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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 1 response by pryso

pryso
1,906 posts
 
For several years I owned a Kuzma Stabi table, the model with the heavy wood plinth.  The platter was thick aluminum with a lead insert on the underside to add mass and the mat seemed to be a treated (?) cloth glued to the platter.  It included a tapered spindle washer and threaded clamp as Ralph describes.

I found that to be very effective for both damping and flattening records. Because the spindle clamp was threaded you could adjust the downward pressure.  With some records excessive pressure could slightly lift the outer edge of the LP.  My table was mounted high enough so I could see if the record lost contact with the outer edge of the platter, I would then unscrew the clamp slightly to regain contact.

This system worked well with dished records, but only for one side.  Moderate warps (wavy) were also reduced.

The Kuzma was silent so I judged that design to be effective for both damping and flattening purposes, though I never tried an outer ring.
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