[nautikal]

Okay I thought about this some more and I'm almost positive that thinning the outer edge of the disc will actually increase wobble and vibrations due to the decrease in inertia. Try balancing a pool cue with the large end on top and then with the small end on top. With the large end on top, it is much easier due to the larger inertia.

So in summary, we have yet to find any scientific basis for the merits of this "tweak". The only way this would make sense is if there are some parts of the disc that are significantly thicker than others. I find this very doubtful as the difference would have to be significant to cause vibrations, and such differences would be easily observable. Not only that, but I doubt the factory would produce a CD so inconsistent .

 

[hempcamp]

Quote:

Originally Posted by nautikal /img/forum/go_quote.gif So in summary, we have yet to find any scientific basis for the merits of this "tweak".

We didn't even need to go down the inertia/no inertia, centrifugal/centripetal path to get there. A good transport even by early 1990s standards would make about one C2 error per disc. You'd be lucky to hear this one little blip of an error even if the C2 correction algorithm (averaging the values on either side of the error) didn't get it right.

There simply isn't any reason to believe that a finite set of data going into a DAC will be any different with or without this tweak. Unless you believe finite sets carry with them some sort of metaphysical superdata, and that DACs somehow (and unbeknownst to the engineers who build DACs) do something with this metaphysical data to place it in the analog signal, then the tweak makes no sense whatsoever.

There is a fundamental misunderstanding of the binary number system and how electronics carry digital signals behind this tweak, and I think it carries over from the analog world where slight variations in rotation would indeed have an effect on sound. Many of the tweaks around today involving vibration/wobble isolation (there are people who swear on their dead mothers that putting your computer desk on pads will increase SQ) blossomed from the analog days in the hands of dishonest salespeople.

--Chris

 

[Mher6]

Quote:

Originally Posted by nautikal /img/forum/go_quote.gif Okay I thought about this some more and I'm almost positive that thinning the outer edge of the disc will actually increase wobble and vibrations due to the decrease in inertia. Try balancing a pool cue with the large end on top and then with the small end on top. With the large end on top, it is much easier due to the larger inertia. So in summary, we have yet to find any scientific basis for the merits of this "tweak". The only way this would make sense is if there are some parts of the disc that are significantly thicker than others. I find this very doubtful as the difference would have to be significant to cause vibrations, and such differences would be easily observable. Not only that, but I doubt the factory would produce a CD so inconsistent .

Inertia doesn't change in different parts of the object. The WHOLE object simply has inertia, the top of the cue and the bottom don't "have" different inertias. The reason you can't balance the cue with the large end on top is because the cue has an "unbalanced" center of mass.

 

[JaZZ]

Quote:

Originally Posted by nautikal /img/forum/go_quote.gif Centrifugal in Latin means "center fleeing." This would imply a force that pushes an object away from a circular path. The real force you are talking about is centripetal force, which means "center seeking" in Latin. This implies a force that causes an object to take a circular path. "Centrifugal force" is merely the absence of centripetal force. See here. Do you know what inertia means? Inertia is the property of matter by which it retains its state of rest or its velocity along a straight line so long as it is not acted upon by an external force. Saying inertia causes movement is like saying a stabilizer on a ship causes listing.

I know what inertia means. And what I meant was indeed centrifugual force, not centripetal force. I have a hard time imagining how you imagine the wobble scenario and what you consider the cause and the exciting moment of it. In fact inertia is the cause for centrifugual force, which, together with mass (predominantly the one on the circumference of the disk), causes the wobble -- due to irregularities in mass dispersion.
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[JaZZ]

Quote:

Originally Posted by nautikal /img/forum/go_quote.gif Okay I thought about this some more and I'm almost positive that thinning the outer edge of the disc will actually increase wobble and vibrations due to the decrease in inertia.

Think about it one more time. Centrifugal force is the dominating force in a spinning object -- and it entirely depends on mass.
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[Kees]

I think it is easy:
Think flywheel: the more mass the more stable it rotates.

 

[stevenkelby]

Quote:

Originally Posted by Kees /img/forum/go_quote.gif I think it is easy: Think flywheel: the more mass the more stable it rotates.

The more the mass, the more force any imbalances will have.

 

[JaZZ]

Quote:

Originally Posted by Kees /img/forum/go_quote.gif I think it is easy: Think flywheel: the more mass the more stable it rotates.

Yes: if the mass is centered. If not, removing mass from the outside will bring the center of gravity closer to the center of rotation (resulting in lower wobble). In the ideal case bevelling with a machine (think lathe) will even create perfect centering.

BTW, the flywheel effect of heavy turntables addresses wow and flutter, not wobble.
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[JaZZ]

Quote:

Originally Posted by stevenkelby /img/forum/go_quote.gif The more the mass, the more force any imbalances will have.

Exactly, thanks!
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[Kees]

Quote:

Originally Posted by JaZZ /img/forum/go_quote.gif Yes: if the mass is centered. If not, removing mass from the outside will bring the center of gravity closer to the center of rotation (resulting in lower wobble). In the ideal case bevelling with a machine (think lathe) will even create perfect centering. BTW, the flywheel effect of heavy turntables addresses wow and flutter, not wobble. .

Centering is most important, I agree, but more mass will certainly make it more difficult to make it wobble.
The wobble effect you are talking about irt turntables is related to the wobbling (unevenness) of the record, not the platter.
It will also be the vertical distribution of mass (even thickness on the whole surface) that will be most important for this wobbling effect.
That is if I understand correctly: wobbling is an uncontrolled movement in the vertical plane.

 

[monolith]

Quote:

Originally Posted by JaZZ /img/forum/go_quote.gif Think about it one more time. Centrifugal force is the dominating force in a spinning object -- and it entirely depends on mass. .

No, it really isn't. Centrifugal force doesn't exist. Centripetal force exists. Centrifugal force is a "fictitious force" introduced to make Newton's second law work in the rotating (ie. non-Newtonian) reference frame. Centripital is the dominant (ie. only) force in a rotating object (obviously ignoring gravity, and other things acting in different directions).

 

[JaZZ]

Quote:

Originally Posted by monolith /img/forum/go_quote.gif No, it really isn't. Centrifugal force doesn't exist. Centripetal force exists. Centrifugal force is a "fictitious force" introduced to make Newton's second law work in the rotating (ie. non-Newtonian) reference frame. Centripital is the dominant (ie. only) force in a rotating object (obviously ignoring gravity, and other things acting in different directions).

That's pure semantics, and we all know how productive it is to debate semantics. In the everyday world centrifugal force does exist, that's why centrifugues work and the rotating CD develops forces causing it to wobble if not centered. I know and have stated that centrifugal force is actually caused by inertia (and a centripetal force to make the object spin around a center at all) -- which is apperently how modern physics define it (as it's not a separate physical force). Interestingly in the German version of Wikipedia centrifugal force is still an accepted term.
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[JaZZ]

Quote:

Originally Posted by Kees /img/forum/go_quote.gif The wobble effect you are talking about irt turntables is related to the wobbling (unevenness) of the record, not the platter.

I haven't talked about wobble in turntables.
.

 

[nautikal]

Quote:

Originally Posted by Mher6 /img/forum/go_quote.gif Inertia doesn't change in different parts of the object. The WHOLE object simply has inertia, the top of the cue and the bottom don't "have" different inertias. The reason you can't balance the cue with the large end on top is because the cue has an "unbalanced" center of mass.

Yes I know. Changing the distribution so the disc is more like a thin hoop will increase the inertia constant to be between 1/2 and 1. Hence there will be more inertia. And you can balance the cue with the large end on top... don't know what you're talking about.

Quote:

Originally Posted by JaZZ /img/forum/go_quote.gif That's pure semantics, and we all know how productive it is to debate semantics. In the everyday world centrifugal force does exist, that's why centrifugues work and the rotating CD develops forces causing it to wobble if not centered. I know and have stated that centrifugal force is actually caused by inertia (and a centripetal force to make the object spin around a center at all) -- which is apperently how modern physics define it (as it's not a separate physical force). Interestingly in the German version of Wikipedia centrifugal force is still an accepted term. .

No. There is no such thing as centrifugal force. To speak of one would imply a non-inertial frame of reference and makes it confusing for others to follow what you're saying.

 

[JaZZ]

Quote:

Originally Posted by nautikal /img/forum/go_quote.gif No. There is no such thing as centrifugal force. To speak of one would imply a non-inertial frame of reference and makes it confusing for others to follow what you're saying.

Semantics again. So sad! You don't seem to be interested in the topic.

I really don't want to make any premature statements about the pretended function of the Audio Desk System -- it isn't even clear if vibration reduction is the beneficial effect or rather reduced scatter light. My only concern was the categorization of this device as similarly unlikely to work as tweaks such as Rainbow Foil, which is clearly not adequate: it has the potential to work. There are the reported experiences in terms of heard and felt vibrations with rotating CDs and the reduction of them after treatment (both consequently ignored and no interest to reproduce the simple tests) as well as the positive listening reports, and there are the persistent decryings and diabolisations of an unknown product as well as the programmed confusion...

I'm retiring from this debate, but will report my listening impressions with the trimmed CDs later (for the people interested in such real-world things).
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