Why is the price of new tonearms so high

Hi,
excellent maths no doubt.
Let's look at some practical part of it all then.

1) Is the **effective** mass of an arm increased if the counter weight it moved further away from the pivot bearing?
(I think so, because the mass / moment is increased)

2) If a spring is used for VTF, the CW is further back from the fulcrum as the spring provides the down force and the CW only the arm balance.
What is the effect, if assumption of 1) is correct?

3) If static down force is used, the CW is closer to the pivot/fulcrum, the mass moment should therefore be reduced. What is the effect as compared to 2)?

Inertia has of course ONLY an effect if acceleration is present, and with any tonearm particularly riding a 'taco warp'.
Incidentally, I find the type of warp lifting a smaller area from the start-wax (~ 1" into the record) more common and more radical in vertical acceleration, plus the one that actually pushed in the (still soft?) start-wax for ~ 1/8" causing VERY nasty lateral acceleration.

This leads me to think that lower accelerated mass (effetive mass?), plus higher compliance be the better solution to this kind of problem.
But I still can not make the connection to the 'dynamic VTF' being of any advantage, since (given 1)'s assumption is right) the accelerated mass of the same arm with only using static VTF be somewhat lower.

Note: SME quotes, the V arm's effective mass 10 - 11 gr. (depending where the CW is positioned...)
Axel

Well - since it is a dynamic model (or should be...) I still see excatly this dynamic aspect missing.
The down-swing and upswing of the pendulum (tonearm with cartridge at swinging end) is different in moment of inertia and force depending on the distance from the dead center of movement.
We are still talking different models.

Dertonarm

That is completely wrong (again). The moment of inertia of a rigid body does not change with movement.

Yes we are talking differnt models. Mine is a model of what is happening, yours is a fiction.

Well - to get as plain as you: I think your model is incomplete.
The resonance frequency of a given cartridge/tonearm combination can be altered by moving a fairly heavy cylinder further away or closer towards the pivot.
The total mass of the moving body stays the same - of course.
But - I guess neither of us has any problems if we do not agree about the model at all.

Axelwahl

Your suppositions are correct and the figures are reasonable.

If we model a 100 g counterweight positioned 50mm behind the pivot, its contribution to the effective mass of a 225mm arm is 4.94 g*. If this is the position for VTF of 20mN, it needs to be moved 4.6 mm to come into neutral balance. The new position will indeed make a higher contribution to effective mass, it becomes 5.89 g an increase of 0.95g.

This would increase the maximal tracking force deviation quoted above from 6.2 mN to about 6.4 mN, about a 3% increase.

* this ignores the moment of inertia of the counterwight about its own centre of mass but since this doesn't change with position it isn't important so I left it out.

Mark Kelly