Arm Differences ...... ,etc.

I'm fairly new to the analog world and you've probably read some of my posts in the past. I've now got a good handle on brands and models, but now the technical.

What are the pros and cons of a unipivot arm compared to a gymbal pivot or non-unipivot? Which work more effectively with a suspended table? Does a type of cartridge lend itself more to a suspended table?

Your responses continue to be most enlightening. Thanks.
Theory first. An arm should remain at right angle to the groove no matter what direction it is traveling. Only in this way can the channels be read properly by the stylus. This must be done with maximum rigidity and minimum friction. Energy put into the arm tube must be damped or evacuated.

The knock on unipivots is that they can allow the arm tube to roll so that the cartride is no longer tangent to the groove. In most unipivots this is addressed by silicone or oil damping. If one were to take a stroke while swimming, then one would see that the part of the stroke taken in air has less resistance than the part in water. If one moves the arm slowly through the water there is little resistance, but the faster the arm moves in the water the more resistance. In theory, a damped unipivot will be excited to roll by a quick, powerful event, the onset of a pinch warp for instance, the oil will resist this event and keep the arm, mostly tangent. Sounds pretty iffy, no? Even some captured bearing arms use damping to address resonant and dynamic behaviour though. Since the unipivot uses a pivot point that is essentially a nail in a cup, the pivot point acts as a tip toe, with a single path for the evacuation of stored energy. There is also the full weight of the arm resting on this point and that give the bearing a lot of integrity. Additionally, since nothing in the bearing hinders horizontal and vertical movement, there is very little friction and very little is added as the arm ages. Sounds pretty bad for the poor unipivot, no?

Captured bearing arms always maintain the same tangency to the grove as their rolling motion is controlled by the vertical and horizontal pivots, usually cone and ball races. Provided that there is no play in the pivots, they will keep whatever tangency they are set up with. The arm is damped by the pivots resisting any motion that is not vertical or horizontal and by the verical bearings on the sides of the arm being equal paths for the evacuation of energy in addition to any damping inherent in the arm tube. This type of arm has some issues also. If you think about it, the ideal is to have infinitely minimal friction accompanied by infinitely tight bearings to prevent play in the bearing assemblies from letting the arm tube wander around and the cone banging around in the race. The two requirements are mutually exclusive in this type of bearing. The more that you tighten it to remove play, the more friction is introduced. These types of bearings are rated on the ABEC scale which basically is a measurement of how imperfect the bearing is. That said, modern machining techniques can make a very, very, good bearing. Two other things to look for in captured bearings are Brinelling, which is caused by external forces rolling the arm against the bearings thus flat spotting them. This can happen during mounting of the arm; excessive twisting causing the ball bearings to deform. Once deformed it is all over as the cone will no longer have a smooth surface to ride against. Captured bearing arms may also have wear issues in the bearings themselves but this is mostly related to materials technology and the initial integrity of the bearing. That said, as the market demonstrates, there are really excellent examples of both types of arms and execution is more important, in my mind, than type. There are also excellent designs using fluid bearings, air bearings, knife-edge bearings, etc. Don't get too hung up on this stuff. As always, listen and compare.
As usual Viridian sums it up nicely. There are excellent examples of both types of arms. Get one that suits your needs and your cartridge best.
Viridian - Thanks for the help. But, "Listen and Compare", is not possible where I live so most of my audio choices are accomplished through homework and faith.

BTW, if you had 5k retail to spend on an arm and cartridge, what would you get?

I've just purchased an Avid Volvare table.

Also, I have a Rogue amp and 100db speakers. Does having very efficient speakers effect analog choices?
If it were me, I'd buy an Origin Live Illustrious and a Shelter 901 cartridge, but you probably already knew that.
Tom's suggestion is just great. I believe that the table was designed around the SME arms which can be an important consideration as far as synergy is concerned, so a model V, or better yet, a IV.VI may prove to be a viable alernative. I'm an old fart and my cartridge preference leans to the Koetsu's, which are a lot more linear now than in the days of old. I have not had the pleasure of hearing the Shelter line. Either the Origin Live or SME arms should be able to accomodate a wide range of cartridges so this may be the point at which to tune to your system. Having high sensitivity speakers will be more of an issue in your choice of phono preamp and preamp than your choice of analog front end.
Audiophiles love arms because there are so many complex angles and dangles to adjust!

The dirty little secret is that a Linear Tracking arm eliminates all these sources of error, many of which cannot be eliminated over the full range of arm motion across the record. Linear tracking arms can have problems of their own, but not as many as a pivoted arm. A decent linear tracking arm beats any pivoted unit.

Excuse me now...I must go to the bomb shelter.
I don't think that the advantages of a linear tracking arm are much of a secret, dirty or clean. Given a much larger discretionary budget.....
I would take issue with the superiority of the linear trakers. The drawbacks are quite different than in fixed pivot arms and ones musical preferences would probably dictate which set of drawbacks one prefers. In solving some problems, others are introduced. I'd go into it but I used up my fifteen minutes several posts ago. I would also point out that since the Avid Volvere, which we are speaking about, is a suspended turntable specifically designed around the SME arms that there may be issues of weight distribution and rigidity associated with tacking on a linear tracker.
I agree linear trackers on a suspended table is a very difficult application. There are all kinds of pitfalls involved with that kind of setup. Most people tend to shy away from that combination.
Marty and Tom are correct, of course. My apologies to Richard for considering only my setup with respect to the linear arms.
Hey, 4yanx what are you running? I am always interested to learn from owners of linear trackers as they have such unique requirements.
Marty, I am not running a linear arm. My post meant to allude to the fact that while I appreciate the benefit of a GOOD linear tracker, I can't afford to pony up for one. :-( I am running a 'Not Spacedeck with an OL Illustrious. Very nice performance, but I'd like to slide Albert's Walker in for a spin.....
I thought you got rid of the Illustrious?

On an unrelated note, what are your further thoughts on the Mat 1?

Well, Oz, I did. But I also have one now.

I've had the Mat1 for only one week and have not logged enough time yet to make definitive appraisal.