"S" shaped tonearm ?

Well it seems quite simple. You can believe:

1. The guys who design and build the tonearms. They have degrees in mechanical engineering, physics, electrical engineering, and acoustic sciences.

2. The amateur hobbyist with a bunch of toys.

I know where to place my bet.

Note to Pryso, actually IMO the Edsels are some of the homeliest cars Ford ever built but cool is in the eyes of the beholder. I grant you it was a poor example.

I'll leave S and J shaped arms to the folks who buy clocks, rocks, and teleportation tweaks.

I'm done.

Being that my daughter never stops reminding me how old I am getting,I'll have to state that OLD is ALWAYS better!! -:)

Professional designers are also beholden to the prevailing design theories and manufacturing methods currently available. Tonearm manufacture can only tolerate a few design types and remain cost-effective and competitive, so designs that don't fit the business model are rejected before they can even get started.

I've been in audio for 40 years and have watched the high end throw one dogma over for another about every decade or two. I remember when horns ruled in the heydey of JBL, Altec, and Klipsch; and then were repudiated in favor of silk domes. For a long time high end dogma dictated that a horn speaker could not be high end. Oops! Along comes Avante Garde of Germany. There was a time when no self-respecting high end speaker design was ported; now most of them are. Most speakers today have to be bi-wire capable, even if there is no benefit to designs with 1st order crossover. If it lacks the features that are in currently style, it won't sell.

Right now in tonearms it's the straight, one-piece armtube, preferably with integral headshell, with a unipivot bearing. A straight, one-piece arm w/integrated headshell is the cheapest to manufacture and may have advantages in rigidity vs. weight. It's also an absolute bit** for mounting a cartridge. Still, current turntable/tonearm dogma dictates that nothing but a belt-drive with straight arm w/unipivot is going to succeed in the marketplace.

The once-ubiquitous dual-gimbal fulcrum has largely given way to the unipivot design. The unipivot bearing is cheap and simple, but has little to no ability to stabilize or control azimuth. A dual-gimbal design allows free movement in the x and y planes while limiting movement in the z plane to bearing play.

And here's an alternate automobile analogy to the 1958 Edsel. Prevailing leading edge engine design dictates an alloy block, double overhead cams, and 4 valves per cylinder. But then there's the Corvette Z06 with a cast iron 2-valve pushrod engine, which at $70K, can beat or stay even with any supercar up to around $250K. And if that isn't enough to push the envelope, the Steve Saleen S7 $400K supercar has a 2-valve pushrod engine as well, yet puts out 550 to 750 HP. The SR-7 racing version has had much success on the competition circuit (e.g., Sebring, Le Mans).

Johnnyb, I couldn't have said it better.

Its a long way from the original question which was why were tone arms s shaped (paraphrasing). However, what this has evolved into is a discussion of one of the hobby's basic questions:
Is design X better than design Y. Tubes better than SS, etc, etc. The answer is almost always, it depends. Depends on what?
1. How you define better?
2. How is the design implemented?
3. Is cost, convenience and/or durability a factor (see #1).
4. What associated equipment is involved?
5. What design decisions were made in the development of the associated equipment?

These factors (at least 2-5, I'm sure there are more) are especially relevant with an LP playback system, since it consists of several different "modules", often sourced separately, that must work together. Cartridge, headshell (perhaps), wiring (perhaps), tonearm, platter, motor etc. In the real world it is very difficult to separate these factors out. And of course many of us define #1 very differently. This is endemic to any artform (I'm talking music, but perhaps that word also applies to TT design). The weight each individual places on each factor (and even the name and number of factors) varies and it is highly unlikely that any two persons would "evaluate" a musical experience identically. In the end, tho, I would argue that design implementation, manufacturing, quality control, and the other elements in the analog chain are more important than whether the arm is straight or curved. As several others have pointed out, not all carts will "work" in every arm and not every arm is right for every kind of table. However, its lots of fun to read and talk about this, so blog on!!!