[dlaloum]

Hi Folks,

just kicking off this topic, based on some tangential discussions on the 100Hz compliance thread.

There are repeated mentions of adding lateral weights close to the pivot point or on the bearing nuts of arms for various arms... There are photos out there of RB300's with lead weights attached to the bearing nuts like a pair of pointy horns going to each side...

There is also an interesting quote from Shibata (the man that designed the stylus profile)

"Cantilever deflection can reach more than a few degrees by side thrusts so that tracking angle error distortion is increased. To avoid such occurrence, the compliance should be kept not excessively high, and linear tracking arm (not swinging but linear shifting) is preferable".

And there has been some mention of needing changed anti-skating after adding lateral masses at the pivot points of an RB300.

It is clear that enhanced lateral stability improves the performance of a tonearm (and cartridge) - as demonstrated also by the Grado Longhorn mod.

Bye for now

David

[neobop]

This reply was written in response to Don and the reference to a VE thread.  It was to go on the 100Hz cu thread.....

Couldn't find that thread.  Maybe it's been deleted or changed again. 
Don, could you post a photo so we can see what you're talking about?

I gather this isn't like adding damping or friction to the pivot or using outrigger type weights.  Weighing down an azimuth adjustment ring?  Adding lateral mass and not vertical?  If its far below the pivot, that would lower the center of gravity assuming that is, its effecting horizontal mass.  I don't think you can lower the center of gravity in one plane only. Like an underslung counterweight effects all planes.  Maybe you can add horizontal mass only?  I doubt it.  Damping pivots doesn't necessarily change any eff mass it might only increase friction or resistance to change.
neo

[Grbluen]

Neo,
It would be more like adding outrigger weights. I'm having trouble uploading photos.
If you've seen the JMW-9 tonearm, then you've seen the stability ring. I've just added mass going outward from the knobs. I am thinking about your post. I'm just not sure that there is a linear relationship between the different planes because of the geometry. Thinking...

Edit: I am fairly certain that the vtf doesn't change appreciably as result of adding mass in this way.
Edit: This isn't the first time this concept had been suggested. I've also heard that the same thing could be accomplished if you added a heavier counterweight, but moved it closer to the pivot to set the vertical tracking force. This wasn't an option for me as I'm already really close to the pivot.

[neobop]

Here's the Agon thread:
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1032024188&read&keyw&technics&&st0

Okay maybe you can add horizontal mass and only effect vertical slightly.  He obviously didn't tweak it right, now he's mistracking or getting hung up in-groove.  I think this guy is using a 103 on an Origin Live Silver.  That's a reworked Rega 250 with slightly reduced mass.  Lots of unanswered questions here.  Could he realize these benefits by adding mass to the headshell or armtube?  What's the 10Hz cu of a 103, 12?  Is his resonant frequency in the audio band with stock set-up and he found a bizarre fix?  We don't know exactly what's going on.  Maybe if he used 8g weights instead of 12g, he wouldn't get stuck in the groove.

This might have some potential, what have you done so far?  I've never played with a JMW-9, I'll see if I can find some photos again.  Especially with a unipivot you have to consider the center of gravity.  Have you tried more conventional outriggers?  They could be close to the pivot and you could vary the height and weight.

A heavier counterweight will do the opposite, it will reduce effective mass.  Distance is a factor in effective mass.  Effective mass is not weight.  It's the same as moment of inertia.
neo 

[Grbluen]

Neo,
I'm just starting to experiment with this. I haven't done much work in this area. I was intrigued by the prospect of being able to adjust the effective mass. I have a lot of work to do, and quite frankly, I'm not sure about the effects of vertical compliance. I like the idea of being able to change the ' lateral resistance', for lack of better terminology. Being stable in the horizontal plane makes a lot of sense to me. Reading thru the A' gone thread, it appears that might have the weights attached improperly. I think that I may have to increase the lateral distance from the pivot. I have taken note of your thoughts on effective mass, and it appears that I need to try to source a lighter counterweight. I'll get on that right away. It matters not how I accomplish this goal.

[roscoeiii]

You can look at the Moerch DP-8 for an example of lateral weight at the pivot point being part of the design. I noticed that the new VPI tonearms (the 3D printed ones only, maybe?) also have outriggers to the side to add lateral mass.

My DP-8 sounds fabulous. A great upgrade over the DP-6 which lacks the lateral weights.

[dlaloum]

The Rega mod using the fishing weights over the pivot nuts...

It seems to me that it may have an aspect of lateral stability but part of its gain may be simply due to the use of a highly effective damping material (Lead) near a cause of vibration (bearings) - it is not clear that the particular implementation discussed in the Agon thread is in fact a lateral mass mod rather than a high frequency bearing chatter mod.

The Moerch DP8 on the other hand is as clear an example as one could wish for... pretty much pokes it in your eye that one!

[BobM]

I've been told by someone close to him that Mike Fremer has a DP8 in his line up for a review. It's been a while since a mag reviewed a Morch arm, so this could be interesting to compare it to the other big boys that appear there frequently.

(Note: I have a DP6)

[roscoeiii]

I've been told by someone close to him that Mike Fremer has a DP8 in his line up for a review. It's been a while since a mag reviewed a Morch arm, so this could be interesting to compare it to the other big boys that appear there frequently.

(Note: I have a DP6)

Yeah, I think that I read somewhere that Fremer was going to review the DP-8 too.

[neobop]

A photo helps:
http://www.moerch.dk/

Don, the knobs on the side are what you're talking about?  Without knowing what's connected to the armtube internally, it's a little hard to figure out.
http://vpiindustries.com/tone-classic1.htm
I wonder who writes their descriptions.  It's enticingly deceptive.

The Rega mod using the fishing weights over the pivot nuts...

It seems to me that it may have an aspect of lateral stability but part of its gain may be simply due to the use of a highly effective damping material (Lead) near a cause of vibration (bearings) - it is not clear that the particular implementation discussed in the Agon thread is in fact a lateral mass mod rather than a high frequency bearing chatter mod.

I agree.  From what I've read, the bearings leave something to be desired and damping could affect more than high frequencies.  I think the Origin version has reworked bearings?  Which leads us to another aspect of these mods.  Is this increased lateral mass or increased damping or friction? 
Maybe if the added weight moves with the arm at least some is added mass?
neo

[roscoeiii]

The 3D VPI arm looks to have even more lateral weights:

http://vpiindustries.com/tone-3d.htm

[Grbluen]

That is exactly what I've attempted to accomplish at home. My weights are a lot smaller. My setup looks like the picture of the 3d tonearm. I'm going to have to find a way to increase the mass judging by the pictures!

[roscoeiii]

You might want to take a look at the Moerch DP-8 manual, since those lateral weights need to be adjusted (unlike the VPI). Not sure the technical reasons why, but there must be some reason that a fixed weight on the sides wasn't used. the adjustments are both in terms of how far out the weights go, but also their angle (hole is asymmetric).

http://www.moerch.dk/files/DP-8%20US%20(letter).pdf

[Grbluen]

Rosco,
I took a look at the Moerch and I'm afraid I'd need the Moerch for dummies primer.
I can't even begin to comprehend what is going on with that setup. I don't think that I would ever be able to approach that type of precision. Do you think there is a detailed explanation of the system? Maybe some of the owners would chime in?

Edit: Taking a look at the manual now!

[roscoeiii]

Yeah, the reasons for some of that are beyond me.

Maybe something in these reviews will help:

http://www.10audio.com/amazon_referenz_morch_dp8.htm

http://www.10audio.com/moerch_dp-8_v2.htm

http://www.theabsolutesound.com/articles/something-new-in-vinyl-playback-the-moerch-dp8-anisotropic-tonearm/

[jschwenker]

This is a pretty interesting concept - given that the majority of groove signal info is expressed in lateral stylus movements.  Stereo channel differences are typically much smaller than the bulk signals.  (pure lateral being an equal strength signal of the same sign in each channel)  As is generally well understood, bass signals are more mono than in any other area.  Also, in significant contrast to the vertical plane, with sundry record warps, etc., the sources of lateral movements beyond signal are pretty much limited to off center disk holes - which would give a very sinusoidal 0.56 Hz frequency that must be fairly freely followed.  This is maybe nearly a factor of 10 lower in frequency than some record warps that need to be freely tracked in the vertical plane.  The Moerch folks, if first to get there, are on to something.  (at least according to this has-been Mechanical Engineer...)

Many tonearms will be adaptable to addition of masses that will affect the lateral effective mass only.  A pretty common design basis is that the vertical motion bearings are carried as a secondary assembly on top of the primary horizontal motion bearings.  To accomplish isolated lateral effective mass increase one would add outboard mass or masses to the horizontal bearing moving structure. 

Unipivot like designs complicate matters a little.  With them it would be more necessary to assure that the masses added are basically centered up and down and back and forth on the pivot axis to limit their effects in those directions and maximize it in the lateral direction.

I am already designing mods to my SME IV.Vi arm.  Next post I promise some discussion of the math and numbers involved.  Being a "retread" with various other interests competing for my time, I make no promises as to promptness and will not be offended in the slightest if others jump in. 

Cheers,  John

[Minn Mark]

The VPI is a unipivot arm (not sure the Moerch, etc). Mine was set up by my dealer, but the manual has a pretty good description of the use of the azimuth ring, and how to set it.

http://vpiindustries.com/manuals/CLASSIC_1_MANUAL.pdf

Gimbaled or other "multi-pivoted" arms may not (?) benefit from additional lateral weights...


Regards,

Mark

[woodsyi]

I wonder if the lateral weights offer different stabilization than what Magnaglide on Graham Phantom arms do.  Or are they addressing the same issue from different angles:  using active magnetic force vs. adding mass to increase passive inertia?

[BobM]

The VPI is a unipivot arm (not sure the Moerch, etc).

The Moerch UP-4 is a unipivot. The DP-6 and DP-8 are not.

[jschwenker]

Math for masses and locations versus effective mass: 

"Effective mass" of a tonearm/cartridge can be boiled down to an equivalency to a simple mass at the cart location on an otherwise massless arm.  If an imaginary tonearm/cart had 10g of mass all concentrated only at the cart, then it would have 10g effective mass.  If it ALSO had 10g of mass concentrated at a point half way along the armtube then that mass would move half as far for a given arm rotation making it half as effective, therefore it would contribute only 5g of effective mass at the cart.  The total effective mass at the cart is therefore a sum of the effective mass at the cart location of ALL of the bits of the full tonearm/cart assembly.  (the parts that move about the pivot axes anyway)  Most arm manufacturers have calculated or measured the effective mass of their products, so all one needs to do is add the cart in directly to get the assembly effective mass number.

Boiled down from other references, the arm natural frequency per mass-spring math is given by:
fn=1000/[2*pi*square root(EM*C)]
Where Frequency fn is in Hz;  eff mass, EM is in grams;  Cart compliance C is in micro-cm/dyne or microns/milli-Newton
Starting with some realistic like numbers:  EM=12(tonearm)+8(cart)=20g;  C=15(x10^-6) cm/dyne
Therefore fn= 1000/[2*pi*sqrt(20*15)]=9.2Hz  (in the range of 9-11Hz that most folks consider ideal)

Next consider how any added masses might alter EM:
dEM=M2*L2/L1
Where dEM is the change in EM in grams;  M2 is the added mass in grams;  L2 is the distance of M2 from the pivot axis;  L1 is the distance from the pivot to the cart.  And of course the EM of the new assembly would be the original arm EM+dEM.

Let's now work out an extreme case for added mass with those realistic numbers:  As done above say for a particular arm/cart I've already calculated a natural frequency of 9.2Hz - in about the preferred range.  By the argument in my first post in this thread I might want to, at the extreme, make the lateral natural frequency as low as 0.92Hz.  Per the mass square root effect, I would need to make the lateral eff mass=10/1 squared or 100x as much EM or maybe approx 2000g of dEM.  If we had an arm that was 9 inches long and were able to place masses about 2.5 inches either side of the pivot axis, the total of the two masses would need to be 2000*9/2.5=7200g or 16 lb.  Not sure the bearings in any tonearm made would come at all close to supporting that kind of a load.  The message from this example is that it might be challenging to get too much mass in the LATERAL direction.

I next looked at the Morch website pictures for the DP-8 arm.  Making very rough estimates, it looks like the side weights added up (2 each side) are maybe 1 inch dia by 1 inch long and may be about 2.5 inches off the axis.  Assuming they may be brass (at about 0.3 lb/cu in) this leads to a total mass of about 215 grams.  From the formula above, we would have a dEM of about 60 grams.  When added to the original EM of 20, the new EM is 80g.  Using the formula for fn, we can get fn=4.6Hz, or about half of the vertical plane fn.  This could be quite an improvement in LF signal tracking - as listening test reports might suggest.

In my next post I'll share some thoughts about what might be reasonable loads to subject a given tonearm to - and what I'm threatening to do to my formerly nice arm. 

Cheers,  John