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coupling or decoupling of vinyl to/ from platter

Dear all,

I'm puzzled by a number of claims about record clamps and mats. 

I own an old Rega Planar 3, and I was reading about the importance of coupling the record to the platter, to add effective mass to the record to reduce vibrations, slippage etc, and improve the solidity that the groove "image" presents to the stylus. 

I also read about the importance of de-coupling the vinyl from the platter to prevent the transmission of unwanted vibrations from the motor. Rega has a very dense platter made of glass with a fluffy felt mat on top. So, felt to decouple lp from platter, is that right? 

Then, I purchased a cork Music Hall mat, which has a dozen raised cork discs on the mat to BOTH "decouple" the lp from the platter and "grip" the lp.  Music Hall claims that clamps are unnecessary with this mat because coupling discs, etc. I also, without knowing this, purchased a Rega Michell record clamp. The clamp seems to do good things regardless of the mat, and of course evens out warped records a little bit. 

There needs to be, it would seem, a clear objective answer to all of  this from an engineering perspective. Coupling does x, and decoupling does y.  If you look at all the high-end turntables, they have massive platters and clamps. So coupled mass is good for flywheel effect and also  for presenting a solid "image" to the stylus? 

Either Rega and Pro-Ject are dead wrong with felt mats, and have been runaway successes in spite of this, or the felt is adapted to their setup: weak motor, relatively light but super-dense platter, and decoupling felt to manage the motor and rotational noise transmitted up the spindle, and to hell with coupling?  

I did some quick and tentative experiments with the Music Hall mat and clamp vs. Rega felt mat with clamp. I need to do more comparison. The results are different but hard to characterize. I'll post again with more comprehensive subjective tests. 

From an engineering perspective, which should be best, Rega clamp w felt, Music Hall mat by itself, or "screw the mods, Rega it great just the way it is, heretic!!!" ?

Let the games begin!

Paul

paulburnett

Showing 2 responses by abnerjack

abnerjack
152 posts
 
I don't understand the answer to the op's question.  Are we decoupling the record from the platter by using a mat, and then coupling the record to the mat via the clamp and sometimes a peripheral ring?

In my case, with a Classic 1, VPI recommends against a mat.  To reiterate the original question, what's the theory?  As Denzel Washington's character said in the Philadelphia movie,"explain it to me like I am a four year old".
abnerjack
152 posts
 
atmasphere,

Thanks for the explanation a four year old can understand.  I did the experiment you suggested, turned the volume down all the way and could hear no groove noise at all with my ear within inches of the cart/stylus.  I am running a MM cart with it's relatively high output and could hear the internal signal of the cartridge.  This is with the VPI Classic 1 with the heavy aluminum platter, center clamp, and periphery clamp.  It seems to work without a mat.  If I had a mat I would try it, but from what I have read from other owners it offers no improvement.

Here are some further words of enlightenment from George Merrill:

  Debunking LP Record Weights and Clamps
by George Merrill

The LP record ranges in weight from approximately 80 grams (Dynaflex 1969) to 200 grams. Most pressings weigh from 100 to 130 grams. One reason the heavier and thicker records sound better is the vinyl will not vibrate to the degree as the light weight records. The 180 and 200 gram records are the choice for less vibration, and can render better sound. The rule is simple, the more damping applied to the LP the better it sounds. This result can be obtained from its own vinyl mass or external. To achieve the best external damping, the record vinyl needs to come in total contact with a vibration damping material (mat). In the past a few record mats have used small rings or points to support the record in a few places. This flies in the face of common logic.

Holding the record to a damping material is the job of weights and clamps. An LP record’s label is thicker than the vinyl playing surface. The label varies from approximately 20 to 60 thousands of an inch thicker than the vinyl. A record mat will have a depression in the center to allow the record vinyl to lay flat, otherwise the label would be the only contact point. If a center weight is used that is very heavy, let’s say 2 lb. the lighter records will lift from the mat. This happens because the mat depression edge will act as fulcrum. This information tells us we should use a center weight tuned for the record thickness and weight. However this is impractical. Here is the solution: Use a center weight that weighs 8-12 oz . This weight will work with all but the lighter records. The alternative to a weight is the screw down clamp. These clamps have pluses and minuses. The plus is down force on the record can be controlled. The minus is if not designed properly (unfortunately most are not) spindle energy is coupled into the record. It takes very little intrusion of external energy to cloud the mechanical output of the stylus. (I wrote a paper on proper screw down clamp design about 25 years ago.)

The best answer is the periphery clamping weight along with a center weight. The weight balance between these two should be calculated for even and optimal down force on the entire vinyl area.

As the stylus traces the groove, energy is radiated in all directions, as it reaches the periphery of the record it then reflected back into the groove area. The periphery clamp will help damp this edge energy before it is reflected into the groove area. The center weight also acts as a damper. The first production periphery clamp was used on the Merrill Heirloom Turntable 1980. Kenwood also introduce theirs about the same time. Other manufacturers are now discovering the benefits of this type of clamp system.​
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