At WAM Engineering, we have decided to dig deep in order to learn how a misaligned stylus travels through a modulated groove. To that end, we've modelled up various groove patterns and stylus "mis"-alignments in a very sophisticated and expensive engineering system called FINITE ELEMENT ANALYSIS. This article offers a very small bit of what we have discovered and will ultimately be published for peer review in a technical journal.
WHAT IS ZENITH ERROR?
Perhaps we should be calling it "yaw error" instead of zenith error, but the parlance stuck when Wally Malewicz revealed the problem to the audio press several years ago. Zenith error is the degree to which the cantilever is not perpendicular to the line formed by the left and right channel groove contact edges of the stylus.
In the stylus/cantilever assembly photo below you can see the groove contact edges circled in red. THEY ARE TINY - and difficult to image and measure. The thickness of the groove contact line is less than 4 microns and the length is barely over 20 microns. By way of reference, a human hair is about 100 microns in diameter.
The assumed perpendicular relationship between the cantilever and the groove contact edges of the stylus is the entire reason we spend such effort, expense and eyestrain to align the cantilever for tangency to the groove at the null points using a cartridge protractor like the WallyTractor. After all, we can see the cantilever - and that is why we align it - but the cantilever doesn't actually read the groove, does it? We are left to trust the manufacturers to get this perpendicularity right.
Unfortunately, it rarely is.
THE EXTENT OF THE PROBLEM
We have analyzed many cartridges at WAM Engineering costing as little as $1,000 and as much as $21,000. We see no correlation between cost and stylus mount accuracy. We have seen zenith error as great as 14° and we've seen effectively perfect. On average, zenith error is somewhere around 2.0°-3.0°. We know that no one would tolerate aligning their cantilever this far off but that is effectively what is being done since the groove contact edges are out of perpendicularity with the cantilever.
SO WHAT? HOW BAD COULD ZENITH ERROR REALLY BE?
We wanted to understand this question exceedingly well so we performed a very high end engineering process called finite element analysis to understand how a stylus that exhibits zenith error travels through a modulated groove compared to one that is perfectly aligned.
The video below speaks for itself. On the left is a perfectly aligned stylus travelling through a horizontally modulated groove. On the right is the same groove pattern but the stylus has a zenith error to it. The video has been slowed down 8500x to make the motion visible. Enlarge the video with the icon on the bottom right of the video so as to see more of the detail in the animation.
You certainly noticed that zenith error causes an INDUCED vertical travel component that is not directly related to the groove content. Instead of travelling left/right/left/right as the properly aligned stylus does on the left, the stylus exhibiting zenith error is travelling in an ovular pattern.
Notice the "spring" above the XYZ axis indicator to get another visual on the vertical motion induced by zenith error.
THE SOUND OF ZENITH ERROR
Zenith error doesn't sound like mis-tracking, "breakup", intermodulation distortion or other such nasties that are clearly obvious during playback. In fact, NO misalignment issue sounds like these things, but that is fodder for another blog article.
Zenith error sounds like "less of everything". Zenith error causes the soundstage to shrink and collapse, imaging becomes diffuse instead of tight and well defined, dynamic slam suffers, high frequencies fail to deliver a beautiful shimmer and long decay, inner detail is lost and overall musical coherence/intelligibility suffers. You might never even know you are listening to a cartridge with zenith error - until it has been corrected and suddenly you hear so much more.
WHAT TO DO ABOUT IT?
We are currently working on two different product development paths that would allow you to measure your zenith error at home. Until then, the only certain solution is to send your cartridge to WAM Engineering for analysis in our lab. HERE is more information on that. Once your zenith error is known (and is found to be no more than 5°) then it can be corrected using the WallyZenith.
If you are the patient sort and are comfortable with aligning your cartridge, it may be possible to sort it out on your own using subjective means, some trial and error and the WallyZenith - but results are not guaranteed. Essential components would be:
33rpm record (ONLY!)
The very innermost musical track (ONLY!)
Complex, large soundstage musical material. Well recorded classical orchestral is best.
Use the WallyZenith to maintain control and repeatability of your cartridge movements. More detailed instructions of this "subjective" process to come in the future. The limits of this subjective method are many; most notably you'll never know if your true zenith error is greater than 4.5°-5.0° - in which case it should be returned to the manufacturer for repair.