Having played with both types of arms, agree in principle with the statement that air bearing linear tracking arms like the ET/Rockport/Air Tangent/Kuzma/Forsell/VoyagerVersa and several others are the way to go. But all air bearing arms, no matter how tiny the gap (and say the best one can get is 1/10^4 inch) are still not the equal of a pivoted arms when it comes to rigidity or transfer of energy out of the arm and thus the low can tends to suffer in comparison to a pivoted arm. In addition, there's the issue of vertical vs horizontal mass of the arm. Finally there's the issue of arm length--that has a great bearing (NPI) on how the arm deals with warps eg. the shorter the arm, the worse the problem.
Where I find the straight line trackers to really excel though in in the upper octaves, resolution and retrieval of ambient space. No pivoted arm I've heard comes close though the longer 12 inch arms come the closest.
HI Miles,
I'm not sure what time frame you are speaking about. I understand the original ET arm had significant problems but I have never seen one. The ET2 was a major revision and largely has remained unchanged since its introduction. The main upgrades have been the arm wands where there are now several different types and the optional high pressure bearing manifold. I bought my original ET2 in about 1990. Since then I upgraded to the high pressure manifold. My new ET2.5 has all the upgrades including the carbon fiber arm wand.
The stock air pump runs at very low pressure, about 2.5 PSI. I have been through several different pumps attempting to jump the pressure using the high pressure manifold. Finally, I decided to bite the bullet and use a shop air compressor. Currently, the pressure measured at the manifold is 28 PSI. It could be higher but it is a trade off between pressure and compressor duty cycle. 28 PSI is the compromise I chose.
With each jump in pressure, the bass performance improved. Is it as good as the best pivoted arm? I'm not sure but it is very good. As for the masses, I have not had any problems. Remember, I use a vacuum turntable where warps are nicely flattened out. So, vertical mass is not an issue. Horizontal mass is only an issue with off center holes of which I have few.
While I agree with your points, I don't agree they are problems. I think your points are mostly theoretical without practical consequences. After all, if I can't hear them, they ain't there in my book.
Further, I have done testing that indicates the tangential geometry is superior. I don't have time to go into it now but it will be the subject of a future post.
The biggest problem I see is finding a good place for the pump or compressor. It's not trivial.
Sparky