Sloped mat?

[jamus]

The rubber mat on my Dual CS 607 seems to be sloped towards the spindle in all directions. The mat has an outside support ridge that is higher than the inside support ridge. When I place a record on the mat, put my bubble level on top, and then slowly spin it, the bubble shows that it is unlevel towards the spindle in all directions. Take the mat off and it is perfectly level.

Why was it designed this way? Or perhaps a better question would be, was it designed this way? I may need a new mat.

 

[cgutz]

My bubble level and straight edge level does the same thing on my Kenwood - very slightly. I level with the mat off, directly on the platter. Perhaps it is so the outside edge of the record is supported more? I've never really worried about it, and the mat is still in very good shape.

 

[illini]

platter ringing, for one thing

http://www.kabusa.com/whats.htm

Oct 2, 2009

I am seeing lots of discussion on platter mats and I wanted to clarify some things. First some observations on the '1200 platter and the raised outer edge. The outer edge is raised only slightly, about 0.008 inch. The purpose of this is to ensure that the rubber mat puts some pressure on the outside edge. If you take the platter off, hold it in by the magnet below and strike it, it will ring. The only way to stop the ringing effectively is to grab the outside edge, touching anywhere inside that perimiter, is not effective. I have never suggested that mats should fit inside this edge, on the contrary, mats should fit over and onto this edge. So far the best system I have seen is the SDS Isoplat Mat 295mm and the thin tecnnics stock mat. these 2 give good overall mat height and stop all ringing. Do not use mats that are under cut, and always remember that you need a fair amount of weight as well to control the resonance in this platter.

The concave shape also helps secure the lp to the table when using a record clamp or weight.

 

[12ax7]

I've noticed this on Dual mats also. It's use as a way to minimize ringing makes sense but I was concerned about a possible 'trampoline' effect (maybe needlessly), especially with a 'not quite heavy enough' weight. Does that make sense?

 

[jamus]

I guess my bubble level is more sensitive than I thought. It is good to know that there are no problems with the mat. Thank you very much.

 

[illini]

but I was concerned about a possible 'trampoline' effect (maybe needlessly), especially with a 'not quite heavy enough' weight. Does that make sense?

I've never heard of that, but I'm not some old hand expert. I know one or some of the VPI platters are/were slightly concave on the record side for the above purpose.

Even my "entry level" Technics p-mount tables have the aformentioned mat overhang and platter lip.

 

[Pio1980]

The later H-K belt drive TTs have a concave platter/mat with a provided weight that is quite effective for flattening moderately warped records.