(Some Australian fans of high-fidelity equipment and playback may think that this article is vaguely familiar. Indeed, it is an edited version of an article I wrote for Australian HI-FI, published towards to the end of 2018. So, no, it’s not déjà vu for you.)
If you are considering a turntable for purchase – vinyl is definitely in now – you may notice that it has an antiskating adjustment. It doesn’t? Well, then reject it and consider another turntable instead. Antiskating is an important feature of any turntable worth adding to your system. But most people really don’t understand the nuts and bolts of why. Let’s get that understanding.
What is skating and why should we be anti it?
Anti-skating is needed on virtually all turntables because without it, the stylus on all those turntables is pushing towards the centre of the record. In this piece we will learn why, but let’s briefly consider the problems that this inwards force can cause.
This force increases wear on one wall of the groove. That increases damage on the record, shortens the life of the stylus and increases playback distortion. Antiskating devices on turntables are designed to counteract this force.
It’s all in the Directions of the Forces
Skating has nothing to do with the quality of construction of the turntable, nor the make of the tone arm bearings, nor whether the arm is straight or curved. It’s all to do with the directions of forces. The only exceptions to the rules are turntables with radically different tone arm geometry. I will return to them.
When the stylus is in the groove of a record, there is friction between it and the walls of the grooves. That means that the vinyl recording is tugging on the stylus. How hard the tugging is depends on several things. One is the precise formulation of the vinyl and the stylus. Different materials can have a slightly different “coefficient of friction” between them. Another is the modulation of the record. Wildly swinging grooves are going to tug a little harder than almost straight grooves. Those are things that the listener has just about no control over.
One other thing affecting friction is the tracking weight. This is a very important factor. We all learned Amonton’s First Law in High School Science, didn’t we? It says: “The force of friction is directly proportional to the applied load.” Double the tracking force and you double the friction.
But you’ll probably be choosing your cartridge/stylus combination only partly on the criterion of tracking force. We all know that you should stick with the manufacturer’s recommended tracking force, absent an extremely good reason to depart from it. In particular, reducing the force is likely to result in more damage to the record due to mistracking.
So, we’ve established we have a force on the stylus. In what direction is that force? It’s aligned with the tangent to the groove in which the stylus is implanted at any particular time. The direction of that tangent can vary over a few degrees as the arm tracks across the record from the outer edge towards the centre, but not by much.
At this point a picture becomes useful. That force is in the direction “B” shown in the graphic:
This is going to seem like a foolishly trivial question and answer, but these are important in understanding how forces interact. So, what is it that stops the stylus from simply going around and around with the record? What keeps it in place on the end of the tone arm? Mr Newton says it would go with the record groove unless there’s an equal and opposite force. And of course there is.
Where’s the pivot?
Most of that opposite force is supplied by the tone arm’s pivot. Well, technically, the force opposing that friction is supplied by the stylus cantilever. The force holding the cantilever in place is provided by the cartridge. Then the tone arm, and then the tone-arm’s pivot. You can trace it all the way back to the planet itself, but the pivot is the sensible stopping point because the pivot is, in fact, a pivot.
That is, because it can swing freely from side to side on low-friction bearings, the only force that it can apply to anything on the horizontal plane is either directly towards the pivot or directly away from it. And here’s the problem. The pivot is not located on a tangent to the groove. It is to the left of that tangent for almost all extant designs. That means that the force it applies is not directly opposite the force applied to the stylus by the groove. You can see in the graphic, where I’ve labelled it ‘C’. The pivot cannot apply any significant sideways force because it is low in friction.
But Mr Newton insisted that the force had to be opposite. So there is something called a “residual” force on the stylus, which is the force left after the force from the pivot and the force from the vinyl dragging on the stylus mostly cancel each other out. Its direction is more or less towards the centre of the record. I’ve labelled this “D”.
That force would swing the stylus in towards to the centre of the record were there not, as continually demanded by Isaac, a force pushing it back out again. And what do you think is applying that force? Yes, full marks: the inner wall of the record groove. It applies a force equal to “D” but in the opposite direction to “D”.
An anti-skating mechanism on a tone arm counteracts that force. The way it’s usually done is by applying a counterclockwise “torque” to the tone arm. Torque is the rotational equivalent of force. That’s often applied by using a small, suspended weight on a thread to add a force in the same direction as “D”, but to the other side of the tone arm pivot. Sometime various spring mechanisms are used.
No Antiskating Mechanism is Exact
Manufacturers can calculate with great precision the amount of torque their anti-skating mechanisms will apply to the tone arm, and then can mark calibrations for various tracking weights. But it will nonetheless be at best approximate in cancelling out the force of the arm towards the centre of the record.
As I said earlier, the amount of friction, and therefore force on the stylus, depends not just on tracking weight but also things like groove modulation. But it also depends on angles, and the angles vary as the arm plays different sections of the record. A well-aligned cartridge will be at a precise tangent to the groove at two points throughout that travel. The rest of the time it will be off by a very slight angle. That changes the direction of the force on the stylus, so that in turn changes force “D”.
When I’m setting up a turntable, I generally use the “groove-less” track on my 1970s LP An Audio Obstacle Course from Shure. But even this applies in only one section of the record, and probably provides lower drag than a real track. That said, in general antiskating calibration seems to be all over the place. Some turntables send the stylus sliding rapidly towards the centre on this track – which means they have way too little antitracking force. Some send it outwards. It’s less certain whether that is a miscalibration.
Hey, playback with turntables is full of compromises and estimations. As a first compromise, just go with the antiskating provided by your turntable. Generally it means dialling it in to the tracking weight of the cartridge, or putting the thread of the counterweight on the notch indicated in the instructions.
Designs Where Antiskating is Not Required
As I suggested way back near the start of this piece, there are turntable/tone arm designs where anti-skating is not required. One solution which was around for a decade or more in the 1970s and 1980s was the linear tracking arm. Instead of the arm having a pivot, it was on some kind of rail so that it could slide smoothly at the back. As the record played, the whole arm would move slowly, remaining parallel to the current groove. Since the arm was always on a tangent to the groove, there were no mis-aligned angles. No angles meant no mis-aligned forces. So, no anti-skating was needed.
Unfortunately, effective linear-tracking tone arms are difficult to build, expensive and could be temperamental. In the end, radial, pivoting tone arms remained dominant.
The other possibility would be a tone arm with its pivot further out to the right, so that when it was playing the tracks halfway through an LP, it would align exactly with the track tangent. The main problem there is that for most feasible lengths of tone arm, there would still be misaligned forces, but in some positions the residual would be pushing inwards, and in others it would be pushing outwards. You’d still ideally have anti-skating, but it would somehow have to work both ways.
Unless the tone arm were really long. That would minimise that issue ... but introduce a stack more problems. They’d include wear on the stylus and cantilever from having to push a higher mass arm around, and likely low frequency resonances that could cause tracking problems. Plus, of course, the problem of having a turntable chassis large enough to accommodate such an arm.
So, absent a linear-tracking arm, choose a turntable with antiskating and then take a bit of time to make sure that you’ve set it correctly.