ET2. Setting the levels accurately Choosing the correct counterweight mass for the cartridge Dressing the cables Setting the VTA correctly When all these are correct the tuning of the I-beam becomes much easier to hear. We should not be encouraging owners to bastardise the arm by removing its primary design advantages as Richardkrebs continues to do. Fortunately I have the advantage of importing and selling these arms many years ago and personally set up approx 12-15 ET2's in one year alone. TT's included my Final Audio Parthenon, Sota, Roksan, Townsend ( Rock ), Oracle, Goldmund, VPI and others I've forgotten; cartridges included the usual Koetsu's, Garrotts, Carnegie, Benz, Van den hul's etc I would never install an ET2 on a suspended TT such as Oracle or Linn because of the shifting mass as the arm tracks across the record. Sota was OK as the suspension is hung and the high mass subchassis is inherently more stable than the Linn/Oracle type TT's. I disagree with your comment on system dependency. In my experience the sound improvements from the correct set up and application of the ET2, including tuning the I beam/counterweight in it's standard configuration can be heard in any system. That is why Frogman, Slaw, yourself and myself have all come to the same conclusions on tuning the I beam albeit with different systems. What we probably have in common are a good set of ears and an open mind. |
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04-29-13: Ct0517
04-27-13: Dover
.....dont be embarrassed about using spotify, I've heard spotify streamed through an Ipad.........
Dover – if you know Spotify then you would know its not available in Canada. Have never heard it. My post on that article had everything to do with music itself – regardless of format and nothing to do with the equipment. It appears my post was misunderstood by you ? and maybe others so the reason for my post.
Dover –in this picture is a mechanically grounded unipivot. Please note the way it has been setup. What do you think happens to the sound when it is set up this way ?
Here is another
example
A little more extreme ?
Ct0517 (System | Reviews | Threads | Answers | This Thread) Ct0517, Spotify - Ct0517 since you mentioned this I thought I should share my experience. Digital can be a very useful tool to benchmark our analogue front ends to, particlularly in terms of speed, timing, transparency and identifying colourations in our systems. It can provide a useful benchmark due to its consistency whilst we tune our analogue front ends. That is not a value judgment on quality - it is the consistency that is of value. Nevertheless, I have heard Ipad/DAC front ends sound better than poorly set up or badly modified analogue TT's. I was unaware it is not available in Canada as I dont live there. Mechanical Grounding - Please explain your point. When I use the term mechanical grounding it was in the context of the bearing itself, not how the arm is mounted. Naim Aro tonearm
By Markus Sauer • Posted: Jun 5, 1995 • Published: Jun 5, 1993
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, and the only spiked tonearm I know of!
I've had less experience with the Eminent Technology ET 2 and Graham 1.5t than with the other two arms, and so don't want to make too strong a statement, but I don't think they can hold a candle to the ARO in the boogie department. The ET 2, on the other hand, presents an even more spacious soundstage and possibly even lower distortion, due to its superior geometrical accuracy. There are clearly pro's and con's with any piece of equipment. In this case of the Naim ARO and ET2 we are trading off the more accurate preservation of the leading edge from the mechanical grounding of the Naim bearing for the superior soundstaging and lower distortion of the ET2 from the tangential geometry. This notwithstanding that adding mass and removing the decoupling from the I beam and counterweight assembly will of course promote distortion, negating the benefits that are inherent in the ET2 as has been explained by the designer Bruce Thigpen. |
Bearing Stiffness – Naim Aro vs ET2 04-21-13: Richardkrebs
c)....the air bearing employed on these arms is effectively rigid at audio frequencies. So they should look elsewhere when looking for the cause of compromised note leading edge performance. 04-16-13: Richardkrebs
I started thinking about this when Dover commented on the superior transient performance of his unipivot. The idea further coalessed when the tests were done with loosening the CW arm bolts. This would change the Q and possibly the res frequency of the CW assembly. My comments on the Naim Aro unipivot were pertaining to the superior preservation of the leading edge of notes - this is quite different from “transient performance”. Unipivots are mechanically coupled, whereas an air bearing is not rigid and loses some of the leading edge. It has nothing to do with Q. The addition of lead mass will alter the dynamic stiffness and compromise the performance of the air bearing. Capturing the leading edge requires secure tracking and speed, both of which are compromised by the addition of lead mass or removal of the decoupling. 04-23-13: Richardkrebs
Stiffness
Many years ago I remember reading an audio magazine which tested the rigidity of the ET2 bearing. It may have been Martin Colloms, but I can't be sure. This was done, again from memory, where accelerometrs were used and a sweep frequency was applied to the spindle. The result showed a bearing that was stiff at audio frequencies.
This is explained by the design of the bearing (it's self centering characteristics) and its extremely high resonant frequency. Many times higher than the audio spectrum. Although the bearing uses air which we know to be compliant, at the frequencies of interest, the bearing medium is stiff.
I also show here a quote from an industrial air bearing manufacturer. While these a big load bearing devices, their design is virtually identical to the ET2
"Outstanding stiffness for small deflections Most engineers visualize an air bearing as being like a hovercraft, and they erroneously conclude that a bearing which floats on air cannot be very stiff. Actually these gas bearings are many times stiffer than a ball or roller bearing. Sapphire orifices within the bearing gap control the pressure in a film of air which is only 0.0003 inches thick. As a load is applied to displace the bearing rotor or slider, the gap decreases very slightly on one side, reducing the flow of air through the adjacent sapphire orifice. This results in a pressure increase in the gap on this side which pushes the rotor back to its original position. In essence, the air bearing is a servomechanism with closed loop control, and maintains a uniform gap in spite of external forces that may be applied. This results in bearing stiffness of millions of pounds per inch for small deflections. Stiffness is linear and does not change with temperature. In contrast, ball or roller bearings have almost no stiffness unless heavily preloaded. The stiffness of a ball bearing is not linear, and varies considerably with temperature." The response above to my original post of 04-17-13 contains misinformation. The comments plucked from the internet are irrelevant as they pertain to ball bearings and air bearings. They were copied from the following website http://www.space-electronics.com/Products/air_bearings.phpThe Naim unipivot does not use ball bearings. The Naim Aro is mechanically grounded whereas the air bearing is not. Unipivots are the most rigid coupling you can get in a tonearm. Air bearings have compliance and gimbal bearings can only be too tight (loaded) or too loose and can chatter. In the Hifi News Review of the ET2 Martin Colloms concluded that the shape of the resonance passing through the air bearing remained intact. This is not per se empirical proof that air bearings are rigid. I note that most users of the ET2 have increased the air pressure up to around 19psi and have reported improvements to the sound as the pressure is increased. When the operating air pressure is increased, the following operating parameters are altered - the Q of the system, the dynamic stiffness of the bearing, the resonance frequency of the air bearing itself, the shearing forces are changed. All of these changes will of course be in themselves be difficult to calculate as the results will vary depending on the resonances in the I beam and cartridge and masses involved. This is precisely why Bruce Thigpen backs his physics and maths up with extensive testing. |
Issues Created When Adding Lead Mass and Removing the Decoupling of the I Beam on the ET2 04-21-13: Richardkrebs
b)....a heavy arm, when and only when, connected to a low compliance cartridge is a high performance, viable alternative This statement is not correct within the context of the ET2. Adding Lead to the arm increases the horizontal mass. Removing the decoupling on the I Beam increases the horizontal mass. The ET2 is designed with a target horizontal mass to be used in conjunction with a decoupled I Beam & Counterweight. Increasing the horizontal mass increases distortion due to the additional side loads on the cantilever & tracking is compromised. Increasing the horizontal mass creates a large peak resonance in the bass that also affects tracking and increases distortion. 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 When you add mass and remove the decoupling how big is the resonance in the bass? Bruce Thigpen has measured up to a 6-12db lift in the bass when testing the removal of the decoupling from the I beam 04-23-13: Richardkrebs
Maths and Physics.
Amplitude
A few weeks back I posted a transmissibility graph showing the effect of excitation frequencies at various multiples of the resonant frequency. This graph can be used to show relative resultant amplitudes for known resonant and excitation frequencies.
For a standard ET2 using in my case a Shelter Harmony, we get a resonant frequency of 8.4 hz. On my heavy arm, this frequency drops to 5.3 hz. If we take the lowest frequency of interest to be 20hz we get multipliers of res freq of 2.4 and 3.8 respectively.
By applying these multipliers to the graph we can see that the system which resonates at 8.4 hz shows a small rise in amplitude about 15%. If we now compare this with the 5.3 hz example we see a much smaller rise around 5%. We have to extrapolate this answer, since it is off the scale of the graph. In other words at audio frequencies the heavy arm produces less bass boost.
You can also see that the damping applied has very little effect on the resultant gain as the lines are trending together. This means that even if we factor in a higher resonant amplitude for the heavy arm, we can see that while it alters things slightly, it has minimal effect.
There is some merit in a discussion of what happens at sub sonic frequencies but the arm with the lower multiplier (lighter arm) will face problems sooner as we decend below audible frequencies. As explained earlier in this thread the maths quoted above is for a single pendulum. The calculations above are based on a singular pendulum. The calculations above do not take into account the fact that the ET2 arm & cartridge have multiple pendulum effects in the horizontal mode – - the cartridge cantilever swings around the record pivoting at the stylus tip - the cartridge cantilever swings around the cartridge at the suspension end - the I beam This is why when Bruce Thigpen measures the impact of coupling the I beam he can measure up to a 6-12db lift in the bass. The calculated numbers in the above post are are theoretical calculations for a single pendulum, which does not apply. No actual test results have been provided that support these numbers and conclusions. Does this resonant peak really matter if it is below the audio spectrum ? 04-27-13: Ct0517
I usually hear only about audio designers trying to come below the audio spectrum – especially with a TT setup ?
That is what the conversations have been based on here as well ? 2hz – 6 or 7 hz. . The fundamental resonance is created by the combination of the compliance/mass of the cartridge vs the effective mass of the arm. Tonearm designers try to keep this as low as possible and minimize its amplitude. The peak rise in bass response generated by the arm/cartridge does not rise and fall at one frequency. The peak resonance has a spread either side of that calculated peak resonant point. Again I need to reiterate that Bruce has actually measured bass lifts of 6-12db when removing the decoupling. Even if one ( wrongly ) assumed this resonance has no effect because it is out of the audio band, one would be wrong because the bass lift ( nasty peak resonance ) can impact tracking adversely. This is why adding lead mass and removing the decoupling as advocated is wrong. Not only is it increasing inertia and side loads on the cartridge, it is also putting a lift in the bass frequency by removing the split resonance functionality that this arm uses to give a flat response. Adding lead mass and removing the decoupling will increase cantilever flex and tracking distortion. |
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04-30-13: John47
The writer should get this, from Franc Kuzma:
'At hi-fi shows, we routinely ask people to pull or twist the Air Line tonearm on a Stabi Reference turntable. The whole suspended mass of 24kg (52.8 lbs) moves back and forth for 1/4!9 while the air bearing maintains zero friction! Most people are shocked.' John47 - thank you for this. It confirms that the ET2 should NOT have additional mass added to it by removing the decoupling and adding lead. The Kuzma bearing operates at about 60psi whereas the ET2 bearing operates at a much lower level. One cannot just increase the pressure; the manifold, airflow and bearing tube have to be designed specifically for the target operating pressures. Perhaps Ct0517 could test his ET2 with 24kg on the end of it. Eminent Technology have 3 manifolds available - The original low pressure - The original high pressure - A large spindle high pressure Increasing the pressure generally increases the stiffness.
Eminent Technology website
ET II Large Diameter High Pressure Manifold - This new manifold is a direct replacement for the original high pressure manifold. You just remove the old spindle and push the old manifold out of the base and then insert the new manifold into the base and slip in the new, larger and heavier spindle. The new manifold allows the spindle, which is suspended on the air bearing, to be increased in diameter by about ¼th of an inch. Now ¼th of an inch may not sound like much, but it is the surface area of the spindle within the manifold that helps determine the stability of the bearing. The surface area of the new bearing is about 25% larger than the surface area of the old bearing, plus the tolerances are closer than in the original high pressure manifold. This makes for a much stiffer bearing.
These comments from Bruce Thigpen do not agree with the view opined in the following post 04-23-13: Richardkrebs
Although the bearing uses air which we know to be compliant, at the frequencies of interest, the bearing medium is stiff. So one could surmise that the Kuzma does have a stiffer bearing if you accept that Bruce Thigpen knows what he is talking about, which I do as he is well studied in Physics, Maths, Audiology and has been designing air bearings for some 30 years. Eminent are in the process of designing a new higher pressure bearing
Eminent Technology website
We are also developing a very high pressure bearing for the ET 2.5 which will operate between 20 and 80 psi. Please contact Eminent Technology if you have any questions.
The main advantage of the ET2 over the Kuzma is the low horizontal inertia and split resonance tuning capability due to the decoupled counterweight assembly. These features ensure there is no bass hump and provides superior tracking of the groove. Superior tracking will preserve the harmonic structure of notes. A good example of this is the test results that Frogman posted
03-23-13: Frogman
For instance, I am not yet convinced entirely that IN MY SYSTEM, going for the lightest weight/mass possible is the way to go. Yet, and speaking of loosening the laces, I decoupled (loosened) the I-beam yesterday, and lo-and-behold, on Donald Fagen's new release "Sunken Condos", what had previously been little more than amorphous low frequency energy suddenly became notes that I could discern the pitch of; completely the opposite of what I expected given my experience (extensive) experimenting with springs of different compliances (single, double, etc.), and the reason I had not tried it yet.
Bruce Thigpen confirms the problems created by increasing the horizontal inertia.
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
This has been the thrust of my posts over the past few months – adding lead and removing the decoupled counterweight takes away to benefits of the ET2 split resonance low mass design, causes an unnatural lift in the bottom end and increases distortion. These suggested modifications eliminate the main benefits of the ET2 design. Frogman, Slaw, Ct0517 and my own testing concurs with this. We have all achieved superior results with the correct tuning of the decoupled counterweight I beam. |
The problems of adding mass to air bearing tonearms. Here is Andy Payors ( Rockport 6000 ) view on it:
Andy Payor – Rockport 6000 Air Bearing Tonearm Designer - May 1996 review of the Rockport Series 6000.
"In linear trackers there is a big difference between the effective vertical and horizontal masses. Being a pivoted system in the vertical axis, a linear tracker's effective vertical mass is low because it consists of the relatively short armtube and cartridge. Horizontal mass is much larger: it includes the entire arm/sleeve assembly as well as the cartridge, all of which must be carried across the record and which do not benefit from being a pivoted system.
"Hang a small weight on the end of a spring and it bounces at a fairly high frequency over a short distance. Put a bigger weight on the spring and the rate of movement slows while the excursion length increases. The high mass of a linear-tracking arm in the horizontal axis can create a very nasty low-frequency resonance. The eccentricities due to the off-center pressing of virtually every LP made will excite this resonance as the system moves back and forth trying to track the shifting groove.
"In any arm/cartridge system, the arm should hold steady while the cantilever remains free to extract information from the groove. If the two were dancing partners, the cantilever would 'lead' and the arm would follow. In an undamped high-mass system the 'tail' (arm) begins to wag the dog (cantilever). Unwanted cantilever movement creates unwanted electrical output. In addition, any electrical output created with the coils uncentered in the magnetic gap is nonlinear, thus making it virtually impossible for the cartridge to act as a linear transducer, which is its job. Cantilevers can actually snap in undamped linear-tracking systems....In my opinion, a linear-tracking arm without damping is simply not viable if the goal is a 'reverse machine tool' accurately tracing what's in the groove."
This is precisely what I have been pointing out for the past 3 months. To recap the debate: 02-16-13: Dover
Richardkrebs
Re: your ET2 mods. Here are a few points for you to consider.
Richardkrebs post of 02-15-13
“I have a view on linear arms in that the rules for pivoted arms and effective horizontal mass do not apply. In fact I have added a lead slug inside the bearing spindle 25 mm long…
This combined with the fixed counterweight means that the arm is HEAVY in the horizontal plane.” This view is indeed strange. Many records are off centre. By increasing the horizontal mass of the arm significantly, when you play an eccentric record the increased resistance to motion from the additional mass will result in increased cantilever flex. On eccentric records your approach will result in phase anomalies during play back, increased record wear and probably cartridge damage in the long term. 02-23-13: Richardkrebs
Dover, for a given resonant system, all else being equal, addition of mass will lower the resonant frequency and reduce the amplitude of this resonance. ….Thou doth protest too much, methinks 03-12-13: Richardkrebs
Below this resonant frequency the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection. I do not need to talk to cartridge manufacturers to confirm this. Do the math. 03-04-13: Richardkrebs
Your scaremongering may have dissuaded people from trying a simple reversible mod Andy Payor and Bruce Thigpen both disagree with adding mass. They both support my analysis that adding mass creates higher distortion, unwanted cantilever motion and non linear response from the cartridge. Please note the key points Andy Payor of Rockport makes. High horizontal effective mass results in: • The high mass of a linear-tracking arm in the horizontal axis can create a very nasty low-frequency resonance. • The eccentricities due to the off-center pressing of virtually every LP made will excite this resonance as the system moves back and forth trying to track the shifting groove. • In an undamped high-mass system the 'tail' (arm) begins to wag the dog (cantilever). Unwanted cantilever movement creates unwanted electrical output. In addition, any electrical output created with the coils uncentered in the magnetic gap is nonlinear, thus making it virtually impossible for the cartridge to act as a linear transducer, • Cantilevers can actually snap in undamped linear-tracking systems Andy Payors view of the world supports my argument for maintaining the ET2 as a low mass design and supports the use of “magnetic” damping. Andy Payors comments on air bearing tonearms are exactly the same as Bruce Thigpens. Bruce Thigpens patented decoupled counterweight design is specifically designed to deal with the unwanted nasty peak resonances inherent in linear tracking tonearms with a high horizontal effective mass. The suggestion of adding lead mass and removing the decoupling mechanism in the ET2 is inadvisable. It results in higher distortion and non linear response. Andy Payors endorsement of Bruce Thigpens low mass approach leads me to wonder why anyone would continue to advocate adding lead mass and removing the decoupling of the I beam from this sophisticated and ingenious high end tonearm. |
05-03-13: Ct0517
Dover - Andy Payor and Bruce Thigpen both disagree with adding mass.
Cant speak for Andy Payor but this is not true with BT. The original ET2 came out when MM’s were popular. When heavier less compliant MC’s became popular. Bruce introduced the heavier 2.5 spindle as well as heavier CF and Magnesium arm wands to deal with MC’s. This has already been discussed here.
http://www.eminent-tech.com/magarmtube.html
thats an old web link btw - the new price for the mag tube is on Bruce's website under Et 2.5 parts list.
A couple of folks here including Frogman and RK have come up with diy solutions. Frogman has used special armtube wrap. RK has added weight to the armtube and spindle. I’m sure others have done other things. Frogman noted as well as BT and myself that the 420str MM seems to gel better with the lighter aluminum armtube. My 420str is now on my ET2. Ct0517 – my point on adding mass being not desirable is in the context that Richardkrebs has advocated adding 30g of lead to the bearing tube and another 35g by removing the decoupling. Removing the decoupling increases the horizontal effective mass. This is a total of 65g of added horizontal effective mass. Far too much and from what I’ve heard when trialled. Thigpens own words are to keep the horizontal effective mass as low as possible. The “heavy” armtube that ET provide for MC’s is not massy. Bruce advised me that Bruce Thigpen
Without the wire harness the weights are respectively 13,17, and 19 ("heavy" version of the magnesium tube) grams. So the heavy armtube is only 2-6g heavier than standard, not 60g as one has advocated. The link states “the new heavy version has over twice the wall thickness of the current magnesium arm tube to reduce the resonance levels in the arm tube “. This is not to deal with the low compliance per se, it is to deal with the increased energy levels generated from having a low compliance that the armtube has to deal with, its about rigidity. This is similar to part of the rationale for having a decoupled counterweight. Thigpen says it allows him have a heavier and more rigid arm carrier/bearing tube and still keeping the horizontal effective mass as low as possible. Dover - The Kuzma bearing operates at about 60psi whereas the ET2 bearing operates at a much lower level
Well this is not totally true either – other than the everyday ET2 with the original pumps Bruce would also custom build them for any PSI and did. Yes I should have used the words “standard ET2” agree with this. I was aware that if Bruce is advised what pump is to be to used he will provide a manifold tailored for that pump. 1) Adding weight to the ET2. As mentioned above and in previous pages here Bruce added weight to the spindle and changed the armtubes for MC’s. If Do-it-yourself (DIY) - adding weight to the spindle and armtube. Consideration needs to be given to vertical and horizontal masses. The ratio is important. Its important to remember that the armtube/armwand affects both the vertical and horizontal masses. . Excellent point on how adding mass can affect either vertical or horizontal effective masses separately or both depending on where it is added. The issue that I have is the addition of some 60g to the horizontal mass. Bruce’s testing and recommendations in his correspondence are to keep the horizontal mass as low as possible, or one will get an unnatural 6-12db lift in the bass, and increased tracking distortion. 2) Decoupled IBeam - The ET2 design is de-coupled. This is a big plus to me right now as it allows me to use any cartridge I want. If you couple it – its no longer an authentic ET2 design. Its your own unique design. Those using it this way seem to have it tailored the setup to one cartridge only? This is their choice. I have no issue with anyone wanting to do what they like with their system. As someone who has studied engineering at university and has a great respect for Thigpen’s design I take issue where misleading information has been provided or maths wrongly applied to support operating the ET2 outside of it’s design parameters and intended use. A bigger evil for me than this ....my pivot arms can’t go straight. No one seems to have an issue with this?
It’s like spending thousands on a new car...on the drive home I discover it pulls to the right. I call the dealer about the problem. His/her answer to me is to let some air out of the front left tire. :^(
Would you accept that? Well - All pivot arm owners including me do. Absolutely agree. But see my leading edge notes below. I love the ET2 when set up properly, but there are some pivoted arms that can provide musical enjoyment as well. 3) Air bearing stiffness. Leading edge notes. My boogie test is older lps up against Master tape dubs – no issues here for me based on my ears. I’m good.
Dover – I am curious to know for fun what your boogie test is? Chris – these are the words of the reviewer. I would not use the word boogie. My experience is that the Naim Aro, being a mechanically grounded unipivot bearing can reproduce the leading edge far crisper, cleaner and more extended the ET. An example would be percussive instruments. This is typical of well designed unipivots. I have a friend with 2 Graham Phantom’s mounted on a Micro Seiki RX5000 and I hear these same attributes. Even an inexpensive Hadcock can display these attributes – although it is not a true unipivot as the point sits in the apex of 3 balls. I associate boogie more with the word rhythm and overall musical timing. In this context arm/cartridge matching plays a big part. The Aro has a narrow operating window – my Dynavector Nova 13D and Denon 103D have better speed, timing and impact on the Aro than with the ET2. The Koetsu Black has more extension in the highs but does not boogie. Whilst it is quick on percussive, has great soundstage & transparency the bottom end timing is awry. I get fantastic “boogie” with the ET2 when the ET is matched and tuned correctly with the right counterweight location and decoupling employed.The ET2 exhibits better timing and boogie when the horizontal mass is kept as low as possible to optimize groove tracking. If you watch the cantilever the timing goes awry when the cantilever is flexing around on an eccentric record. This is one of the big issues with adding 60g horizontal effective mass. In my experience adding mass and removing the decoupling destroys the speed, timing and boogie factor. With regard to springiness – there is an optimum air pressure for the mass at which an air bearing self centres. The design of the air bearing is critical to this, as is the surface area of the bearing and the mass and forces being supported. http://demo.amplio.si//AmplioCMS2/UserFiles/File/29/theory.pdfThe main problem is that the cushion of air in the gap behaves like a spring. This means that, under dynamic conditions, the cartridge and tube assembly will move in various directions and the cartridge will not stay in the position of the cutter head but will be pulled along the groove and twisted due to the forcesmoving the cartridge in the grooves. Of course this also happens in pivoted arms, but due to differences in construction ie. loose bearings, vibration of bearings and other parts.
To practically avoid this effect we must use a stiff bearing, which automatically reacts to these external forces. Construction of a stiff airbearing is dependent on the air gap, air pressure and bearing surface. Higher air pressure means a stiffer bearing which can carry a heavier load. The same effect can be achieved by a small air gap between the moving parts of the bearing. In the best bearings the gap is limited to a construction of 10 microns. This is actually less than in most pivoted tonearms which have air slack in their bearings to move!!
A stiff bearing will not in itself stop the tonearm bearing from moving closer to one side of the bearing shaft when force is applied to one side. The bearing must be constructed in such a way that it is self-centering. That means, in practice, if force is applied to one end, the gap will decrease but a properly constructed bearing will respond to this by increasing airflow to the smaller gap, restoring the equilibrium.
In practice the gap stays the same if forces are not overloading the bearing and the cartridge position under dynamic conditions remains stable. If we apply force to one end of the bearing sleeve, we have the same problem. To have a self-centering effect along the axis as well as along the diameter of the rod, the airbearing must be properly designed. This supports my view that if someone adds 60+g of mass to the ET2, not only would they have to increase the bearing stiffness, but would almost certainly have to redesign the bearing itself. This would still not negate the problems of increased distortion from running a higher horizontal effective mass and removing the decoupled counterweight on eccentric records. |
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. |
The kong,
thanks, pictures are interesting - the stiffness around the arm connection is obvious. The 6000 does look quite flimsy, whereas the Sirius has a tapered armtube to a larger armtube clamp. The energy control should be much better.
Also interesting are the similarities to the ET - the tapered armtube for MC's and the use of a relatively small counterweight quite a long way away from the bearing. Having less mass in the counterweight further out lowers the horizontal effective mass ( clearly a design goal for Payor ) but increases the vertical effective mass ( good for low compliance MC's ). This is exactly the same strategy employed in the ET.
Re the van den hul bent cantilever - I ran a Shure V15Vmr on the ET2 for about 10 years whilst I had a hiatus from audio in the 90's. The Shure is around 20 yrs old, still has the original cantilever & stylus, has only ever been used on the ET2 and the cantilever is as straight as a die; this I think a testament to the ET2's relative light mass and decoupled cantilever and of course the electromagnetic damping discussed earlier in this thread would have helped as well. |
05-13-13: Richardkrebs
Thekong.
It should be no surprise that the arm weighs in at that figure or even higher with the heavier counterweights. It is neccessary for it to perform well with low compliance carts. This is not correct with respect to the ET2. In my experience adding mass to the ET2 with low compliance cartridges reduces the speed, articulation, transparency and harmonic structure of the music. Increasing mass with the ET2 also increases tracking distortion and can result in a bass hump of 6-12db by loading up the cartridge with high mass. A quote direct from Bruce Thigpen 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 Quote from ET2 Manual – Bruce Thigpen P29
It is desirable in most cases ( low to medium compliance cartridges 5x10 dynes/cm – 20x10 dynes/cm ) to use the minimum number of weights, far out on the cantilever stem. This decreases the horizontal inertia of the tonearm while increasing its vertical inertia. Adding mass to the ET2 increases the inertia to lateral movement and on eccentric records will result in increased cantilever flex and distortion. Any excessive cantilever deflection in a moving coil will result in phase anomalies as the coils attached to the cantilever are driven into a position where the response becomes non linear. This is what Bruce Thigpen is saying. Furthermore, with higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and uncontrolled cantilever flex are inevitable. This explains why when Richardkrebs added fluid damping the sound appeared to be better controlled or in his words had “greater presence and focus”. This is because the addition of lead mass and removal of the decoupling mechanism from the I Beam in his ET2 pushes the horizontal mass too high and the cartridge cantilever motion goes out of control. He would be better off reducing the horizontal effective mass by removing the lead he added to his arm and putting back the decoupling in the I Beam that he removed. If you go to the Eminent Technology website and read the ET1 manual (that’s the arm that precedes the ET2) you will discover that the ET2 was a design decision to move away from the high mass/fixed counterweight model utilized in the design of the ET1 to the low mass decoupled counterweight model utilized in the ET2. These new design considerations embodied in the ET2 resulted in substantive improvements in the quality of sound reproduction. The decoupled I-beam methodology employed by Bruce Thigpen in the ET2 is designed to minimize horizontal mass and ensure that the resonance of the I-beam and counterweight remains below the horizontal resonance of the arm so that the 2 resonances (arm and beam) do not couple together to produce a large peak resonance in the bass. |
05-14-13: Richardkrebs
The cartridge still has to push this mass sideways. Either a relatively low mass with the ET2 or heavier with a Rockport , Kuzma, Walker or Krebs arms. In an undamped system with a fixed counterweight we see a large rise in amplitude at resonance. This is easy to control with damping. The adding of lead mass will increase distortion due to the higher inertia of the arm. Basically you have added a peak resonance in the bass, then tried to tame it by adding damping. Both the added mass and fluid damping will increase inertia, and compromise the ability of the cartridge to track the grooves accurately. On an eccentric record this will be even worse. The Krebs arm has some 65g of horizontal effective mass added - an increase of inertia close to 300%. This increases cantilver flex and distortion as per Bruce Thigpens commentary. 05-14-13: Richardkrebs
With a stiff cartridge; the only way to get Fr low enough to avoid interaction with audio frequencies was to make the arm heavier. The Fr of my arm/cart is 5.2 Hz. This is not true. Most tonearm designers target a FR of around 8-12hz. This is based on an assumption that most systems dont produce much response below 20hz and footfalls are in the zone of around 2-3hz, dangerously close to your 5hz. Secondly, the increased distortion from the added inertia of the arm resulting from the increased horizontal effective mass certainly impacts the audio frequencies. The phase anomalies from the increased distortion on the cantilever can be heard quite clearly in a system that is reasonably transparent and quick. Furthermore the peak resonance at 2-5hz that you quote can invoke instability in tracking, its the same as walking past a turntable on loose floorboards. 05-14-13: Richardkrebs
In past I have damped the resonant peak by adjusting the air pressure and deliberately dressing the lead out wires to damp horizontal movement. This method is fussy and not particularly robust. Basically what you are saying here is that you like the sound of the ET2 with additional drag inhibiting the free movement of the arm to track the grooves. In my experience this slugs the sound. Other users have found improvements by removing this drag - they have removed their fluid damping and replaced it with electromagnetic damping which has the benefit of not inhibiting movement until the movement happens. 05-14-13: Richardkrebs
My counterweight is 32 grams.
I have added 30 grams of lead inside the spindle in the center of working travel, such that it does not leave the bearing sleeve when tracking modulated grooves.
The ET2 can be optioned with the heavier magnesium wand. 8 gms heavier.
It comes with up to 40 gms of counterweight. 8 gms heavier.
In terms of bearing load carrying capability I have added 30 gm to a lightly configured ET2. If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams. Your mathematics is incorrect : The bearing spindle without arm/counterweight is 14g The aluminium arm is 11g The CF arm is 17g The Magnesium arm is 19g So the total horizontal effective mass of your 9gm cartridge on a standard ET2 arm with a 32gm decoupled counterweight is: 9g(cart)+11g(arm)+14g(bearing spindle)=34gm The total horizontal effective mass of your 9gm cartridge on your altered ET2 "Krebs arm" with 30g of lead added and the 32gm counterweight coupled is: 9g(cart)+11g(arm)+14g(bearing spindle)+30g(lead that you added to the spindle)+32g(counterweight that the cartridge now sees because you removed the decoupling)=96g Therefore you have increased the horizontal effective mass from 34gm to 96gm, an increase of 62g. I cannot see how you get to 6gm in your maths. Coupling the 32g counterweight adds 32g to the horizontal effective mass. Adding 30g of lead to the spindle increases the horizontal mass by 30g, even when placed inside the bearing. 05-14-13: Richardkrebs
If we option it with the magnesium and use all the supplied weights my weight adder is now reduced to 14 grams. This is another area where the underlying assumptions are misunderstood. Bruce's recommendations documented in the ET2 manual on low compliance cartridges is carry as little weight as possible as far out on the I Beam as possible. This keeps the horizontal effective mass low but increases the vertical effective mass. It is not recommended to load the I Beam with all the counterweights if one can shift the counterweights further out. |
05-14-13: Richardkrebs
.. if my heavy ET has problems with cantilever flex, bass boost, phase shift and so on; so do the other heavy arms. Rockport, Walker, Kuzma. This because the horizontal effective mass is solely determined by the total weight that is moved sideways at the frequency of interest, since all of these designs are virtually frictionless. Thats correct and thats why the lower mass ET2 has a big advantage over the heavy arms when kept in its standard format. The level of damping of course changes all this. This is not correct. The damping may ameliorate the amplitude of the resonant peak, and result in less bass boost, but the high mass still provides an inertia, a resistance that the cartridge has to work against to track the groove, particularly on eccentric records. It is this inertia that causes the cantilever to flex and increase distortion. |
05-15-13: Richardkrebs
Dover.
My calculation of weight delta was based on how much weight the air bearing has to carry. Not the horizontal effective mass. You voiced concern that I had taken it outside its load carrying capability. Optimum load capacity. You have added 30g of lead to the mass the bearing has to carry. This has 2 negative effects - it pushes to mass to the extreme and one would redesign the bearing if one were knowingly going to operate the arm at a higher mass level. Secondly the added mass will impact the shearing forces involved - the arm is not frictionless and the bearing is not absolutely rigid - these are some of the reasons why users are hearing different results with higher pressures. As a point on your calculations on FR I led slide the error in your calculations - the bearing has a resonance, the bearing tube has a resonance and the total resonance will be a sum of the resonances inherent in the arm. One really needs to measure the resonances to see whats going on , thats why Bruce does extensive testing. The maths you are using for FR calculations is not the complete story. 05-15-13: Richardkrebs
Re heavy arms. I assume you are saying that ANY heavy arm, and this includes the Rockports, Walker and Kuzma have serious problems with distortion. Further, by implication, you are saying that the owners of these arms are deaf to these distortions. I think you should use the word preferences, when making judgments on other folk, but certainly they may well be. Some folk like fat bottom ends others prefer speed and musical timing. For me music is about timing and nuance - I can certainly hear the slugging of the sound and loss of musical timing when adding too much horizontal effective mass to the ET2 as others in this thread have also found when they removed the decoupling from the I Beam. You may also like to read the comparison of the Kuzma to the Walker in the Absolute Sound mag December 2006 where the reviewer articulates the differences - the Kuzma being dark and solid vs the Walker having more of "the "gestalt" of a live concert, more lifelike presence of instruments, their colors, their dynamics, and the space they play in" of the Walker "fuller, more realistic in tonal color, bigger, bloomier, wider, deeper, more layered in soundstaging, and a bit more authoritative dynamically". 05-15-13: Richardkrebs
Targeting say the 12 hz you mentioned would mean that it is causing phase and amplitude problems at 36 hz. This is not good. Depends how big the amplitude problems are. Some of the heavy arms you have mentioned have additional measured resonances at 100hz & 200hz. In your case you you have reduced the theoretical resonance from 8.08hz to 5.17hz. so yes you have a small residual at 24hz in a standard unmodified arm - but this is outweighed by the amplitude of the resonance being much higher when you added 62g of horizontal effective mass. Furthermore that small secondary resonant peak at 24hz with the standard arm can be dialled down with careful tuning of the counterweight spring. I very much doubt whether many systems are truly flat to 20hz in a real home environment. In your case you have shifted the secondary resonance from 24hz to 15hz, but have increased the amplitude of the 15hz resonance substantially - probably 6-12db higher in amplitude compared to the smaller resonance at 24hz with the arm as standard. |
05-15-13: John47
Bruce Thigpen:
"The ET-2 with the
damping trough will exhibit almost perfect low frequency phase response."
You don't like the ET-2 set up to have near perfect low frequency phase response?
Thats fine, its a free world, but it means you accept/enjoy DISTORTION. No I dont believe Bruce Thigpen does enjoy distortion. On the contrary Bruce Thigpen has cleverly designed an arm that tracks superbly and can be fine tuned via the adjustable VTA, Azimuth, and decoupled counterweight. Bruce Thigpen does not add 60g+ of horizontal effective mass and remove the decoupling of the I Beam. The perfect phase response that Bruce obtains with the damping is achieved by operating the arm within its design parameters. Keeping the horizontal mass as low as possible is part of the design. Adding 30g of lead to the arm and removing the counterweight decoupling will indeed create significant distortion, including an inflated bottom end and phase anomalies, but that is not how Bruce runs the arm. |
05-17-13: Richardkrebs
Dover
I do wish you would stop repeating your fundamental error ad nauseum. I am not aware of any errors on my part. Please read my last post. It outlines the errors you have made. Let’s address the fundamentals: The ET2 has a unique patented decoupled counterweight. The decoupled counterweight is damped at its natural resonant frequency of 2-5hz. This decreases the rise in frequency response at the fundamental resonance. ( page 9 of the ET2 manual ). So with your cartridge a standard arm would have a fundamental resonance at 8hz, and the decoupled counterweight reduces the amplitude or size of this resonance. Removing the decoupling as you have done will see an increase in the resonance of 6-12db – as shown in Bruce’s testing, documented on his website. Now you state you have added some 62+g of mass to your ET2 and removed the decoupling. So there are 2 points here: 1. Removing the decoupling increases the fundamental resonance by 6-12db. 2. Increasing the mass has reduced your FR to 5hz. One can see that by adding mass you have placed the fundamental resonance in the same zone as the natural resonance of the decoupled counterweight. This would be a disaster as the 2 resonances will likely sum together to create a large one. You can deduce from this that removing the decoupling not only takes out a fundamental design feature of this arm that provides a flat response in the bass, it actually compounds the problem of the FR peak and makes it doubly worse. Now let’s assume that your system has no response below 30hz, just for arguments sake, not that I’m suggesting it does. The reality is that phase shifts at fundamental resonance ( bass in my language ) will affect the rest of the frequency spectrum. In other words it affects the mid and highs. ET website
If a tonearm/cartridge system has a substantial rise in response below 20 Hz as most do, the phase response at the low end will be shifted and phase shift will occur beginning at 2 to 3 times the resonant frequency down to Fr. The time in which low frequency signals come from the tonearm will be shifted slightly with respect to mid-range frequencies within the audible range and substantially shifted up to several periods at resonance. One can clearly hear these distortions when adding mass to the ET2 and removing the decoupling spring. 05-17-13: Richardkrebs
Bruce measurements show that this rise in response is reduced by 8db with the addition of an oil trough. This in test conditions which used a deliberately high Q and a low compliance cart. The amplitude of resonance decreases the further you move away from Fr. BT suggests that resonance effects frequencies up to 3xFr. This testing is irrelevant in your case because of what you have done to your ET2. The testing was conducted with a standard ET2 with a decoupled counterweight and fluid damping added - the total horizontal effective mass was approx. 54g. You have altered your ET2 by removing the decoupling of the counterweight, which increases FR by 6-12db and increases the horizontal effective mass by 32g. You have also added 30g of lead to your tonearm. Your tonearm weighs approx. 114g compared to the 52g tested by Thigpen. Thigpens test results cannot be applied to support your argument that your arm does not have a rise in response in the bottom end because you have doubled the weight of your arm and removed the decoupling mechanism from the counterweight. What you have not addressed, other than the discussion on the impact of FR, is the tracking distortion that is generated by increasing the mass of the arm, in your case more than doubling it. 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, You have doubled the weight as seen by the cantilever. A conventional pivoted arm with an effective mass of 14g with a cartridge of 9g will have a total effective mass of 23g. The standard ET2 has a horizontal effective mass of 34g or 52g with the damping mechanism. With your addition of lead and removal of the decoupling, and added fluid damping, your altered ET2 has an effective mass of approximately 114g - 4 times the effective mass of a conventional pivoted arm. Readers should try to imagine waking around with the weight of three adults sitting on their shoulders, and pretending the weight is of no consequence. This is what the cantilever has to endure with the Krebs alterations to the ET2. |
Thekong – The answer to your question regarding frequencies impacted by horizontal Fr from Richardkrebs are mostly wrong. It is important that they are addressed. Impact of Fundamental Resonance: 05-20-13: Richardkrebs
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. This statement is not correct. I quote from Richardkrebs earlier post 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. . As you can see Richardkrebs appears to be confused. On the 15/3 he cites Bruce Thigpen as saying that there are phase and amplitude problems at 3 times Fundamental Resonance, then on 20/5 he cites Bruce Thigpen as saying the rise in response is almost zero. Neither of these statements are correct. What Bruce Thigpen actually says on his website is that on an undamped standard ET with decoupled counterweight there is a resonant peak at 3 times the fundamental resonant frequency, and that this is reduced with fluid damping on a standard ET with decoupled counterweight. The other mistake that Richardkrebs continues to make is to use as a reference a graph for a single harmonic oscillator that plucked from Wikipedia. Wikipedia - http://en.wikipedia.org/wiki/Harmonic_oscillatorRichardkrebs - http://s1173.photobucket.com/user/CT-993/media/ResonanceGraph_zpsdd78e0f4.png.html?sort=2&o=7This graph does not represent the forces on the cantilever because the cantilever and cartridge is not a single harmonic oscillator. A cartridge tracking a record groove has a fulcrum point at both ends – the stylus in the groove, about which the cantilever pivots, and the cartridge end of the cantilever which has a suspension. Forces are exerted on BOTH ends of the cantilever. The graph represents a pendulum with only one fulcrum point at one end only. The mathematics that Richardkrebs uses does not apply. 05-20-13: Richardkrebs
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. . This assertion is wrong on several fronts. The cantilever deflects. Firstly – the record grooves are cut at 45 degrees. The cantilever deflects. For a moving coil cartridge the cantilever deflection moves the moving coils within a magnetic field. That is how sound is reproduced from a record player. This video shows how RCA Living Stereo stereo playback is achieved. http://www.youtube.com/watch?v=Jq2sjGFvNnM If there is no deflection of the cantilever then Richardkrebs system cannot be producing any sound that resembles music. Secondly, the statement defies physics. I quote Bruce Thigpen directly: 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.” Furthermore, Richardkrebs assumption with regard to Bruce Thigpens views on eccentric records are not supported by what Bruce Thigpen actually says in the ET2 manual. 05-20-13: Richardkrebs
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. This assumption again is just plain wrong. I quote from Bruce Thigpen’s ET website: ET2 Manual page 47 :
“if you like to play severely eccentric records, ones with run out greater than 1/8th of an inch, then we suggest you use a low mass pivoted arm.” In summary, Bruce Thigpen is very much of the view that the horizontal effective mass should be kept as low as possible, and the decoupling employed to minimsie fundamental resonant peaks at FR and 3xFR. He has also expressed his view that increasing mass increases distortion, and I quote Bruce Thigpen - 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, Thekong , I trust this clarifies the queries you raised. |
05-27-13: Richardkrebs
Dover says.
"....on an undamped standard ET with decoupled counterweight there is a resonant peak at 3 times the fundamental resonant frequency, and that this is reduced with fluid damping on a standard ET with decoupled counterweight."
I say.
"At 3x Fr the rise in response is almost zero."
In response to this question..
In the technical section you talk about phase shift beginning at 2 to 3 times the resonant frequency down to Fr.
Does this mean that there is a resonant peak at 3 x Fr or is this the point where the phase and response errors have reduced to low levels?
Bruce T says...
"This is the point where, above this frequency, the phase shift becomes minimal, as you approach the resonance frequency, the phase shift increases. I hope this helps, thank you very much." Richardkrebs, you continue to conflate apples and oranges and misrepresent statements. The technical section you refer to is for a standard ET, with a substantial rise in response below 20hz. FLUID DYNAMIC DAMPING FOR THE ET-II
If a tonearm/cartridge system has a substantial rise in response below 20 Hz as most do, the phase response at the low end will be shifted and phase shift will occur beginning at 2 to 3 times the resonant frequency down to Fr One can achieve a flat response by tuning the decoupled counterweight and keeping the horizontal mass and Q low as outlined in the ET manual and demonstrated in the Stereophile testing. Your ET is not standard. You have doubled the horizontal mass of your arm by adding lead and you have removed the counterweight decoupling mechanism. The effect of the 2 modifications you made to your arm is to increase the amplitude of the fundamental resonance by some 6-12db as shown by Bruce Thigpens testing. 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 The arm Bruce used for testing was deliberately set up with a high Q and very low compliance cartridge. The standard ET when used as outlined in the manual with a decoupled counterweight has a lower Q. A low frequency sweep was performed twice on the tonearm, once without the damping trough and once with the damping trough. The cartridge used was of very low compliance and the tonearm was set up so that a high amplitude high Q resonance existed. The results of the test show a reduction in the amplitude of the resonance of about 8 dB (horizontal). You continue to ignore Bruces stated view that increasing horizontal mass increases distortion 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, Clearly the reduction of 8db is for a standard arm. In the case of your arm to which you have added lead, doubled the horizontal effective mass and removed the decoupling mechanism, all you are achieving is some reduction in the problems and distortions you have built into your arm. You have misrepresented Bruce’s view on eccentric records, 05-20-13: Richardkrebs
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. This assumption again is just plain wrong. I quote from Bruce Thigpen’s ET website: ET2 Manual page 47 :
“if you like to play severely eccentric records, ones with run out greater than 1/8th of an inch, then we suggest you use a low mass pivoted arm.” It would be helpful to move this thread forward if you acknowledged the issues related to adding mass and move away from using examples, maths and quotes that are irrelevant and taken out of context. |
06-12-13: Richardkrebs
Slaw.
"Variations in the degree of trueness"
Totally agree. Since I had the luxury of building the arm and TT, almost concurrently, I could deal with these topics in real time.
Getting accurate alignment when two components are brought together from different manufacturers, without the ability to adjust, would be pure luck. Yes I suppose almost concurrently could be considered real time for some folk. What you have forgotten is that the ET2 has 3 adjustable feet that ensures that the arm can be leveled for any turntable. I should also point out to readers that engineering wise it is almost impossible to machine 2 flat surfaces, without manufacturing 2 or 3 of each component and flipping, polishing and lapping in the 2 surfaces to be mated. So in most instances the 3 footed approach of the ET2, properly anchored, will be inherently more stable than 2 “flat” surfaces mated together. |
06-16-13: Ct0517
Richardkrebs - Here is a conundrum. Stylus drag is significant, being able to slow some TT platters. What about the other side of the coin?
What about a TT platter system that doesn’t slow down with stylus drag, but can’t slow down fast enough after a real tough vinyl passage?
That can sound interesting? Some really like this sound. :^) Ct0517 – the question I ask myself is How can someone listen to a direct drive for 30 years, before discovering that the timing is out, and finding a “fix” ? It would seem to me that they must be less sensitive to timing errors and other artefacts from the speed instability to have put up with this for so long. Is it possible that the insertion of a lead slug and the removal of the counterweight decoupling on the ET may help to slow down the “sound” on those passages where the composer or conductor got it wrong? |
06-15-13: Slaw
I can only add: when I set up a cartridge, I try hard to set the appropriate VTA for said cartridge in the "neutral zone", (my term), of the arc block. The "neutral zone".... This to me is the (center range) of the arc block, where as if I adjust upward or downward, it will have the least effect on overhang, ( which I choose to reserve for differring weights of vinyl), this is in fact the center of the arc. Logic 101! Yes, I choose to make this adjustment for the differring thickness of vinyl records. What makes the ET such a great arm (for me)is for such a choice. Despite what is written in the manual, an up or down adjustment of the arc block results in another adjustment that needs to be corrected for overhang. There is no doubt about it!
06-16-13: Ct0517
Slaw- from my experience if another adjustment is needed for overhang, something is off in the setup.
If the ET2 is setup properly, the mounting base post should be level and true with your platter. The mounting base post is after all what holds the VTA gearing that raises and lowers the ET2. The platter is what the stylus overhang reference gauge rests on. The two are a marriage.
Check level on both. How true they are to each other will determine imo how true your overhang is when you raise and lower the VTA. Some discussion on overhang is required here. Back in December last year I posted a postulation that one could consider mounting the cartridge slightly forward of the tangent line. The theory is that if you are running at the tangent then there are no lateral forces on the stylus and it will “chatter”, slowly eroding the high frequency grooves over time. If you also go back to the Stereophile review posted and read it you will also find that when tracking at the tangent then one channel leads the other by a few milliseconds. See bottom page 86…. http://s1173.photobucket.com/user/CT-993/library/?sort=2&page=1 which can be corrected by running the cartridge forward of tangent. Slaw- the answer to your VTA adjustability and overhang may be to add a lead slug and remove the counterweight decoupling. With this mod you wont hear any difference if the VTA is out a bit. The only downside is that playback appears in 3/4 time, even when played in 5/4 time. Alternately, you might be better setting the VTA for the thickest record, and then use shims under the record matt to adjust up the thinner records. This way you will not have the “overhang” problem. The issue I had with changing VTA on the fly is that the bearing tube can go out of level very easily when adjusting VTA. This may have been due to the fact that I used a single point ground when tightening the bolts holding the bearing to post. Whenever you loosen or tighten the pillar bolts you need to recheck the bearing tube is dead level. |
Ct0517
The best Pinot Gris in NZ are from the Central Otago region as are the best Pinot Noir. Even the cheapies from this region will usually be better than from elsewhere in NZ. The Hawkes Bay region is known for its Cabernet/Merlots's and the Marlborough region for Sauvignon Blanc's.
Unfortunately for those with a lead fetish, they must avoid wines with high lead content as it can lead to irrascibility, irritability, confusion and even delirium.
Some of the vinyards to look out for are -
Mt Difficulty - very very good, a tonic for those who are struggling with their ET.
Wooing Tree - something aromatic you could share with Dorothy
Dry Gully - for those that are shall we say "having trouble with the waterworks".
Two Paddocks - this is owned by Sam Neil the famous NZ actor, probably one for those with too many Kangaroos in the top paddock - hence the name Two Paddocks.
As you can see there is a suitable wine for all occasions. In fact after a particularly good meal and Pinot Noir the other night I had a brainwave. I'm going to eliminate the counterweight completely. By my reckoning I can use a helium balloon to hold the cartridge up. I'm just trying to work out how to adjust tracking force up and down down in increments of 0.001g. I think I can do this with a temperature controlled environment used in tandem with the helium balloon. |
Ct0517 - I have listened at length to several SP10's both MkII and Mk3 both with and without the krebsupgrade. To my ears none of them are particularly transparent. Both the Micro Seiki 5000 ( air bearing ) and Ipad (on BDR cones with Cambridge 840 DAC ) sound more resolving, more fluid in terms of timing and have an openness that eludes the Technics.
Re the mats - I've compared the std, stainless and copper and preferred the copper - a bit more focus and cleaner through the mids. The Mk3 is substantially better than the MkII - less jittery and grainy, but bear in mind the Mk3 platter is considerably heavier and more damped than the MkII. In my view playing around with mats on the MkII merely highlights its shortcomings, and you may be better off with something relatively benign rather than resolving. |
Ct0517 - further to my previous post, my experiments with copper mats is that you get more out of them when used in conjunction with a record clamp to ensure tight coupling of the record to the copper. |
06-23-13: Richardkrebs
My TT and Pre happen to sit on granite surface plates, surplus left overs from our machin shop. They are used, not of their flatness but their energy sinking properties. This is not correct. Granite is very very hard and therefore tends to pass energy straight through in both directions, it does not sink energy in of itself. Therefore what the granite sits on becomes important. For example HRS use a polymer to dampen the natural resonance their granite shelves. Readers should also be aware that granite contains high levels of uranium and can be considered radioactive. My own experience with granite is a hard edge to the sound in the upper mid lower treble - granite has a definite sonic signature related to it's natural resonance. |
06-24-13: Richardkrebs
Dover
Correction, you have not heard the full krebs upgrade.Two people in NZ have.
Please confine your comments in posts to those that are actually true. Richardkrebs Your assertion is wrong. I have listened at length to the Technics krebsupgrade on 2 occasions in the past few months. I stand by my comments. At least 3 of your turntables are in NZ and some overseas. I know some of the owners well. |
