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Re: plinthing with ply

Posted by Fred J (A) on June 15, 2005 at 02:28:44

In Reply to: plinthing with ply posted by J.D. on June 14, 2005 at 21:36:13:

JD
As Mosin indicated this stuff is anything but all worked out, which I found over a a great deal of digging, Googling and researching various sites and discussing the engineering theories with a number of experts and experienced plinth builders.

I have read a number of brilliantly written and very compelling explanations and articles written by folks with extensive engineering backrounds explaining their understanding of the theories of plinth construction and how it relates to controlling damping and altering resonances, the problem is that many of these writings directly contradict each other to one degree or another.

Some of this stuff seems as if some of us seemingly confuse Loudspeaker cabinet or even Violin construction design aspects with plinth design.

Some aspects are obvious as you don't want an absolutely dead 700 lb. lead plinth or a very light highly resonant plastic plith either.

And you'll see the same situation in the engineering involved in
various commercial turntables, some very highly regarded tables tout
construction with a layer or layers of Sorbothane between the layers of MDF, both the use of Sorbothane and MDF as an exclusive material
in plinths is generally considered verbotten in most prevalent schools of thought, and any number of other approaches that are counter to prevailing thought on the subject.

The main benefit of the heavy dense constrained damped plinth is IMHO taming the torque impulses and inherent resonances of the reletivly large powerful motors used in Rim and Platter drives, in the words of Jean Nantais "The motor wants to move the table" ( I'm paraphrasing here)
and as these reletively large and very powerful motors are attatched to directly the top plate and not isolated by a belt,this would seem to be a very serioysly critical aspect.
Those powerful motors and their respective drive rim or platter drive systems are what give these tables their amazing speed stability, over coming the changes in pitch inherent in most belt drive tables which to one degree or another allow for some degree of stylus drag, degrading their PRAT and ultimatly musicality to whatever degree. This is easily demonstrated with a Hunt or even AQ brush, just put a little too much pressure on the brush and the reduction in platter speed is obvious in most belt drives
with a Lenco or Rek O Kut (the tables I have experience with) tables
are unaffected, these effects become glaringly apparent when use various tables as RCM's.

The bottom line is by building a heavy Birch Plywood or Birch Ply/MDF layered plinth is highly beneficial to the sonic performance
or Rim and Platter drive tables.

I'm kind of hedging my bets by bolting my plinth's together rather than gluing, so at some point when I and if get the urge I can substitute layers of different materials and see if I can percieve the differences (if any), or if the missing variables or whatever become Known I can incorporate the changes to make my plinths optimum.

My advice would be to just go ahead and build yourself one now based on whatever your common sense, preferences or gut feelings tell you is best, rather than waiting while attempting to determine the correct approach as you're quite likely going to end up waiting until you're too old to actually build a plinth, another bit of Jean Nantais wisdom is that this stuff is supposed to be fun, and I couldn't agree more,if it's not fun, then what's the point ?

The differences (if they even are perceptable) are VERY subtle
to say the least, but the differences with a heavy plinth with a machine like your 301 are anything but subtle.

Regards FredJ

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