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Linear tracking turntables, whatever happened?

Curious as to the demise and downfall of the seemingly short lived linear tracking TT.
Just from a geometry point of view I would have thought a linear arm should be superior to one with a fixed pivot that sweeps through an arc.
Obviously there is much more to it than that, sort of the reason for this thread.
I am genuinely interested in trying one out for myself as well.
128x128uberwaltz
bdp24's avatar
bdp24
9,865 posts
 

My knowledge of physics is rather limited, so let me ask those of you who finished high school (;-) if the following is correct:

To achieve higher moment-of-inertia (same as mass?) in the vertical plane, the mass of a counterweight should be located as near as possible to the line described by the arm tube running through the arm’s bearings. In other words, extending left and right of that line in the lateral (horizontal) plane as little as possible, i.e. as close as possible to the arm's bearings laterally. The opposite of that is the Groovetracer counterweight made for Rega arms, which is in the "longhorn" style---extending a couple of inches to the left and right of the rear stub onto which it is installed.

If the above is true, I can envision, say, lead weights being attached to a counterweight above and below the hole running through it for the arm tube’s rear stub, but not to either side of that hole. Correct?

ct0517's avatar
ct0517
2,041 posts
 
Bdp24 - My knowledge of physics is rather limited, so let me ask those of you who finished high school (;-) if the following is correct:

@bdp24 
I never learned Physics in school. It was learned through real life experiences...especially near death ones. 8^0
Picture this - approaching a corner at speed, just after a rain, in a 1996 rear engine 993.

************

I am not sure what you're asking Eric; but I can tell you the Eminent Tech Tonearm has a horizontal inscribed line on the center of the manifold housing. When doing setup the User is supposed to set the record level with this line. Another area where setup error occurs.

If you follow the center of the air bearing out to the counterweights one can see that all is in the same line. The I Beam is level with this inscribed line.

Now the interesting part. If one loosens the end cap that holds the I Beam and Weights. and tilts it downward a bit - one can tune the bass and give it more heft. You will also be changing the VTF when you do this. Like wise in reverse - tilt it up - and the signal becomes leaner.
  
One can set the sound to ones room depending on the gear. If the room is bass heavy tilt it up a bit and vice versa if the sound is lean.

******************
@whart 
 are you able to loosen a bolt on the Kuzma Airline to tilt the counterweight rod up or down ?

terry9
2,348 posts
 
Moment of Inertia is denoted by I and is the angular analogue of mass. It is defined as the sum of (mass of molecule x distance to pivot squared). This is approximated by an integral (calculus), which is easier to calculate.

Thus, for a beam of just sufficient length and just sufficient strength to support the counterweight, the greatest Moment of Inertia I will be obtained by positioning the beam extending from the pivot parallel to an extension of the arm wand.

The obvious tradeoff is the amount of material required to position the beam that way.

There are other tradeoffs - one wants adjustability and rigidity and resonance control in the beam. Thus a system of a light but rigid tubing (say magnesium), with a lump of tungsten on the end, threading into a nut on the end of the arm, would give you the highest I/m ratio, but may be compromised with respect to resonance. I should try that on the Trans-Fi.


whart's avatar
whart
3,050 posts
 
@ct0517 - another good question which will require a little exploration by me. Just when I thought I knew how to set this thing up after all these years! Your learning is valuable and obviously transferable--
Just literally removed my regular cartridge- have a rebuilt vintage cartridge arriving today as a stop gap (of all things, one of those old Monster Genesis 1000s). So, I can at least mess around with the arm a bit even though the cartridge I'll be using for now is far different in mass (and other things) from the Airtight that is going off for a rebuild. 
whart's avatar
whart
3,050 posts
 
https://flic.kr/p/S8x8RW Dunno if this will work but here’s a shot of where the counterweight threaded tube mounts on the back of the air-bearing housing- looks like it is a threaded hole. Period. Thanks, @ct0517 if you click on the image link, and then click the image itself once it opens, it will enlarge. 
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