Belt stretch

Hello,

Well, I disagree, but I am certainly not alone. Here's a quote from another post, but others can also be found that offer empirical data contrary to any notion that belts do not stretch, or to the concept that they by default drive perfectly and do not creep, which is yet another artifact of belt drives. How the effect is handled is left in the hands of the turntable's designer, and certain implementations can be applied that lessen the effect, but it does exist. Some designers do a great job overcoming the issue, but others fail. Such is the lot of turntable design, but we already know that.

"A propos of nothing in particular except that I came up with a neat proof of the existence of belt creep from first principles, namely the conservation of mass.

1. To transmit torque between the pulley and the platter the belt must have higher tension on the drive side than on the non-drive side.

2. Tension on the belt will cause it to stretch and simultaneously thin slightly, so the belt on the drive side has less mass per unit length than on the non-drive side.

3. The amount of mass per unit time passing any two points must be equal.

4. Mass per unit time = mass per unit length x speed so the speed of the belt on the drive side must be greater than the speed on the non-drive side.

5. This speed difference exists either side of the drive pulley so the belt must creep over the length of the contact patch to make up that speed difference."

Posted on another forum by Mark Kelly

Best,
Win

.

Again...

You aren't hearing from other skeptics because your argument is with pure science, not conjecture. Belt creep is a matter of sheer physics; it isn't a theory. That said, there are some very ingenious workarounds for the problem. Frank Schroeder has one that addresses belt creep and implements noise cancellation simultaneously. I heard his turntable at some length, and it works. There are others who offset or minimize the issue in their designs, too. Whatever the drive system, it is the implementation of it that separates the men from the boys.

Doug is also correct in his assertion that rubber deforms. The key to success here is in choosing an optimum footprint, density, pressure, physical configuration, and mass of the rubber, so that it does its job in the least invasive way. This means that the rest of the turntable has to be designed in keeping with that aspect. It can be done, however.

The bottomline, I suppose, is that the type of drive isn't quite as important as the makeup of it, and if that makeup includes slip, there's your first obstacle to overcome.

Hi again,

If you are trying to gather a result from two samples of different drive types, that may be your first error because the simple fact that they are different drive types cannot possibly be used as a standard for any sort of test to measure the effectiveness of the drive type. Are all other parameters the same? Of course, not. The platters, spindles, plinths, etc. are not the same. So, how do you separate sonic differences? Are you saying that you never hear speed differences, regardless of the nature of them? Is the difference merely one of pitch, or could a lack of openness or a smearing of various tones be due to a speed difference? Could there be some other cause? Or, do you never hear such differences?

If you are saying that the precision of a given turntable, or the lack thereof, when it comes to speed control makes no difference, I'm not sure what Doug or I can possibly say to change your opinion. In fact, I'm not really sure what else can be said. What I do know is that I most definitely hear it, and so do many others. Why you wouldn't is something I do not know.

"Doug, that is exactly my point. If the tt is properly set up and all youve done is change the belt and it strobes the same as the belt you had on before mabey your not hearing speed variation mabey what your hearing has something to do with coupling, damping or? With all the enthusiasm for the idler drive lately why assume the performance is solely (or at all) due to speed regulation since it seems these small deviations have yet to be measured or quantified or much less correlated to a paricular hearing sensitivity."

Actually, this isn't so hard. Take a turntable, your flavor, and try it without an outboard speed control, and then try it with a very precise one. Even you will hear the difference. But, there is a caveat; there always is, and that is the turntable itself has to be good enough that you can distinguish differences. The system needs to have halfway decent resolution, too. I assume this to be the case with the majority of AudiogoN members, but a better system will detect more than a mediocre one. You know that, however. I mention it only because I am aware of some turntables which have signatures that color a lot of the signal fed into them. Still, you will hear the difference, but maybe not so pronounced as you would with a perfectly silent running frontend.