by Julian Hirsch
Forty or fifty years ago only the most dedicated discophiles were much concerned with record wear. In fact, the highly abrasive shellac 78-rpm discs then in use could reduce a steel or sapphire stylus to a stump in very short order. Most users were properly more concerned with stylus wear than with record damage.
The introduction of the vinyl LP in 1948 changed that situation radically. Since vinyl is a relatively soft material, even though tracking forces were lowered from several ounces to several grams, serious listeners began to be concerned with disc wear too. Today, with the introduction of the digital Compact Disc system, LP record wear is more important than ever. Few of the performances now available on LP will ever gain the permanence of a laser-read CD pressing. You should be concerned with record wear because you may not be able to buy a replacement copy for a worn or damaged LP in the future.
There are many interrelated factors in record/stylus wear. These include the basic interaction between a diamond stylus and soft vinyl grooves, the stylus shape, stylus wear, stylus tracking ability, and, last but not least, tracking force.
Let's take them in turn.
The basic cause of record wear is the work that must be done by the groove to move the stylus. The stylus is required to trace abrupt changes in the direction of a wildly undulating groove, sometimes at such high rates that the stylus's acceleration is on the order of several thousand times the acceleration of gravity, an acceleration comparable to that applied to a high-velocity shell or missile. Even the most ordinary recorded material can subject the stylus to accelerations of tens or hundreds of "g's." The power for this acceleration ultimately comes from the turntable motor, and the force to move the stylus must be applied through the soft vinyl groove wall. The vinyl material is deformed by the pres sure of the stylus as the disc turns, but the actual pressure on the groove wall depends on many factors. Some of the deformation disappears as soon as the pressure is removed, so that one can visualize the stylus as passing over the surface of a jelly-like substance, causing a temporary depression that follows the stylus path like a ripple along the groove surface.
If this were the only deformation, and no permanent change resulted from the passage of the stylus, there would be no record-wear problem.
Unfortunately, in practice the vinyl is permanently (if only slightly) de formed by the pressure, even if the stylus is ideally shaped and unworn.
A deformed groove results in an increase in noise and distortion.
When this becomes audible, the record can be considered worn even if it is listenable.
About thirty-five years ago, Professor F. V. Hunt of Harvard published a paper in which he concluded that the critical tracking force, below which no permanent vinyl de formation would occur, was about 0.25 gram. While I do not recall his specific assumptions concerning stylus shape and dimensions, the message is that all of today's cartridges, even the most refined, almost certainly exceed the elastic limits of the vinyl and cause some permanent deformation of the groove wall.
Since no cartridge available will track properly at 0.25 gram, there's simply no way around record wear.
Stylus Shape
Groove deformation is proportional not just to the tracking force, but, more accurately, to the total amount of pressure exerted on the groove wall in the area of its contact with the stylus. Because of a groove's shape, the force exerted on a groove wall is about 40 percent greater than the total tracking force.
Furthermore, this force is applied over a microscopic area whose size is a function of the stylus shape and the way it contacts the groove.
A groove may actually experience a pressure in the range of tons per square inch, even if the cartridge tracking force is only a gram or two.
This effective force is greatly multi plied if (as is normally the case) the groove is modulated. Picture the stylus essentially "running into" the undulations of the groove; the points of greatest acceleration as the stylus "turns a corner" are those receiving the highest instantaneous pressure.
---- Clean groove with one-channel test tone
A conical or spherical stylus has a roughly circular contact patch (foot print) on the groove wall. The popular elliptical stylus shape applies an ovaloid footprint, with the contact area being narrower (than that for a conical stylus) in the direction of groove travel. This is desirable for low-distortion tracking of high-frequency signals. At the same time, an elliptical stylus extends its contact area upward along the side of the groove, at right angles to the direction of groove travel, resulting in a relatively large overall footprint.
Therefore, with an elliptical stylus the actual force exerted per unit area can be less than that of a conical-shaped stylus having comparable high-frequency performance.
A number of stylus shapes are even more "extreme" than the elliptical type. Many of these were first developed in the days of CD-4 discrete quadraphonic discs, which required a frequency response extending to 40,000 Hz or higher. Although these advanced styli vary in their specific dimensions and shapes, and each carries the name of its designer or manufacturer, they share the quality of being extensions or exaggerations of the basic elliptical shape. As a class they are often referred to as "line-contact" styli.
All of them decrease the footprint size in the direction of groove travel (for better high-frequency performance) and increase it vertically over the groove wall (for decreased pres sure on the groove).
Elliptical and line-contact styli, though superior from a record-wear and audible-performance stand point, do require careful attention to manufacturing details and to mounting in the tone arm. The angular orientation of the stylus's contact surfaces relative to the two groove walls is a potential problem with any stylus shape other than conical. If the two contact faces of the stylus are not aligned along the same record radius, they do not simultaneously trace the corresponding portions of the two channels. The result is a phase shift between the stereo outputs of a cartridge, as well as a possible degradation of frequency response and higher distortion. This condition can occur if the stylus is mounted incorrectly in its cantilever, if the cartridge is mounted incorrectly in the tone arm so as to produce an excessive lateral tracking error, or if there is a significant vertical-tracking-angle error from either de sign or installation. In sum, for decreased record wear, use an elliptical or line-contact stylus, but make sure it is mounted properly in the tone arm.
Stylus Tracking
In addition to the shape of the stylus, other factors of cartridge design can have a significant effect on record wear, though in these cases it should be called record damage.
Chief among these is tracking ability, the ability of the stylus to stay on and in the groove regardless of the violence of its modulations. If the cartridge has poor tracking ability, if the vertical tracking force is too low, if the antiskating force is set improperly, or if the pickup/tone-arm damping is inadequate, the stylus may not remain in continuous con tact with the groove. This "mis tracking" is-aside from scratches, dust, and dirt-the most damaging thing that could happen to a record groove.
Bernard Jacobs of Shure Brothers makes the distinction between two different types of uncontrolled stylus motion during mistracking. One is where the stylus "bounces" from point to point along the groove wall.
The other is where the stylus is forced up and out of the groove, but not necessarily into a neighboring groove, because of a disc warp or a low-frequency cartridge/tone-arm resonance. Both situations can damage the groove in two ways.
First, a crashing, careening stylus can actually gouge out deformations in the groove walls. These can sometimes be heard as a horrendous increase in distortion as the damage is being done and afterward as added clicks or pops. Second, a stylus going its merry way along a groove may alter the groove to suit.
This can account for a "mellowing" of the sound of some records after they have been played several times with a poorly tracking stylus. All the "hard parts" have been smoothed out.
Mistracking damage is irreversible.
The solution, of course, is never to let the stylus get out of control. Aside from using a cartridge with superior tracking ability, the best way to keep the stylus on and in a groove is to use the right amount of tracking force, but not too little. Never operate a cartridge below its minimum recommended tracking force in the mistaken belief that you are reducing record wear. You are simply inviting mis tracking. It's better to err on the high side.
On the other hand, you should also choose a cartridge with as low a recommended tracking force as possible. Below 2 grams is good, and at or below 1.5 grams is better still.
Groove damage can also stem from a worn or chipped stylus. This area also has some unexpected facets. For example, a stylus that has been worn down by playing only an "easy" unmodulated "silent groove" is potentially more damaging to a normal music disc than a stylus worn down by a series of music recordings. The former stylus's "flats," the portions where the diamond has been worn off by the groove, have sharp edges. A stylus worn by music recordings has had its flats burnished and rounded by the varying groove shape.
The best way to detect stylus wear is by an examination of the tip under a microscope (a 40 X model will do). Unfortunately, it takes a little training and experience to get the stylus and light angles just right to see any flats, and it takes even greater experience to tell whether the locations and degree of wear are significant. The second best way to detect stylus wear is to listen for increased levels of distortion and a greater tendency to mistrack. But by the time you might notice some thing wrong, the damage has al ready been done.
Preventive maintenance is the best solution here. If you play discs for one hour each day (a higher-than-average figure), you should have your stylus checked by a competent technician twice a year. You should also consider replacing the stylus assembly (or, if necessary, the entire cartridge) after every 1,000 to 2,000 hours of playing time, whether you can actually hear any signs of stylus wear or not.
--- A groove containing a complex music signal
Other Factors
Foreign abrasive material (dust, dirt) on the record surface can be ground into the groove wall by the stylus pressures, which, as you re call, can be enormous. Once the vinyl has acquired these foreign objects-and the noise and distortion they contribute-it may not be possible to remove them by any cleaning method; the disc can be considered permanently damaged. Even if you can get some of the dirt out, the holes it leaves behind will be an audible reminder of their presence.
The vast number of accessories marketed to clean LP's should be an indication of how important cleanliness is for disc longevity.
A number of manufacturers of high-quality phono cartridges emphasize another potential source of record wear: the polish of the stylus's diamond surface. Only under a rather powerful microscope can this be seen, and (as with stylus shape and orientation) there is little the consumer can do but take the word of the manufacturer about the care with which his styli are polished and mounted in their cantilevers. If the stylus surface pressing into the groove has any roughness, it is certain to carve its initials (so to speak) into the grooves of every record it plays. In the .time needed for vinyl to wear off the imperfections of the stylus, many records can be prematurely aged. After all, one can hardly imagine two materials more unlike each other in hardness than diamond and vinyl!
The Bottom Line
It should be apparent that if you play your records you can't eliminate record wear.
About all you can do to minimize it is to use a good cartridge from a manufacturer who takes the trouble to finish his styli properly and mount them accurately. Try to choose a cartridge that can track at a force of less than 2 grams, but never try to operate it below the manufacturer's rated minimum force.
Take care to install the cartridge properly in the tone arm to derive the benefits of the precision stylus alignment the manufacturer has presumably built into it (and for which you have paid, often considerably) Set the antiskating compensation of the tone arm correctly (failure to do this will create unnecessary wear on one side of the groove). Have your stylus checked periodically. Keep your records and your stylus clean.
And, as a final note of optimism, think about how many times you are likely to play any given record. I would guess that few discs are played more than a couple of dozen times, especially if you have a large collection-who has the time with only twenty-four hours in a day? That means that you are unlikely to wear them out in your lifetime. The diamond of your stylus will certainly wear out sooner. "Diamonds are forever" applies only to jewelry.
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Also see: Turntables -- What Are Your Options (Jan. 1985)
Source: Stereo Review (USA magazine)