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 |
Chris
Good to read about the mag wands performance. Thanks for giving us a clear view on what it does. Also impressive engineering all over again from Bruce. |
Yes, some interesting materials and ideas being used in platters these days. Isn't VPI also making a ceramic one?
Then the Clearaudio, in their Statement and Basis are using plastics.
Take your pick. |
Chris
I built this version of the ET2 around 15 years ago. Drawings are long gone but it could be reverse engineered. The arm is optimized for low compliance carts. As you can see, just, from one of the pics Ketchup found, it has a fixed counterweight. 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. This is glued in place halfway along its length. ( it can be removed if I go to high compliance carts)
This combined with the fixed counterweight means that the arm is HEAVY in the horizontal plane. I have tried magnetic dampening and oil troughs but prefer the pure mass approach. I run at around 12 psi, lower pressures may be problematic when adding so much mass.
On the magnetic dampening front the negative I heard was possibly caused by the induced circulating currents interfering with the cartridge output
The manifold and arm pillar are made from acrylic. Lead is inserted and epoxy glued inside these to sink energy. VTA is adjusted by a removable screw after loosening 4x M5 cap screws. Manifold and pillar are locked solid once these are tightened. The arm was designed with a lifter like the ET but I found a subtle improvement when this was removed. Same goes for the VTA adjustment screw. I. E in its operating form there are no bits to flop about. Arm pillar is fused to the plinth effectively making it one assembly.
Cartridge leads are single strand silver lightly twisted at about one turn per 8 mm. Continuous to the preamp
Big jumps in performance were the goose neck. (This was made from the same grade of aluminum as the wand.) The bracket that joins the wand to the spindle.
There are 2x M2 grub screws outboard of the bearing sleeve orings. These pass thru the manifold and contact the sleeve. Two small pieces of shim metal are inserted at 120 degree increments away from the grub screws. Once tightened the grub screws eliminate the compliance of the orings. There should be nothing soft in the loop between record and cartridge. This is a major improvement. There may be room on the standard manifold to do this but Beware anyone doing this it would be easy to break the manifold.
I use 2x 50 liter containers for the surge tanks. They are stuffed with long hair unspun wool to increase their effective volume. They are seperated by 6 meters of 1/4 hose entry and exit points are at opposite ends of these tanks.
Chris you have a regulator, water separator. It looks like it uses brass fittings and appears to be close to the arm. Try soldering a wire to the exit fitting and earthing this. I don't know why this works but it is possibly something to do with static electricity build up in the air stream.
On the topic of static electricity try rubbing the wand with AFC anti static foam cleanser. The stuff they use on photocopier glass.
Have removed the Teflon in the head shell and replaced with a square of 1/2 mm thick lead and superglued in place. Others have tried different materials here also with good results.
I have a new arm on the drawing board based on what I have learnt from this one. |
Ketchup
Yes your shim idea is a good one. I wonder if it would be possible to fashion tiny wedge shaped shims and push them in. Could maybe eliminate a bunch of trial and error with individual parallel shims.
And yes I agree, there is considerable compliance in the orings. Also in the original goose neck and arm pillar/ manifold interface.
Chris, yes I have the CAD CAM machines that could make the goose neck and a complete arm. ( excluding spindle and sleeve. ) It would however be costly due to the likely small runs.
The original Counter weight mechanism has been discarded. Adjustment is by means of two knurled discs, either side of the weight, on a M10 threaded rod. You can kinda see this in one of the pics Ketchup found.
Ref horizontal mass, I realize that this is controversial. I simply encourage those of you who feel the urge to try it. Particularly those of you that have full range systems. ( response into the lower 20s )
If we redefine horizontal effective mass as resistance to lateral acceleration we will see that magnetic and oil dampening are similar to " pure mass" all three options resist lateral movement and all three increase this resistance as the lateral movement increases in frequency.
All three impose lateral forces on the cantilever when the record hole is not centered.
The reason that I believe that the rules for horizontal effective mass are different for pivoted and linear arms is this.....
With a pivoted arm the horizontal effective mass in multiplied by the head shell offset. Only a percentage of the cantilevers lateral movement is resisted by the arms horizontal mass in trying to rotate the arm the rest of this movement is resisted by the cantilevers efforts trying to bend the arm tube itself. Linear arms do not impose the second characteristic on the cantilever. This I believe is one reason that the pivoted arm guys complain about a lack of gestalt from linear arms. We largely fix that with oil troughs or magnets. Pure mass is another option
Lead is strategically placed in an ascending hierarchy throughout the arm and TT itself. Tests with a number of soft and hard materials in the head shell and elsewhere convinced me that "local" sinks are beneficial.
While the magnetic dampening was an improvement over the oil trough, it was not as good as the recently added lead slug. It is speculation on my part why this is, but the induced currents seem to be a logical possibility. If they do exist, I suspect that they would be AF in nature, not RF.
I heard this, admittedly, small problem with the original arm wiring, OFC Litz headphone wire I then used and with the silver I now use.
Twisted pairs of wires are less susceptible to RF due to common mode rejection.
In my TT, the arm and motor are rigidly fixed to the same upper acrylic layer.
Dover, are you still running an ET2? |
Chris.
No I have not measured these forces and would be very interested to read Bruce's comments on same. I assume it is a big file, so can I ask you to email it to me at the contact address on my web page, if not too much trouble. Or if appropriate post it here.
As per my earlier post, both an oil trough and a magnet impose a resistance to lateral movement as seen by the cantilever. They behave much like weight in the lateral plane. I have simply used weight alone.
I did my initial tests on extra horozontal mass by disabelling the leaf springs on the counterweight beam and winding equal lengths of solder around the goose neck and counterweight assembly. This way I kept the lateral balance of the arm static. It didn't look pretty but was informative. I also tried this configuration with and without magnets.
I currently adjust for different cartridge compliances by using a range of counterweights.
Dover, I seem to remember from this thread or another that you no longer use an ET2. If so, we would be intereted in what you are currently using and any reasons for the change. As we all, I think, agree, the ET2 is pretty darn hard to beat. |
Chris.
Thanks for the offer but I must respectifully decline. I am just dialing in my Shelter and newly renovated enlarged room. More distractions, while delightful, are unfortunately just too much for now.
re my building a new arm. The design would allow for bolting to a flat surface with three screws. Simalar to the ET. It has fully adjustable horizontal mass independant of the counterweight. I am struggling with the wand design at present, which is a little radical. While I can visualise it, I'm not sure I can build it. The whole project may founder on this. If I am to build a new arm, I want to be pretty sure it will be a step up from the present version.
Dover, what did you do, loose your ET2 in a drunken poker game or something? |
Dover.
Magnetic dampening will vary with the speed of horizontal motion..... so does pure mass. The formula F=Ma you quoted in another thread confirms this. Try shaking say a 1kg weight backwards and forwards at 0.55 hz (record hole centering error) and try again at 20 hz, (music). Much more force is required at the higher frequency. If this weren't the case, the R&D dollars speaker driver manufacturers spend on reducing the mass of the moving parts would be for nought. As I said earlier all three dampening methods increase in resistance with rising frequency of excitation.
That said, I agree with you, I do not like the effect of the oil trough.
To be clear, I do like, mostly, what magnetic dampening does. Further it is elegant and kinda cool, but I hear a slight negative which does not exist with the mass approach. As I said, I think that it is caused by induced currents circulating the spindle. Do you really want these currents anywhere near your delicate feed from the cartridge? I would be using mag dampening today if not for this slight negative.
Mag dampening increases cartridge output, yes agree, same holds for mass. My take on this is perhaps different to you. While is reduces micro vibrations which is a good thing, I think that the higher output is because the cartridge has more lateral resistance to work against because it cannot move the arm laterally as much. And move due to the cantilever tracing the groove it must, F=Ma again. More cantilever lateral movement equals more output.
Yes the Dynavector is an arm design that I have studied because it is unusual in using mass and magnetic dampening. But currents near the cartridge output?
Look, I don't actually care if people agree with me on this mass thing. I said earlier that it was contentious. Anyone with a full range system down to the 20s, might want to try it. They could well be surprised at what information is lurking in the grooves. |
Chris.
While I have built a number of BD turntables, they all employed pivoted arms.
The eddy currents induced by the magnet are everywhere within the spindle since it is conductive, so having the magnets at the opposite end to the wand does not take them any further away from the cartridge signal. Therefore it is "near". The negative effect was apparent before and after I changed the goose neck to conductive aluminuium.
I made the internal slug by rolling up 1/2mm thick lead sheet strips. Cut to different widths. The roll OD was equal to just less than the ID of the spindle. Different widths gave me the ability to experiment with different weights.
A string was passed thru the center of this roll and thru 1/4" plastic tubes like that used for the air feed. String tied off one end and a length left at the other. The tubes were cut to length such that one tube protruded a few mm once the tube/lead/tube assembly was slid inside the spindle. Thus when the counter weight end cap was reinstalled it slightly compressed the tubes. Tubes were equal length to position the lead in the centre of the spindle. The pull string allowed the whole assembly to be removed.
Everything causes cancer. |
Chris
My apologies if this has already been covered in the thread, but can you tell us the sonic differences between the ET2 and ET2.5
Many thanks |
Dover.
I pretty much agree with everything you say. Where we diverge is in the sublties. It is easy to add too much mass in the horizontal plane. I went there in my tests. The trick is finding a compromise point.
Dynavector put the reason for high horizontal mass far better than I could. I agree with their conclusions.
Sarcher30 Dynavector's quote covers their views on this.
Further, from memory, the ET in standard form has a horizontal to vertical effective mass ratio of around 6:1. So it is already a differential mass arm. It is just that in my view this ratio is not enough. As per before I don't care what people think about this, they are free to give it a go, or not.
Also as before, I like what Mag dampening does right, I just cannot put up with what it does wrong. |
Chris
I initially used one fridge magnet then went to multiple fridge mags. Finally using Neodymium before abandoning the idea.
I tried first at the counterweight end then transferred to the wand end. There are differences. Now the reasons for that could be a whole new controversial discussion.
Frogman
As per an earlier post, when I rebuilt the manifold I used 2 shims and one grub screw arranged at 120 degree increments each end of the manifold. This allowed for tightening by doing up the grub screws. Do this on a standard manifold at your own risk
Ketchup
You got me running to the arm to check these little screws. Still tight after 15 years, phew.
So now some may be asking why I haven't cleaned the sleeve in 15 years.
Well, we do have very clean air here in NZ.
With the air pump running I break the air line next to my pressure gauge and squirt in CRC CO contact cleaner. Then reconnect.
I have previously placed paper towels at each end of the manifold. Then move the spindle back and fwd.
The cleaner is forced thru the sleeve and its tiny orifices. Leaving them to be nice and clean
I do this approximately every 6 months with positive results. |
There is a sound engineering reason to put any mag dampening to be at the wand end of the spindle. Since the mag tends to resist spindle movement, it acts as a pivot for any non axial spindle motion
Since the cartridge is at the end of the wand and not at the end of the spindle, there is a force moment induced by stylus movement. The spindle can, at frequencies below the air bearing resonance point, move about this pivot point in a non axial manner.
Having this pivot point at the wand end causes less teter totter due to spindle sleeve clearance than would be the case if the pivot point was at the counterweight end. This benefit is clearly audible.
Exactly the same design feature is present in TT's with inverted main bearings.
Of course the mag is closer to the signal wires.
The choice is yours. |
Chris
Yes various magnets tried in..,...completely original ET2 , ET2 with fixed counterweight. My manifold with and without lead slug.
All iterations also tried at wand and counterweight end.
( not both ends simultaneously )
All tests done at 12 psi
Dover, for a given resonant system, all else being equal, addition of mass will lower the resonant frequency and reduce the amplitude of this resonance.
I had a dual manifold arm on the drawing board well before I rebuilt the ET. Feel free to check with RW for confirmation.
I currently have a pseudo active dampening/mass system in the early stages of development. It doesn't use mags or conventional feedback and IMO it is elegant in its simplicity. If it works it would eliminate the lead weight.
And to miss quote the Bard just a little......
Thou doth protest too much, methinks |
Ketchup
No it doesn't incorporate the arc on the VTA adjustment
I didn't have the machining technology to do this back then
I tune in the approx VTA then check alignment. Then final fine adjustment of VTA and recheck alignment again.
The new arm will likely have the arc feature. |
Ketchup
I should have added. The lack of the arc feature is not a big deal for me since I don't change carts often. Others who do, would find this feature helpful. |
Ketchup
Yes agree, I would use a rotary table which we now have. But is it really a big deal if you don't change carts often. Critical in any design would be rigidity once set. |
My view on a stereo system is that it is just a machine. Actually lots of machines chained together to give an output based on inputs. As such it is logical and the output is predictable provided we have sufficient understanding of the machine. ( none of us have sufficient understanding )
What we are talking about here is a small part of the machine. The coupling, decoupling of a counterweight on a linear arm.
Frogman and Dover say that they prefer a loose connenction and one leaf spring.
Chris says that triple springs produce a sound that is too lean.
Rockport, Walker, Kuzma and I say that there should be no spring at all.
I believe ALL of the above statements as I think that they are actually saying the same thing along a continuum.
It all depends upon the voicing of your system and our biases, and we all have biases.
Also an improvement can actually sound worse as it can expose more clearly problems elsewhere in the machine chain. Sometimes when we open the window wider, we do not like what we see. We then need to work on the new "view" to correct a previously unseen problem. It does not mean that the original change was wrong
I have said that I don't think that it is a good idea to have a mass attached to two dissimilar springs who's resonances are in the same neighbourhood. The transmissibility graph I posted shows the potential nasty consequences of this. At least a 6 x seperation of the two resonant frequencies would a target.
Using one spring lightly coupled to the spindle pushes the resonant frequency down below the arms core resonance. This is good. (As Frogman points out, there may be other factors at play here with the loose screws.) Double or triple springs push the resonant frequency above the core resonance which is also good.
We have to be carefull when using stiffer springs that we don't move too close to the audio spectrum, since the same transmissibility graph data will bite us. We also have to be carefull that we do not go to low with lite springs since we get close to eccentricity frequencies again with possible nasty consequences. So what if we pushed the resonant frequency up above the audio spectrum. We have no risk of any of the issues I raise here.
My early fixed counterweight designs resonated somewhere in the midrange. It was easy to hear adding a nice, but not accurate bloom to voice and midrange instrumemts. If my system was not already "full" in this range I may have stopped experimenting, thinking that the arm was acurate. Increasing its rigidity more, pushed the resonance above the frequency of audibility. This is desirable and is the final logical progression to the tests that have been listed in this thread.
Gnnett. Do you live in AKL? It would be nice to meet. You can contact me directly via my web page if you wish. |
Dover
Adding mass to the spindle helps to stabilize it.
To repeat, for a given resonant system, extra mass lowers the resonant frequency and reduces the amplitude of this resonance. This is F=ma again. Force the same, Mass up, means acceleration must go down.
I agree that adding too much mass is potentially a problem. Where we disagree is at what point this extra mass becomes a problem. Pivoted arms, as seen by the cantilever, have high effective mass due to the head shell offset. Yet nobody seems to worry about this. I would also suggest that anti skate is significantly more dileterious to the cartridges health.
Placement of magnets..... Below the bearings natural resonant frequency, it is effectively loose, above it is nearly rigid.
So the thought experiment is where is it best to place a restriction to movement which creates a pivot point in order to minimize unwanted movement of the wand. If the mag is placed wand end, the bearing clearance allows wand movement at frequencies below natural resonance but not as much as when the mag is placed at the counterweight end. This is not a bearing stability issue, it is just optimizing the bearing geometery. Like I said this the same principle employed with inverted bearings in TTs. |
Chris
Yes happy to try this mag dampening variation. One more time around the block will do no harm.
It will be awhile though as I am still dialing in my remodeled room and new shelter cart. The system is a bit of a moving target at the mo.
Thanks |
Chris.
Shagging is something done here in NZ between consenting adults. |
I have finished testing Dover's mag configuration on my modified ET2, along with individual mags independantly at either end. This has been the most extensive test I have done with magnets, spanning 3 nights of listening. The results were consistent and largely the same for all mag configurations. Differences being the degree of change. I used both weak fridge magnets and what I believe to be strong neo magnets.
Test records were..
Corelli, Harmonia Mundi 7014, track 1
Oscar Peterson Trio, We get requests, Analogue productions V/V6-8606 track, You look good to me.
Saint-Saens, Respighi, Proprius 7857, track 3
The descriptions here are all referenced to no magnents, being the control example. All changes noted were minor but repeatable over the three nights and were present with both magnet strenghts.
With the magnets in this is what I heard....
Corelli. The harpsichord notes lost some of their attach. The spaces between the individual instruments of the orchestra was reduced with the sound stage being compressed laterally and front to back. The piece begins with a series of very short movements, each stopping abruptly allowing the sound to decay naturally into the hall. The tail of this decay was shortened.
Oscar Peterson. This track begins with a bowed bass followed by the piano and drums, it steadily builds to become quite loud by track end. The effect is dramatic. The bowed bass had less bite. Less slip stick of the bow on the strings. Ray Browns usual muttering as he plays is less apparent. Less space between instruments and smaller sound stage. The build up to the final notes was diminished.
Saint-Saens. The singer uses vibrato to good effect adding interest to this piece. This vibrato was rounded, smearing her voice. An aside is the airconditioning that can be heard on this track. It rumbles along beneath her voice. With the mags in place this becomes more of a low frequency hum. Sound stage and hall cues were diminished.
With all iterations, there was a fog added, this covered up low level detail. There was also a slight feeling of unease, a tension which by the third night had become annoying.
The greatest negative change was with the 4 strong magnets, becoming less of a problem as I reduced strength and number.
All of these differences were slight, but it is the litle bits that make this hobby of ours interesting.
For those of you who may be interested in adding mass. I would bring your attention to Morch's latest arm which uses massive weights to increase horizontal mass. On their web site it does not say what these weights are made out of, but brass or stainless steel would be reasonable asumptions. Extra weight like this would dwarf the 30 or so grams I have added to my ET.
An appology. Some of you have contacted me via my Technics upgrade web page krebsupgrade.com While I can see the mail, I cannot at this time open them or send replies. I will get it fixed asap.
|
Manitunc.
Now you are just being greedy!
Got to be fun, running all those arms.
cheers. |
Dover please re read my opening sentence.
"I have finished testing Dover's mag configuration on my modified ET2"
This clearly states that my ET is modified as anyone reading this thread recently would know. My testing was done in that context. That fact is obvious. The Dover Mag dampening test was as you proposed to Chris and that he asked me to try. I also took the opportunity to revisit earlier versions with strong and weak magnets independantly each end.
I have not said that mass, mag dampening and fluid dampening are the same other than that they all resist motion and that this resistance increass with frequency.
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. Lateral movement of the cantilever mounted on a pivoted arm tries to rotate the arm about this pivot point. This added mass, flywheel, serves to resist this rotation tending to keep the cartridge still, a desirable trait. As viewed by the cantilever this is no different to me adding mass in the linear plane to the ET. Adding too much mass would result in unwanted cantilever movement due to record hole out of center problems. We agree on this, as you say it would load up the cantilever, but Morch with their flywheel do not appear to have reached that point nor have I with my arm. |
Dover
As you said we will never agree on this.
The difference is that I have tried both light and heavy ETs. As far as I can tell, I am the only one who has done that. If so, I am the only person here who can speak with any authority on the subject.
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. Your scaremongering may have dissuaded people from trying a simple reversible mod, which is a pity since we could have advanced the collective knowledge of this diverse group. And isn't that exactly what these forums are for? |
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. |
Maths and Physics.
Stiffness
Many years ago I remember reading an audio magazine which tested the rigidity of the ET2 bearing. It may have been Martin Colloms, but I can't be sure. This was done, again from memory, where accelerometrs were used and a sweep frequency was applied to the spindle. The result showed a bearing that was stiff at audio frequencies.
This is explained by the design of the bearing (it's self centering characteristics) and its extremely high resonant frequency. Many times higher than the audio spectrum. Although the bearing uses air which we know to be compliant, at the frequencies of interest, the bearing medium is stiff.
I also show here a quote from an industrial air bearing manufacturer. While these a big load bearing devices, their design is virtually identical to the ET2
"Outstanding stiffness for small deflections Most engineers visualize an air bearing as being like a hovercraft, and they erroneously conclude that a bearing which floats on air cannot be very stiff. Actually these gas bearings are many times stiffer than a ball or roller bearing. Sapphire orifices within the bearing gap control the pressure in a film of air which is only 0.0003 inches thick. As a load is applied to displace the bearing rotor or slider, the gap decreases very slightly on one side, reducing the flow of air through the adjacent sapphire orifice. This results in a pressure increase in the gap on this side which pushes the rotor back to its original position. In essence, the air bearing is a servomechanism with closed loop control, and maintains a uniform gap in spite of external forces that may be applied. This results in bearing stiffness of millions of pounds per inch for small deflections. Stiffness is linear and does not change with temperature. In contrast, ball or roller bearings have almost no stiffness unless heavily preloaded. The stiffness of a ball bearing is not linear, and varies considerably with temperature."
Amplitude
A few weeks back I posted a transmissibility graph showing the effect of excitation frequencies at various multiples of the resonant frequency. This graph can be used to show relative resultant amplitudes for known resonant and excitation frequencies.
For a standard ET2 using in my case a Shelter Harmony, we get a resonant frequency of 8.4 hz. On my heavy arm, this frequency drops to 5.3 hz. If we take the lowest frequency of interest to be 20hz we get multipliers of res freq of 2.4 and 3.8 respectively.
By applying these multipliers to the graph we can see that the system which resonates at 8.4 hz shows a small rise in amplitude about 15%. If we now compare this with the 5.3 hz example we see a much smaller rise around 5%. We have to extrapolate this answer, since it is off the scale of the graph. In other words at audio frequencies the heavy arm produces less bass boost.
You can also see that the damping applied has very little effect on the resultant gain as the lines are trending together. This means that even if we factor in a higher resonant amplitude for the heavy arm, we can see that while it alters things slightly, it has minimal effect.
There is some merit in a discussion of what happens at sub sonic frequencies but the arm with the lower multiplier (lighter arm) will face problems sooner as we decend below audible frequencies.
As before these are all first principle discussions. It is what it sounds like that matters. |
Chris.
Glad that you like the aluminium goose neck. I designed it to be as stiff as possible. The tighter fit into the wand and spindle is deliberate. Also it is made from the same grade of aluminium as the spindle, 6061 T6. This to minimise the different material count in the arm loop. |
Frogman.
I enjoyed your post, thankyou. How much blutac did you add to the headshell? By way of comparison I have added a net 0.77gm to the headshell of the ET2. (Lead in, teflon out.) Not a lot of extra weight.
On damping... If it is not meant to move, make sure it doesn't.
To everyone..I'm sure that you have experienced this. Last night's listening was great. All the planets seemed to align. So what causes this? Clean power? Just the right room temp, humidity? My own state of mind? Off topic, I know, but I am curious to read your views on this.
thanks
Richard. |
Chris
Yes when you talk to Dover and I you are conversing with the future.
I agree with you. Clean power and I think that we should not underestimate the effect of our own state of mind.
I think that every professional reviewer should prefix their review with...,
Today I feel..., or over the period of this review this was my general state of mind.
BTs comments are interesting. I know the effect of the shims and grub screws. It is definitely positive. As in the drive thread, I believe that there should be nothing soft in the loop between LP around to cartridge. The o'rings are quite soft.
My testing, with and without the bearing sleeve clamped seems to support that view. |
I have been researching possible bearings for a new Arm and I came across the Kuzma web site and the Airline Arm. This appears to be unique in using a porous material rather than multiple drilled holes like the ET. It also has a sliding sleeve instead of the sliding spindle of the ET
Wow this is a spectacular looking arm which is definately on my wish list.
This brings me to the subject of horizontal effective mass again. I asked them for this figure for the Airline. It is probably not appropriate for me to publish this here, since it was a private conversation and the number is not shown in their specs. But I can say that it is higher than my heavy modified ET2 arm. 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.
He directed me to a video of the arm and cartridge tracking the lead out grooves with a oscillation amplitude of 12mm. See www.Kuzma.si ,tech support,tech info, Airline video.
This Video was posted by them to allay fears of cartridge damage due to high horizontal mass.
This arm is amongst the best currently available. It has a large differential between its vert and horizontal effective mass figures and does not appear to be a cartridge killer.
I'm sure you will agree that this motion is violent and way beyond what any record eccentricity would produce. He assures me that there is no problem with the cantilever under these extreme circumstances.
I want one.
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Dover.
You need to research the difference between the two air bearing types. The Kuzma is unusual in its choice of bearing construction. So how am I wrong in my statement that the use of porous material appears to be unique?
This in no way detracts from the ET2 bearing. I was just showing that other options are out there.
At frequencies below resonance the cantilever is free to push the mass of the arm sideways. This does not defy physics, it is physics. In other words the cartridge suspension is stiff enough to accelerate the arm mass sideways. 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.
No, the video does not show the cantilever, that is why I asked him if it was a problem. I have to take his word on this that it is not, and resonance formula back him up. Further this confirms what I see when my arm is tracking eccentric records. I repeat the video is shown specifically to allay fears of problems due to high horizontal mass.
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Frogman.
20 years! It gets scary when you start thinking back doesn't it?
I also have a continuous run to the pre but put it inside purely for cosmetic reasons. My thoughts would be to route it such that it stands off from the wand a little. In theory there would still be some interaction between wand and wire, due to proximity. That said, the level of this may be just too tiny to notice. Have you per chance tried this? |
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. |
Thekong
We look forward to reading your comments. |
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. |
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. |
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. |
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. |
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. |
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. |
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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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 |
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 |
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. |
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. |
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.
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Dover.
:Yes the outcomes are entirely different if the counterweight is fixed....so.
:We have established that it will not be the end of the world for the cartridge if the horizontal mass is increased, this by reference to other arms that are heavy.
:Countary to stated design goals yes.....so.
:While BT designed the cw arm to swing at frequencies below the core arm frequency, it does not neccesariy prove that using 2 springs will result in that criteria being met. It is almost certain that the use of three springs, as Chris did will push the frequency above core.
:I know that BT designed the arm to have the two spring systems, Cart and Counterweight. I just don't think that it is a good idea because they talk to eachother. Has anyone thought about why the CW spring(s) and their damping are so fussy to set up?
:Yes I pulled the resonance graph and math from the net. This because it explains the effects more clearly than the literature we regularly refer to here at my work. Those readers that understand the math will know why I chose a 6 times multiplier.
:My prime reason for fixing the counterweight is to restore the full bass drive. You have in an earlier post talked about not needing response below 30hz and that response in this region can be problematic, or words to that effect. I do want response in that range and yes it can be difficult to sort this area but with effort it can be done and the results are most rewarding.
:We are all biased, it is astonishingly arrogant to suggest that you are not.
Chris.
Agree the room is critical, same for the air feed.
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Dover.
To address the points raised.
Scaremongering.
This comment was posted in response to your claim that the weight of my arm was sufficient to cause damage to cartridges. You actively warned others against adding mass because of this belief. During the course of this discussion it emerged that the Kuzma is actually heavier than my arm.
While it is self evident that the forces seen by the cartridge will be higher with the Kuzma, you have posted zero evidence that these forces are sufficient to cause damage. The Kuzma has been around for long enough now for any problems of this nature to have surfaced.
Scaremongering....Absolutely.
My comment about being the only person who could speak with authority on the subject was referenced to the sound of my modified ET in its current form. That is a true statement.
It must have been 5 years since we heard each other's systems.
I have not commented on my impressions of yours because I assume that your system has improved since then and any comments I made would be out of date.
I would expect the same courtesy from you.
For the record. While the room is small, it is larger than you recall.
Re the acoustats, they may still look like 2+2s but that is where the similarity ends. Further someone once said something like. .. many a fine tune played on an old fiddle.
BTs letter is clear and well understood.
My position has always been that there are valid alternatives
Rockport, Walker, Kuzma. Just like Bruce, these arms are designed by people who are obsessive in their quest for ultra quality accurate record reproduction. The sales and reviews of these products would suggest that they have indeed achieved superlative results. With a design approach that you claim is fundamentally flawed.
Their designs are valid and I would say that it is l disingenuous on your part to suggest that the owners of these arms possess equipment that needs to be "looked at" , that they are all listening in comprised rooms and that they all prefer one note, excessive bass, along with the sound of miss tracking cartridges.
Yes the ET2 is a brilliant design. There are other brilliant designs |
Hi, I hope that you all had a great Easter break with Family and Friends.
Chris. I don't have any first hand experience with arm pods. They tend to go against the grain so to speak, in the quest for absolute dimensional stability between platter and arm. That said it seems that there are many admirers of this approach and, other than to quote others, it would not be prudent for me to comment on the sound of something I have not personally heard.
Re arm wiring and earthing.
For anyone looking to earth the aluminium wand. Anodised al is an insulator so you would need to scratch thru this to bare metal. Something I would be reluctant to do.
Earthing the air stream should be done as close as possible to the arm. I have a pressure gauge close by and have grounded the metal part of this that protrudes into the air line. Simply cutting the hose and rejoining with an appropriately sized metal tube would do. Solder an earth wire to this. You can expect a quieter backdround and a good jump in transients.
I have been waiting for someone to run the arm wiring completely outside the wand and spindle. The results would be interesting, assuming that there are no RF issues.
Wouldn't look to pretty however. |
