Dover, thanks. It appears to me that re coupling/decoupling of the I-beam/weight we are dealing with two issues that, on the surface, may seem to be one and the same, but are actually two separate considerations. We have 1. the degree of coupling due to the stiffness of the spring, and 2. the degree of coupling due to how tightly the I-beam is secured to the arm. I make this distinction because, although I would have thought that the two are effectively the same, I am experiencing different and unexpected results from each approach. I suspect that each has different ramifications as concerns resonance, hence the very different results. As I mentioned above, I have almost always preferred (after much going back and forth) the double spring with most of the cartridges that I have used over the years; these, of every persuasion and compliance. The less compliant double spring usually yielding a more controlled, defined sound with tauter and faster bass. More compliant springs have produced sound that is generally fuller, but less-well defined; fuller mids and lows, but less-well integrated highs.
I usually approach system tuning with the idea that there is always a theoretical ideal, but a necessary practical compromise. I prefer fuller sounding tube amplification, so the perceived leaner sound of the double spring has suited my system well.
This leads me to the issue of perceived bass speed. This relates to (in my fairly non-technical mind, anyway) to the above issues and to the issue you brought up re energy storage of soft dampening. In my experience, perceived speed cannot be completely separated from perceived tonal balance. To be clear, for me speed refers to the ability of a component to let music (or, for the sake of this discussion, the bass range) move as it should; to allow it to swing, rock, crescendo, whatever, with the swagger that it does live. I have always found this aspect of reproduced sound to be THE most elusive of all. I have heard components that were unacceptably dark and excessively full sounding that let the music move as it should with great dynamic nuance; and others that were tight, defined, and sometimes too bright overall that sounded dead, as if the musicians were half-asleep. At the same time, since how a component handles the leading edge of transients has a profound influence on the perceived speed, a system tuned to the darker/fuller side of things can benefit (speed-wise) from a little help by way of what the double spring brings to the table.
A long-winded way of saying that I am a little mystified as to why the loosening the I-beam yields a superior result than simply using a more compliant spring. BTW, I am speaking strictly about bass performance; I need to spend more time, and experiment more in the ways that you suggest, to get a better handle on things.
Thanks again. |
Frogman,
Thanks for the positive feedback.
With regard to the loosened I beam this is where I got to:
When I first imported the ET2 the spring was prone to coming off. If I recall correctly there used to be a little piece of dampening stuck to the spring.
At that time if I recall correctly Bruce didn't have multiple springs, but offered springs with the dampening stuck to 1 side only or 2 sides.
Basically I found the decoupled methodology I used by trial and error.
I knew rigid coupling didn't work, because somebody told me it was better, I tried it and it was awful. At this point in time I was importing audio and had a shop full of high end TT's. We had Sota/ET2's combo's in three listening rooms with different gear, along with Oracles, Linn's, Pink Triangle's, Roksan's, Well Tempered's etc
In the home system at that time I had the Denon 103 Garrott/ET2/Sota Vacuum - I played around with the looseness of the spring and noticed how changeable the sound was.
So I went to 2 extremes – completely rigid, no good, then completely loose, way way better but not perfect.
Then I just experimented from there,, started with a loose I beam, packed the spring either side with tiny lead shims to dampen the swing motion - results so so, then tried teflon shims - much better.
The teflon shims either side of the spring in conjunction with the loosened end cap bolt gave a very smooth damped motion with the beam, so I stayed with these and then just slowly dialled the pressure up by slowly doing the end bolt up – listening as I went.
The bass timing improved but at a point it lost timing, so I backed off slightly and hey presto.
At the optimum bass speed/timing the I beam could move freely and very smoothly.
A repeat of the procedure with other cartridges seemed to work consistently.
In hindsight it looks like my treatment of the I beam is similar to Bruces and in keeping with the design parameters. My decoupling methodology dampens the I beam movement and most importantly leaves the frequency of the I beam motion very low below the horizontal frequency as outlined in the manual as one of the key design principles.
In case there is any confusion I dont advocate reducing the arm mass substantially. I did remove the heatshrink and sponge foam from the arm wand because in my view soft dampening stores energy and releases it out of time with the music. |
The discussions (arguments?) between Dover and Richard have been extremely thought-provoking; and very interesting to say the least. I think that the well-intended participants who look for complete harmony, agreement, and absence of confrontation run the risk of they, themselves, doing more to derail what has been one of the best threads on Agon than either of those two gentlemen. Personally, I don't feel Richard is owed an apology at all; certainly, not one instigated by someone on the periphery of these discussions. We all have different styles of communication, and when the issue is something that one feels passionate about, we throw the gloves off (well, we at least loosen the laces) and expect everyone to be a big boy. I have seen no profanity used; no personal attacks, certainly nothing that, at the very least, could not be up for interpretation.
I have found value in both participants' contributions, even if I don't agree (yet?) with all the pecifics about each of their respective stances re set-up of this arm. 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. Point is, let's all be big boys, try things and have a little more confidence in what we hear as being the right way to go. Dover and Richard please continue contributing to this thread.
Regards. |
As a New Zealander I would like to apologies for the behavior of Dover. It is a narrow country and this breeds narrow mindedness.
When I look at the pictures of RK's arm I do not see an ET2. It is something specifically crafted and tuned to his system. It is not a universal tonearm. A little bit like the highly modified ET1 that Lloyd Walker uses actually.
Nor for that matter is the ET2 a universal tonearm, as I can attest to from my experience of its truly poor performance in my system. Quite frankly it was clearly out performed by my humble G707 and has remained in the closet ever since.
Now that I am in the process of moving on from my LP12, I will give the ET2 a second chance. In doing this I will be applying a great deal of good advice from Dover, but when Richard gets off his backside and makes a decent new tonearm, you can bet I will be dumpster diving out the back of his place to score the discarded bits from his current arm.
What Bruce has created is a truly outstanding achievement, but here is the rub, in everything I have done with hifi, at no stage have measurements, be it mechanical, electrical, or acoustic, ever done anything but get me in the ballpark. Was is Saul Marantz who has been quoted as saying: "If it measures good and sounds bad, it is bad and if it measures bad and sounds good, you are measuring the wrong thing."
To get back on topic I will just say this. Neither of these guys have a clue. One uses a 'Japanese DD' turntable and one uses a Heath Robinson 'belt drive'. If they used a real turntable there would be much less of this idler bickering.
Ouch, just bit my tongue. Might have to move to Oz now to avoid getting lynched.
Best Regards
Grantn |
Well I am not sure what to say now. I gotta admit that the folks from down under and specifically NZ, are not a subtle group by any means. You all seem to be in close proximity to one another? Can you by chance hear each others stereos when you turn them up ? BTW – Does Canadian Shania Twain still live in NZ ? I always had a crush on her. Richardkrebs
Do you really think that it is a good idea to have a spring driven mass, ( cartridge and arm ) attached to a spring suspended mass ( ibeam and counterweight). Both with resonant frequencies in the same neighbourhood? 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
************************************************************ Page 49 of the ET2 manual. LOW FREQUENCY RESONANCE MEASUREMENTS The curve below shows the typical response for the vertical resonance of the the tonearm. This was done with a medium-high compliance cartridge (30 x 10-6 cm/dyne) with a mass of 7 grams and two counterweights 15g + 15g. This counterweight combination gives a vertical effective mass for the tonearm of about 12 grams, which results in a resonant frequency of 6 hz (measured). Horizontally the resonant frequency will be much lower because of the tonearms higher mass (30grams). The horizontal resonant frequency is damped by the decoupling spring and is very well controlled. ************************************************************ Actual measurements and graphs for the above are also shown on page 49. Thoughts on the above ? At this rate we will probably have the whole ET2 manual on the thread by Christmas? My personal take on this as an amateur hobbyist. Bruce makes a lot of sense and has done the analysis and measurements to back it up. The ultimate test is "hearing is believing". My reference point for sound in my room is 15 IPS master tape dub. Both the MM 420str and MC Benc Micro that I discussed earlier play beautifully on my ET 2.5 with the CF armtube. I have the MM 420str on the ET 2.0 right now with aluminum armtube / other room and it sounds great there too. Each of us have different gear and rooms. We need to experiment with the different leaf springs to see what sounds best to us. But it is very obvious and clear to me that we should be trying to get *** AS FAR OUT ON THE I BEAM AS POSSIBLE - THIS IMPLIES THE LEAST AMOUNT OF WEIGHT ******* I haven’t tried a rigid counterweight with damping. If anyone would like to volunteer up a DL103 or similar low compliance cartridge I can give it a longer term try on the ET 2.0. If a good cheap DL103 pops up on the classified I can try to snap it up. I don't have a problem experimenting. Time permitting. Cheers |
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.
Chris (such a lovely guy):
"You come across as a real hard ass .."
Acronym: PITA
BTW did Richardkrebs pick on you at preschool? |
Dover.
....Sigh.....
My comment re "All or nothing" was designed to open useful dialog on the subject. I was trying to be subtle.
So now, not so subtle..
Do you really think that it is a good idea to have a spring driven mass, ( cartridge and arm ) attached to a spring suspended mass ( ibeam and counterweight). Both with resonant frequencies in the same neighbourhood?
If you refer to the math and resonance graph I posted, it shows that this can be problematic. The two resonances need to be far away from each other to avoid any interaction. At best a good compromise can be achieved with adjustment of the parameters. I don't like compromises. Better to eliminate one of the compliant joints in the system completely.
As I have said earlier. If fixed, the counterweight beam must be very strong. I note that Kuzma also know this as the counterweight beam is substantial indeed. Three springs don't cut it.
It is no accident that other arm manufacturers have a rigid joint there....it simply sounds better.
I don't understand why you are so set on trying to stop people experimenting on this area of the arm. It will do no harm and at the very least add to our collective pool of knowledge. A big hand will not come out of the sky and squash anyone who deviates from the original design parameters, it will be a bit of fun and it may just bring the owner closer to the absolute joy of listening to music, which is what this hobby is all about.
|
Richardkrebs Astounding! After 25 years of tinkering with your ET2 tone arm, you now reveal in your recent posts that you have only just worked out how the arm works. Only now have you realized that the sprung I beam has a resonance and the tuning of the I beam and the number and position of lead weights used is critical to optimizing the performance of the ET2. This is clearly explained in the manual and was discussed at earlier on this thread.. Let me quote your recent posts: 03-19-13: Richardkrebs
I don't have any proof of this, it is just a recent thought. While higher or lower weight is obviously a factor, I think that the one leaf spring, two leaf spring plus number of weights thing, has probably a whole different set of cause and effect issues. So with reference to a rigid or sprung counterweight beam, it is probably an all or nothing event. In other words because we have the "potential" interaction of the swing frequency of the beam and the resonant frequency of the arm assembly, depending on the number of leaves and the number of lead weights used. 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. Others may have already thought of this but, it is just an idea to put out there for comment.
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.
This is close to the resonant frequency of the arm itself. This could have performance implications. For the last 5 weeks I have been saying that you do not understand how this arm works. At the same time you have been promoting your modifications that include adding significant amounts of lead mass and removing the decoupling of the I beam which, I keep repeating, takes this arm out of its designed operating parameters. Your latest revelations make it clear that you have not understood the set up procedures described in the ET2 manual, nor do you understand their purpose and what principles they are based on. For this reason I would continue to caution readers that your advice on adding lead mass, M10 bolts and coupling the counterweight to the ET2 should be disregarded. |
Dover - if I may say - you come across as a real hard ass sometimes in your posts; but you have a very direct sense of humor. lmfao.
btw - what I just said my kids say to me alot. they unfortunately both being only 18 have not yet seen alot of my humor. I try to save it for you guys as I my wife just doesn't appreciate it either. This thread is 11 pages long now. She will never be able to trace back to what i am saying here.
|
Thanks for the info Richard. 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. The figure I quoted is from the manual and I believe it is for a stock single I Beam with the weights that are supplied with the stock ET2 tonearm - not the ET 2.5 – which we agree is a different animal with different resonances. I gotta believe that adding a leaf spring plus adding the ET 2.5 larger spindle changes things? I would need to confirm this with Bruce. |
Chris
I tune the arm with a set of different size weights. Don't know if manufactures of linear arms with fixed weight beams offer this, but it would make sense to do so.
Kuzma do suggest that their arm is most suitable for use with carts below a certain compliance. So they have considered this topic.
The weight I have added inside the spindle can be removed or adjusted in weight. No modification of the spindle is required.
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.
This is close to the resonant frequency of the arm itself. This could have performance implications. |
Chris - I assume you know the driving dogs are Kiwis ? NZSPA trained no less, here in Auckland. Not sure if they run ET's, but they demonstrate the benefits of high compliance. At the Engineering faculty I also remember Dr Fassbender, who had a fetish for experiments with rubber bands - http://www.youtube.com/watch?v=M0QShhpqtS8 |
Richard - re your last post. .....So with reference to a rigid or sprung counterweight beam, it is probably an all or nothing event. In other words because we have the "potential" interaction of the swing frequency of the beam and the resonant frequency of the arm assembly, depending on the number of leaves and the number of lead weights used. 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. Others may have already thought of this but, it is just an idea to put out there for comment. Would not the rigid solution and the all or nothing event - be only applicable to a one cartridge guy and the specific cartridge cantilever needing to be – really stiff ? As an end user I feel with the sprung counterweight it allows me to use all of my cartridges. Just a thought. Also In your custom ET2 setup – are you able to use higher compliance cartridges if you remove the lead from the spindle ? or are there other factors like a custom manifold involved ? that keep you from using higher compliance cartridges – sonic preferences aside for the moment ? Cheers |
Hi Dover- ... interesting post. thanks Wikipedia is ok ...Youtube can be effective too? I hate theory so the animation helps me alot; another reason I like posters here on the forum that talk to their direct experiences - not what if this or that. I am no physicist and I am bad at math to boot. I hate formulae. Btw – I have found myself the easiest what to find out about physics is to partake in a “hobby” that can kill you if you slip up. You learn really quick. Ever track a car ......around an oval track that kind of sort of resembles an lp ? |
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.
|
Re quality factor, Q. ... under, critically or overdamped systems, as they relate to the ET2. My running the arm at 12 psi is no accident. I addressed the Q factor of my arm years ago. And the bearing has no issues at all carrying the extra weight, even at this pressure.
I don't have any proof of this, it is just a recent thought. While higher or lower weight is obviously a factor, I think that the one leaf spring, two leaf spring plus number of weights thing, has probably a whole different set of cause and effect issues. So with reference to a rigid or sprung counterweight beam, it is probably an all or nothing event. In other words because we have the "potential" interaction of the swing frequency of the beam and the resonant frequency of the arm assembly, depending on the number of leaves and the number of lead weights used. 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. Others may have already thought of this but, it is just an idea to put out there for comment. |
03-13-13: Ct0517
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 ? 03-18-13 John47
Mr Kuzma replies to MF
[quote]"A question of damping..."
........ 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. John47 - Thanks for confirming my assumptions with the Kuzma. Dover - My ET 2.5 has the CF armtube and was the one I referenced in my post with the Benz Micro. So many variables here. Plus the specs I listed are for the stock cartridge – it is now a Ruby cantilever SS retip. I have no idea if the specs were changed when it got retipped. Does anyone know what a Ruby cantilever does over the stock Benz Micro one ? The cartridge came with the VPI TNT I bought years ago, and it needed a retip when I purchased it so I never heard it in stock form. Richard – the triple leaf spring is tight but not 100% tight. It has a tiny bit of flex in it but you need to force it a little. If you hold it by the I Beam and shake it - it doesn't move. Still it is not as stiff as if you stuffed two toothpicks on either side. Cheers |
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.
|
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. |
Hi Thekong
Lead is also banned in Canada. Based on the shape and size of the ET2 counterweights here is an easy DIY alternative.
Go to any tire shop and pick up a couple of the lead weights that they use on wheel rims. They are of substantial size. They are easily snipped and the hole drilled to make any size weight you need. To get the nice square look as BT’s take them to a machine shop. Otherwise you could be up and running in the same day with the lead.
Nice speakers btw ! I am glad we have distance and a lot of water separating us otherwise I would be tempted to come over and ask to borrow them for a while.
Some more impressions.
The lead weight reminded me of something.
I “experimented” with a form of higher mass quite a while ago but only at the counterweight end. I had at the time email conversations with a couple of high profile Audigon members who were in this "lets add more weight to the counterweight camp” with their past experiences with the ET2 and ET 2.5. I really hope they see this post.
I added more weight to the counter weight end and tried to get as close to the spindle as I could. I found the sound seemed to get “bigger” each time I did it. It was addicting. I also did not have my Studer at the time for a reference point in my room for the sound. I made extra lead weights sourced from the tire shop I referenced above.
The horizontal mass of the arm may not have been seeing “some” of this extra weight as it was decoupled, but the air bearing spindle itself was. I talked to Bruce about this. Now lets imagine that he has heard every story you can probably think of in the last 20 + years from tweakers, hot rodders and experimenters of his tonearm. He was very clear to me. Try it and see...
So he encouraged me and said at some point I would affect the balance of the spindle, the air would not be able to sustain the spindle weight properly, and rumble would occur. something like that.
I never got as far as actual rumble occurring and then the light came on for me. The ET2 counterweight ” I” Beam is the most misunderstood part of this tonearm and the EASIEST to screw up. The ET2 arm comes with a set of lead weights along with a range described in the manual of the minimum and maximum cartridge weight they can counter. This range can be modified btw - but thats another discussion. How many of you have thought to yourselves, I don’t want to lose them. So lets put them all on the counterweight. Who hasn’t done this when you first started out with the ET2 ?
How many have even done it with a light MM cartridge?
NOW the really big question - imo.
How many Michael Fremer types (professional reviewers) have done the above - used all the weights when they were not needed ?
Has anyone ever read an ET2 review where a description of the weights (how many used/positioning on the I beam was actually described.
There positioning is as critical to the sound as the fine tuning adjustments made to the cartridge itself. Very sensitive. Without the knowledge about this ..
Well as noted in the previous posts from Dover the manual doesn’t say add extra weights like I was doing in the experiment. It says it is preferable to get as far out on the beam as you can. This implies less weight on the I beam itself as its intent is to be decoupled. Think about it – the weight is on a leaf spring. ITS A HORIZONTAL VERSION OF A CAR/TRUCK LEAF SPRING . Get that in your head and your home free with this tonearm – IMO.
So this Iight came on for me around the first couple of pages on this thread. Someone that calls himself Frogman reminded me.
Btw – I thought this person that calls himself Frogman was a scientist that spent his time where its wet; looking for Frogs. Monikers being what they are. Boy was I wrong !
Re-applying less weight further out on the beam; the tuneful bottom end returned with more speed and coherence. Similar wording to one of Dovers previous posts.
*********************************************************
Warning - The above post about adding "mass to the counterweight" does not relate to the mass spindle dampening being discussed. Persons reading this thread do so at their own risk.
********************************************************* |
Thekong, Richard, I sometimes use brass weights (supplied by Thigpen) instead of, or in combination with, the usual lead weights. IMO, the concern is not so much the possibly inherently-different sound of something like brass as compared to lead, but the fact that using a material with a different density may necessitate placing it on a different spot along the I-beam, since as Dover points out:
****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.****
In my case, the use of the supplied brass weights usually results in having to place the weights further in along the I-beam. In my set-up, this is usually not ideal, with inferior overall bass performance. I suppose that it would be possible to have the exact size of brass weight machined to match the weight, and hence placement, of the lead. But, that is not the case with the weights that Bruce sent me. |
"..... 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. |
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. |
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 |
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.
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 |
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. |
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? |
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.
|
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.
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. |
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.
|
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 |
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. |
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 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". |
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. |
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. |
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 |
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 |
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.
|
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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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. |
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 ? |
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/Dover - Do either of you play flute? |
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. |
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 |
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 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! |
