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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 effischer

effischer
568 posts
 
As always, atmasphere has the straight story.  I bought a Planar 2 new in 1981, and its glass platter was thinner than the 3.  Accordingly, the standard issue felt mat wasn't quite thick enough to get the VTA into a decent sounding range.  I went with an Audioquest Sorbothane mat and clamped my vinyl with an AQ clamping weight.  Took out some warpage, dishing and pretty much killed all resonance.  Used the rig with a Dynavector MR23 Karat LOMC to very good effect.  Others here have had very positive things to say about cork with Rega and others, so you might want to research the archives for more info.

I never got an opportunity to try a cork mat; didn't have any dealers vending them at the time and I wound up upgrading to a Sota Sapphire in early 1984.  Its mat was both resilient and non-resonant out of the box.  I fitted a Magnepan Unitrac I to it, so never had to worry about VTA again.  I did find that the AQ clamping weight wasn't quite right, so I went to the Sota I-Clamp (low mass screw type compression) and was happy for a number of years.  Even so, the I-Clamp was awkward to use.  Found the Sota Reflex clamp second hand at a very good price and love it.  I highly recommend it for use on any table.

Either way, have fun and enjoy your Planar 3 - it's a very nice unit!
effischer
568 posts
 
IME, the difference in image you are hearing between the 2 mats is almost entirely VTA.  Even a very minor adjustment makes an enormous, immediately audible difference regardless of cartridge.  It's the reason why VTA adjustment on-the-fly can be such a desirable feature in a tonearm.  

An easy way to confirm if that's what you're hearing is to play a well-recorded thinner record and then play a well-recorded thicker one next using the same mat without a clamp.  Then repeat the process with the same two records with a clamp.  Repeat that combination again with the other mat.  You will learn much.

Happy listening!
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