Linear tracking arms and compliance...

Dover - your solution is interesting - with the magnetic damping...

The Revox setup is also primarily in the horizontal plane rather than the vertical plane (it will have some influence vertically but far less).

I am hearing a number of people posting with damping solutions for LT's focused on the horizontal plane... even with the Revox LT where horizontal mass should not be such an issue - perhaps part of the reason for the damping requirements is that due to the need to shift the pivot point (or the entire arm) - the movement itself might activate the resonance - so damping is required to keep it controlled? (just a wild guess, throwing it out there...)

Moerch's (new?) TOTL arm the DP8 has high horizontal mass, with damping, and optional damping for the vertical motion... (with effective vertical mass adjustable through armtube changes - from 4g to 8g) - again horizontal damping, without vertical damping?

JVC's servo damped arms in the 80's included the top models with both vertical and horizontal damping - but the more basic models (the bottom of the servo range) had only horizontal damping... (QL-Y3F).

Atmasphere, you are right - and the Revox can be a bitch with a warped record.... if you have a mid or mid-high compliance cartridge on it. (no point even talking about low compliance with that arm!)

But with a very high compliance low mass cartridge, eg: original early OM30 with 35cu compliance and the optional weight removed - cartridge mass 2.5g... arm mass 4g... total system mass less than 7g all told.
It rides those warps with the greatest of ease, and no audible effects.
Another option that works brilliantly on that arm is the Shure brush damped family - I'm sure the damping is helping as well - but the cartridge again has no problem negotiating warps. (In my case a V15V-SAS)

Although it is meandering off topic a little, it seems to me that high compliance cartridges handle record imperfections (warsp, eccentricity) more easily than their lower compliance brethren.

I am not sure whether this is due to the high compliance, or the combination of ultra low mass and high compliance...

Theoretically speaking - all arms must contend with the forces involved in the rise and fall of a warp (and the effects of eccentricities) - the tonearm effective mass measurement is a measure of the actual inertia at the stylus tip - ie the amount of force the stylus must cope with when warps or eccentricities are encountered.
A low compliance design, with its matching higher mass arm, must perforce cope with much higher forces applied.

With regards to VTA - it is true that a shorter arm will also have greater VTA changes when negotiating the warps - potentially with audible variations.

In the case of the Revox, the pivot point is raised when the arm us cued, and lowered for playing the record. - it obviously remains above the plane of the record (as the arm passes over the record) - but is lower than is immediately apparent when in playing position. (the entire linear gantry is lowered into playing position).

Some of the really nasty warped records are not trackable by the Revox, but still track (albeit with difficulty... and audible issues) with my 10" pivoted JVC arm. But this is not what one bases decisions on, unless one is aiming at archiving damaged records!

For the levels of warp that "normal" records (in decent condition) have, my experience has been that the variations are not noticeable/audible.

There is a Shure paper http://shure.custhelp.com/app/answers/detail/a_id/4072/session/L3RpbWUvMTI5NzAxMDc1OC9zaWQvbDl4aWhZbGs%3D

This includes a range of material presented to the AES during the 70's.

Included are discussions of "warp wow" and "stylus scrubbing" along with the pro's and con's of pivot/arm damping ... it is focused of course on their ingenious world beating solution - the damping brush... so don't forget your pinch of salt when reading(!). (mind you I really like those brushes!)

It is interesting that although they discuss both vertical and horizontal stylus scrubbing - they appear to contend that only the vertical effect is of import.... Perhaps related to the fact that eccentricity generates wow at a resonance of 1/2Hz and is therefore relatively innocuous?

There may be another advantage to ultra short arms - when it meets a warp, the cartridge rises and falls WITH the warp - actually maintaining a geometry which is much closer to ideal, than with a long arm. With a long arm, the warp changes the angle of the record surface, but the cartridge rises remaining parallel to the platter (relatively... more so the longer the arm) - but not the record...

So perhaps a case can be made that in fact a short arm maintains VTA closer to ideal than a long arm for warps?

More questions than answers?

bye for now

David

David,

I'm trying to visualize a short armed linear tracking tonearm negotiating a warp and I can't help but see the cartridge alignment doing the exact opposite of what you're saying. You are right that the long arm keeps the cartridge closer to parallel when going over a warp. You are also right in that the short arm changes the angle of the cartridge more than a long arm when going over warp, but it changes in the opposite direction that the record surface changes.

Imagine looking at your cartridge from the side with the record surface moving from right to left. A warp comes to the cartridge and lifts the tonearm. The cartridge tilts, lifting the cantilever end more than the tonearm cable pin end (although both lift, the cantilever end lifts more... and much more with a short arm). The record surface does the opposite. As the cartridge climbs the warp, the record surface is higher on the right side of the cartridge than it is on the left side of the cartridge. It's tilted in the opposite direction. For the two to remain in alignment, they must be tilted in the same direction. Please correct me if I don't have this right.

Hmm - no you are quite right - I was visualising the downside of the warp, and you are visualising the upside of the warp (rise vs fall) - during the rise the short arm is at a disadvantage, during the fall the short arm is at an advantage.

So we are both right in different parts of the cycle....

I guess it may come down to designs of styli that minimise the audibilty of variations in VTA....

If LPs were perfectly concentric like they are supposed to be, I can imagine that having a high lateral tracking mass would have its advantages. But in real life, concentricity is something that we hope for and often come very close to getting, but its not perfect. IOW the arm does need to negotiate such imperfections in the LP. I imagine some of the issues can be tuned out with the leaf-spring device mentioned earlier- so does that mean that you have a different setting depending on the LP?

One other issue of air bearings I forgot to mention is the coupling that needs to occur from the platter surface to the arm tube of the arm. The idea is that the arm and the platter move together as a single unit. That is to say that if there is air-borne vibration, it affects the platter in the same amplitude and phase as it does the base of the tone arm. If there are differences between the two, this will be heard as some sort of artifact, IOW it becomes something that the cartridge can react to. This is why the plinth can have such an affect on the sound of the 'table.

When you have an air bearing, this coupling is not as profound as it should be. One of the demonstrations that this is a very real phenomena is the fact that as you increase air pressure in the bearing (increasing coupling to the base) the arm sounds better.