If you are concerned about lateral mass, contact Dave Garretson via this site or via Audio Asylum. With his custom-made parts, he has taken it down way below 80 gm for the Terminator. I expect he will chime in here anyway. He is using a high compliance Pickering and some others.
Its high compliance=low mass and low compliance =high mass in all the arms I have used. The higher the compliance the lower the mass of the arm should be, I don't see why air bearing arms would be different but I have not used them.
Airbearings have a much higher lateral mass than fixed pivot. Seems Trans-Fi is about 80g (stock), MG1 appears to be about 65g with Grado. More worried about stressing the ruby cantilever with a really high comp. cart.
Lots of info on an earlier string around this subject. Heavier cartridges and heavier arms will result in more stress however my polling of people who actually own linear arms (air bearing arms) does indicate that the better quality arms do not show a significant track record on causing damage. I currently use a zyx universe cartridge with Silver base, Airy 3 with silver base, and have used a VDH frog with no problems. My Maplenoll apollo has a very short arm that is ceramic and the air spindle is a light weight material. I did upgrade my ariadne reference and signature with a carbon fiber wand and spindle with fantasitic results and those modifications dramatically lowered the mass. I have used my universe cartridge many hours with no deflections or damage to date. That being said, lots of feedback from some very passionate and knowledgeable people who prefer pivots strongly advised about the potential damage you are refering to. In addition, there is a basic mechanical fact in that the stylus does carry the horizontal vector force resulting from the lateral movement of the arm.
However, 6 years of linear arm use and several thousands of hours (i listen to a lot of music)of use has never resulted in a problem.
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.
Rcthweatt, The ET manual is a well-spring of technical information, but I am confused on the subject of horizontal mass. If I understand correctly, moving horizontal mass is 25-35gm wand+manifold, plus up to 40gms counterweights, plus optional 18gm damping trough.
Yeah, I do think the counterweight was overlooked. The damping trough is attached to the horizontal moving mass asemmbly....interesting.
Ooops! You are correct, as p.5 indicates, spindle 14g,arm tube 11g, so 25g w/o CWs, which are 5 &15g, small and large. I assume the spindle weight includes the CW arm, and the clamp, post, etc. (I'm not disassembling to weigh it tonight!)including the lead piece which slides into the clamp. So, my horizontal mass would be 25+5(1 small weight)+8(cart)+1(screws, also neglected),39g;using 9 cu, 8.49HZ,which still agrees pretty closely with test record. Now- this cu figure is at 100HZ,which isn't the frequency we're at, 10 HZ would be better, so supposedly one should multiply this by 1.5-2,or halve the static figure(35); trouble is, using these I get 6-6.9HZ: at those frequencies, arm is perfectly stable. Hmmm...not horizontal, but vertical resonance? 7+8+1g times 18cu(.000018), I get 9.378HZ, also close. Way to settle- add mass, and see if 2 resonance points develop..unless there's a test record with a wider range?
For those with a technical bent, John Ellison described a simple and clever way to measure actual tonearm/cartridge resonance, over on Vinyl Asylum. I suspect you can find it by searching on "resonance" or something like that. But you do need some tools to do it.