[Grbluen]

John,
This may be a silly question, but I have to ask anyway. In your last example you've added something like 4 gms. in the vertical direction. This question gets to the heart of the discussion.
The mass from the Moerch example is added roughly 2.5 inches laterally, but when considering the vertical plane, isn't this mass at a distance of zero in the vertical direction?


Never mind, I get it.

[dlaloum]

Perhaps I should have called the thread "Lateral tonearm stabilisation"

I just reviewed the Graham Phantom design, and specifically the "magnaglide" lateral stabilisation system - which appears to create a similar effect to what we are talking about with lateral masses.

The Revox Linatrack linear tracking unipivot has a well nigh identical system of lateral magnets keeping the unipivot stabilised....

Graham describe it as being a combination of stabilising and damping.

It is not clear to me what effect these magnets would have on the lateral resonant frequency - but (intuiting) - it would appear to be similar to adding lateral mass (lowering the res F).

The comments about damping are less clear - the forces acting on a lateral magnet stabilised unipivot seem very similar to those from a lateral mass stabilised arm... technically speaking that therefore does not appear to be a form of damping...?

The influences being discussed involve a variant / different lateral resonance to the vertical resonance, and therefore it may make sense having a design like the Ortofon Serato stylus which has differential damping in the horizontal and vertical axes....

[neobop]

John,
Welcome to the vinyl circle.  Great stuff.

This discussion of lateral mass reminds me of recent conversations about tweaking the Terminator air bearing linear arm. 
http://www.trans-fi.com/terminatortonearm.htm

About 2/3 down the page there's this description:
"The inertias of the vertical component is different from the horizontal component. Horizontally, because there is no pivot, the inertia is equivalent to its mass, in this case ~ 80g. The vertical component, by design, is approx 25x less, ie ~3g. Horizontal resonance is typically between 12-16hz, vertical 5-7Hz."

I think resonance is stated backwards. Lateral should be low @ 80g EM and vertical will be high with a low mass arm.  Confusing.
People are tweaking vertical eff mass to match their cart cu.  Best of both worlds?
neo

[Grbluen]

Neo, I'm curious, why do you think the designers of that arm found it desirable to have a low effective mass in the vertical direction?

[jschwenker]

Hi Folks,
Yes, good discussion.  Let me see if I can catch up with several of y'all here:

Grbluen:
Sorry about that.  Not quite sure I'm seeing where it is that I might have led you astray about 4g.  There is a disconnect in the numbers between the 1st and 2nd paragraphs of my last post - numbers in the 1st paragraph being used to just demonstrate the incremental calculation and build up of eff mass.  2nd para  on I use numbers that continue into succeeding paras.  Next to last para, in the extreme case, I explore the possibility of adding 2000g of eff mass.  In the last para the eff mass increase is about 60g coming from my wag of 215g of added side masses in the Moerch DP-8 arm pictures.

Your curiosity about mass location specifics does raise some issues that could use more coverage.  IF one is able to add mass ONLY to the horizontal bearing frame, in terms of mechanical dynamics, it does not matter much where the mass is except its horizontal distance from the horizontal rotation axis.  (a secondary concern I'll discuss more later is whether the oddly located masses might produce off-axis forces that might wear and/or de-stabilize bearings)  In the case of the SME arms and may other similar designs, the horizontal bearing yoke is fairly accessible - as you'll see in my later postings once I get this thing rolling.  In the particular case of the Moerch DP-8 arm, even though it is Double Pivot (DP) the outer construction appears to be a shell off which all masses are suspended - making it, for these masses, effectively a unipivot design.  Yes, the side masses appear to be on the pivot horiz plane, making them not effective in the vert direction - which is what we want here...  (also of small curiosity to me, the masses appear oriented orthogonal to the armtube as opposed to aligned along the cart offset angle as one would assume might be best - but that is a secondary issue)

dlaloum:
Afraid I'll have to go look at those magnetic damping refs more to be able to comment much.  If it was a design that drove some sort of eddy currents, it might be able to behave like an alteration of lateral mass but otherwise I'm having trouble seeing the similarity.  Certainly sounds like they're trying to attack the same issue though...

Speaking of damping, on the SME arm I'm proposing to modify, I am using the factory option horizontal damper assembly.  I've always thought this arm performed pretty well in LF recovery with this device.  Maybe as part of this work I'll see if I can find a test method to allow me to quantify that level of damping and see if it is at all appropriate to the EM and fn - before or after my mods.  Gasp!  The head of Medusa grows yet more snakes...

neo: 
Right-o on the basic read there.  I think that a long hidden property of value with linear tracking arms has indeed been that they are typically lower in lateral natural frequency than in vertical fn.  (does look like maybe the fn numbers were reversed there)
Yes, with record warps as a main driver, and the interval between warps and useful signal, maybe 7Hz down and 15Hz up respectively, being pretty small it is logical that folks have concentrated on getting the vertical direction resonance nailed about where desired.  The "new" wrinkle here is trying to address the lateral direction a little more appropriately while leaving what's pretty well known about vertical largely unchanged.

Grbluen:
Hopefully the immediately above might address your last question too...

Happy G'Night all
Cheers,  John

[dlaloum]

The Revox Linatrack patent describing their system is at:

http://www.freepatentsonline.com/4170362.html

[neobop]

Neo, I'm curious, why do you think the designers of that arm found it desirable to have a low effective mass in the vertical direction?

1) They want to keep vertical resistance to motion as low as possible.
2) It's much easier to add mass than subtract it.

Lots of homework with this thread.  Air bearing arms have a distinct advantage when it comes to increased lateral mass.  Apparently the lateral effective mass is equal to the weight of the sled on which the arm rides.   On that Terminator page there's another link that makes for interesting reading.  We're directed to read about arm #2, but read the whole thing.  There'll be a quiz later:     
http://n4rp.com/airbearingarm.html
neo

[Grbluen]

All,
I'm starting to wonder about this a bit more. There has to be more to it than just the masses and distances. The bearings both new and used would have to factor into the equation.
I'm adding new veneer to an Onkyo table and had to remove it's arm. The arm from the Onkyo feels like a toy compared to the JMW-9. The effective mass for the Jmw-9 is estimated to be around 8 grams. The effective mass for the Onkyo is around 12 grams, if I'm not mistaken.
Am I still missing a piece of the puzzle?

[jschwenker]

On bearings and lateral mass mods:
Some of the weights I calculated in earlier posts are clearly beyond what one would want to place on a tonearm's bearings - others may seem closer to reasonable.  There are some design guidelines that tonearm makers are working to that deserve at least some thought before one adds some DIY device mass. 

1)  Ultimate limits:  A tonearm's bearings must be rugged enough to withstand little un-intended bumps, jolts or temporary loads here and there, especially when shipping and installing.  Such possibly much larger than regular duty forces, while they might temporarily flex things (balls, races, even internal supporting structures) it would remain within the "elastic limit" and all parts would return to normal after the disturbance goes away.  During the disturbance it is possible that loads on parts are high enough that if it was operated for a long time with these loads in place it would fail as a bearing within a short period of time.  So in a hand-waving engineering discussion way, just because a bearing can endure a large temporary load without permanent damage does not mean it would be okay to run it all the time that way.

2)  Operational limits:  Most ball bearing based arm designs have two ball bearing assemblies on each "shaft", vertical and horizontal.  The bearings are usually separated from each other by some distance for good stability but they are adjusted axially to be precision loaded against one another to drive the running clearances down to zero or maybe even a slight preload condition.  This produces a condition of no play and design level low friction.  There are some tolerances or margins built into this design such that some small (very small) errors in the setting of this preload won't allow the bearings to run with play or preload that is outside of some design limit range.  In the hand-waving engineer's world , this is the area we may be free to play with in terms of adding some, but not unlimited new weight to bear on a tonearm's design.

Per spec, my SME tonearm weighs about 700g.  Eye-balling parts, I'm guessing that maybe about 400g of that is in the full assembly that rides on the horizontal direction bearings.  As someone who has specified and worked with bearing preload cases a few times, I'm betting that the design has operational margins that would allow it to carry at least a half again that load, without seriously altering the running conditions.  Therefore I'm designing an assembly that adds something like 200g of mass hung out to the sides of the horizontal bearing yoke.  ("pictures at 11")  My arm, while a beauty, is some 20+ years beyond its warranty, haw, haw!!  It is also interesting to note that this is close to the estimate I'd come up with for the side masses on the Moerch DP-8 design.  For a feel for things, 200g is about the weight of one of our premium LPs.  Go big or go home!  Wish me luck anyway...

One further design nuance, pertaining to good bearing practice.  I said earlier that it did not really matter where the masses are, only their distance in that horizontal plane.  For inertia mechanics that is true.  However, the best bearing friendly designs will be ones that keep the load basically balanced about the bearing axis.  Off axis loads (say a single mass on one lever arm) could lead to conditions where bearing balls get too loose or tight at parts of the races - and in worst cases lead to crazy things like ball-race scuffing and premature failure.

Whew!  Think that might be all for now.

Cheers,  John

[jschwenker]

Responding to Grbluen's last question:  Adding rotational inertia (mass at a lever arm) is the only way to directly affect the effective mass of the arm, and add the sought after increase in "slugishness" to its lateral motion response.  Bearings that are worn, mis-adjusted or just low quality could here and there add some resistance to lateral motion but it could just as easily end up being a herky jerky effect which would at places actually CAUSE undesirable arm motion.  (think of the bearings as they encounter debris or damage - on one side of a chunk it would be like climbing a hill and on the other side it would be like going down)  The ideal is complete freedom to move with LIGHTNESS in rotation, when responding to SLOW change inputs, well below audio but have significant RESISTANCE when inputs are FAST, making the arm sit still while actual audio frequency inputs are being made.  This describes a behavior of something with inertia.  Friction, even if it were carefully set to an intentional level, with good bearings, would not do the same thing - it would provide constant resistance at all speeds.

Yers,  John

[neobop]

Which brings up another question(s) for an individual pivoting arm.  How much mass to add and where to put it. Obviously there are limitations, not all arms are created equal. 
Maybe a low mass arm could use outriggers part way down the arm tube, like a longhorn.  Vertical mass would be incrementally increased depending on proximity to pivot, and lateral stability increased?  This might be good on a unipivot.  Adding mass at the pivots brings up the discrepancy between the pivot orientation and offset angle. 

Think back to antiskating 101 - the cart is moving toward the spindle at an angle around 20o or so different than the arm pivot.  How is this addressed with Morch?  We're effecting the motion of the arm, but if we increase lateral arm resistance/mass aren't we also increasing stylus drag, skating, and angular torque on the stylus/cantilever? 
neo

[Douger]

This is a blast from the past! Very welcome....  Back in 2002 I read the whole thread on Audiogon and kept following it over the years, seems like it grew  to more than 4000 posts including tons
of theory from many engineers, physicists and more when A'Gon finally truncated it. The original intent applied to Rega RB250 and RB300 arms. One was advised to rig up a temporary trial using a rubber band or paper clip to listen to the results. I have an RB250 which improved greatly so I used JB Weld to fasten the weights on either side.
Now that I use a Nottingham Anna arm on my Space 294 there is no need, it has lateral weights built in.
I really miss TWL and 4yanx from A'Gon, and Doug Deacon is back there again. All priceless sources of analog info!

[jschwenker]

"but if we increase lateral arm resistance/mass aren't we also increasing stylus drag, skating, and angular torque on the stylus/cantilever? 
neo"

Good question.  If we are doing so by only increasing arm inertia in the lateral direction, the answer is no, no and no.  Patience please dear scientists.  In something like a week I expect I'll have pictures up that will make it fairly plain how purely it can apply to a type of tonearm.  Then the discussion as to whether or not it can be made decently applicable to other situations or by other means can proceed.  All the best!

Cheers,  John

[neobop]

I seemed to remember the guy from Agon (link on page 1) saying something about antiskate and skips. 

"The only slightly negative thing about it, is that it increases the anti-skating force, so you have to cut that back a little, and if you have some marginal scratches that might skip, they are more likely to skip with this mod, due to the resistance to sideways movement provided by the outriggers. I had this happen once last night, but I didn't consider it a problem."

I think by "skips" he means getting hung up in a groove.  "due to the resistance to sideways movement provided by the outriggers"  would imply that.

So, is this increased lateral eff mass or damping, or both?  I don't think they're exactly the same.  Arm bearings not up to it?  We don't really know what he has except he alluded to a Rega style bearing housing and he's using a 103.  The Ortofon cart that David mentioned (somewhere) with asymmetrical damping, is a DJ cart tracking at 4g.  I don't think this is used in their regular carts.

Even if this works great on an SME IV, it might not be so great on another arm?  I'm not a scientist or a ME, but I don't like it when it skips or gets hung up. 
neo

[jschwenker]

I seemed to remember the guy from Agon (link on page 1) saying something about antiskate and skips. 

"The only slightly negative thing about it, is that it increases the anti-skating force, so you have to cut that back a little, and if you have some marginal scratches that might skip, they are more likely to skip with this mod, due to the resistance to sideways movement provided by the outriggers. I had this happen once last night, but I didn't consider it a problem."

I think by "skips" he means getting hung up in a groove.  "due to the resistance to sideways movement provided by the outriggers"  would imply that.

So, is this increased lateral eff mass or damping, or both?  I don't think they're exactly the same.  Arm bearings not up to it?  We don't really know what he has except he alluded to a Rega style bearing housing and he's using a 103.  The Ortofon cart that David mentioned (somewhere) with asymmetrical damping, is a DJ cart tracking at 4g.  I don't think this is used in their regular carts.

Even if this works great on an SME IV, it might not be so great on another arm?  I'm not a scientist or a ME, but I don't like it when it skips or gets hung up. 
neo

Well stated Neo.  Yes, effective mass (rotational inertia) damping and friction are all slightly different animals in the motion control world.  At a gross level the first two are speed dependent resistance (some of which is desired in the audio band) and the last is not.  I'm not understanding the interaction of eff mass and anti-skate forces suspected there.  While can't say it is impossible, it is hard for me to imagine even on purpose designing a mechanism that would accomplish that interplay.  What I'm proposing should not have any effect on the vertical direction properties or settings, including VTF, and thereby the anti-skate force requirement.  Like you I suspect there was a little something else happening there, other than a pure change in lateral eff mass.

And yes, my approach may be variously hard to very hard to implement on other arms.  Even with my setup I'm having to design very carefully to keep away from applying loads to the vertical bearing yoke that would alter the bearing preloads there.  (can't just casually start clamping things on to any available structure or un-doing factory assembled screws...) 

I way hear you on not wanting to do anything to introduce skipping or hanging up to an arm that is otherwise behaving very nicely in that regard.

Cheers,  John

[Wayner]

[dlaloum]

  Longhorn II...

The only downside here is that it adds EM vertically as well as horizontally - so if the arm is too light to start off with all is fine, but if it is well matched to the cartridge, it may not be ideal.

I also like the fact that it seems to be using plasticine/modelling clay - an added bonus of midrange arm vibration damping.

[neobop]

Pretty cool Wayner.  I do something similar with my Unitrak, only without the clay.  The arm comes without a finger lift and a conventional one seems to throw off the lateral balance.

Actually, Longhorn II isn't a tonearm stabilizer.  It's a cart stabilizer mounted on the headshell.  The weight is 90o from the offset angle and not the on the plane of the pivots.  It could increase the force vector that causes skating.  Not sure if it makes much difference though.
neo

[BobM]

A little bit different for me, since this mod is not really about lateral mass, but about the effect of crystals. Here's what I did to my tonearm and cartridge, a DIY approach to the Walker Black Diamond crystal tweak. Here's the results of my "on - removed - on" test

(1) crystal on - Sounded really nice. spacious, meaty, textured.

(2) I pulled off the crystal and re-balanced the arm. OK, so things definitely seem a bit flatter now. Less nuance. Less space. Absolutely a difference was heard.

(3) Glued the crystal back in place and re-balanced the arm again. Yup, there's that nuance, space and dimensionality.

Conclusion: so I guess this did make a difference to my ears, whether from actual RFI/EMI reduction or from just having added mass at the headshell - I don't know. But I did hear it; subtle but there.

But, to keep this "in thread" perhaps I could try using 2 smaller but identically weighed crystals on either side of the cartridge instead of one on the front. Hmmmmm.

[MaxCast]

Imagine a 20" arm with the cart mounded in the middle...has that been tried before?