Philosophy of design

[Andy]

The sandwich arrangement would certainly go some way to explaining the relative success of the ply plinth. I built a prototype (for a belt drive) a couple of years back, using a polyurethane adhesive which didn't fully harden (it ended up a bit like expanding foam). Another idea I tried on this particular plinth was to screw the layers together with approximately 50 screws per layer, equally spaced between each individual layer, the screws not being long enough to connect more than two layers. The idea was to create a labyrinth of sorts, to drain energy into the lower layers. I can't say for certain if it was a success in comparison to others but it did produce a very quiet turntable with regard to motor and bearing noise. If anything, it sounded accurate yet polite which could well be an indication of low distortion.

I'll re-visit the idea one day.

Andy.....

[haydn]

sandwiches of disparate materials are very interesting. Two materials, on their own, having poor damping qualities, once combined (and glued together) can provide excellent damping figures. I have tested a few of these composites, and get consistently good results. I don't know the reason for this, at the moment, but it will be complex, I have no doubt.

So we're back to talking CLD Bryan?

[Bryan]

So we're back to talking CLD Bryan?

don't think so, h, CLD is quite specific (to me at least). The mode of action of the composites may have something in common with CLD, but I doubt it. After all, there is usually no viscoelastic layer in composites, just glue, although talking to people (not on this forum) the type of glue is very important.

I'm sure CLD has its place, but its usually to damp a panel thats already vibrating. What we need in a plinth (IMHO) is a material (or a composite of materials) which have intrinsic damping qualities that damp the vibrations before they cause problems.

Just for the record, and so that we understand each other, CLD is an application where a viscoelastic layer is contrained by a stiff layer, in a ABC configuration, where A is the panel to be damped, B is the viscoelastic layer, and C the constraining layer. Sometimes, A and C are made of the same material, rarely the same thickness. CLD is not plywood (or any variations of any wood) stuck together, these are called glulams, or glued laminates. Nor are screws involved, although fasteners are possible in true CLD designs. So are stand offs and strip panels, but that is for another day.

I would guess that composites have something to do with a mismatch in acoustic impedance, but accepting that the different layers are glued together, thus maximising contact, and therefore bending/damping. Common to the things I've measured to be good is that the different materials have very different properties, one hard, the other soft. I was looking at how a shellac disc behaves when put onto a platter mat. On its own, a shellac disc has a damping factor of ~0.014, very poor, and the platter mat I was using (a place mat from Ikea) I measured at 0.062, just below the level at which damping begins. But put the shellac on the mat and I measured a value of 0.28, a respectable value for damping. A vinyl record showed similar, although less dramatic differences, but when I put a mass on the record, it decreased in damping value. Lots more work to do, I think.

[Andy]

I quite agree that CLD is a misnomer in our application but rightly or wrongly (ok, wrongly), this goes back to the early days of the Audiogon thread. The legacy is that most of the people who have read that, have adopted the term to describe a multi-layer plinth. In some respects, a typical ply plinth will act in a similar manner up to a point but as you say, the glue used would have a huge contribution.

In a composite material, the resonant frequencies of the individual materials would have a huge part in the combination's success or failure. It would certainly be pointless if the layers could excite each other. One key to success would be to use materials which would naturally damp each other. RFs which differ vastly should work well together, assuming you can avoid any harmonic interference. Perhaps this is where the whole is less than the sum of it's parts, in resonance terms at least.

We need to be careful with absolute damping however, as the desirable attribute of rigidity could easily be lost. If one were to choose materials based mainly on their (self) damping properties, wouldn't this tend to move away from ultimate rigidity? As a complete unit, this problem may not be immediately apparent but on a micro level, it's sure to have an influence.

I suppose the path to Nirvana was only ever going to be a tricky one. The fact we have to travel in opposite directions at the same time only makes it harder .

Andy.....

[Steve]

I found a plain stack of birch plywood, fastened sequentially with screws (~50), and with three hefty lead feet (also screwed) killed virtually all the motor noise.  I have a Decca cartridge on it now, this is very unforgiving of spurious noise...still nothing.  The armboard does not touch the top most layer of the stack, only the layer directly underneath.  My conclusion from this is that to effectively dissipate the motor noise, one only need screw the deck to something rather heavy.  I originally planned to experiment with different materials between layers, the screws were meant to be temporary.  But after getting it up and running, I was very pleased to find it works perfectly well as it is.

All this is quite aside from the issues regarding tonality.  Killing the noise is but one part of the design task, right?  A Les Paul has a maple cap on a mahogany body for reasons of tonality.  Solid maple gave it too much sustain, solid mahogany made it too dark in tone...A Fender, with its swamp ash, or alder body and bolt on neck has its own sound, entirely.  A similar set of parameters are in play in a plinth's design.  Toward a different end, of course.  In any case it is this question of tonality that really needs to be pursued empirically.  

Don't forget Goedel's Proof: first you must make some basic assumptions which can not be proven, only then is it possible to construct a system of logic.  There is mystery, even within the numbers.

[daiwok]

ok a change of view......... forums are great read and great for discussion but the real proof is in the pudding  

I travel a bit as part of my work and I try to take a few days or fews hours off from work when I am moving around to visit people here from LH. Seeing and meeting people in real life is the most enjoyable part of my travels and I have to admit I have met some of the nicest people here. The friendliness, the kindness shown is beyond words sometimes and yet we are really strangers in the real world.

May I say a big thanks to all of them !  

The gesture is also returned here locally as I open up my home to many people past by or make a stop over here in Hong Kong.

ok the cheesy bits are over now  

I like to hear peoples systems, see their Lenco and discuss our love of music and hi fi. The system becomes second nature to everything - its not about who has the best, but how we can improve, enjoy more and learn from this crazy hobby.

So Bryan, if you have all the boxes ticked may I visit you one day ?  

I am a practical type of guy and I believe that hearing is believing so I like to be involved in hearing what you are talking about ........

"Tell Me and I Will Forget; Show Me and I May Remember; Involve Me and I Will Understand."

Confucius 450BC .......

yeah yeah its real old stuff  

BTW there are many roads to Rome  

[wmax]

Just for the record, and so that we understand each other, CLD is an application where a viscoelastic layer is contrained by a stiff layer, in a ABC configuration, where A is the panel to be damped, B is the viscoelastic layer, and C the constraining layer. Sometimes, A and C are made of the same material, rarely the same thickness.

Thanks for this comprehensive and really understandable definition of CLD!
I´ve read about CLD a few times on this and other forums, and already knew that most of time CLD was a misnomer and had to involve some visco-elastic layer, but I´ve never read a clear definition as yours.
The only thing I still can´t get my head around (I don´t have any special scientific/engineering background) is what exactly a visco-elastic material would be. To me something viscous would be something more or less fluid and something elastic would be something that returns to its original shape after deformation (e.g. a rubber band), but what material combines these properties to be used in a CLD? Probably you can shed some light on this for me, Bryan?

[Steve]

Philosophy of Design:  I love the heading, it's an interesting subject, and is what originally drew me to this forum.   As a design philosophy regarding record players, I would argue that sucess should be judged by how the finished deck sounds.  This means attaining minimal noise, but also includes somewhat less tangible attributes of its tone.  To a large degree this is set by the choice of using a Lenco, but many other factors are also at work.  Here the food and wine analogies are good qualifiers, but to quantify...this becomes a little more tricky.

A couple of examples that come to mind:
In the case of a Decca cartridge, the pathetic looking plastic bits are deceiving, I could hardly believe how good it sounds.  Maybe this could be partially quantified with an accelerometer somehow, but there's more to it than just its superior dynamics.

Or take the famous case of the Stradivarious.  If you google "what makes a stradivarious?" the difficulty in quantifiying their special tone is clear. There are complex interactions involved.  Measurements certainly are important, but sometimes it's hard to know which ones count the most.

So how to evaluate?  If I find myself pretending to conduct the orchestra, then it's keeper.  When science can explain why a Picasso costs so much, then we'll know for sure.

Next time around, I think I'll to try the alternating layer approach. I don't think I can get too much lower on the noise floor than the first one though.  I have basswood and mahogany waiting in the basement.

BTW if you google "CLD" one of the first things that comes up is Chronic Lung Disease, constrained layer dampening is way down the list.  Apparently those letters can have various meanings...

[haydn]

Thanks for this comprehensive and really understandable definition of CLD!.....
The only thing I still can´t get my head around (I don´t have any special scientific/engineering background) is what exactly a visco-elastic material would be. To me something viscous would be something more or less fluid and something elastic would be something that returns to its original shape after deformation (e.g. a rubber band), but what material combines these properties to be used in a CLD?

wmax, on my research travels, I recalled reading ages ago a number of short articles on viscoelastic damping using adhesive materials and I've managed to find the links. There's quite a good explanation of what they are on about on using a visoeleastic layer betweeen two sheets of metal on this this URL -
http://www.roush.com/LinkClick.aspx?fileticket=oaGb3PTGBwA%3d&tabid=212&mid=920
but the main Roush site also has a number of other published articles - URL http://www.roush.com/Downloads/Published_Articles.aspx,  some of which give some further insights into this subject.

h

[haydn]

Common to the things I've measured to be good is that the different materials have very different properties, one hard, the other soft.... Lots more work to do, I think.

Bryan, in your research and testing of materials, have you looked at the use of materials (probably metals but other materials could also work) containing some form of containerised nano-particles - such as titanium 'dust' or non-metalic materials, such as perlite or tiny polystyrene balls - as damping materials? I've read a number of Japanese (backed up, more lately by Chinese and Indian researchers) published articles that show when the particles are no more than 10% of the volume of the container, it's especially good at damping. I did consider using this technique but decided on using the Delrin purely to see what it could do.

h

[Bryan]

David,

I haven't completed a three tick box (TTB) plinth (yet, there is one in the design stage), but I continue with Darwin, which continues to evolve. You are always welcome, but I would put off a visit until I move to Devon, and finished my whole system building (or several systems!). The TTB will be done shortly, and it is not beyond a possibility for me to send you an example, if you have a L75 to put on top. There is provision for other arms, on and off the deck, but a listen in your own system will tell you more than listening to it in mine.

haydn,

I haven't tried any of your suggestions, I wanted to try tungsten trioxide, but that is no longer available on eBay. Strangely, the characteristics required of the filler are not to do with damping, its far more complex than that, I would guess. One thing I must confess is my inabiity to guess whether a material has good damping properties, or not. I have been amazed at some materials, and very disappointed in others. C'est la vie.  

wmax,

I think a good example of a viscoelastic material is magic (sometimes called smart) putty. It flows slowly, breaks if pulled quickly, but bounces if rolled into a ball. It hasn't a large damping factor on its own (0.134) but it is used to good effect in a cld type environment.

[glady86]

David,

I haven't completed a three tick box (TTB) plinth (yet, there is one in the design stage), but I continue with Darwin, which continues to evolve. You are always welcome, but I would put off a visit until I move to Devon, and finished my whole system building (or several systems!). The TTB will be done shortly, and it is not beyond a possibility for me to send you an example, if you have a L75 to put on top. There is provision for other arms, on and off the deck, but a listen in your own system will tell you more than listening to it in mine.





 

  Now this will be interesting,a scientifically correct plinth design vs. a flavour of the week or month plinth material.I look forward to this and hope your plinth design sounds better than slate,if it does then maybe you show us how to do it?  

[Bryan]

always a possibility, our Glad,

[Sk8Ter]

here is an interesting article on the  Philosophy of design

http://www.enjoythemusic.com/magazine/manufacture/0208/index.html

[pedcab]

Man, this post reminds me of the few times I saw my parents argue. They didn't argue a lot and we still are a happy family, but when I see a happy family throwing arguments arround it makes me embarassed, and sad...