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In Reply to: only one of us is wrong posted by Mark Kelly on December 17, 2005 at 17:33:45:
Mark,
But then there is a time factor, plus the mass or thickness of the acrylic platter. I guess I'm wondering how much resonance an acrylic platter can absorb or hold and the time factor before it bounces back into the vinyl. I'd much rather have the resonance going into a 1-2" thick acrylic platter than staying in the vinyl raising merry Ned with stylus/cantilever.
Henry
Follow Ups:
The models assume elastic materials on both sides of the interface. In the real world there is some loss, and the standing waves (what you call resonance) increase until the loss balances the input. Expanding the model to include this viscous loss makes the whole thing much more complex.Basically viscous loss is velocity dependent and, for a given displacement, velocity is proportional to frequency so the viscous loss increases with frequency. That's all very well and good but this frequency dependent lossiness also reduces the ability of the material to transmit vibration at the higher frequencies therefore the platter is acting as a non-linear filter. This partialy explains the common observation that application of lots of damping material makes for mushy and indistinct sound.
Mark, with trying to model the interactions of materials being "much more complex" is platter and mat research mostly trial and error testing of various materials and thicknesses? Not necessarily a bad approach; some of mankinds (and certainly vinyl addicts!) most significant discoveries have been found that way.And, like solid state vs tubes vs hybrids, where there probably isn't a "best" solution since people have different tastes in sound, are there generalizations about the type of sound you get depending on the platter and mat (and even cartridge) combinations?
Henry, I'm still getting things figured out with the whole system so haven't tried platter/mat combinations yet. But I'm paying attention to your discussions (and research!) on this topic.
Hmmm. That explains some things. I'm using an Iron Audio acrylic platter mat atop the acrylic platter on my MMF-7. The mat is about 2-3 mm thick with what Iron Audio calls "acoustic coupling compound" on the underside. It feels kinda like Sorbothane, but is only tacky, not sticky, to the touch. It is only about 1 mm thick.
Henry
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