TURNTABLES: Platter Mats and Record Clamps

Both stylus and the vinyl disc vibrate, and they each vibrate differently. These vibrations in turn set up additional resonances in the cantilever, cartridge body, tonearm, and the disc itself. The resonances set up in the disc are interpreted by the stylus as part of the audio signal, intentional elements of the music.

The cure (never total) is to couple the record tightly to another surface that can dissipate the vibrations. This is the function of platter mats and record clamps. They can also help to flatten records, and so mitigate “warp wow” distortions. The perimeter clamp on the George Merrill table is particularly effective here.

Vacuum clamping is an all-out attempt to minimize record vibrations and warps. The record is held by vacuum suction to the platter, thus ensuring both flatness and excellent coupling to transmit resonances away from the record groove. There are claims that vacuum clamping may physically damage the record and increase surface noise. Speculations as to the cause range from the suction pressure embedding dust particles in the vinyl to actual alterations in its chemical balance. Less suction applied continuously is thought to have corrected the problems. However, the results are not all in.

A platter mat plus clamp, while perhaps less effective, serve very well. These accessories—“necessories”—allow you to adjust the sound of your turntable system, sometimes for the worse, hopefully for the better. Be careful not to confuse “different” with better—a change can result in an improvement, an impairment, or simply a step sideways that offers a different combination of tradeoffs.

Some tables come with their own clamping systems, like the Merrill peripheral clamping ring, the VPI spindle-threaded screw-down clamp, the SOTA vacuum-clamping system. Such an integral clamp may be the best choice for that table, or you may want to experiment with other clamps. Some tables also -come with special platters, made for example of acrylic, which are intended to eliminate the need for a separate mat. Again, respect the designer’s intentions but don’t necessarily ignore the possibility of experimenting with mats (as well as clamps) nonetheless. How a clamp sounds may depend on the mat it is used with, so these are best considered in combination.

Mats are placed between platter and record. They come supersoft, soft, medium, and hard. Each represents a different theory about disc / turntable interaction and each represents a slightly different conjunction of tradeoffs and compromises. No two will sound the same.

In addition to damping and isolating the disc, the mat must also provide a good grip for the disc and thus prevent slippage and resulting speed irregularities. It must also not interfere with a tight coupling in the mechanical grounding loop.

As summed up by Peter Moncrieff, the mat should be firm enough to support the stylus in its larger excursions, yet soft enough to terminate the entire surface of the record and table platter so vibrations will die as quickly as possible and minimize smearing of the music. The softness should have a damping rather than springy quality so the mat doesn’t store the energy it absorbs from the record only to release it later, thus smearing the music that way.

A hard mat (as a category) will tend to give a more “lively” sound to the music, which can be attractive but is actually distortion. Vibrational energy from the record is not being stored and dissipated by the mat but is instead being reflected right back into the vinyl, where it continues to reverberate. There is an idea that a hard mat is most like the LP and therefore, since like materials transmit vibrations between them more easily than do unlike ones, the vibrations will be transmitted through the mat away from the record and then dissipated into the mechanical grounding loop. A. soft mat (again, as a category) will tend to reduce transient impact. You really have to listen for yourself on your own system to decide on a mat that matches well with it.

When using a clamp, the stylus tracks better; focus, imaging, and soundstage improve; and the sound is more pellucid overall. The only problem is that some clamps add their own coloration, or rattle and vibrate. Again, audition these in conjunction with your mat.

Record clamps come in three basic forms: a simple weight, a reflex clamp that slips over the spindle and then locks downward onto the record, and a screw-on clamp that requires that the spindle has already been threaded to accept it, like the VPI. Merrill uses a combination of weight and special peripheral clamping ring, which secures the record around its perimeter. Holding the LP both in the center and around the edge, this system is excellent both at locking the record to the platter (or mat) to minimize vibration, and at (temporarily) flattening out warps. This system is almost as effective as a vacuum, while, being less expensive and having none of a vacuum system’s drawbacks.

The weight style of clamp, which simply slips over the spindle and holds the record by its heavy weight, is probably used safely only on tables whose bearing assemblies have been specifically designed to support this. Such a weight may also slow platter rotation. Though it is better than nothing, it is probably less effective than either a screw- down or a reflex clamp.

Some clamps are friction-fit, like the Souther. A small disc of plastic, this fits snugly over the spindle and couples the record to the platter. The clamp’s hole is cut square and on the small side to ensure a tight fit, and the sides expand very slightly to fit a variety of spindle sizes. It’s probably the least expensive good clamp around, since the Radio Shack one has been discontinued. With this type of pressure-fit clamp, be careful not to push down too hard, for two reasons: If you become too enthusiastic, you can cause the edges of the record actually to become slightly lifted off the platter, and you can also “bottom out” the suspension. While this probably does no harm, it doesn’t feel right and will probably require more frequent adjustment of the suspension springs as a result of their being so often compressed.

Reflex clamps use neither weight nor screw threading nor pressure- fit. This design slips over the spindle, with no pressure applied to the table bearings; then a collet grips the spindle and pulls the clamp slightly downward until it presses against the record, coupling it snugly to the platter. This method, for an aftermarket clamp, is probably the most effective and entails least risk of any possible destructive action. The SOTA reflex clamp works very well and is beautifully made. Audio- quest has a similar design.

The bottom of a reflex or friction-fit clamp should either be slightly dished or use some other method that permits the placement of a spindle washer under the record. Without this washer, when the clamp clamps down on the record’s center, its outer edge will be raised away from the mat, negating the benefits of the clamp—and then some.