What is the best material to use as a substrate for making Isolation plinths/platforms, for damping the excitation of parasitic modes of vibration as well as HF resonance? That looks cosmetically appealing as well?
Well jollygreenaudiophile, I'm not sure if this is what you mean, but I've had great results with Soundcoat adhesive sheets. I have it stuck on all my electronic chassis's as well as on the top & bottom of the upper platform (which the TT sits on) of my rack. You can get it at parts connexion. Hope that helps.
It works great on the 1/2" steel plate platform my TT sits on. It's now the best of both worlds, ridged & dampened. There was less of an improvement (though a good improvement nonetheless) with the electronic chassis's. It's pretty cheap, around $12 a square foot
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. 😛
So Jeff, your saying you believe in "Sympathetic Vibration" and "Compassionate Resonance"? I'm unsure about the resonance and have found no way as of yet to prove anything positive about those vibrations. Clue me in. As far as the Sorbothane goes you may have used too much in mass of the wrong durometer. I've also had problems with it not loading to spec. Besides that, It smells funny.
And yeah I've been experimenting with the constrained layer damping since before it was given that monicker I believe. It's one piece of the puzzle. No more, No less. I quit solving for "X" as an absolute a long time ago. Everything has it's place up to a point.
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. 😬
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?
I've found using differing materials in cascading layers "For different Freqs" I start at about 10k and work down. It more easily defines problem area's by isolating migratory vibration but there are still area's of regeneration. I think fields are interacting and may be performing as a type of wave generator. Juries still out on that one. Coincidental entrapment seems to work very well though. You simply have to make the law of averages work for you by trimming the variables with the cascading layers actively as well as passively damping plus transduction "several types". To the point where the deck is basically stacked in your favor. Have you ever tryed introducing disruptive pulse voltages at very low freqs'? This seems to help with sensing also below 6 htz.
Um, ok. I do believe you are correct Sir. But that's not the use of the verb in the context in which it was meant. At least it fits my thoughts on the matter much better than - "Complimentary Vibration" which is as nonsensical to me as it is indeed logical. The misnomers abide me not well tonight.
Jeff, the entire Shun Mook "thing" is beyond me. I've never been one to cry "shenanigan's" to what another swears by because I've experienced too many as of yet, unresolved occurences myself. Yet if it was truly that much an epiphany, would not they at least be available with an money back guarantee? Are we sure "Shun Mook" isn't Swahili for 'Purveyor of fine snake oils? Hmmm. shall I alert the "shenanigan's" armed response unit/ bobsled team?! And why aren't we all growing Mpingo tree's in our basements under immense high pressure sodium lighting as an erstwhile yet felonious endeavor?
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.
Ok, If you can tell me these things dont have a half-life of 3 months I'll probably bite. So whatever this is works in conjunction with a variable density medium, is very small, and passive, hmm. Battery operated? Very small field generator? So Shun Mook 'IS" from the 9th dimension which evolves through the center "Torus" per string theory! Ok where do I pick mine up? Or do they simply appear, but only for us whom are enlightened? Is there a currency exchange involved? I still believe in the barter system. Here, hold this duck whist I.......... But seriously folks, Can I buy used? Scratch and dent clearance?
As Acoustic engineer my advice is first to determine what frequency range you want to dampen (for example 20Hz -100Hz) and then find a material that is suitable. I know that sounds trivial but most people just start throwing names before even analyzing the problem. To find the suitable material I would check the transmissibility curves of different materials. A transmissibility graph is basically an input/output graph; everything above "1" means that you get amplification and below "1" means damping. Obviously you don’t want any resonance peaks in the region that you want to improve, otherwise you can end up making things worse. By comparing the graphs of different materials you can select the one that provides the most damping in the frequency region of interest. Those transmissibility measurements are really basic and any serious company should be able to provide you with those graphs. If they don’t I would question their seriousness.
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.
Ha ha ha, I mean't negative in the context of ; " That cannot, will not work nor have any realized effect at all because it's not in the book and teacher has not mentioned it." Old saying; Those whom cannot do, teach.
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.