Confused about compliance matching with airbearing

I am not at all clear on the significance of lateral mass. There are posts on the internet to indicate that ADDING lateral effective mass, e.g., by fixing weights to either side of the pivot (in a pivoted tonearm, of course) has a beneficial effect. Persons who comment on this mod do not mention a differential effect for low vs high compliance cartridges. Indeed, there are several classic Japanese tonearms that incorporate the same idea, e.g., SAEC. The Dynavector tonearms (old and new) are designed deliberately to have a high mass in the lateral plane, and this is touted in their brochure as a benefit of their design without regard to cartridge compliance. On the other hand Fremer often comments that a disadvantage of most linear tracking arms is their inherently very high mass in the lateral plane. The equation for resonant frequency does not contain a term for lateral effective mass, only vertical (if memory serves; I did not check this), so I don't see that lateral mass will affect resonance. Yet, it is not hard to see why a high lateral effective mass might place undo stress on the cantilever of a high compliance cartridge as compared to a low compliance one, just as high bearing friction in the lateral plane could also do. As far as I am concerned this issue is very muddy.

With cartridges of high 30-50 compliance it has been easy to see cantilever deflection in action, to hear the associated distortions, and to compensate by releveling the manifold to "center" the cantilever. I can't measure level accurately enough to know precisely where the optimal position is relative to true level, but I think it is with the manifold tilted slightly down toward the spindle to invoke gravity as compensation for lateral inertia. Then one should readjust azimuth...

With Trans-Fi a lightened sled improves the sound of a high-compliance cartridge, but this may also owe to superior damping properties of the low-mass carbon/foam construction of my lightened sled. I need to experiment with weighting this sled in order to separate these variables.

At the opposite extreme, Vic of Trans-Fi mentioned that with a low-compliance Denon 103 cartridge he tried weighting the sled with up to 100gm additional, and heard little difference.

Finally there is the impact on performance and wear of bearing friction-- which is presumably lower on an air bearing than on a pivot arm. This is a small force in either case, yet one more variable to add to the murk.

I can't comment on stylus wear, since of a half-dozen high-compliance cartridges in my possession none has exceeded several hundred hours.

It just occurred to me that Fremer cites the large differential between mass in the vertical and lateral planes as being likely to cause vertical and lateral resonance to occur at two very different frequencies. I am not sure that's a bad thing, if the two frequencies are favorably related to each other so as to broaden and flatten the net resonance. Nor do I know how the formula for resonance in the lateral plane compares to the one for vertical and how it takes compliance into account, if it does.

The horizontal resonance will be considerably lower, because of the higher mass. The ET-2 specs are 7g vertical, 25-35g horizontal effective mass(in horizontal plane, effective is actual, given lack of a pivot). This has a fortunate effect,in that horizontal is mono info, and deep bass is mixed to mono; the greater inertia enables higher output(the cartridge is shifted less, thus greater displacement of cantilever with respect to the cartridge windings). And, since warps are vertical, there's no penalty in that regard. Off center spindle holes, however..

In practice, I've found the loading of the cantilever suspension by horizontal mass does effect the over-all sound- too high, and it's like being off level(the stage in one channel collapses-same effect as with maladjusted anti-skate) in both channels. This is obviously cartridge compliance dependent. I use an ATOC-9 in an ET-2, and minimize the horizontal mass by putting the counterweight at the extreme end of the beam, thus using as little mass as possible. Using the Shure test record, I noted resonance at 9HZ only(range on the record is 5-14 HZ). If I use the dynamic compliance spec for the cartridge(9 cu), I calculate close to that for horizontal resonance(9.235 HZ @33g,25g plus 8g cartridge ). Vertical resonance calculates as 14.71HZ with 5g effective mass vertically(this is suggested by ET-2 manual as value, not 7g, why I don't know). I have no tracking issues, even with off center lps, stage is huge, but I do note tight coupling of lp to platter is needed to produce satisfactory dynamics; greater mass would yield more, but at a price I don't want to pay.

The ET2 is quite low mass then. I'm at about 60grams with cart, counterweight, and entire arm assembly on the MG1.