The Placement of Tonearm Counterweights

"Decoupled" was perhaps misleading. The idea is to vary vertical effective mass using a system other than the traditional relationship between arm wand length & mass. Freed from considerations of mass, the wand can then be optimized solely for rigidity and low resonance.

Fixed mechanical damping as engineered into a cartridge suspension operates on the combined mass of cartridge and tonearm and the cantilever spring rate as a third variable. If all three variables are tuned, then perhaps the stock cartridge damping is sufficient. However in the real world external damping probably should be added. The idea of a gas-shock is a good one if it could be miniaturized and variable. As in a motorcycle suspension, the amount of damping material is determined by spring rate and rider weight.

I can't understand what benefit completely decoupled counterwieghts could function. They would have to exert a force on the arm, in some way to be effective. I have to ask what the most ridgid structure would be? I understand the shorter the better so lets effectively eliminate an are beyond the slide for a cartidge to run arm as in the linear tracker.
Isn't the usual damping used on the stylus enough to maintain the effective downforce to track the groove effectively despite some inevitable vertical deflections. Why not extend the stylus beyond the pick up coils and attach a vertical gas filled shock absorber. WTF do I know but could the MC type cartridge still function with this restaining mechanism? Should I patent it?

If an arrangement of dual counterweights placed front and back of the pivot point is entirely decoupled from the arm wand and offers a wide enough range of adjustment for an exact match of tonearm inertial mass to cartridge compliance, then it is possible to separate the problem of dynamic behavior of inertial mass from other problems related to arm wand length. The optimal wand length can then be dictated by the most significant variables. Having separated out the problem of effective mass (and also barring obvious warps from the discussion) how much vertical angular deviation is induced by a short linear arm as compared to a pivot arm? The vertical geometry of both types is of course intrinsically flawed, but is the actual difference in vertical geometry between the two significant as compared to the combined variables of horizontal tangency error, arm tube rigidity and resonance? These last three are all areas in which a short arm has advantages.

As the thread subject was the role of inertial mass, it is interesting to separate that issue from the others.

Big problem however is - no matter how good a prospective vacuum, periphery ring and/or clamp holds down the record and tries to achieve "flatness" - the record in itself is far from flat and the journey of the stylus through the groove is a constant high speed drive through a hill and valley B-road. There are hundreds of small mechanical dips and peaks during the 20+ minutes of the record side.
Each up and down works in a most unwanted way hand in hand with gravity and the moment of inertia.
The dynamic drive of the cartridge's stylus guided by the tonearm through the groove seems not that big task when you look at it displayed on a high-end TT.

If you look at it through a microscope and see the poor mechanical periphery conditions of the "track" and the many unwanted movements it gives quite a different impression.

Part of the reason why pivot tonearms with longer effective length and/or dynamically balanced mode have their advantages to minimize the dynamic-mechanical problems induces by the inherent problems of the record itself.

I try for the simpliest approach that addresses the main problems of physics. The first principles are:

The ideal arm is such that on a flat LP, stylus deflection associated with normal tracking produces no vertical movement of the cartridge. (Horizontal movement is a necessity.) In this regard there is an optimal effective vertical arm mass (as well as a unique compression and rebound damping factor) associated with each unique cartridge compliance. This is because cartridge compliance is integral to the tonearm system that in aggregate controls tracking. From a practical viewpoint, continuously variable effective mass is the first order of business in matching an arm to a specific cartridge. Otherwise we are relegated to trial and error and the approximation of trying arms of generally "light", "medium", and "heavy" mass. This is expensive fun, but is unnecessary in view of the reasonable prospect of engineering an arm of continuously variable effective mass. Moveover, while reviewers like to say that a particular cartridge is fine with a particular arm, who really knows how good a particular cartridge can sound without an *exact* match to tonearm?

Assuming availability of an external mechanism to match tonearm effective mass to cartridge compliance, the ideal arm tube is infinitely rigid and weightless: a perfect conductor or absorber of residual cartridge vibration that does not reflect vibration back into the cartridge or itself add movement to the system. In this sense the optimal arm is no arm at all-- the shortest possible arm as available only in a linear tracker.

The rest of it can be dealt with in conventional terms. If the above problems are addressed, in the final analysis the only problem with a linear tracker is fluctuating geometry over warps. In a world of record clamps, vacuum hold-down, and periphery rings, this is an ancillary matter.

Dgarretson
I am curious about some of your tone arm parameters. I am not suggesting that you are wrong I simply am an ignorant analog novice trying to learn something. Why can't the arm wands be effectively damped to stop resonance. Is it because damping materials used would be too heavy? Or do the laws of physics dictate that any length of a tubular structure will have a resonance frequency regardless of efforts to minimize its effects or to get it out of the audible spectrum?
How does the arm interact with the cartridge if the correct effect downforce and minimal restriction on the pivot point is observed such that the stylus compliance would be altered? I guess the mass of the arm restricticts it's motion to some extent but why would'nt the stylus be free to move as a function of its suspension?
I like linear arms BTW but never afforded anything beyond a number of ebay Technics TT in marginal condition.

Hi Bob,

The Moerch is certainly beautiful, and like other pivots does variable effective mass and other nice things with interchangeable armtubes. However I'm done with long resonant arm tubes and the inevitable junctions in wiring attendant to detachable wands.

http://cgim.audiogon.com/i/vs/i/f/1293020811.jpg

In addition to varying effective vertical mass the counterweights mass-load the point bearings.

Someting like the new Moerch arm Dave, ith counterweights to both sides and one in the rear?

This makes good sense. However varying mass v. distance on just one side of a conventional pivot arm has the limitation of a relatively small range of adjustment. To devise a "universal" arm with continuously variable effective vertical mass, I've been working on an approach that uses counterweights on both sides of the pivot of a short linear arm. So far this is doing a great job of optimizing set-up for cartridges of varying compliance. In fact, this adjustment is a very significant variable in accurate set-up, and the feature has vastly simplified the issue of cartridge/arm synergy.