Damping to exitation of parasitic modes of

There is quite a wide variation in the sound of viscoelastic materials commonly or uncommonly used in constrained layer damping applications, which the OP sort of hints at when he mentions substrate. Without really addressing which material is best for this application, notice the OP begs the question why not address vibration isolation first? Then the whole question of which substrate material to use will kind of fade away into the background, you know, since the turntable plinth will not be subjected to vibrations that excite it’s natural frequencies, that are generally in the region 10 Hz to 15 Hz. I.e., seismic vibrations. Once you have an isolation design then all you really need is a stiff and light plinth. So what about acoustic waves, you ask? Since they don't contain frequencies low enough to excite the natural frequencies of the turntable you can ignore them.

 
jollygreenaudiophile2 OP
I Have never heard anything negative about Shun Mook, so there "should" be something to it. At least I hope so if he's getting my ducky!

I hate to be so judgemental but if you've never heard anything negative about Shun Mook you probably haven't been paying attention. 😀

I kind of doubt any manufacturer provides transmissibility curves for either damping materials or for components. Vibration Isolation manufacturers sometimes provide transmissibility curves, but only for structureborne vibration, including vibration below 20 Hz, which is significant because below 20 Hz is not only below the standard audio band of 20 Hz to 20 kHz but also because the spectrum below 20 Hz is very detrimental to the sound and by and large not addressable by damping techniques per se. Finally transmissibility curves probably do not apply to induced vibration such as that produced by Transformers, capacitors, motors, CD transports, etc.

There is something inside a Shun Mook Mpingo disc which makes it even more difficult to wrap one's mind around. There’s a small circular discoloration in the wood where someone obviously drilled out a hole on one side of the disc and inserted this thing, then covered it up with a circular insert. You can hardly tell it’s there. The Moingo discs are directional, both top to bottom and as you turn the disc around. That’s why one side has some Chinese character engraved in it, so that’s the side that’s facing down. I’ve knocked off more Moingo discs than the average bear and know how to mark them for direction. Call it a skill.

Speaking of vibration and damping has anyone tried damping the dust cap on the woofers of speakers. Well, first I should ask has anyone run a test tone through the speakers at around 200 Hz or so to hear just much much those bullies distort and ring?

If you don’t have any Shun Mook Mpingo discs in the system you’re really missing out. You have my sympathy. Even one Mpingo disc in the room, properly placed, will cause your jaw to hit the floor. Your wife will call out from the kitchen, "Honey, what did you do to the system?" Finding that precise location, as fate would have it, is what drives audiophiles to the brink of, well, the brink of something. Of course, resonance control is my middle name and I have many resonance control products, including a rather largish constrained layer damper. The specific material I use for the viscoelastic layer is, however, proprietary. If I told you I’d have to kill you. 😬

Give my sympathy to your liver, Joyboy.

For micro vibrations best to use constrained layer damping as well as very hard cones that will allow such unpleasantries to escape the system. I also am a fan of natural cork for damping and isolating printed circuit boards, capacitors, those pesky large transformers and gulp, fuses/fuse holders. Sorbothane not so much. I've had trouble with the sound degrading. 😛