There are many different, and even contradictory, commonly held beliefs about skating force and anti-skating force that remain held close to the chest in the audio press and on online forums. Surprisingly, many of those same beliefs are even held by a few tonearm and cartridge designers. Unfortunately, many of these beliefs are simply not true and are keeping owners of fine equipment from getting better performance from what they own. This article will cover a few of these myths, but first a primer:
SKATING FORCE IS A FUNCTION OF TWO ELEMENTS - FRICTION AND EFFECTIVE MOMENT ARM (EMA)
We trust everyone reading this understands friction, so what is EMA? This issue was covered in an attachment on one of our past blog articles but below is the relevant slide. To visualize the EMA for any tonearm in any given position across the record surface you have to draw a series of three joined lines with each joint at 90 degrees. Start at the spindle and is draw to the stylus location. The second line runs from the stylus to a point where the line will be at 90 degrees to a line drawn to the pivot point of the arm. The last line segment completes the journey to the arm's pivot point. Remember, each join angle must be 90 degrees.
As long as the third segment in that series EXISTS (the Effective Moment Arm in red drawn below) there will be a skating force. The longer the EMA, the greater the skating force.
In the drawing below you can see how the EMA is longest with the stylus at the outer area of the record followed by a decrease and then increases again at the inner area of the record. If you were to draw this line segment sequence for a tangential bearing arm, you'd see there was no third line and therefore, no skating force.
MYTH #1: Longer arms do not have skating force (or such force is negligible)
If you were to model the line sequence as directed above on a longer tonearm you will note that the length of the EMA line (red line) does not change. However, skating force DOES decrease in longer arms because the ratio between EMA and effective length of the tonearm changes. Since 12" arms are about 30% longer than 9" arms, does that mean that skating force decreases by 30% for 12" arms? NO! This is because friction remains independent from arm length. Remember that friction is the second element required to have a skating force develop. It takes a more sophisticated algorithm to calculate the true decrease in skating force when moving to a longer arm. I won't dive that deep in this article, but suffice it to say the decrease in skating force is nowhere near 30% less skating force when moving to a 12" arm.
MYTH #2: You can adjust anti-skate by ear by listening for the balance between channels
Cartridges are velocity sensitive devices. The higher the velocity, the higher the output. Given a groove with equal modulation levels in both channels, to say that changing the horizontal force of the stylus on the groove walls will change the tracing velocity with which the stylus will trace one groove wall versus the other just doesn't hold any water. You can claim (rightly) that the higher the horizontal force, the more groove deformation occurs in one channel. You could *maybe* further an argument for groove deformation vis a vis higher inertial forces resulting in slightly greater excursion distances over the same time period resulting in slightly higher output but I'm not aware of any study that hasn't found mistracking occurs far before measurable channel output changes (much less perceivable ones) . Maybe it's out there, but I've not seen it.
It is FAR, FAR more likely that the reason people hear a change in channel balance when adjusting anti-skating is because they are imparting enough horizontal torque (via either skating force or anti-skating force NET of any arm stiction and the tonearm’s internal horizontal torque force) that the coils rotate with respect to the 45 degree groove wall. In other words, you are changing azimuth!
We know very well that when you change azimuth, it is possible to generate up to 2dB channel imbalance. We've seen it hundreds of times in the WAM Engineering lab. It takes very little rotational force to shift a coil bobbin around its central axis.
There are so many problems with optimizing a cartridge and tonearm by ear that we could write a book about it. Notice we are not saying there are problems with IMPROVING the sound by ear. (Improving and optimizing are not synonymous because the latter aims at known goals that will deliver the pinnacle performance using both objective and subjective measures.) While IMPROVING your sound by ear is entirely possible you will often never know if the NET improvement you just heard resulted in a deterioration of one or more other parameters.
There are 7 targets to hit to get the most out of the groove. Our point is: why not take each one down in a UNIVARIATE manner rather than using a multivariate attempt such as listening (or using a test record! - exception on azimuth, of course). Multivariate tests are almost always the foil to certainty and optimization.
Almost all adjustment functions on a tonearm will change at least two - and up to five - other parameters. We don't want to wonder whether the improvement we just got by listening for improvements when adjusting something resulted in enough of an audible improvement to mask a deterioration in other parameters. By using univariate means of setup and optimization, one need not wonder.
This is exactly what the WAM Engineering process does!
MYTH #3: Since skating force is a moving target, it doesn't matter enough to get things precisely tuned because it will never be perfect
Yes, skating force changes with EMA length (as above) and it also changes with the coefficient of friction (e.g., groove amplitude, vinyl formulation, etc., etc.). However, we KNOW THE RANGE OF VARIABILITY. If we know the range of variability, what is the best thing to do to be right most of the time? AIM FOR THE MEAN.
A distribution curve has a high point and two tails. We aim for the high point in the dataset since that is where most of the action is! That is what the WallySkater does!
MYTH #4: I can trust the tonearm manufacturer's anti-skate setting recommendation
The degree to which this is a myth varies by tonearm manufacturer. There are tonearm designers who really do understand skating force. There are tonearm designers who understand skating force but can't seem to design an effective anti-skating device. There are tonearm designers who don't understand skating force at all and there are even a couple designers who have defeated the laws of physics somehow because their pivoted tonearms "don't need it".
Even with well calibrated anti-skate mechanisms, we need to be concerned with the internal torque force of the tonearm WITHOUT anti-skate engaged. Is this force (since it usually exists to at least a small degree) complementary or fighting our anti-skate target?
Many designers are quite ham-handed with their application of anti-skate and a lighter approach is needed. One exceedingly expensive design is quite the opposite. In any case, the instructions to apply a prescribed amount of anti-skate force cannot apply to every given arm off an assembly line since every arm comes off that line with varying degrees of internal horizontal torque force - usually caused by the tonearm wires themselves but sometimes the bearings as well.
MYTH #5: Look at the alignment of the cantilever during playback to set your anti-skate
We almost didn't want to mention this one as it is kind of "out there". Assuming you can get a good view of the cantilever while playing on a record, against what fiducial will you align? How will you ensure you've eliminated parallax error? How do you account for tonearm bearing stiction? At what radius are you doing this measurement? With what groove amplitude are you doing this measurement?
So many issues on this one. Enough said.
MYTH #6: My arm sounds better without anti-skating applied
The first question whenever you hear this claim should be, "Did you control for the variables that can influence the horizontal behavior of the tonearm BEFORE coming to that conclusion?" Unfortunately, you are likely to get a blank stare at the question.
What is meant by the question? A frequently encountered example:
I have been to many people's homes who claimed their arm sounds better without anti-skating force applied. In every case, THEY WERE RIGHT. However, they were right about what matters (the sound) but ascribed the basis of their claim to the wrong thing (the anti-skate mechanism). In every case, these audiophiles' tonearms had their own horizontal torque forces generating as much as, or more than, the required anti-skate force necessary WITHOUT EVEN ENGAGING THE ANTI-SKATE DEVICE. Of course, when they would engage the anti-skate mechanism the sound either became too sibilant, the arm would start mistracking, skipping or at least sounded more "closed-in" and robbed of life. They did not know their arm had a significant internal horizontal torque force doing the anti-skating job for them in the first place.
So, for those who say their arm sounds better without vs with anti-skating applied, they probably already have it applied by the arm itself without knowing it.
Of course, in these situations you can be nearly certain that at the time of their cantilever alignment they messed things up pretty badly. Why? Since they did not know that horizontal torque force was present at the time of cantilever alignment the horizontal torque force generated on the cantilever by the arm would have skewed it visually and made it to LOOK like they needed to revolve the cartridge counterclockwise to align properly but...you know how the story goes, I hope!
MYTH #7: You can use a test record or a grooveless record to set anti-skating
We have gone over this one a bit HERE but didn't fully explain why such methods are not good.
Test records use highly modulated grooves intended to induce mistracking in one channel with instructions on your end to adjust the anti-skating until the mistracking occurs in both channels. However, as you learned from above, friction is one of the main two elements that create skating force. Highly modulated grooves have a higher coefficient of friction than quieter grooves. These test tracks use groove modulations that no responsible engineer would ever put into records with musical content. Therefore, you are using a MUCH higher frictional force on your stylus to set your anti-skating against, which will guarantee you will use way too much anti-skate force.
When clients send their cartridges in to WAM Engineering for analysis, we can see who lives with this situation by the uneven stylus wear patterns and/or shifted dampers/cantilevers.
The use of grooveless records isn't much of an improvement because the variability of the conditions is enormous. You are instructed to adjust the anti-skating mechanism to allow for a "slow" progression of the stylus towards spindle, but what does "slow" even mean and how do I know when I've attained it? At what radius are we to make this assessment since skating force varies slightly depending upon playing radius? How much plasticizer is in record being used? (more plasticizer = more vinyl deformation = higher friction = higher skating force) What is the profile of the first few microns of my stylus tip? (Varying profiles will provide varying frictional forces) At the location of the test is the cross-sectional profile of the record flat or tapered?
In other words, the coefficient of friction existing between your stylus tip and a groove-less record bears no consistent relationship to the coefficient of friction found in the typical groove containing musical content.
SUMMARY
We have ALL been sold a bad bill of goods by a number of clueless manufacturers and audio reviewers on this issue for years. The published scientific studies on skating force have been known about for decades and repeat tested time and again with the same outcomes. Why does the will to misunderstand persist?
Whether or not you choose to purchase a WallySkater in order to accurately assess the performance of your tonearm or not is up to you. At very least, BE WELL INFORMED.
Comentarios