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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
atmasphere's avatar
atmasphere
7,068 posts
 
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.)

George misses an important element of clamps, which is that to gain the most out of them quite often a spindle washer of some sort is used beneath the LP so that the clamp can dish the LP against the pad surface. This can also be used to reduce warp.

I generally don't use the clamping aspect of the clamp I use (Basis; one of the better clamps made), I just use it as a weight. Its easier.

Many years ago I saw a demonstration of how profoundly a mat can affect a turntable. A friend of mine who has been involved in several damping products over the years (Analog Survival Kit, the damping rings used by ARC, the Ultraresolution Technologies damping platform) spent some years developing a platter pad. He arrived at a fairly high degree of refinement with the mat. What local audiophiles found was that any turntable that could accept the mat (due to height and weight; it weighed about 3 pounds) sounded better and also sounded better than nearly any turntable that lacked the mat.

This seems to hold true to this day. IMO/IME most mats out there don't seem to do the job as ideally as I laid out in my opening post (IOW it was a statement of the engineering principle behind the mat, not actual execution). This is why you see so much variance in opinion about the topic.
pryso
1,501 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.
harold-not-the-barrel
799 posts
 
atmasphere, I wanted to say reduce/lessen (motor) noise (excuse my clumsy English). Of course, this alone can´t  fix defective motor or wrong placement of motor. Rubber mat on metal platter lessens noise from outside and lessens metal´s ringing. This is basic physics ? Thick and heavy Groove Isolator on aluminium/magnesium platter reduce noise (ringing). ORACLE´s clamping system is exactly "dishing" record tightly against Groove Isolator and thus platter, and reducing warps. Actually all three become an unity. A very effective damping method, one of the reasons why ORACLE sounds so good, IME at least. This damping method simply works surprisingly well (can´t explain it really). Unfortunately ORACLE took a few steps back replacing Groove Isolator with hard acrylic.

On the other hand, damping the record too much may have serious side effects like compressing the sound, in various extents depending on platter /mat in question. Very complicated anyway.

As I said I´m not excited in damping the vinyl TOO much, I meant to say.
The other option is let the vinyl breathe, but that, of course, is another story.
paulburnett OP
13 posts
 
This is so interesting that you say this about breathing Harold. Tell us more about this other story! 

Using the clamp and Music Hall cork mat, the signal seems more locked, with the proverbial blacker background. But I get a more left-to-right, 2D soundstage. On the other hand, unclamped with the felt mat, the Rega seem to present a more three-dimensional, front to back soundstage. Am I just interpreting smearing as depth? One possibility is that the two mats alter the VTA, which looks like it might be the case. And since I can't adjust the VTA on my current setup, the Music Hall will likely have to go back.

Can I get the 3D image with the black background and locked image please? ha ha.  The other issue might be that the Music Hall raises the record off the platter with a dozen cork discs, so it's not truly coupled to the platter.  I'm ordering a Herbie mat for comparison. 
effischer
477 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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