Belt stretch

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?

Doug, I would love to do that thanks. Im hoping its understood that what I mean by belt stretch is that with a properly fitted belt in good condition the speed fluctuation as in the differential tensions discussed before would not be audible (except to Mozart) same with stylus drag. Mark is referring to a worn stretched belt (I think) which of course I agree would have an audible effect. One of the things I have observed is that on a turntable that has adjustable belt tension (like the one I built which can be seen over at vinyl nirvana) Changing belt tension makes no difference to measured speed stability until the belt is so slack it slips and surprisingly the loosest tension before slip yielded the best sound although the speed remained the same. This is actually what started me thinking about this in the first place. Thanks for your inputs

My ears started ringing and I knew I was being called :-)! Hi Rccc, I'm not here to flame you, been there myself, so let's stick to facts and logic. I'm the fellow who has historically made an issue on this forum and some others on the issue of stylus force drag (via the Lenco turntable and the "Building high-end 'tables cheap at Home Despot" thread), and the issue of the superiority of idler-wheel drives over belt-drives, and I'd like to point something out. Because we track our cartridges at anywhere from 1 gram to 3 grams or so, we tend to think that the braking action of the stylus in the groove is minimal and that a belt-drive is then able to overcome this negative force with ease. This is the first false assumption.

Stylus force drag is very serious indeed. I took the following from the website "www.Micrographia.com", (here's a link to Pressure) on the issue of the pressures involved: "Neglecting factors such as the elastic deformation of vinyl, the distribution of forces in a V-shaped groove and the accelerations at the stylus tip during tracking, simple calculation based on these figures gives a stylus pressure of 240 grams per square mm, or 340 pounds per square inch. The transient pressures exerted by a stylus tracing a heavily modulated groove during playback will of course be much greater, but beyond my ability to calculate." As an addendum, pressures have been estimated up to the several tons per square inch during high modulation passages. So you can see we are not talking negligible force.

All theories stand or fall by the results of experiments designed to test them (in a perfect world anyway). In terms of stylus force drag, belt-drives and idler-wheel drives (and DDs), the easiest way to test them is to listen within a sound system, rather than design more tests which themselves are based on various theories and assumptions. Measurements divorced from actual listening only lead to more theories.

I'm not sure what you are listening for, but any switch of a tonearm/cartridge combo to a high-torque idler-wheel drive (I'm not sure the Verus is high-torque relative to Garrard and Lenco motors, don't use the Verus as a standard) from a belt-drive shows the idler to most obviously and immediately have deeper and more powerful bass, faster transients, and a greater dynamic pallette (i.e. it is plainly more dynamic), as well as various other auditory artefacts. Maybe you'll like this, maybe you prefer the gentler presentation of belt-drives. Whatever the case, this isn't listening for wavering notes and screwed-up sustains, but for other things. Of course, in my experience, the sustains as well are superior on large idler-wheel drives (and large DDs), though these come in different flavours and abilities (as do DDs, the Technics SP10 MKII for instance having monstrous torque relative to most other DDs).

Anyway, the effects of stylus force drag on a belt-drive vs a higher-torque system (high-torque DD or idler) is plainly audible in increased dynamics (or decreased dynamics if the idler is the standard), more powerful bass and much faster transients. It doesn't take a Mozart to hear this.

As an aside, I didn't read the figures for pressures of the stylus in the groove first and THEN seek out various systems (letting theory guide me); instead I had a history of high-end belt-drives under my, ahem, belt, (Maplenoll, Audiomeca, experience with a variety of others), and THEN I heard my first idler, a humble/cheap-o Garrard SP-25 record changer (which nevertheless had stunning bass SLAM and transient speed relative to my high-end belt-drives, which themselves were known for their dynamics), which record-changed my audio life. I let experience guide me, to question the theory/then-dogma I too had been steeped in (i.e. that the belt-drive system was the best of all vinyl systems, as was generally accepted at that time, only a few years ago).

In considering the Lenco, which easily outperformed hosts of highly-regarded belt-drives in comparisons (VPIs, Well Tempereds, Linns, Nottingham, the list goes on and is recorded), I found nothing of any stupendous quality: instead only a pressed metal frame on which was bolted a decent but not spectacular main bearing and a good but not incredible motor (but things being relative, the motor is superb in many ways). There was nothing to account for the facts (the Lenco's evident superiority - and this in every way: detail, imaging, rhythm/timing, etc. as well as dynamics, bass and transient speed to various high-end belt-drives) but torque, and this, in turn, meant that the Lenco's torque was better able to combat stylus force drag than an "equivalent" belt-drive. Deadening/controlling the Lenco in various ways only increased these qualities, which are shown to be inherent in the system/implementation. It is ESPECIALLY when groove modulations are extreme that the extra torque is heard and the losses of the belt-drive system is heard: precisely bass notes, fast "rise times" on dynamics and transients, where idler-wheel drives like the Garrards are generally accepted, even by diehard belt-drivers, to be superior to belt-drives.

As I wrote back in 2004 (currently under my "system") when I started the Home Despot/Lenco/Idler thread, "Idler wheel drives in general were originally designed to overcome stylus drag, as in their day cartridges tracked at 10 grams. As tracking forces diminished, idler-wheel drives became more refined, but retained their resistance to stylus drag. As time went on and VTF dropped to below 2 grams, it was thought stylus drag could be combatted by the simple use of mass, and not the brute force of rumbly idler-wheel drives, which were discredited, even though their rumble figures were in fact better than those of the then-rising Linn LP12. If you remember your history, you will remember that CD as well was touted by the majority of the press and the industry as superior to the previous technology, vinyl. The Lencos do not rumble, and they prove that in fact it does take a certain amount of (refined) brute force to counteract the all-too-audible problem of stylus drag, which belt-drives are ill-equipped to combat, their Achilles Heel being their belts and weak motors. This is clearly audible in the attack of a Lenco (or large Garrard), the tremendous bass reach (bottomless) and bass detail of a Lenco (which affects both air and imaging), and of course its perfect timing and speed stability under real-world conditions (actually playing a record)."

Anyway, as Dougdeacon suggests, the best way to gain a better understanding is to let go theory and embrace experience: hear it for yourself. A stiffer belt certainly helps, but that's only half the story, the other being weak motors and grip (a rubber wheel grips without deformation). There's more too, but that's enough for now ;-). Good luck in your audio ventures and experiences!