I would encourage anyone interested to read Gilson's 1981 paper, which is in agreement with Firebaugh's approach of finding a balance between angular error-related distortion, and other tracking-related errors. Unfortunately, this paper came out at the end of the turntable's dominance in musical playback, and so I don't think there has been any follow-up research as Gilson points towards. However, it was a divergence from the norm provided by Stevenson and others, who focused mainly on reducing tracking angle error.
http://www.audiomods.co.uk/papers/gilson_alignment.PDFPut simply, Gilson wrote that in reducing angular tracking error to achieve the lowest distortion, one necessarily increases lateral tracking error. They are inversely related. So there is no free lunch, one has to also control lateral forces, and one has to find the best compromise between the two where audible distortion is minimized.
Based on my comparisons with other arms using the same cartridges, I believe that Firebaugh's tonearm design is consistent with Gilson's redirection away from focusing simply on reducing tracking angle error, and instead, onto the interplay between angular error, lateral forces, and resultant distortion - which may not even be audible below a certain level. The fluid bath itself of course damps distortion, and what I've found is a very controlled, musical arm that tracks better than most arms I've used, and is much easier to adjust than most arms I've used once dialed in.
Like Firebaugh, Gilson's approach starts from an assumption that the type of distortion, in this case the second harmonic, is likely inaudible even at 5-10%. In the blog I linked to in my earlier post, Firebaugh gives the example of 5 deg tracking angle error producing only 0.2% distortion, again primarily the innocuous second harmonic.
The graphs in the blog are hypothetical and provided for example only, not based on experiments from the actual Amadeus arm itself, as he states tracking angle error used for the illustrations is 20 degrees (!). Firebaugh could have provided more helpful information in his blog, based on his actual findings rather than theory. But in practice, his arm really does deliver the goods, even though a fixed tracking angle does have me scratching my head. Using as a basis the decades of study that Gilson, et al. have directed towards tonearm design, one possible rationale for the arm's level of performance is in its control of lateral forces and distortion.
IMO, using a golf ball as half of an arm pivot, placed into a viscous damping bath - both of these together acting as the pivot - clearly deserves more study. Even though he doesn't make much of antiskating in his manual or his blog entries, I think Firebaugh's arm is so successful because he has found a way to decrease lateral forces by increasing lateral drag or inertia, accomplished by setting the arm pivot itself into a viscous damping fluid. In addition, antiskate force is provided in the twisted thread from which the arm hangs, but this is minimal compared to other arms I have used, and is also subject to the same inertial forces from the fluid.
Now, assuming that the lateral skating forces are effectively controlled by both the viscosity and the twisted thread trying to unwind, this leaves a lot more room for error (literally) in getting tracking angle right. Given the complex relationship between overhang, offset angle, and pivot-to-spindle distance, Firebaugh's decision to provide only fixed mounting holes, at a predetermined angle, when cantilever lengths can be so radically different, without providing a list of cartridges that he has tested and their associated parameters, invites controversy.
So, the owner of the WTL arm can trust that Firebaugh's experiments with 20-odd cartridges includes all possible ranges of overhang distances, and just place the golf ball as close to center as possible, mount the cart at 19 degrees, adjust slight until satisfied, and be done with it. Or, one can do this, listen to results, and then methodically use models to find alternative, possibly improved alignments based on observed problems and deficiencies using specific carts. This is what I have done, and interestingly, my final alignment is consistent with the WTL mounting template provided in the Simplex manual - and against conventional wisdom provided in this thread not to use that template. The only caveat is that I have good tools to do this, in the Feickert protractor, loupes, lights, and lots of experience.
Again, the blog info and the experiences given by others on this forum are based on Amadeus arms or its variants, and so they may hold true if you have an Amadeus, GTA, or Versalex. The Simplex arm is different, and I have found that one size does not fit all. Maybe you're not satisfied with sibilance, IGD, or something else with one of your carts. Don't be afraid to try something different, I followed conventional wisdom, but was able to find a better fit.
