Starting a new thread as finding this buried in the old thread was a
pain.



I've always wondered how those air bearing arms provide
a stable based for the arm.


This is a straight-line arm, right?


The air bearing is formed by the space between two pices
of angle stock, one sliding over the other.


Angle stock? All the ones I've seen have a tube sliding
over another tube.


That makes the bearing self-aligning, and provides a
large surface area for the bearing.


Seems to me preventing the arm base from oscillating
would be a big problem


Doesn't seem to be a problem with real-world designs.
There is the question.... I've seen a lot of horrific
arms that seem to be able to work.



Well, you perceived that they were horrific.

Horrific looking... didn't sound all that great either
but differentiating tone arms isn't something I've much
experience.


The question is.... is a mildly unstable (in microscopic
terms) base worse than a pivot that
is subject to a constant torque?


The goal is to avoid stiction.

Thats one goal... BTW.. on my own servo control LT stiction
is one its design flaws. I've always thought of replacing the
wheel bushings with bearings. But when the arm runs at
high speed chasing the stylus in the run out groove
you can hear what I think is stepper motor noise
and stiction isn't in play here. I often though I could hear
a bump on occasion that was the stepper motor moving the base to
correct tracking angle...but on the silent grooves of the Hi-fi
test record... I can't... and my new cart is quieter yet.
So now I'm wondering if reducing stiction might actually increase
stepper motor noise. I think a spring or a cushion on the drive
cable might help.

You haven't proven that instability can't be managed.

True.. I'm just speculating as hobbyists are prone to do.
In any case.. I think minor base instability with freq components
in the audible range would be a thing to avoid but I don't
see how an air arm can do that.



and banging around on the support tube
The bearing has a large surface area.

Yes... But if you source air on the inner tube... you
get the outer entering and exiting air
vents which tends to temporarily unbalance things



No, you supply the bearing from a vent that is always covered.

I dont think the Forsell arm I saw does that.
How would they accomplish that?


or just noise from air turbulence.
Turbulence can be kept low.
Low enough that it can't be measured?


LP playback is rife with problems that can be readily measured. Thus
reducing turbulence below measurable levels is an unrealistic criteria.

In any effort to maximise performance one must deal with issues
as best they can.... and apply the serenity prayer.

ScottW