Damping Platter With Liquid Latex

[Ldg]

Raw measurements look plausible, CS. Given that they are seperate platters, but the from same model Lenco, if I understand right. Except........where is the fundamental peak..........as a rule that is prominent, and it's conspicuously absent ?

You can see how complex, multi modal, and non-monotonic platter resonant behaviour is. This, and the absence of a prominent fundamental, can't lend itself well to basic log dec methods though.

I still don't believe the usefulness or transferability of those damping factor figures, of course. But as you posted, they are made your own way, that's entirely your prerogative, CS. And hey, presumably, you can now see at least some of the hazards to that method by looking at these latest results........there's far more going on than it can evaluate, let alone in a verifiable way.

[davidsrsb]

lead oxide is used in paint, and its lead acetate that is sweet.

Lead nitrate was used making chrome yellow and is soluble, as is the acetate. Both have a sweet taste. The nitrate is more likely in drinking water. Lead oxide is not very soluble.

The lead in petrol was tetra-ethyl lead. I remember seeing the heavily armoured road tankers coming into my town every week to supply the oil refineries back in the 70s

Basically metallic lead is safe enough so long as you keep it away from acids and don't eat it - solder paste with its very fine particles always struck me as dangerous

[wordwizard]

Interesting quest....

[cats squirrel]

Raw measurements look plausible, CS. Given that they are seperate platters, but the from same model Lenco, if I understand right. Except........where is the fundamental peak..........as a rule that is prominent, and it's conspicuously absent ?

thanks, different platters, same model. Agree the fundamental is usually the most prominent, and it is when I use an accelerometer. It is probably under the blue trace near the beginning, but it is there.

You can see how complex, multi modal, and non-monotonic platter resonant behaviour is. This, and the absence of a prominent fundamental, can't lend itself well to basic log dec methods though.

I have seen traces like this, sometimes there is a very well defined pattern to follow, sometimes not, and I would agree that in this case, it is not. But I didn't use log dec in this case, I used loss per second, which I have found to provide good agreement with log dec when I can measure both.

I still don't believe the usefulness or transferability of those damping factor figures, of course. But as you posted, they are made your own way, that's entirely your prerogative, CS. And hey, presumably, you can now see at least some of the hazards to that method by looking at these latest results........there's far more going on than it can evaluate, let alone in a verifiable way.

These traces are not typical of what I usually measure, they are usually easier to handle, the more the damping, the easier the trace. One great advantage of having loads of measurements from one source is that they should be consistent, even though the exact nature of the sample will (and does, sometimes) make a difference. And so does the frequency, which I know Rap has mentioned a few times.

[johngordon]

LD and Cats

Can you describe the profile of the platters? Both I know are of the one piece, supported on the bearing in the centre, type, as opposed to the Thorens split platter/ sub platter type.

And were they freely supported in the centre or upside down on a mat?

CS Can you do log scale, to see better the lower frequencies?

I'd love to contribute, but all my stuff, such as it is, is in Spain, and I'm in London.....

This all is reminiscent of the scientific search for the the holy grail in guitar soundboards, except in reverse...
John

[cats squirrel]

John,
the Lenco platter is essentially a flat disc, 3-4mm thick, at the edge is a 27mm deep rim, with a 7.5mm ridge machined in. When placed in the 75/8 Lenco, it makes the platter only look 10mm thick, not the whole 30mm at the rim. it is 314mm in diameter.

The log scan does not show much detail, as most of the ringing is above 1kHz, but it does show that the fundamental is present.

Placing the platter upside down on a mat is one thing, but what the mat is on will have a profound effect on the final result, as Rap will no doubt testify. My platter was 'simply suspended' by the bearing hole, as all my results are measured in a 'simply suspended' system, in free air. I believe 'simply suspended' is an accepted scientific term, implying without affecting the final result.

[Ldg]

..... I have seen traces like this, sometimes there is a very well defined pattern to follow, sometimes not, and I would agree that in this case, it is not. But I didn't use log dec in this case, I used loss per second, which I have found to provide good agreement with log dec when I can measure both.

Unsurprising as they are effectively the same method. But neither is much use here. Essentially, you are looking at envelope decay rate. Then manipulating using an assumed monotonic frequency to obtain 'damping factor'. But it is absolutely plain there are multiple resonant modes and frequencies in play. Each has its own decay rate, res f and damping factor then ! The single figure you obtain is, at best, just for one persistent mode, and is structure specific. My point is, your 'damping factor' obtained this way is not really useful or transferrable. And certainly not a material property, per se.

I really don't see a clear fundamental in your spectrum plot, BTW, CS. Looks like there's far more energy in higher harmonics. Sometimes this happens, it's structure specific. Violins do it, I'm told !

I agree there's not much point in examinng behaviour of the platter laying on a retained surface, because that really is not representative of use, and so difficult to isloate the effect of the retaining surface. The platter I measured is mostly a flat solid disc, thickness 3mm with a 10mm thickness at an outer rim band (with a width of 30mm), and overall diameter 310mm. Material is some type of Aluminium alloy I guess. Mass is near 1kg. As posted, I have a spare spindle, and for this test the spindle was mounted inertly, and for practical purposes the plot is for platter only, with a centre spindle suspension. As per normal play.

Common sense bears out the measurements, (or is it the other way round ?) that mats are a pretty effective way of damping platter resonances, on the whole.

[cats squirrel]

fundamentally I would agree with you. However, within software, it is possible to select frequency bands, and even single frequencies, and the waveform can become a lot easier to analyse. This is what I do more often than not now, and is why I quote the frequency or centre of a band. Of course, resonance frequencies are dependent on material properties and dimensions, so unless the materials are standard shapes and sizes, and frequencies are reported, a damping factor is more or less useless. I usually work on 100mm x 100mm samples.

This is a graph of some damping compounds I'm formulating, and it can be seen how damping factor is related to frequency.



I don't remember seeing any frequencies mentioned for any other damping factor measurements, even for 'standard' methods.

[Ldg]

However, within software, it is possible to select frequency bands, and even single frequencies, and the waveform can become a lot easier to analyse. This is what I do more often than not now........

And there lies one of the flaws. By doing that you force the analysis to be monotonic and single mode, because that's all it can handle. Whereas, in applications like this, one is generally interested in all modes/frequencies. Especially in a case as you posted where vibration energy is so widely distributed between many modes and frequencies.

This is a graph of some damping compounds I'm formulating, and it can be seen how damping factor is related to frequency.

No, that graph just shows artifacts of your method, it's not a material property you are measuring ! Loss factor, the material property, is generally not particularly frequency sensitive/selective. That's why you don't remember seeing any frequencies mentioned for any other damping factor measurements, even for 'standard' methods, CS !

It's obviously something you are passionate about, CS. But the basis for what you're attempting here is badly flawed, and readily produces meaningless results, which aren't transfrerrable, or verifiable. And by the look of things don't often accord with standard results. Unsurprisingly. The rhetoric may be appear pretty, but results based on it are not much general use. Anyways, there's plenty enough clues here to see some of the problems !

[johngordon]

As I understand it, loss factor, in our case, involves energy in, energy out, in a time frame. The point being to reduce the input to the cartridge as quickly as possible.

Is there another definition more appropriate?

So, how best to do that.

Eg as LD says re the Technics "This specific platter rings like a bell with no mat, and appears fairly inert with it."

Obviously, this is good.

Can we make other platters do the same without getting too involved with semantics and definitions of what is loss factor? There will be a way of reconciling data, but why not just use whatever experimental information we have, and go from there.

I mentioned testing upside down because the mat is a factor that does not affect the rim and its contribution to resonance. eg The Garrard 401 with and without o-rings irrespective of mat ( or other "rimmy" platter - I note that both the above platters are solid types with thick rims...

ie For a 320 diameter piece of material, or a 500 by 400 piece of material how dead can it get? Does it depend on shape? Material? Colour? (not joking...)

Comparing apples and oranges who cares? What is important is that we need to know about good oranges and bad apples... (well, some of us more than others...)

[Jim Leach]

I've been reading, but not commenting.

I'm changing that now.

I know a bit about this stuff. Not even enough to be dangerous, but enough related observations to contribute my 2 cents (which, in today's market is worth exactly nothing).

Anyway, I've been playing drums since age 6. I'm over 40 now (and bad at math) but I've been playing a long time. In that time frame, I have hit a fair number of cymbals (and crashed them together in marching and concert bands as well) so I have a reasonable idea of what this sounds like.

I have also spent time experimenting with various damping methods on cymbals to alter their sound and resonance time.

Here's my point: What I found is that although you can alter the resonance time, you also alter the mass and therefore alter the resonant frequency.

Background: Counter to what you might feel as intuitive, at the same diameter, thin cymbals have a lower fundamental tone, and thick cymbals have a higher fundamental tone. (same with drum heads- thin are low pitch and thick are high pitch) Also, thick cymbals are louder (project more) and thin ones are quieter. Response time (to impact) of the thin cymbals is faster, and thick ones slower (Newton et al)

Relevance: No frickin' idea. BUT (based on all that stuff), if you go with a heavy platter, you could well be moving fundamental resonance into the easily audible range. Too thin, and you could get into a resonant situation with the arm. Damp it (with mass) and you could also raise the fundamental, although you lessen the amplitude.

The relevance is based on and assumes the same exact material (like with the cymbals). So, if you alter the material (to alter the fundamental) and also alter the mass (to move the fundamental) you may be able to control resonance to a low enough amplitude to not be intrusive and perhaps also move it toward a frequency range where it is also less intrusive.

Then you come to combining materials. I have two materials in mind that I think would make an excellent combination. I chose one because the fundamental is relatively high, and the material is relatively 'lively' in common alloys (but I would use the pure element) and couple it (with an adhesive I have yet to select, as well as mechanically) to another that has a low fundamental and is relatively dead. I do not expect them to 'cancel' anything; however if I can get an amplitude low enough across a wide spectrum with minimal peaks, I think it would be a good choice. Neither 'dead' nor 'alive', as i feel either situation is less than ideal. Neutral is the goal.

We now return you to your regularly scheduled programming...

[Ldg]

That's interesting JL. When I was striking the undamped platter, the way tones develop reminds of a gong/cymbal somewhat. Cymbals are just fantastic in the way complex tone develops over seconds, as you know. One would be hard pressed to define what differentiates a great cymbal sound from a bad one mathematically, but you sure know when you hear it !

No doubt you'll also know what you have to do to tape down heads and kill specific prominent resonances in toms/snares etc. It's not always intuitive, and a bit of an art really. But then, one is not trying to completely kill the natural drum sound.

Same is likely true in classic platters like the 401. After all, the character of the TT exists in such things, and one wouldn't want to kill it dead in the case of a classic, methinks. If there are 'ugly' rim resonances, such things probably respond to a rim band, if a mat doesn't do it. More things point to CL's rim band being damping oriented, i think.

[Jim Leach]

I gave up long ago trying to damp cymbals or heads. It's always just 'wrong' sounding.

Bass drums are a particular challenge, especially considering the sound I prefer- which is percussive in the attack, but the fundamental tone is not totally killed... I get the attack, and a nice, resonant tone that is quite low (recording engineers are not so keen on it however... ) If I 'bury' the beater in the head, it is 99% attack and 1% resonance, and if I bounce the beater off the head, I get a nice tone maybe 25% attack 75% resonance). So, with one bass drum I can accommodate many styles of music with my style of playing the drum.

It is tricky to get the way I like it, but that's 'my' sound.

Drums are Yamaha Recording Customs (the old birch ones) so they are easy to tune almost any way you could want them to sound.

As to cymbals, I just spend a LOT of time picking them out... I still have the first crash cymbal I ever bought, and rarely add anything. I prefer the Zildjians because they have the most complex sound out there. My china-type is a Wu-Han for the same reason. The Zildjian china types just don't quite get it...

[wordwizard]

When I was striking the undamped platter, the way tones develop reminds of a gong/cymbal somewhat.

Just one observation:

If testing with different dampening materials, you should develop a method to consistently deliver the same striking force at the same place in the platter.

That would remove one variable from your equations.