WPC,
Very helpful information. Scary to think that the LPs are warping in their sleeves for reasons other than gravity/heat(!)
Given your level of insight, perhaps you are the man to ask about MRA? Any idea why there appear to be such severe differences in different samples of 180g vinyl? Some appear to exude very little and can be played "straight out of the bag" while some are real stinkers and are more akin to trying to plow a field :(
Is it just bad chemistry?? ;^)
Cheers, |
06-02-15: Lowrider57
The record labels and the pressing plants all say that demand is so high for manufacturing vinyl that their orders are backed up. There was a thread on Steve Hoffman, I believe, where somebody stated that the cooling stage had been shortened as one way to speed up the process. I'm sure there are other areas where vinyl production specs don't measure up to the original days of record cutting. Especially quality control as previously mentioned. Lowrider, I am certain your are correct. Bad manufacturing practices just make all the problems I have discussed even worse.
06-03-15: Moonglum
Given your level of insight, perhaps you are the man to ask about MRA?
I am not familiar with MRA's quality issues but what you describe (if I had to guess) is probably more related to bad practices. |
Let's face the truth, you will find always AND everywhere expanations why this or that is the way it is... forget it. You can sum it up in one sentence today:
No clue from anything.
When the plants closed in the 90's all the know how was gone, too. Those who knew something lost their job, retired or looked for a different work. With the comeback of vinyl everyone was hired who was able to recognize a record two out of three tries. |
So WPC is it safe to assume that a heavier 180g record will potentially warp more than a 120g due to there simply being more material which could pull in multiple directions ? |
Not necessarily. There are many variables involved. The wider wall stock will reduce the pressures required to make the puck which can result in lower internal stresses so it helps in that regard but the more plastic the more shrink which as you state could make things worse. I have no direct experience with how these to countervailing influences effect records.
Complex finite analysis models are used to predict these things but they are only so accurate. There is no substitute for prototyping the mold and making actual parts to get the best result. |
Lowrider57: Your post was my impression. I felt that quite a lot of the warps were due to taking the lp off the press too soon. Your post is a similar finding. |
A 180g record, while offering no advantages (except marketing, perhaps) requires more time to cool down. Failure to allow sufficient time for cooling down seems to be a major cause of warping.
Actually, if most of your records are 120g or so, 180g records are a disadvantage for some who are scrupulous about their SRA. More adjustment. |
Does any one recognize the fact that the SRA is always changing as you play a warped record?
On a true high end turntable one can hear warps very easily, there is a change in sound (SRA) as it rides up then down and compresses the stylus, it is acting as a suspension system.
Take the warp away and the cartridge WILL track to groove very much more effectively is simple physics.
Let the stylus read the groove and any cartridge can perform a lot better.
This is more and more prevalent with heavier cartridge down forces... |
TTW, it's not just the movement of the suspension system that causes a change in SRA when playing a warped record. Even if the suspension didn't move at all, SRA would change as a cart tracked a warped record since the record surface is not horizontal as with a flat record, but angled one way as the cartridge goes up the hill and angled the other way as the cartridge goes down the hill. The tonearm angle also changes when going up the hill and down the hill which adds more changes in SRA. So, all three things add up and change SRA when tracking warps: The angle of the record surface, the angle of the tonearm, and the angle of the stylus as the suspension deals with the warps (there is more force on the styles/suspension when going up the hill and less force on the stylus/suspension when going down the hill). |
...Not to mention dynamic changes in VTF as it rides the warp (depending on the arm) ;^)
Funny thing is, although we can easily detect small, consistent changes of VTA, our ears seem to ignore them more when dealing with warped discs...
(Or perhaps it's just subconscious "denial" ;^) |
Moonglum,
Your "dynamic changes in VTF" are what TTW and I referred to as suspension movement... I think! Maybe you're talking about something different, such as the platter slowing down as the stylus goes up the hill due to an increase in friction between the stylus and the LP due to an apparent increase in tracking force and the platter speeding up as the stylus goes down the hill due to a decrease in friction due to a reduction in apparent tracking force. I don't know what you meant, I'm just thinking of other ways that warps can mess up the sound. |
Dear Ketchup,
Although I'm not a mechanical engineer it's an effect that relates to the mechanics of the tonearm design and the position/height of the pivot relative to the stylus? An analogy I use to help me guess which way the force increases is what happens when a tonearm is balanced.
If you balance the arm then briefly push the "stylus end" downwards the arm will react with a restorative force which eventually restores the arm upwards back into a balanced horizontal position. (i.e. analogous to less VTF).
By the same token if you lifted the "stylus end" then released it would fall due to a similar restorative force, eventually settling in the manner of a damped oscillation. (Otherwise the arm would defy gravity and stay exactly where you released it?)
(I believe) the behaviour is the opposite of what you'd expect if you viewed a declined or inclined tonearm playing an LP? Typically, warps encourage increased rather than decreased VTF.
Qualified M/Eng's might volunteer to offer their insights. ;^)
Cheers, |
..To elaborate further you can use the VTA calculation/rule-of-thumb promoted by MF & others to work out roughly how much of an increase will occur due to the height of the warp...
(As a rough "guesstimate" you could be looking at a few hundredths of a gram or more, so in theory it could push the suspension slightly beyond the cart's Specification)
Hope this helps. |
"Here's a heartening story for the OP : I often accumulate new LPs but don't play them with the intention of getting them cleaned first. Yesterday I took a chance and played one that had been stored, uncleaned from new since 2013. Opening it for the first time, it was "ruler flat", no discernible warps. Hole and label registration were very good. The LP played as if it had just been scrupulously cleaned. Noise floor was inky black. Transient peaks tracked perfectly and cleanly throughout the entire record. This 180g was a triumph of LP manufacture that harked back to the halcyon days of the 70s & 80s when no one had even heard of MRA and uncleaned LPs bought new still sound perfect today."
Emboldened by my own experience (above) I've started playing new LPs without cleaning them. After warming up the stylus on a 2nd-hand LP, the next two that I tried were "For Your Pleasure" (Roxy Music), 1x180g LP, and "The Raven That Refused To Sing" (Steve Wilson), 2x180g LPs.
To my pleasant surprise all three of them gave the same result as above. Each had a nice glossy black patina.
I paid particular attention to the quiet/silent passages on the Steve Wilson because it had a bit more dynamic contrast than the other album.
Even though I listen at levels of 85db or so - measured at a distance of 5-6m there were no clicks or pops just inky blackness. As a double-check I stepped into the near field during quiet sections and got the same result.
The run-ins and run-outs were also smooth and untroubled.
I sense the beginning of a grand experiment to see how many new, uncleaned, LPs I can play & obtain such gratifying results from before I crash-and-burn on an MRA-riven one! ;^) |
Funny in the 70s I would buy a record for $5 bucks .Now there $50 an can be warped...no thanks . |
For $50, you bought it new and can return it. I have purchased some new re-issues, on the odd occasion, that sound bad compared to the originals, but none have been seriously warped. Harder to return them for poor sound quality.
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