Idler Drive Plinth Question

[KenCalgary]

I hope, soon, to build a new plinth for a Lenco idler drive turntable I've just purchased, and noticed that many people strive for a heavy, dense plinth to handle the power of these idler drive motors. Plinths weighing in the order of 75-100 lbs. are claimed to be superior to lesser weighted options.

I will be placing my turntable on the heavy, black walnut butcher block shelf of my equipment rack, so I was wondering if I could aim at a less heavy plinth and obtain similar results. That is, would coupling - using spikes - a 50 lb. (for example) plinth to a 25 lb. dense wood shelf be as effective in damping motor vibrations as creating a 75 lb. plinth?

[cats squirrel]

Hi Ken,
contrary to most audiophiles' conceptions, mass does not damp, per se. Materials with good damping factors damp. Mass can increase losses in a plinth, but the resonance peaks (fundamental and harmonics) will have very high, sharp peaks if the material has little damping qualities. Most materials don't damp well, many don't damp at all (metals, stone, most wood) so having a decent mass without damping is rather missing the point.
I have several Lenco's, and don't run heavy plinths with any of them, and they 'handle' the motors very well indeed.
Have a look on my web site for ideas of what could be used to best (sound) effect.

[J.D.]

Ken,

On the opposite side of the semantics coin, it's not only about Materials and their properties. CS and I have had disagreements about this in the past, but what I'd like to forward as an example is this:

Certainly one of the worst materials for intrinsic Buoyancy in Water is Steel. Many other materials float-- much better than steel. And yet we don't see large oceangoing craft manufactured from balsa wood or styrofoam. Generally they're made of steel.

Turntable building and design philosophy is not a problem that is solved by looking up a material on a chart or list and declaring victory. Materials in combination with other materials, or even in combinations with themselves-- ie, layered materials, say-- behave differently in combination than what the chart says about their intrinsic properties.

Counterintuitively ---steel floats, in an appropriately designed project.

What I expect the attraction for CS may be in the charts and lists is the potential for finding a position that is contrary to the accepted methods, and thereby standing apart from the crowd.

And yet. If you did your shipbuilding project from a Buoyancy Chart Of Materials, you'd end up designing your QEII from balsa or styro.

Bon Voyage.

[Eoin]

I would point out that cats has done some experimental measurements on various materials. While that'll never tell you the whole picture on the sounds it may at least help make an informed choice.

Slate while not good in theory seems to be having some sucess amongst DIY plinth builders.

[cats squirrel]

Ken,

On the opposite side of the semantics coin, it's not only about Materials and their properties. CS and I have had disagreements about this in the past, but what I'd like to forward as an example is this:

Certainly one of the worst materials for intrinsic Buoyancy in Water is Steel. Many other materials float-- much better than steel. And yet we don't see large oceangoing craft manufactured from balsa wood or styrofoam. Generally they're made of steel.

So steel floats, does it? No, it doesn't, just looking at its density (a material property) will tell you that. It doesn't take a rocket scientist to understand it's the enclosed air that is giving the buoyancy (from one who has actually worked on steel boats).

Turntable building and design philosophy is not a problem that is solved by looking up a material on a chart or list and declaring victory.

well, may be not, but it is a far better starting point than the usual 'suck it and see' approach.

Materials in combination with other materials, or even in combinations with themselves-- ie, layered materials, say-- behave differently in combination than what the chart says about their intrinsic properties.

so you have changed the material, and wonder that it's different. Thankfully, modelling of layers of materials will provide the answers, saving years of kit bashing in the shed/garage.

Counterintuitively ---steel floats, in an appropriately designed project.

intuitively, steel does not float, fresh air encased in steel floats!

What I expect the attraction for CS may be in the charts and lists is the potential for finding a position that is contrary to the accepted methods, and thereby standing apart from the crowd.

The attraction, if you want to call it that, for CS is that he wanted to show that all the rubbish talked about this or that material was just that, rubbish. And he showed this by measurement, backed up by real life builds, by himself and others who believed in the priciples, and there are many builds.

And yet. If you did your shipbuilding project from a Buoyancy Chart Of Materials, you'd end up designing your QEII from balsa or styro.

or fresh air clad in steel.

[cats squirrel]

I would point out that cats has done some experimental measurements on various materials. While that'll never tell you the whole picture on the sounds it may at least help make an informed choice.

exactly, Eoin.

Slate while not good in theory seems to be having some success amongst DIY plinth builders.

But who says they are good? the plinth builders! If you compare slate with wood, even I could probably tell that the wood was adding more of its own sound signature, but whether the slate plinth was giving a true representation of the recorded sound is debatable.

[mosin]

The key word in this thread seems to be damping.
Here are four others for consideration: isolation, redirection, transformation and rigidity.


Win

[J.D.]

" ...he wanted to show that all the rubbish talked about this or that material was just that, rubbish. And he showed this by measurement, backed up by real life builds, by himself and others who believed in the priciples, and there are many builds.... "

Wow, sounding like a religious text. "And he said unto them, behold, panzerholz .."
Himself and His Believers are too funny.

[cats squirrel]

The key word in this thread seems to be damping.
Here are four others for consideration: isolation, redirection, transformation and rigidity.


Win

Hi Win,
isolation from what? Aerial and seismic intrusions. But if the plinth is not damped, how are the vibrations going to be dealt with?
redirection ??????
transformation?? do you mean the vibrations are transformed into heat?? (Some is re-radiated as sound).
rigidity, yes, also called stiffness, or Young's modulus, necessary to cope with low notes, if they exist in a plinth/turntable.

The main considerations are stiffness, mass and damping, but without damping, vibration peak amplitudes will be high and sharp, whereas with materials with intrinsic damping, the peaks are low and much less of a problem.

JD you started with the third person stuff, very rude!!

[Anyway, Ken is continuing by PM.]

[cats squirrel]

I thought some may be interested in this plot, it's of a few FFT scans of materials used in plinth building. The position of each scan is arbitrary, it's just to give an idea of the difference in frequency response of slate, carbon fibre and panzerholz. I leave it up to fellow music lovers to draw their own conclusions.
[all samples tested in exactly the same way].


although slate and CF are stiffer, maybe it's the damping which makes the difference

[vincitsemper]

Hello,

A body immersed in a liquid receives a vertical upward thrust equal to the weight of the liquid it displaces. Or something like that!

Unless of course Cats damps the body!

Regards,

Victor.

[cats squirrel]

if the liquid is water, it is already damp .......
[hi Vincint]

[vincitsemper]

Hello Cats,

Just add cat litter in that case.

How are you my friend? Hope the fresh air and calm surroundings are of your liking.

Regards,

Victor.

[J.D.]

One aspect that isn't being noted here is that thorough manufacturers did their homework and 'voiced' their tables, generally on plinths of wood. Changing that is fine, anyone's call, but : going to an overdamping extreme just isn't going to be the likely winning approach. All is not lost, however. One look at the graph tells me that I should be designing my oceangoing ships in pure virgin Panzerholz. Not turntables though.

Lovely graph and all, but panzerholz would make sense only for turntables that are as loud and rumbly as Tractors. Consider the radical-rethink Stradivaricats Violin, refitted for uber-damping with an all-panzerholz resonant body; tone and timbre that you can cut with a fork and knife.

I guarantee anyone with an already well-functioning turntable that a luxurious panzerholz plinth will afford you hour upon hour of dense, lifeless, pace-free music.

And lucky us, the Clichéd-Analogy shop just in with this timely item:
Super-overdamping a turntable is like having your martini fitted with a sizeable sponge in the bottom of the cocktail glass. You get the one dense, mealy olive, served up proudly on a puffy bed of mushy muck.
Cheers.