It sounds better Hi Richard, I am no engineer, so has absolute no idea about the physics behind it. However, as Lloyd didn't use the decoupled counterweight (which is not hard nor costly to implement), I also believe it probably sounds better that way, at least to his, and apparently also to your, ears. Actually, I have also fabricated a fixed counterweight for my ET2.5, but unfortunately have no time to test it yet. When it happens, the ET would be compared to my favorite arm, the Rockport 6000! |
Thekong
We look forward to reading your comments. |
Richardkrebs Referring to your last post 03-12-13: responding to Dover. At frequencies below resonance the cantilever is free to push the mass of the arm sideways. This does not defy physics, it is physics. Correct In other words the cartridge suspension is stiff enough to accelerate the arm mass sideways. . That is an assumption that will depend on the compliance of the cartridge. If the compliance is low enough then possibly, but before the acceleration commences the cantilever will flex. You seem to be unaware that cantilevers are mounted in a rubber elastomer that is not rigid. Think of a tension spring with a weight suspended at one end. This combination will have a resonant frequency. If you hold the spring end opposite to the weight and move it up and down at a frequency below resonance the weight will move up and down in sync with your movement. The spring will NOT stretch as a result of this movememt. . A curious analogy, yet again, you compare apples and oranges. Your analogy compares 1. Holding the end of a spring with a fixed weight on the other end to 2. The stylus point sitting in a groove, not held, at the end of a cantilevered beam, at the other end of which is a rubber suspension ( not a spring ), and the other side of the suspension has a mass loading that is constrained at 90 degrees by the rigid air bearing some 6 inches away. Your analogy is a triumph of the imagination to consider these two scenarios in the same manner. Your discourse on resonant frequency is irrelevant. Quite frankly I cant be bothered doing the maths, but I defy anyone to show me a cantilever that does not flex when playing an eccentric record. This does indeed defy physics unless you have a cantilever that has zero compliance. No, the video does not show the cantilever, that is why I asked him if it was a problem. If you agree the video does not show the cantilever then why do you repeat the following statement that is misleading? I repeat the video is shown specifically to allay fears of problems due to high horizontal mass. . I assume from your lack of response that you have not sought any advice on this matter from any cartridge designers. I would have thought this was the first port of call for a thorough and complete understanding of the problems of navigating eccentric records. |
Thekong Thanks for sharing your experience. I agree with Fremer. Thigpen does appear to hold patents on the decoupled counterweight. Whereas Walker uses a fixed counterweight at 45psi in the Proscenium, Richardkrebs advocates using a fixed counterweight, adding additional lead weights and running a relatively low pressure of only 12psi in his ET2. In my view his modifications increase inertia and increase the loading on the cantilever suspension when side forces from eccentric records are presented to the stylus. He employs no dampening to control this increased mass. Once it moves there is more induced cantilever flex from overshoot. This is way outside Bruce Thigpens original design concept of low mass and decoupled counterweight and should in no way be construed to be an ET2. There is always the risk of cartridge and or record damage with Richardkrebs added mass-low pressure approach. Richardkrebs advice in a previous post for those concerned about possible cartridge and record damage was, quote People are free to try, it is entirely their choice. Install an alternate cheap cartridge, play a record you don't like, if you are that worried about damage to same. This advice is probably about the only thing that Richardkrebs and I could agree on. |
very interesting discussion guys. I am personally going on over 9 years with the ET2’s – never had a problem with a cartridge. I think I represent a typical music lover – meaning - I own xxxx records. At any one time there are xxx in 4 or 5 rows on the floor against the wall in my room that get cycled. Now none of them are eccentric enough to cause the spindle to move around like crazy. Most of the time I can barely see any movement in the spindle at all. I’d have to look really hard. Very interesting discussion on the various air bearings. It should be noted that of the ones mentioned so far , the Kuzma and ET2 I believe are the only two that can be mounted on any TT. There is the Terminator too (it seems from pictures/videos to occupy alot of space on the TT?) Maybe DG can elaborate? Its a BIG DEAL in my book to not be TT dependent. And fwiw - Any tonearm comparisons should be made imo mounted on the same table as this is a hobby about resonances and vibrations. So I have to ask here - Richard, Dover, Kong, others ..... what kind of records are you guys actually playing that you are so worried about eccentricity of the record ? I refer back to this post with data from the ET2 manual. http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1325551242&openflup&372&4#372Specifically the wording. This means that any given cartridge works against lower horizontal forces in the Model Two tonearm (.1 gram or less) compared to a conventional arm (.2 grams/gram vtf). These figures apply if you use records that are not severely out of round. If you like to play severely eccentric records, ones with runout of greater than 1/8”, then we suggest you use a low mass pivoted arm. --------------------------------------------------------------- Richardkrebs - We went on to talk about potential problems with cantiliver flex. His response was the resonant frequency due to the combination of a typical low compliance cartridge and horizontal effective mass was in the region of 2.5 -3.5 hz.(this has been published by them elsewhere), this is well above the 0.55 or 0.75 hz for 33 or 45 rpm eccentric records. Therefore the cartridge does not "see" this movement. Richard , so as shown above, Bruce has measured the lower horizontal forces in the Model Two tonearm (.1 gram or less) compared to a conventional arm (.2 grams/gram vtf). Are you able to get us the actual “lower horizontal force number” in the Kuzma Airline from Mr. Kuzma. I am very interested in this number – this is where the tire hits the road to me, no ? --------------------------------------------------------------- I have to admit something here to everyone as well, since I have been giving the discussions we have had thought. I really like the fact that the ET2 does not put any constraints on me as far as the type of cartridge I can play, anytime and anywhere. I can put on a Sonus Blue Gold with a single leaf spring, • Dynamic Compliance: 50 x 10-6cm/Dyne. • Tracking Force Range: 1.0 to 1.5 grams. than switch it over to a triple leaf spring beam with my XV1. Is this flexibility not worth something ? sorry for the following asterisks but this "IBM dos like" based forum does not allow for bolding and colors. *********************************************************** Is there another tonearm in existence that allows for the above to occur regardless of cost ? *********************************************************** btw - If I do find a record I like alot - that is so off centered (runout of greater than 1/8” as Bruce says) and cannot be replaced. Why not just drill out the center hole and use a heavy weight on it ? Richard/Dover/Slaw - is this not possible ? You guys have discussed drilling out of holes before.... Cheers |
correction last post - I am in my 10th year now with the ET2's. When this thread started it was 9 years. lol. |
The ET2 gooseneck – the part that connects the armtube to the spindle is made from Carbon Fibre. I asked Bruce about making one in aluminum. It can be done in a special run if there is enough interest.
I told him I would find out how many are interested. If you have an interest you can contact me at
bcpguy(at)bell(dot)net
Cheers |
Dover.
If the cartridge does not have a (damped) spring inside, please explain to us what causes the cantiliver to return to its rest position.
My discourse on resonant frequency IS the whole point, since the resonant frequency is set by the horizintal mass of the arm plus cartridge AND the cartridge's compliance.( plus some other complications around the systems overall rigidity) The system has a resultant resonant frequency which takes into account the stiffness of the cartridge's suspension. 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.
Chris, I do not worry at all about playing eccentric records, nor do I worry about hanging my Shelter Harmony on the end of my arm. I have had one cartridge failure in 35 years of this hobby and this was caused by my son using it as a chisel to make a nice tangential groove on a record.( maybe he didn't like my choice in music) The other cartridges have simply faded away after long and fruitful lives.
While making some assumptions around the rigidity of the cantilever, wand and goose neck, my spring/weight analogy is valid.
Right at the start of my involvement in this thread, I said that my arm had been optimised for low compliance carts. Chris, in doing this I have compromised its versitility regarding cartridge selection. High compliance carts are out. Low compliance carts are individually adjusted using different counter weight shim washers.
I made this compromise in the pursuit of sonic performance. |
Ct0517, At CES Franc K. mentioned a horizontal mass of around 100gm for Airline. He said that this worries some pivot arm guys, though in practice is "no big deal" w/r to LF performance. The Airline interests me as well-- incredible fit n' finish. I've read that one of its key advantages is very tight bearing clearance. At the high pressure necessary to float a "hard" captured air bearing of small surface area, this implies a low rate of airflow and thus relatively low turbulence and vibration.
Terminator can be mounted on pretty much any turnable. Porting the arm across turntables requires pedestals of varying heights to match the varying distance from a particular arm board to the top of the turntable mat. The pedestal can be ordered with an off-set stud mount that spins to accomodate any existing armboard hole vacated by any pivot arm. I made a DIY brass pedestal with this feature. |
Thekong
Actually, I have also fabricated a fixed counterweight for my ET2.5, but unfortunately have no time to test it yet. When it happens, the ET would be compared to my favorite arm, the Rockport 6000! Thekong – look forward to your impressions of the ET 2.5. Do you know what table it will be going on? I came across this pic in this other thread. Is this still your setup ? http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1301061425&openflup&16&4#16Very nice - btw Cheers |
DG - thanks for that info. Curious if Frank K happened to mention to you what his favourite tonearm was - of the ones he makes. |
Hi Ct0517,
Yes, that Rockport Capella II is still my main turntable. When ready, the ET2.5 will be set on the brass armboard opposite to the Rockport 6000. Actually, you can see a bit of the ET at the left edge of that photo already, just that the whole counterweight assembly was not installed yet!
BTW, the Rockport 6000 can also be installed on nearly all turntables! |
The Kuzma looks like a nice arm, but one thing that always made me scratch my head is the air supply tube. We ET-2 owners pay so much attention to tonearm wire routing. What about that stiff plastic tubing on the Kuzma? It seems like it would have a huge effect on the arm's movement even if both of the fittings swiveled. Does anyone know any details about the tube's fittings or if it hinders the arm's movement? |
Comparison of lateral forces on Kuzma/Terminator/ET2/ET2krebs For those who are interested in understanding the side forces on the cantilever : Force = mass x Acceleration, where acceleration = mass/(velocity squared) If the record is 12mm out of true, the arm travels 24mm in and out with each revolution, which takes 1.8 seconds. On an eccentric record the acceleration will be the same for each arm – 0.0024metres / (1.8 sec x 1.8sec) = 0.00074 metres per second squared The horizontal effective masses of the 3 arms mentioned in this thread are: Kuzma has been quoted as 100g Terminator 80g ET2 25g The force on the cantilever is as follows: Kuzma = 0.1kg x 0.00074m/s2 = 0.000074 Newtons Terminator = 0.08kg x 0.00074 m/s2 = 0.000059 Newtons ET2 = 0.025kg x 0.00074 m/s2 = 0.000018 Newtons Summarising then you can see that the increased mass of the Terminator and Kuzma arms increase the lateral forces on the cantilever by 300-400% over the ET2. Now Krebs has modified his ET2 by adding 30gm of lead to the spindle. This adds 30g to the effective mass of the ET2. Krebs also couples the counterweight ( no spring ) which adds another 30g to the horizontal effective mass. So Krebs has increased the horizontal mass of the original ET2 from 0.025kg to 0.085kg. The Krebs modifications have increased the lateral forces on the cantilever by over 300%. Furthermore he employs no dampening to control this mass and runs his ET2 at a lower pressure of only 12psi. The arm moves in and out every 1.8 seconds. This equates to a frequency of 100/1.8 = 55hz The resonant frequency of the unmodified ET2 is roughly 3.5 – 5hz. Krebs argument is and I quote: Below this resonant frequency the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection. He is wrong. This statement defies basic physics. Below 0.55hz the cantilever WILL deflect on an eccentric record. I assume he has misunderstood the explanation given to him by Frank Kuzma, and seems unable to comprehend this. |
What about that stiff plastic tubing on the Kuzma? It seems like it would have a huge effect on the arm's movement even if both of the fittings swiveled. Does anyone know any details about the tube's fittings or if it hinders the arm's movement? Hi Ketchup, My Rockport and my friend’s Airline shares similar arrangement in the airhost. Actually, they are not that stiff, and they can be detached at the point where they enter the bearing. So, you can twist them a bit to attain a hanging n shape for minimizing the effect on movement. I can’t say they have no effect on movement, but they certainly don’t hinder it, at least not to the point of causing mistracking. If the record is 12mm out of true, the arm travels 24mm in and out with each revolution, which takes 1.8 seconds. Hi Dover, While it may not affect you conclusion on the lateral forces of the 3 arms, a record that is 12mm out of true (24mm in and out, that is nearly 1 inch!) is probably unplayable even with a pivotal arm. I think, on average, 1mm (2mm in and out) is more like it! |
Dover
The fact that it takes considerably more force to accelerate a heavy arm sideways is self evident.
What I have constantly said is that this force will not be enough to deflect the cantilever while tracing an eccentric record, provided the resonant frequency of the arm / cartridge system is above 0.55 hz for a 33 rpm and 0.75 hz for a 45 rpm record.
The analogy I used earlier is a good practical test to show this phenomena. For those interested it would take 5 minutes of your time.
All you need is a rubber band representing the cartridge suspension ( spring) A weight, representing the arms effective mass, attached to the rubber band such that it bounces up and down at a few HZ, representing the resonant frequency of the combination. Remember the resonant frequency is a function of the arms effective mass and the cartridges suspension stiffness ( springiness)
The groove modulation is simulated by rapidly moving the rubber band up and down. ( The cantilever driving the suspension) Do this at frequencies higher than the bounce frequency and you will see that the weight stays still. In other words the cantilever is moving and the arm is not.
Now move the rubber band up and down at a frequency lower than the bounce frequency. This simulates an eccentric record or the lead in, lead out grooves. Now the weight moves up and down in total sync with the rubber band. The whole arm is moving and the rubber band is not stretching or retracting. The cantilever is not deflecting. |
Thekong,
Yes I agree with you. I only used the 12mm as that was what was used on the Kuzma video Richardkrebs referred to.
The key point as you have indicated is that the Kuzma and Terminator arms will have 3-400% higher lateral force on the cantilever due to their horizontal effective mass being 3-400% higher.
In my view this isn't great and I would worry about using medium to high compliance cartridges with these arms. From your comments I can see you are very careful on setting up your arms.
Will be very interesting to see what you think of the ET2.5 when you have had a chance to set it up. I would encourage you to try my set up recommendations, using my decoupled counterweight suggestion - which means running the I beam very very loose, and tuning the bottom end response by slowly adding dampening to the movement.
Bruce Thigpen has clearly put a lot of thought and experimentation into the decoupling methodology and the low mass.
If you read his manual and patents he starts with a low mass arm, and then brings the effective horizontal mass up very very gently by providing variable spring rates. This is to keep the resonances between horizontal, vertical in sync with the compliance of the cartidge and the Q of the system. The Q is related to the dampening of the oscillation - the use of magnetic dampening will shift this slightly. Very small adjustments can give quite dramatic changes to the sound, especially in speed and articulation. |
Hi Thekong Yes please post a pic of your ET2.5 with the modified counterweight when you can; would love to see it and look forward to your ET 2.5 impressions as well. I have had my ET2 on the left side of a table. I found it very awkward both from a handling and viewing (the cantilever) perspective. Then again I don’t get driving on the left side of the road either..... I am curious about the Rockport and Kuzma based on what Ketchup and yourself said regarding the tubing. Ketchup
What about that stiff plastic tubing on the Kuzma? It seems like it would have a huge effect on the arm's movement even if both of the fittings swiveled. Thekong
I can’t say they have no effect on movement, but they certainly don’t hinder it, at least not to the point of causing mistracking. Based on my ET2 experiences, the arm can be lined up properly and if the pump is decent it will track fine. But nowhere near its potential if the wiring is affecting its travel. So would not the best air bearing design/solution mean no wire(if it was possible) and tubing attached to the moving pieces, giving the cartridge/armtube the greatest freedom ? I'm just sayin' as a user. The Rockport and Kuzma tubing makes me think of my past experiences with my VPI JMW 12 tonearm. That tonearm’s wires are used as its antiskating method. Their positioning pushes the tonearm back toward the outside. Could the tubing being in a loop at the centre of the Rockport and Kuzma arm, be acting as a type of dampener for the arms motion in both directions ? Cheers |
Could the tubing being in a loop at the centre of the Rockport and Kuzma arm, be acting as a type of dampener for the arms motion in both directions ? Hi Ct, I think the tubing is just a necessary evil in the Rockport / Kuzma design. As for whether it affects the tracking, when I adjusted the arm to free floating (i.e. 0 VTF), I can put the arm in any position without it going in or out. So, I suppose the affect is minimal. However, there is one interesting point that I still can’t understand. When moving the arm in and out by hand, the feeling of the ET is smoother (or I should say requires less force) than the Rockport! While I don't have the spec. of the 2 bearings, I have always assumed that the Rockport has a tighter tolerance / air gap. This can be shown when trying to move the arms without the air supply. While you can still move the ET quite easily, a lot more force is required for the Rockport in this condition. But, when air pressure is supplied, shouldn't both of them be virtually frictionless? I think if the Rockport indeed has friction, the cartridge would probably mistrack. Or could it be the horizontal mass that we have been talking about? Based only on the look, if the horizontal mass of the Airline is 100g, I would estimate the Rockport is about half to 1/3 of that, so in the 35-50g range, not that far away from that of the ET! |
|
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. |
Hi Richard,
Thank you for the suggestion!
As this is only for experimenting, it is a bit rough. Would certainly take your suggestion into consideration if I decide I like this arrangement and fabricate the final counterweight assembly! |
This post includes feedback from Bruce Thigpen Dear gentle reader, Over the past month Richardkrebs has argued the case for adding substantial lead mass to the ET2 and replacing the decoupled counterweight with a fixed counterweight. In Richardkrebs recommended setup he advocates increasing the horizontal mass by over 300% from 25g to 85g by adding lead to the bearing spindle and coupling the counterweight rigidly to the arm. This is well outside the design parameters carefully formulated by the designer, Bruce Thigpen. The laws of physics are very simple: Higher mass = higher inertia ( resistance of the arm to movement ) Higher mass, means that when the arm moves back and forth on eccentric records it places higher lateral forces on the cantilever. The added lead mass will cause the cantilever to flex more on eccentric records as the arm oscillates in and out. Furthermore as the arm oscillates back and forth the side loads on the cantilever will increase by over 300%. I have raised the issue of the additional loads on the cantilever from the added lead mass, and resultant increase in cantilever deflection. Richardkrebs has consistently denied the laws of physics by claiming there is no deflection because the resonant frequency of the eccentric movement ( 0.55hz ) is below the arms resonant frequency; 3.5-5hz for the unmodified ET2.. To quote Richardkrebs 02-15-13: Richardkrebs
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 with its OD equalling the ID of the tube.
03-11-13: Richardkrebs
the resonant frequency due to the combination of a typical low compliance cartridge and horizontal effective mass was in the region of 2.5 -3.5 hz.(this has been published by them elsewhere), this is well above the 0.55 or 0.75 hz for 33 or 45 rpm eccentric records. Therefore the cartridge does not "see" this movement.
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.
03-13-13: Richardkrebs
What I have constantly said is that this force will not be enough to deflect the cantilever while tracing an eccentric record, provided the resonant frequency of the arm / cartridge system is above 0.55 hz for a 33 rpm and 0.75 hz for a 45 rpm record. A fellow Audiogon member has contacted Bruce Thigpen, the designer of the ET2. Bruce Thigpen has confirmed that Richardkrebs assertion that ‘the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection’ is wrong. The following are quoted from the correspondence with Bruce Thigpen: the cartridge will "see" .55Hz mounted in any tonearm, more so in one with higher horizontal inertia
I don't think Kuzma means the stylus does not deflect at all at .55Hz, that would defy physics
I hope this puts an end to this matter as it is becoming boring having to sift through gobbledygook, pseudo science and rubber band conflations. On the other hand some of the more entertaining highlights posted have been: Claims that rotational forces of a pivoted arm are the same as the linear forces of a tangential arm The Morch adds what appears to be considerable mass at a radius out from the pivot point. In so doing they have made a flywheel.
As viewed by the cantilever this is no different to me adding mass in the linear plane to the ET.
Comparing tone arms and cartridges to a rubber band: All you need is a rubber band representing the cartridge suspension …
The groove modulation is simulated by rapidly moving the rubber band up and down.
Now move the rubber band up and down at a frequency lower than the bounce frequency. This simulates an eccentric record or the lead in, lead out grooves.
Being called a scaremonger Your scaremongering may have dissuaded people from trying a simple reversible mod
And of course, meeting a legend I am the only person here who can speak with any authority on the subject.
Bruce Thigpen has clearly put a lot of thought and experience into designing a low mass air bearing arm that includes a decoupled counterweight to optimize the arm and cartridge. If you read his manual and patents he starts with a low mass arm, and then brings the effective horizontal mass up very gently by providing variable spring rates on the decoupled counterweight. This is formulated to keep the differential resonances between horizontal and vertical in sync with the compliance of the cartridge and the Q of the system. The Q is related to the dampening of the oscillation - the use of magnetic dampening will shift this slightly. Very small adjustments can give quite dramatic changes to the sound, especially in speed, transparency and articulation. I would not recommend adding lead. Adding mass creates a risk of damage to my expensive and irreplaceable cartridges - Ikeda Kiwame and Dynavector Nova 13D. For the Richardkrebs of this world – here’s a simple test. It will only take a few minutes. Put your gumboots on and fill them with lead shot. Now try and move your feet sideways, out and in in 1.8 seconds. That’s what your cartridge sees. Lead filled boots are not required to get the best sound from this outstanding tonearm. I do not doubt that Richardkrebs beliefs are sincerely held. However they defy physics and are clearly wrong. |
Hi Thekong
Thanks for posting that pic and allowing us to be part of this !
What a cool setup with those armboards and counterweight. It appears that the rod is “welded” to the square which attaches to the spindle end ? These are grounds I have not stepped on. Richards comments about flexing are very interesting.
Can you tell us what cartridge you are using and the psi you are running ?
We have been discussing the advantages of the single, double, triple leaf spring counterweights here a lot. I am assuming you have a stock single leaf spring that came with the ET 2.5? Most of us I would think use the leaf spring counterweight. It would be valuable for me and others, if later on at some point; after tweaking and listening with your custom fixed counterweight; you could put on the leaf spring counterweight and tell us the differences you hear.
Anticipation builds. :^) Thanks again for including us in this.
Cheers Chris |
Richard/Dover
If both of you guys ever decide to join forces and start up a cover band, please let me know. I will personally make the trip to NZ to hear you. I would not miss it. As long as you close the set with a little Jethro Tull. |
Richard/Dover - Do either of you play flute? |
Dover.
I don't think that personal attacks advance this thread, so lets both agree that we stick to our opinions on the subject or post relevant information.
Shown here is a link to the Math on driven harmonic oscillators, a mathematical representation of an arm/ cartridge assembly. It shows in both formula and graphical terms what I have been trying to say. The Math is a bit of a struggle but fortunately the graphs show the results.
http://en.wikipedia.org/wiki/Harmonic_oscillator#Driven_harmonic_oscillators
We can see from the sinusoidal graph that the Transmissibility, for input frequencies that are say 25% or less of the resonant frequency, is 1. This means that there is total transmission of the input frequency into the structure. It moves as one. In other words the whole arm moves. At input frequencies above 25% up to resonance we get increasing gain and this area should be avoided.
For input frequencies that are 300% of the resonant frequency we get transmissibility of around 15%, unless the structure is highly damped and we all agree, I think, that lots of damping doesn't sound good.
So at 3x the resonant frequency we are loosing around 15% of the groove modulation, as the arm is still at this point moving back and forth sideways slightly.
This is not a problem provided this 3 x resonant frequency is not a valid audio signal. Actually you would need to extend the graph out to around 6x resonant frequency before the transmissibility was approaching 0. Until we reach that point, part of the low frequency goove modulation goes into moving the cartridge and arm sideways and not into generating an output voltage.
It was the discovery of this characteristic that led me to look into possible performance improvements in the LF area of the ET2. Since if the resonant frequency was say 6 hZ we would not have total transmission of LF modulation until we reached say 36 hz.
Kuzma state that the horizontal resonant frequency for low to med compliance carts is in the range of 2.5 to 3.5 HZ, with an effective mass of 100gm.
Resonant frequency is inversly proportional to the square root of the mass. So my arm at around 85gm would fall into the range of 2.7 to 3.8 HZ
If we take the mid point for these resonant ranges 3 hz and 3.2 hz respectively, we are, in my opinion, in the Goldilocks range for the Kuzma and my arm. In that it is sufficiently high to avoid gain caused by eccentricity, since 0.75 Hz for a 45rpm record is less than 25% of the resonant frequency. But low enough to give virtually complete conversion of desirable groove modulation into output voltage. 19.2 hz (3.2 x 6) being at the lower end of what most systems can produce.
If we look at the same numbers for a standard the ET2 we get a resonant frequency range of 5 to 7 hz for a 25 gm effective mass. This is comfortably above the 0.75 hz eccentricity problem, but if we take say 5 hz as the resonant frequency, we see that it will not be until we reach say 30hz before we have complete conversion into an output voltage. I dont think that this is desirable.
Making the arm lighter still will extend this frequency upwards.
http://en.wikipedia.org/wiki/Harmonic_oscillator#Driven_harmonic_oscillators |
Richard The resonance frequency figures we have from BT that we have discussed here. ET 2 (5 - 6 hz) ET 2.5 (2 - 3 hz) due to the larger spindle plus weighing a little more - not sure what the actual gram number is. So at 3x the resonant frequency we are loosing around 15% of the groove modulation, as the arm is still at this point moving back and forth sideways slightly.
This is not a problem provided this 3 x resonant frequency is not a valid audio signal. Actually you would need to extend the graph out to around 6x resonant frequency before the transmissibility was approaching 0. Until we reach that point, part of the low frequency groove modulation goes into moving the cartridge and arm sideways and not into generating an output voltage. Based on what you are saying Richard - does this not then mean: ET 2.5 = 6 x 2.5 hz (midpoint for the ET 2.5) places it at 15 hz ET 2.0 = 6 x 5.5 (midpoint for the ET 2.0) = 33 hz The number 6 that you multiplied the resonance frequency by. Would this number need to change for a really high compliance versus really low compliance cartridge to be more accurate ? |
Chris.
The 6 x multiplier is a factor extrapolated from the graph I posted the link to. 6 x being a figure where the resonant structure would likely be still, with some safety margin. It would not change with cartridge compliance. But the system resonant frequency could change outside the published figures if you were to use an outlier cartridge.
A really stiff cart would push the resonant frequency up, moving further into the audio band. A really floppy cartridge would push the resonant frequency down, with a real risk of problems due to eccentricity. |
Hi Ct,
During the testing phase, my ET2.5 will be set up with a ClearAudio Sigma. When the final comparison comes, I will be using the Ortofon A90 between the Rockport and the ET.
I am using 15psi for the moment with a compressor together with its integral surge tank, and 2 regulators before the air enters the arm. I can easily increase the pressure up to 34psi, which is what I am using for the Rockport, for testing.
About the counterweight, the aluminum square is tapped and the threaded rod just screwed into it. I “reinforced” it a bit with superglue !
Hi Richard, Dover,
I don't have the knowledge to even start participating in the discussion on the physics of moving mass, however I have some general observation.
It seems to me all the other arms that we have discussed recently (Airline, Rockport, Terminator, Walker) have much higher horizontal mass than the ET with the decoupled counterweight.
Take the Airline as an example, if its horizontal mass is 100g, then it is even higher than the 85g of Richard’s modified ET. While I don't have the Airline myself, 2 of my friends have it for a couple of years already and have no problem with cartridge damage. I have also never seen any actual negative report regarding this matter on the internet. The same applies to the other 3 arms.
Looking at the massive construction of the Airline, I couldn’t help but wonder whether Kuzma could reduce the size and weight somewhat without sacrificing rigidity. They didn’t do so appears to me that they have no concern on this high horizontal mass being detrimental to the performance, or worst yet, causing cartridge damage.
Could all these arm designers be wrong when their products are getting very positive comments from actual users, not just magazine reviews?
Of course, all these other arms, with the exception of the Terminator, are very expensive, so they most likely are being matched with highend MCs with medium to low compliance. Maybe the high horizontal mass is less of a problem in these conditions?
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Thekong -
I would ask you to consider the looking at this the other way round. Just because everyone says something sounds the best, is it. Most people thought the world was flat at one time.
My experience with high end audio is that most audiophiles dont hear much and have no sense of timing. Products that produce "impressive" bottom end or top end sell well, and even get reviewed well. Of course it's like car reviews, the next one comes out and all the flaws of the last model get written up.
If we look at the wealthier clientele that Kuzma is targetting, most of them will have large multidriver speakers, eg Wilsons etc. Large full range speakers are incredibly difficult to get coherent in a domestic environment. Alternately we get the wealthy single ended group - these are just tone controls, pleasant, but usually at the expense of speed timing and coherence.
My experience of the higher mass is that it might have a "bigger" bottom end but at what cost in terms of speed and coherence.
Most folk who own these expensive arms are also likely to be changing cartridges regularly - are they really tested. I'm sure some cartridges may be fine, but it's not a given, and the additional forces on the cantilever and stress on the suspension are present, to argue otherwise defies physics.
My ran my ET in the manner it was designed ( decoupled counterweight, no added mass ) simply because it sounded better that way.
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Richardkrebs OK now I understand where you are going wrong in your thinking. Shown here is a link to the Math on driven harmonic oscillators, a mathematical representation of an arm/ cartridge assembly. The arm/cartridge/record interface has 2 fulcrum points - The stylus point around which the cantilever pivots. The cantilever suspension point, about which the cantilever also pivots, but which is partially constrained by the rubber suspension damping. The forces involved are double ended - you have the groove applying a force to one end of the cantilever via the stylus. The other end of the cantilever has an restorative forces being applied from the arm motion. The 2 forces are not in sync because there is a suspension joint between the cantilever and the arm. Think of 2 people holding a pipe and each one trying to move it sideways out of sync with the other. That's what the cantilever experiences. The model you are working with is irrelevant. It is too simplistic. If you had studied mechanical engineering you would understand this better. if we take say 5 hz as the resonant frequency, we see that it will not be until we reach say 30hz before we have complete conversion into an output voltage. I dont think that this is desirable.
Making the arm lighter still will extend this frequency upwards. This is the classic mistake made by an untrained ear. Let's add mass, lower the resonant frequency and we get more bottom end. Dont worry about the increase in distortion through the upperbass, midrange and top end from the cantilever being forced to deflect further. Richard, you have not answered the question posed in my earlier post.. Bruce Thigpen has confirmed that Richardkrebs assertion that ‘the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection’ is wrong.
The following are quoted from the correspondence with Bruce Thigpen:
the cartridge will "see" .55Hz mounted in any tonearm, more so in one with higher horizontal inertia
I don't think Kuzma means the stylus does not deflect at all at .55Hz, that would defy physics The question I am still waiting for a response is: Does the cantilever deflect below resonance ? Just give me a straight answer - Yes or No |
Hi Thekong During the testing phase, my ET2.5 will be set up with a ClearAudio Sigma.
When the final comparison comes, I will be using the Ortofon A90 between the Rockport and the ET. Look forward to your observations. Based on their specs for compliance and weight with similar spec carts I own, I have had really good experiences with the double leaf spring I beam. It would be very easy to compare your custom counterweight later on to the decoupled counterweight. If you contact Bruce he can send you a couple empty I beams with 5 loose leaf springs that you can glue in yourself to make a double and triple I beam. The beams cost about 10 or 15 dollars. Three are shown in this pic. single, double and triple The double in the middle does not have the extra weight on it so looks thinner. The one I am holding is a triple and it makes the I Beam very rigid. Will use it with the heavy, low compliance XV1. I posted this earlier somewhere from Bruce on his opinion of the different I Beams. With respect to the i-beams, this is correct: a stiffer (lower compliance) I Beam works better with a lower compliance cartridge.
Hope this helps - brucet Cheers Chris |
Dover
Again you enter into needless personal attacks
Does the cantilever deflect due to the higher lateral forces imposed upon it?
I see no movement with my cart tracking eccentric records and the math predicts none. However in absolute terms no one could say that there is zero deflection. A more appropriate question would be. Is the additional horizontal mass dangerous to the health of the cartridge, which has been your accretion all along. It would seem that this is not so. There appears to be no issue. If there was it would be all over the web that arm XYZ is a mass murderer.
The second important question should be. Does increasing the effective mass of the ET2 make its performance better or worse. For those of us with untrained ears the answer is yes.
We would need to include BT in at least a semi trained ear camp, as he advocates stiffening the counterweight beam on the arm he designed when using low compliance carts. This is counter to what you advocate when you loosen further the leaf spring.
I like your analogy of a pipe being moved independently at each end.
This of course presupposes that the cartridge body is moving relative to the groove. If it is not, which is what we want, the cantilever has one fixed pivot point at the suspension. The stylus end describes an arc as it traces the groove. |
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 With regard to cantilever deflection on eccentric records, it is clear you are confused. Let me explain: Your original statements on this matter were and I quote 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. 03-13-13: Richardkrebs What I have constantly said is that this force will not be enough to deflect the cantilever while tracing an eccentric record, provided the resonant frequency of the arm / cartridge system is above 0.55 hz for a 33 rpm and 0.75 hz for a 45 rpm record.[/quote] Now however your position is, and I quote from your post of 03-16-13: I see no movement with my cart tracking eccentric records and the math predicts none. However in absolute terms no one could say that there is zero deflection. Richard, you have made two conflicting statements in two consecutive sentences in your latest post of 03-16-13. Your first sentence states the maths predicts no cantilever deflection. Your next sentence contradicts that sentence and all your previous assertions for the past week or two and states that no one could say there is no deflection. Should readers of this thread take it that you now agree that Bruce Thigpen and I are correct and there is cantilever deflection below the resonant frequency. You were incorrect when you stated "Below this resonant frequency the cartridge is able to move the arms weight, start it and stop it, without cantilever deflection". |
Dover.
No confusion at all. In Engineering, the term absolute is.....absolute.
By way of example, over on the TT drive thread, a fellow poster said that " there is no stretch in the silk thread I use to drive my platter." or words to that effect. Within the loading the thread sees, this statement is almost certainly true. However if he had said that "there is absolutely no stretch..." he would be making an indefensible statement.
One would also be very unwise to say that "tracing an eccentric record with a standard ET2 causes absolutely no cantilever deflection"
Hasn't this discussion run its course.
Like the light weight ET2, there are many heavy weight linear arms in use, performing well, producing beautiful music. |
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. |
Some impressions – First Some text from Richards very interesting post of 03/14/13 http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1325551242&openflup&527&4#527For input frequencies that are 300% of the resonant frequency we get transmissibility of around 15%, unless the structure is highly damped and we all agree, I think, that lots of damping doesn't sound good.
So at 3x the resonant frequency we are loosing around 15% of the groove modulation, as the arm is still at this point moving back and forth sideways slightly.
This is not a problem provided this 3 x resonant frequency is not a valid audio signal. Actually you would need to extend the graph out to around 6x resonant frequency before the transmissibility was approaching 0. Until we reach that point, part of the low frequency goove modulation goes into moving the cartridge and arm sideways and not into generating an output voltage. Now Page 9 of the ET2 manual. Adjustable Effective Mass
The effective mass of the tonearm is adjustable, both vertically and horizontally. The arm has low-medium mass vertically and medium to high mass horizontally.
Four counterweights allow the vertical / horizontal mass to be changed. For example; if the user decreases the amount of counterweights used, and moved the this position back (higher scale number) the horizontal inertia of the tonearm would go down and the vertical inertia would go up.
Decoupled Counterweights.
The effective mass of the arm horizontally is equal to the sum of its component parts. (It does not pivot) it needs to be as light as possible for low mass, however, making the arm too light sacrifices rigidity. By decoupling the counterweight system horizontally, but not vertically, the mass of the counterweight is not seen by the cartridge above a certain frequency and is lowered. This allows the use of heavier (more rigid) components in tonearm design without increasing effective mass.
The decoupling mechanism is damped at its natural frequency (2hz – 5hz). THIS DECREASES THE RISE IN FREQUENCY RESPONSE AT RESONANCE IMPROVING LOW FREQUENCY PERFORMANCE Well it looks like Bruce studies this and note the text in upper case. ------------------------------------------------------ MY IMPRESSIONS ET 2.5 at 19 PSI. Use of a Time Aridyne Medical Pump which produces very little resonance at the source. (I don't dare say "never" on this thread :^) ....just joking....not http://www.alliedhpi.com/images/zs168-263-002.pdfIt dumps moisture at the pump down a tube just like a cars AC unit. Have never seen a drop in the second regulator in my room – except for that incident where the pump outlet clogged (minerals in moisture) and sent moisture down the line. My room water trap bulb was half full before I noticed it ! Test Cartridge Benz Micro MC3 Soundsmith Ruby Retip. 15 x 10 – 6cm/dyne (1.6 - 2.2 vtf) (weight 7.2 gms) Used at 1.8 gms wide open at 47 k and loaded at 100. My wiring is unshielded http://cgim.audiogon.com/i/vs/i/f/1332259084.jpgWith the preamp inputs about two feet away from the ET2.5. I have been listening to this cartridge for a few months now with a double leaf spring. Very enjoyable. I inserted the triple leaf spring which effectively for any anyone that has tried this, turns the counterweight into a rigid one – imo. No movement at all. Defeats the decoupling. Bass performance changed with the triple leaf spring in my room with the 801 monitors. Lets understand this is relatively speaking as the 801 have prodigious bass. But the effect of the leaf spring versus no leaf spring was noticeable in the ears with the sound compression in the room and this (15 x 10 (– 6)cm/dyne) cartridge. Bass performance was not as good with the triple leaf spring with this specific cartridge in MY room. So I believe what I heard supports what is in the ET2 manual. Maybe I will have different results with the even lower compliance XV1 soon ? It may sound better with the triple leaf spring. This will have to wait as I have amps arriving this week. Its easy to swap out Leaf springs. I am not going to hurry with the XV1 - for those aware of its history with me. Guys - I have made a promise to myself not to email or contact Bruce anymore with questions until first reading the manual. It really is like having his knowledge in your back pocket. Hi Thekong – do not know what speakers you are using but the above impressions, further support the reason I recommended the double leaf spring with your test cartridges based solely on their specs. Cheers |
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.
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Chris.
I also thank you for your insightful testing of the ET2.5.
It confirms that adding too much mass, by way of locking the counterweight is not a good idea, if it takes the arm out of the appropriate resonant frequency range. I did say earlier that in my testing of the ET2, I added too much weight and had to backtrack. The key point being where does the arm in standard form sit relative to the optimum.
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.
Now bringing the ET2 down to this optimal range, that would be interesting. Are you able to fit 3 leaf springs to an ET2 carrying a low to med compliance cartridge?
Another question please. How stiff is the beam with the 3 leaf springs? As I mentioned earlier, the arm is very sensitive to any resonance at this point. I would urge caution if the resultant assembly rings in the audio band. |
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. |
Dover.
Mea culpa. Although it is blindingly obvious that Thekong will be using a ET2.5, since he states same several times, I completely overlooked that fact, thinking that he was working on a ET2. My mistake.
It would still be informative if Thekong is interested since the rigidity of the counterweight arm is critical in non decoupled applications. While I would expect similar results to Chris, there would likley be some material differences which would be well shared with the rest of us.
ALL of my comments re weight and the ET2 stand. Its resonant frequency tells us that it is a completely different animal.
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Hi Ct,
I am using the Apogee Fullrange, so should be able to tell the bass difference between the different setup. However, I will need to order the extra left springs from Bruce.
As I got my original ET2 secondhand, I am missing the lead counter weight. I remember asking Bruce a couple of years back but the price was really high, due to some special reasons (high cost to machine lead as it is hazardous to health ?).
So, I would like to check with other users whether using other substitutes would cause a big difference? |
After a week in Australia for F1 racing, I checked this thread.
Surprised I was, that it continues: high horizontal/lateral mass wrecks cartridges (words to that effect), or at least Richardkrebs arm setup does (words to that effect).
It catalysed me, finally, to read Michael Fremer’s review of the Kuzma Air Line Tonearm.
I figured as Franc Kuzma uses significantly MORE horizontal mass than Richardkrebs with his low compliance cartridge, Mr Dover would implicitly conclude Kuzma doesn’t know what he’s about, selling a defective design.
Well, revelation: Michael Fremer says (after initial academic objections to the design)
“Ultra-black backgrounds; enormous, airy, startlingly stable soundstages; palpable images perfectly placed and sized; ear-popping harmonic, dynamic, and transient complexity—I could blather on about the Air Line's convincingly natural performance and brilliant overall balance.
I'd rather just get to the point: In every playback parameter I was able to delineate, the Kuzma Air Line's presentation was staggeringly better than that of any other arm I've auditioned—with the exception of the one included with the $70,000 Rockport System III Sirius.”
“With the addition of a damping trough, the Air Line could very well be the finest tonearm ever built.”
Mr Kuzma replies to MF
"A question of damping..."
A system will resonate only when disturbing forces appear at the resonance frequency. If there are no disturbing forces, then there are no problems. However, if a system is overdamped, then instead of one resonance, two smaller resonances occur, one below and one above the previous resonance, which can create further problems. There is, in fact, a level of effective damping on the Air Line tonearm. The cantilever suspension, and the air supply tube add damping. Our choice was for either too little or adequate damping; we chose the latter.
"Eccentric LPs and any deviation from absolute horizontality will create...problems..."
Horizontal disturbances of an eccentrically spinning record occur only at 0.55Hz or 0.75Hz (33rpm or 45rpm). This is well out of the Air Line tonearm's resonance in the horizontal plane, which is between 2 and 5Hz and does not cause problems tracking virtually all LPs. Plus, if one has a defective disc so poorly pressed or off-center that it might cause such problems, it is perhaps most prudent to simply not play it.”
(Sorry guys if these comments are already part of the thread).
After such a classy weekend I cann’t energise myself to provide a series of theoretically derived, professorial quotes.
It is self evident Franc Kuzma is the real deal, producing superlative product with inherent sonic performance at the far end of world class designs.
Suffice to say Franc Kuzma can be trusted to confidently illuminate the subject.
The same cannot be said of Mr Dover’s bombastic contentions. |
Thekong.
Just for clarity. Will you be adding the fixed counter weight to the ET2.5 or the ET2?
You mentioned the ET2 in your latest post.
thanks |
Hi Richard,
I will be using the ET2.5 in my test. My ET started out as a 2, which I later added the 2.5 bearing from Bruce.
I was asking whether replacing the lead counterweight with something else (brass/bronze ?), while still using the decoupled I-beam / leaf springs, would cause a big difference in the sound. |
Thekong
Thanks for that
The advantage of lead is of course its high specific gravity, it is dense and self damps quite well.
Don't know the effect of other materials there.
This could be a new line of exploration. I look forward to your findings.
Thanks |
Richardkrebs/John47 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. 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 Thigpen recommends. Re the comments on the Kuzma There is a lack of comprehension of what is claimed with the Kuzma. Frank Kuzma is quoted as follows Horizontal disturbances of an eccentrically spinning record occur only at 0.55Hz or 0.75Hz (33rpm or 45rpm). This is well out of the Air Line tonearm's resonance in the horizontal plane, which is between 2 and 5Hz and does not cause problems tracking virtually all LPs. That is all he is saying. Kuzma does NOT say the cartridge does not see this resonance, it simply means that it does not cause problems tracking. This is because if the resonance of 0.55hz were within the tonearm resonance range the two resonances could at worst sum and “double up” which could cause tracking problems. I quote 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 Note that Thigpen says that the 0.55hz is seen “more so” with higher horizontal inertia. I would suggest this is one of the contributing reasons for Thigpen recommending a lower horizontal mass for low compliance cartridges. You continue to ignore Bruce Thigpens' recommendations based on the laws of physics and his extensive testing, because it would appear you do not grasp the physics and engineering principles involved. Unless you understand those principles then you are unable to understand what underpins Thigpens' and Kuzmas' comments and designs, and are speculating at best. |
"..... do not appear to grasp the physics and engineering principles involved."
MF wasn't speculating when he heard 1 of the best 2 arms in the world - I guess you'll never be able to look out the door and see blue sky and appreciate that (the Kuzma is just about the best arm on the globe, dispite it contravening your design principles ..... uuuuuuuuuuuum how many arms have designed and manufactured?
I hope Franc Kuzma casts an eye over your 'advice' to correct his fauly design. |
