Eminent Technology ET-2 Tonearm Owners

Richardkrebs/Chris :
Magnetic Dampening vs Mass.

I have been away on business and my responses have been brief. I can now expand on my previous comments.

With a lower mass the arm will move more rapidly initially to align with the eccentricity of the record, minimising cantilever flex.
The magnetic dampening only commences its action once the arm starts moving, and is proportional to the rate of movement. I should point out that the dampening is created by eddy currents which are only generated when the arm moves relative to the magnet.

By contrast, adding mass means the arm will not move until the driving force from the eccentricity is enough to overcome the higher inertia. This increased resistance to movement from the added mass means that the cartridge cantilever is forced to deflect to keep the stylus in the groove. This defeats the purpose and advantage of an air bearing tonearm - the uninhibited degree of freedom to accurately track the groove.

This higher mass is not dampening, it is increased inertia - a resistance to movement.
Magnetic dampening is dampening the arm motion once the arm has commenced movement.

I'll restate this :
Magnetic dampening allows the cartridge to move to the correct position in a damped fashion.
High mass means the arm wont initially move, inducing the cantilever to bend.

Any excessive cantilever deflection in a moving coil will result in phase anomalies as the coils attached to the cantilever are driven into a position where the response becomes non linear.

Furthermore, with the higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and more cantilever flex is inevitable.
With magnetic dampening the lateral movement of the arm is always damped when moving.

Dover.
I pretty much agree with everything you say. Where we diverge is in the sublties. It is easy to add too much mass in the horizontal plane. I went there in my tests. The trick is finding a compromise point.
Dynavector put the reason for high horizontal mass far better than I could. I agree with their conclusions.
Sarcher30 Dynavector's quote covers their views on this.
Further, from memory, the ET in standard form has a horizontal to vertical effective mass ratio of around 6:1. So it is already a differential mass arm. It is just that in my view this ratio is not enough. As per before I don't care what people think about this, they are free to give it a go, or not.
Also as before, I like what Mag dampening does right, I just cannot put up with what it does wrong.

“Magnetic dampening will vary with the speed of horizontal motion whereas the added mass approach is simply increasing static inertia considerably.”

"The magnetic dampening only commences its action once the arm starts moving, and is proportional to the rate of movement. I should point out that the dampening is created by eddy currents which are only generated when the arm moves relative to the magnet."

How was no static magnetic effect achieved: did you switch off the magnet?

John47 - you misunderstand how it works. It is not magnetism that provides the dampening. It is the eddy currents created when the arm moves across the magnet. Read this
http://en.wikipedia.org/wiki/Eddy_current

Eddy currents (also called Foucault currents[1]) are electric currents induced within conductors by a changing magnetic field in the conductor. These circulating eddies of current have inductance and thus induce magnetic fields. These fields can cause repulsive, attractive,[2] propulsion, drag and heating effects.

"you misunderstand how it works".

Not so.

Please reread my post.

I was referring specifically to the static effect - hold a magnet near apppropriate metal: does it have zero effect?