Lewm
I normally don’t contribute to this thread, because I do not own and have never owned an ET2 or 2.5. However, I concede that it is probably a great tonearm. But when you speak of Newton, keep in mind that the net force exerted by a small weight at the end of a long lever That is required to balance a cartridge at a specific VTF will be the same as the force generated when you use a larger weight mounted closer to the pivot or fulcrum. Therefore I am wondering why mounting a large weight close to the pivot point makes any difference as far as overcoming the air pressure and collapsing the air suspension , Assuming the same VTF is thereby achieved in both cases.
Lewm
Setting VTF on a pivot arm is two dimensional. With the ET 2, the mass is adjustable so you could call it a three dimensional setup. Did you know that the counterweights are decoupled by a spring, and that the cartridge itself only sees the vertical mass and not the horizontal mass ? The word "stressed" is a better word than "collapse" Many years ago I never did collapse it with extra DIY weights, but if I added even more weight who knows. The experiment was over before that.
Page 9 of the ET2 manual on design. Adjustable Effective Mass
The effective mass of the tonearm is adjustable, both vertically and horizontally. The arm has low-medium mass vertically and medium to high mass horizontally. Four counterweights allow the vertical / horizontal mass to be changed. For example; if the user decreases the amount of counterweights used, and moved this position back (higher scale number) the horizontal inertia of the tonearm would go down and the vertical inertia would go up.
You can download the ET2 manual here
http://www.eminent-tech.com/techsuppt.htm
If you read the first 10 pages of the manual and the tech section, I believe you will get a good understanding of the tonearm.