Belt stretch

Reading the posts to date make me wonder if I am misinterpreting what is being argued.

It all seems very simple to me.

In your post you say that belt stretch is inaudible. In the next sentence however, you don't deny that it may produce measurable speed fluctuations.

In records that I am very familiar with, I can clearly hear differences of 1 or 2 rpm on a 33 1/3 rpm record. That's how I know when to change the belt on my table. And when I do change the belt, the records sound "right" again.

There are many turntables (or used to be) where you can adjust the rotational speed of the platter. I can remember sitting around college dorm rooms with my friends playing with turntable adjustments to see how the sound was altered. Adjusting speed was one of the things we used to do.

So I find that belt stretch, which in turn affects rotational speed, is easily audible. At what point it becomes audible, I don't know. But as I say, 1 or 2 rpm is certainly enough for me to hear a difference.

Im not saying there is no audible difference in sound between different systems or even belts. What Im saying is is that the audible difference isnt rpm related. Possibly coupling or who knows. Of couse you can hear if your tt is 1 or 2 rpm off, if it is it isnt working right and I have yet to see ( or hear ) a belt drive table that anyone on this forum would own that would be off that much. If stylus drag produces any speed anomolies that would be audible then Im saying that system needs to go in for repair. An example of what Im proposing is that the superiority of sound from an idler or rim drive which is being much discussed these days may have nothing to do with speed accuracy and be related to damping from the drive wheel instead. What I have yet to see is anyone demonstrating a hearing sensitivity of X to speed fluctuation and correlating that speed difference to a belt drive system.
ps: I knew I was going to be mugged when I started this post thanks for the great responses

You said:

"What I have yet to see is anyone demonstrating a hearing sensitivity of X to speed fluctuation and correlating that speed difference to a belt drive system."

Here is the sequence of events for me:

My turntable, which is a Linn, works fine.

After a period of time, I notice the drop in rotational speed through my hearing.

I treat the belt with a rubber renewer to stop belt slippage if the belt is stating to get worn and hard.

Sometimes this works and I'm good for a while longer.

If the rubber renewer doesn't work, I replace the belt on the assumption it is getting stretched and this is affecting the transfer of torque from the motor to the platter. Speed slows and the difference is audible.

The turntable then works fine and sounds right.

I can measure the difference in rotational speed with a stop watch before and after. I can also hear the difference.

The only variable changed in my set up was the belt and the problem is solved. Rotational speed is restored. Audible diffferences result.

I have clearly demonstrated to myself, if not to you, that the belt was correlated with the drop in rotational speed and the audible dfferences.

I don't need to demonstrate anything else for my hypothesis. The facts are consistent with my hypothesis that the belt was the problem. The onus is now on YOU to demonstrate the plausiblity of an alternate hypothesis, with facts. And it is a hypothesis that must be consistent not only with your observed facts, not speculations, but it must also be consistent with my observed "facts". Unless of course you can refute my facts which at the moment you can't. Until you can do these things, your points of argument exist only as an abstraction that is not consistent with known and demonstrated observations.

I'm not saying that at the end of the day, you might not be correct. The correlation I have observed between worn belts and rotational speed and audible effect is not the same thing as cause and effect. Using correlation to infer cause and effect is an incorrect use of correlational observations and statistics (eg. the fact that the sun rises when I get up and sets when I go to bed means they are "correlated". However, my going to bed and arising doesn't "cause" the sun to set and rise). I'm saying that its' up to you to prove your point, because right now, my proof is to the contrary. And my proof is based upon observations, not untested hypotheses.

So you can perform a simple experiment. Take a turntable. Take two new belts. Get a good grip on one of them and stretch it to the point where the belts are different measureable lengths. Play the same record with both belts.
If they rotate at the same speed and sound the same, then you have good evidence that belt stretch is not a critical variable. This observed fact would support your proposition and you can develop an experiment to test your hypothesis.

On the other hand, if the rotational speed does change and it is audible, as it is in my case, then your hypothesis must explain both your proposition and also my observations.

And we can take it from there if you get to that point. Science and hypothesis development and testing is a never ending cumulative process until we discover the ultimate "truth", if there is such a thing.

I may regret this, but I have one nagging question. What about the inertia of of the mass of the platter? It seems to me that the miniscule amount of drag caused by heavy modulations would be ameliorated by the mass and inertia of the platter. The more massive, the less effect there would be on speed variation.

Having fairly recently returned to vinyl, is there a rule of thumb as to when to replace the belt? (VPI)

Thanks, and enjoy,
Dan

Rccc,

Thanks for taking all the responses so civilly. I hope you don't feel too "mugged".

What I have yet to see is anyone demonstrating a hearing sensitivity of X to speed fluctuation and correlating that speed difference to a belt drive system.

I guess that's the core of your position, an honest skepticism about the audibility of belt stretch or slip (assuming a properly set up rig of good quality). Fair enough.

Forget the theoretical arguments. Just listen for yourself. Come over and visit. We'll play some tunes using our most optimized belt. I'll then switch to some other belts we've tried, which are stretchier and/or more slippery.

If you hear the difference (which I guarantee) would the demonstration be convincing? Or am I missing your point?