The Placement of Tonearm Counterweights

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

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.

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.

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.

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.