Turntable Mat question

Atmasphere, I have been using vacuum hold down for 30 years and have never damaged a record. I suppose if you threw sand on the platter before the record you might be able to do some damage. No flat mat of any material can control a record that is not flat. They can dampen platter resonance and to some extent in the record (fortunately vinyl is pretty lifeless stuff) A properly designed vacuum system works perfectly all the time and every time regardless of the condition of the record at some additional expense and another box ( big box for the Walker) 

Ralph....in response to your latest post, I need clarification ...I am confused....explain complementary mat shape   
since the record is the same size as the platter and being used as a mat,both mat and record are same size and shape.Please explain
Thank you

@rocky1313 you’re thinking about diameter, but think about the thickness and concave of the vinyl, look here

Then look at the proper mat and try to understand why it is not flat as a pancake, but curved inward on the label area and on the area under the edge of the record.

SAEC engineers were a bit smarter and designed their mat not only for LPs, but also for 45s, this is why SAEC SS-300 mat shape is not flat. There is an inward curve circle for the 7 inch size of the recod.

Using an LP as a mat is bad idea. The best mats designed 30-40 years ago, you can’t find a better solution than Micro Seiki CU-180 / CU-500 Mats and SAEC SS-300 mat in my opinion.

rocky1313,

In my post, the Platter Pad is the name of an actual mat that is almost 1/4" thick. It was a somewhat flexible, but firm mat. This was sold back in about 1980 and is probably not being made anymore. Someone might still have one if you put in a wanted ad.  The combo with the KD-500 and Grace 707 was very highly reviewed back in the late 1970's to early 1980's.

Bob

Rocky what Ralph is saying  is that the center of the mat should be recessed to fit the elevated label area and have a total diameter slightly less than the record so that the fatter record lip can hang over the edge of the mat. This way the playing surface of the record is in fill contact and supported by the mat assuming the record is flat. Any mat or platter that does not do this should be avoided. Now no record is perfectly flat.
There are three systems to press there are three systems to press the record into the mat forcing it flat. All systems use a center record clamp. The there is the periphery ring ala VPI, Clear audio. Vacuum hold down ala SOTA, Basis, Air Force and finally the SME, Walker, Kuzma solution which is a bit harder to describe. There is a thin washer about 1" in diameter placed over the spindle under the mat. The record clamp is designed so that it only contacts the record label at  the clamps very periphery. So, now you have the record floating in the air the thickness of the washer so that when you screw the clamp down it flexes and forces the record into the mat. If you try this with an old 78 (shellac) it will crack and they warn you not to do this but vinyl is suitably flexible to take this.
My own opinion is that the periphery ring is a PIA. The SME clamp method works but stresses the record and I have seen 200 gm records crack a little at the center. 180 and below no problem. I personally like the vacuum method best assuming it is designed correctly using low vacuum pressure and a noiseless pump. It is easy to use and it works brilliantly. I think the bass and dynamic range are improved but I have no evidence to back that up and as always it could be psychological. If you want to think it sounds better it will.