Kronkan,
jag vill egentligen inte hacka på dig, men när du uttrycker dig så kategoriskt måste jag reagera.
Det verkar som du bara har erfarenhet av statiskt balanserade tonarmar där man justerar nåltrycket genom att justera motvikten.
Då stämmer dina iakttagelser.
Dynamiskt balanserade tonarmar får sitt nåltryck via fjäder eller annan anordning. När man bytt pickup på en sådan arm justerar man motvikten så att den är i balans när nålen exakt på samma höjd som den skivtjocklek man optimerar för. Sedan brukar det finnas ett vred att ställa in nåltrycket med.
Denna lösning är överlägsen när det gäller spårningen av buckliga skivor för att nåltrycket förblir konstant.
En gång i tiden gjorde Dual ett reklamnummer av sina dynamiskt balanserade armar genom att spela en skiva och samtidigt resa upp verket nästan i 90 graders vinkel (skivklämmor hade inte blivit på modet ännu) och pickupen spårade helt oberört.
Numera har dynamisk balansering blivit mycket ovanlig på billiga armar, men såvitt jag vet har SME V det och Ortofon har båda sorter
http://octaveaudio-usa.com/products/ortofonArms/
Information about dynamic tone arms :
* 9 and 12 inch, with dynamic balance graduated vertical tracking force (VTF) control through a new spring design.
* The new short wire spring, housed in the pivot case, eliminates unwanted vibrations in the tone arm.
* VTF in the range 0-5 grams can be precisely adjusted by means of the supplied digital force gauge.
* Anti-skate control adjusted by calibrated dial in the range 0-5 gram.
Sedan finns begreppen stabil, neutral och ostabil balans som har med höjden på armens lagringspunkt i förhållande till skivans plan att göra.
Graham beskriver det bra
http://www.graham-engineering.com/-- At this point, a brief description of Balance Theory may be helpful: There are basically three types of static balance systems, Neutral, Stable, and Unstable.
STABLE BALANCE, normally seen in laboratory scales, occurs when the CG (center of gravity) of the moving system is placed BELOW the pivot point. This system resists a change in postion; when a tonearm utlizes this type of system, and such a tonearm is displaced from its preferred rest position, it will generate an immediate and opposing force which tries to return to that same position.
UNSTABLE BALANCE, when the center of gravity is placed ABOVE the pivot point, is entirely useless for tonearm design, and will exhibit serious problems, including reduced tracking force as the arm is raised.
The third, and most desirable system for tonearms, is NEUTRAL BALANCE. With this system, the pivot point and the Center of Gravity of the moving system are in the same plane. When the arm is raised or lowered, there is no opposing force trying to return the arm to a rest position; the pivoting system doesn't really know or care if the stylus is at the record surface level or a half-inch above or below it; as a result, there is no opposing force to the arm as it is traversing record deflection during play. The only downward tracking force is that of the adjustable counterweight, which remains a constant. --
Previously, all true unipivots - that is, those with a single contact point for the bearing and NO secondary stablizing surfaces, bearings, etc. - required the use of side weights or a significantly lowered counterweight in order to provide stability. And generally speaking, those arms with a secondary stabilizer point require a lowered center of gravity in order to provide constant contact with the stabilizer guide bearing.
The drawback to both these conditions is that this design becomes a Stable Balance system, which will cause a tonearm to have a preferred rest position and always tries to return to this point. ANY time the tonearm is raised, as in tracking warped records, it results an immediate and equally opposing force that tries to push the arm back to its rest position. The higher the warp, the more counter-force is applied.
This unalterable Law of Physics will work against the cantilever, deflecting it during warps and causing the magnetic system inside the cartaridge to be displaced. This, in turn, will certainly affect the reproduced sound, with diminished performance in all areas, including soundstage compression, loss of detail and dimensionality, not to mention record wear. (This is why most tonearms must have their tracking force measured at the record surface level; any height change during the measurement will cause an incorrect reading).
A tonearm with Stable Balance can be identified by measuring the tracking force at the record surface level and again at a raised position above the record. If the tracking force INCREASES at the higher position, the arm has Stable Balance. Our own previous designs - the best we could make at that time - also had this limitation due to the use of side weights to provide lateral stability.
Other unipivots with low-slung counterweights will all exhibit this force; the lower the weight, the more counter-force is applied. Although this technique is often promoted as a "high-stability" design, it does so at the expense of consistent tracking force and linear cartridge performance. . It actually results in varying tracking forces during play when traversing even small warps, accompanied by non-linear cartidge operation, and increased record wear.
Once Neutral Balance is chosen for use in a unipivot tonearm, one must remember that both the vertical and lateral planes will be affected the same way; without proper lateral stability, such a design would not have consistenent, proper vertical alignment, and the pivot would tend to flop over to one side or another (usually in the direction of the weighted cartridge offset angle mounting). Obviously this condition must be avoided.
Edit: stavfel (olydiga fingrar)
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