Are linear tracking arms better than pivoted arms?

I have been doing some research on the issue of stylus pressure that a pivot arm vs a linear arm exerts as the record progresses from the outer edge to the inner grooves. There is some pretty good information on the airtangent and Kuzma airline arms concerning this issue. In fact i found one reference where a reviewer compared the Airtangent to an SME arm on a VPI table. In addition, I had several discussions with some pretty good engineers who helped me understand the issue a little better. After going over it several times, I recognize now what Dertonarm, Raul, Atmasphere, and others were trying to relate. The easiest way to say it is that for two tonearms of equivalent mass, the pivot arm will result in less pressure applied to the stylus and suspension system of a cartridge as the stylus moves across the record. If you state the issue as forces applied and represent the forces as vectors in the xy horizontal plane. (assume x axis is the path of the linear arm), the linear arm forces are entirely represented by the x vector. As the pivot arm actually strikes an arc across the record, the distance the stylus moves is further and part of the forces is represented in the x axis and part of the forces are in the y axis. In addition, the pivot point also reduces the net force needed to move the arm. It is a similar to why a lever can lift a 100 pound weight with less than 100 lb downward force. Having said this, the better linear arms attack this issue by having less total mass that a typical pivot arm. The airtangent site clearly indicates this issue and explains how they attach this issue by using the spindle as a fixed part and using a bearing sleeve as the moving part as well as using a carbonfiber armwand to decrease weight without giving up stiffness. In addition, the manufacturing tolerences of the arm is pretty small to minimize the "Slop" that Dertonarm indicated was an issue with these types of arm. Similar comments are also on the Kuzma site outlining their approach to the problem. I ended up addressing this issue (by accident) as I modified the maplenoll arms by eliminating the aluminum wand and heavy, cumbersome vta adjustment bracket with a carbonfiber arm, spindle and wood headshell. My arm on my apollo is a very short ceramic armwand and very lightweight spindle. I have not compared the total weight to my modified arm on my ariadne signature but i believe it is lighther due to the very small length. Obviously, without the vacuum platter, this short length would be an issue. I appreciate the various contributors to this string as it opened my eyes to some more opportunities to continue to improve the system i have. I have invested pretty heavily into some top notch cartridges and understanding this issue better will help me protect that investment. Having said this, I do like my modified arm and look forward to trying to develop a smaller mass arm for my apollo.

Dear Oilmanmojo, let me briefly add that the vertical mass in the best linear trackers does indeed match the mass in most pivot tonearms.
But the horizontal moving mass is a completely different manner. In the pivot tonearm the mass in more or less equally dissipated on both sides of the bearing - i.e. on two antagonistic levers.
As it is moving around a center it puts no additional force on the stylus (if the bearing is any good....) especially so, as the bearing, armpipe (aside from slight off-set...) and cantilever are in line.
In the linear tonearm the horizontal mass is pushed forward by one (cruel...) lever only and at the tip-toe of that lever is the stylus /cartridge while most of the mass is far away but has to be moved by your stylus and the suspension.
The force pulling from 90° off which is not what your cartridges' suspension system was made for.
This dilemma was minimized by attempts as the ones of Lou Souther and Versa Dynamics with ultra short armpipe - only to add problems in other areas (very sensible to wrap/height changes in vinyl (the Versa Dynamic did feature vacuum hold-down for good reason - it is mandatory with its tonearm)).
I still believe that the striking and logic promise of linear tonearm will one day bring out a design addressing all the big problems - but so far this has not been done.
I haven't seen yet a linear tonearm really taking into account the way the suspension system of any cartridge is working.

03-01-10: Dertonarm
I haven't seen yet a linear tonearm really taking into account the way the suspension system of any cartridge is working.

Great explanation of the lateral forces, Dert.

It would be interesting to know if this heightened lateral force in linear trackers results in increased distortion and/or cartridge suspension/motor wear & damage. It would be nice to hear from cartridge manufacturers if they'd noticed any wear on their retip/repairs unique to carts used with linear arms.

While that force may be greater, it may not actually affect performance/longevity in the real world. Although, I'd find that hard to believe if it is as significant as it seems.

I will state up-front that I have been a fan of the ET2 for more years than I can remember. I have used the same sample on four different tables; currently a TNT6. During this same time period I have owned Rega, SME V, Grado, and Syrinx PU3 (still own). I used at least two of each of the aforementioned pivoting tonearms on each of the four tables that the ET2 has sat on. I keep the Syrinx PU3 as a backup, in the event that I have a problem with the air pump for the ET2; or some other issue, such as placement of equipment due to a move etc. There is no question that the use of the ET2 is more complicated than any of the pivoting arms that I have used. But well worth the trouble. I have consistently found the ET2 to yield a sound that is more like the sound of real music: spacious, well defined (especially with a higher pressure pump), with dense images, and good extension at both ends; and no emphasis on any one frequency range. Only the SME V gave me "more" bass; but that bass was unrealistically bloated. Never have I experienced a problem with cartridge/cantilever wear that I can attribute to the arm.

My point is, that with all the assertions, postulating about their superiority, and all the supposed technical advantages of pivoting arms, there has been in this thread, a conspicuous absence of accompanying discussion about the way that they sound. This is, unfortunately, a familiar story in audiophile circles; isn't it? Focus on the technical points as a way to justify our own preferences and bias, without a commesurate emphasis on what it's supposed to be all about: Does the arm make music? That, defined as getting closer to the sound of the real thing. It's always the same story: this or that has less of this kind or that kind of distortion, so it must be better. This or that phono pre has less deviation from RIAA standards, so it must be better. Blah, blah, blah. HOW DOES IT SOUND!? Compare how it makes a string section sound on a good recording. The ET2, BTW, lets strings sound glorious. The SME, pretty good except for the celli, and basses; way to bloated. The Rega: not even in the same league, with little harmonic complexity. Just as an example.

03-01-10: Frogman
Never have I experienced a problem with cartridge/cantilever wear that I can attribute to the arm.

That, is the million dollar question. Unless this greater lateral force can be proven to cause increased distortion or cartridge wear, it is really a non-issue outside of the theoretical realm.

In which case, it all boils down to what sounds best in each particular system and owner's mind.

I think I might make a few inquiries tomorrow with some reputable cartridge manufacturers/repairers to see if they've noticed excessive or unusual wear due to linear tracking arms.