Question about tonearms

[dunhillrecords]

Okay, I hope I don't get too much flak for this question as I know it may be very basic for many of you, but I have never had a good handle on why a particular tonearm is better than another. So, why is this so? Is it weight, shape, length, balance, none-of-the-above, all-of-the-above? I have never owned a TT on which I could change arms, so I guess I have never really considered this subject before, but reading these forums has piqued my curiosity. Please educate me!

[Metralla]

if you think about the physics for a second, you'll see how difficult the problem is.

At the end of a tube approximately 9 inches away is an electric generator that's bashing about at enormous forces - huge, at this tiny scale. Giant waves of vibrational energy are thrashing up and down the tube and through the bearings.

In order for the sound to come out uncoloured, the platform for the cartridge needs to remain in relationship to the record at the smallest of dimensions. The bearings have to work in two planes - and not the third. They must have no friction and no play.

Furthermore, the changing geometry of forces with varying anti-skating demands, but a constant force, play havoc with the equilibrium of the system.

All the energy from the cartridge needs to be removed from the scene of the crime, lest it interfere with what the stylus is trying to measure - that is, the music.

The basic Newtonian mechanics of springs, effective mass, and damping characteristics come into play and they are all at odds with the desired aim - a stable frictionless platform that stores no energy for the cartridge to attach to and do its thing.

[Steve Hoffman]

Okay, I hope I don't get too much flak for this question as I know it may be very basic for many of you, but I have never had a good handle on why a particular tonearm is better than another. So, why is this so? Is it weight, shape, length, balance, none-of-the-above, all-of-the-above? I have never owned a TT on which I could change arms, so I guess I have never really considered this subject before, but reading these forums has piqued my curiosity. Please educate me!

Good, legit question.

Welcome.

Nice essay, Geoff.

[adhoc]

to add on to Geoff's excellent post...

Another important factor is the materials used in the construction of tonearms.

For example, carbon fibre is stiffer than steel, but not in all planes, as steel is. An example would be a tonearm which I own - the (carbon fibre) Infinity Black Widow. It's a lot stiffer than similarly made steel rods in the L-R (horizontal) plane and up-down (vertical planes), but is a lot more apt to "roll" (twist clockwise or counterclockwise). You win some, you lose some. :(

An ever-present conundrum faced by tonearm designers is that of stiffness vs mass.

You want your tonearm to be as stiff as possible, so that it doesn't "flex" with the vibrations being transmitted down it (pretty obvious why), yet the more sturdily you build it, the more massive (and heavy) it gets, and it begins to exert it's own momentum on things. Different designers choose different methods, with varying amounts of success.

Finally, another important choice is that of tonearm type.

You may be aware of the 3 main "schools" of tonearm design - (double) gimbal [e.g. Grace 707], knife-edge [e.g. SME 3009/3012] and unipivot [e.g. Hadcock 242]. Each brings something good to the table, at the expense of some things.

Gimbals give the greatest stability, but are fragile and need close bearing tolerances to succeed (for low friction and to reduce "bearing chatter") - this is very difficult and expensive to achieve, due to the impossible task of fabricating perfectly spherical ball-bearings. They also transfer the most extraneous vibration (e.g. from the TT motor) to the tonearm.

Knife-edges provide superb vertical movement performance and stability (the "knife-edge"), but this is offset somewhat by the difficulty in making a perfect "knife-edge" and the common inclusion of ball-bearings for movement in the horizontal plane (there are double-knife-edges though).

Unipivots, being nothing more than a single-point-of-contact-pivot, offer the lowest friction of all the design types and greatest isolation from extraneous vibration, but inherent to their design (minimal contact = minimal stability) is a tendency to "rocking" in a clockwise/counterclockwise manner. Different designers have come up with different methods of addressing the various weaknesses inherent in their chosen "school" of design, once again to varying success.

So... It's pick your poison, I guess; I, for one, prefer unipivots, feeling that IME they provide a more "alive" and "airy" sound. They are a b*tch to set up properly though, with by far the steepest learning curve of any tonearm type.

No one ever said tonearm design was easy! ;)

[PMC7027]

Don't forget air bearing straight line arms (the ET-2 owner said).

[Dinsdale]

I hope you don't mind me adding a related question: SH has said many times to get a good tracking cart to take care of your records, but how much does the tone arm itself play into not harming the vinyl, versus the cartridge?

I'm thinking of inner groove distortion in particular, and I'm thinking less about great music reproduction and more about, uh, safe record playing, although I know they're related.

[Dinsdale]

bump

Bad question? Oft discussed topic?