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

.

Rccc,

What makes your limits (or mine) the ultimate arbiter of the possible? There may be one being who could claim that, but you're not Him/Her.

Let's test your hypotheses with a few questions, taken straight from the musical casebooks:

Do you have perfect pitch? If I hit a random key on a piano can you tell me which note it was? If your answer is no, do you therefore argue that no one else has perfect pitch either? Tell it to my mother, she'll laugh in your face. Test her, she'll prove you wrong.

If I play any two consecutive bars from one of 600 long, complex pieces of music that you've heard, can you infallibly tell me:
a) which one of those 600 pieces the two bars came from?
b) what movement they came from?
c) which instruments carry the melody and harmony?
d) what happened in the bars immediately preceding, and what comes next?
You can't do that? Well, neither can I. But Toscanini could. Fritz Reiner could. Vladimir Ashkenazy can.

Can you go to a concert, hear a Mozart symphony for the very first time, then go home and write it out - note for note? You can't do that? Tchaikovsky could and did, when he was 12 years old.

Could you travel to another city to jam with a famous string quartet, and after 10 seconds announce to the first violinist that his instrument was tuned 1/4 tone higher than your piano back home (though you hadn't been home in a week)? Max Reger did that. He was 10 years old.

Can you tune your piano for any chosen key so it's correct out to five harmonics above the fundamental? Debussy could. Did it nearly every day of his life.

I prefer to expand my horizons by being amazed at what is possible, not limit them by deciding what isn't. To each his own of course.

Dougdeacon, great post!

I dont doubt the theoretical possibility or even likelihood of differential belt tension what Im saying is that it isnt audible. I dont tune pianos but I do have perfect pitch and have spent much of my life in concert halls and enjoying Hi Fi. Its possible Mozart would have been able to hear those anomalies in a belt drive table, how many Mozarts are there on this forum? So let me rephrase what I stated. Aside from the esteemed genius's mentioned above no mortal can hear the effects of belt tension as has been reported in the audio forums and press. Why I started this thread is that knowledgeable people in the audio business have made reference to belt stretch,stylus drag etc but never quantifying it in any way but theoretical. I have both belt and direct drive and have never heard any speed related differences. Since this comes up from time to time I have asked freinds and associates in the music industry if they have and no one has been able to actually demonstrate the audibility of this variance. Im simply trying to debunk this myth or hear from someone whom can demonstrate that it is in fact audible to someone besides Mozart. I appreciate the thoughtful reponses but we have only addressed the possibility of some pitch shift not that it in fact exists and is audible.

Rccc, Assuming you own high quality examples of belt-drive and direct-drive turntables, have you done the experiment of listening to each one with the same tonearm and cartridge? If so, do you hear any differences that could therefore be ascribed to one or the other turntable? What are the differences if any? If you have not done that experiment, then maybe you are premature in declaring that the inherent mechanical differences between belt-drive, dd, and idler-drive are irrelevant or inaudible.

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.

The technology necessary to measure the effects of stylus drag and belt stretch exists today, but the people that have access to such equipment don't give a damn about it. They're probably too busy smashing atoms together and sending things to space.

The technology that was around when most records were cut was primitive at best and probably exhibited major speed fluctuations. Achieving super accurate speed precision today probably just enables one to better hear the inaccuracies of yesterdays equipment, but what do I know. I own a stupid belt driven turntable :)

Stylus drag and belt stretch is an idea (something, such as a thought or conception, that potentially or actually exists in the mind as a product of mental activity).

I have an idea. Perfect speed precision will guarantee slow transients.

I think we might be better off if we tried to figure out the inaccuracies of yesterday's equipment (such as how it reacted to cutter drag) and compensated for it. If a lathe slows down while the cutting head cuts a big transient on a lacquer, our TTs need to speed up the disc for the same transient. If you disagree that a lathe slows down when cutting a big transient on a lacquer, you might be indirectly saying that a cutting lathe has perfect speed precision while cutting a lacquer. Buy one and mount a tonearm to it and you should hear more accurate speed precision than any TT can provide. I don't know, but I bet that a cutting head on lacquer produces more friction than our styli do on vinyl.

Rccc you can believe whatever you like but you should do so in the face of the available evidence:

1. Belt creep exists (see Mosin's post for one argument, there are several others)

2. I can measure it.

3. Doug Deacon can hear it.

Ketchup, if the lathe slowed down for a transient the recorded signal would rise in frequency. The playback would need to slow down by an equivalent amount to replicate the "original" signal.

The folks at Pristine Classical in the UK have extensive digital files of works which they have taken off disc and have performed analyses of the changes of frequency within sustained notes. They do this so they can find artefacts of the recording process and correct for them. From what I have seen there is no great effect attributable to the lathe slowing down under cutter drag.

I can think of two reasons why this might be: firstly, don't forget that the cutter head was heated and used on a relatively soft acetate formulation - very much like a hot knife through butter.

Secondly, modulation drag exists because the hysteresis of the cartridge suspension removes energy from the system, the larger the modulations the larger the energy lost. The only source of "make up" energy is the motor (everything else is passive).

The cutter on the other hand is actively driven so the larger the modulations the larger the amount of energy being put into the system. If the energy lost through frictional heating equals the energy inserted into the system we'd be in net balance.

I don't think you even need high quality equipment or perfect pitch to hear the effects under discussion. I owned a Well Tempered Record Player (belt drive), and now own a Technics SP-15 (direct drive) in the heavy Technics base. I definitely don't have perfect pitch, but I could easily tell the difference between the cheap stretchy 3rd party belt on the WTRP, the outrageously expensive precision ground flat plastic-like OEM belt, and the Technics, with the Technics easily besting the WTRP on all measures of speed stability. If you have better equipment, or ears like Dougdeacon's partner Paul, I'm sure the differences are both more readily apparent and probably really irritating.

Ketchup, as far as mastering goes, here's some interesting reading:

http://www.kabusa.com/1200agon.htm

Of course, the Technics wouldn't be factor for older recordings, which might very well exhibit the effect you postulate. These guys:

http://www.trutone.com/mastering.html

claim the Technics drive motors are way better the the original Neumann. I have no idea whether stylus drag was audible on the old lathes. Your theory has been discussed before here on Audiogon.

Anyway, I'm firmly in the camp that says belt stretch is audible, because I've heard it.

David

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?

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!

Jean you are quite wrong.

Referred to the platter the actual output torque of a Garrard motor is around 0.5 N.m. The Lenco is in the same ballpark (I don't have one to measure so I can't say exactly)

Typical synchronous motors range from 0.5 to more than 1 N.m. so they are equal to or higher than the Idler motors.

A mid range DD like the SL1200 is around 0.2 N.m and the SP10 Mk2 is around 0.6, so most direct drives are lower torque.

Jean,

You were doing okay until you said, "a rubber wheel grips without deformation".

Pardon me, but that's nonsense. Rubber is an elastic material. Elastic materials ALWAYS deform under load, then rebound back toward their original shape when the load is reduced - that's what "elastic" means.

Another aspect of this is that energies stored in an elastic material by compressive deformation are released with a time delay when the material is allowed to rebound. Depending on the TT design, this energy normally feeds back into the platter at a fairly low frequency. The cartridge picks this up as "mud" - nothing you can specifically hear, but a lack of clarity and some opaqueness to low level detail. Very TT specific, but a real engineering problem nonetheless.

If you believe a rubber idler wheel (or a rubber anything) is not deforming, you're fooling yourself. The amplitude and frequency of deformations may be adjustable by choosing rubber of different durometers, but they can never be eliminated.

That said, we're in agreement that Rccc should listen for himself. He'll hear what he hears and can make informed TT choices based on his own sonic sensitivities and musical priorities.

Geeze, I cant believe there's not one other belt slip skeptic out there. So you dont think that the idler sound may be attributable to something other than speed like say damping or ? I still havent heard anyone actually talk about a measured deviation in the belt system or if the speed is spot on wouldnt the differences in sound be due to something else or what resolution is audible (inaudible). What Im proposing is that the difference in sound may be due to some other forces. As I said before I could hear a difference in sound with different belt tensions while the speed remained stable. Although I follow the logic, bass extension and dynamics could be enhanced by other forces. Where the hell is HW when you need him?

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.

Mosin, Im not arguing that belt slip exists or that rubber deforms or that there is some theoretical friction from stylus drag. Im questioning the audibility of these conditions and other than "I can hear it" and attributing "it" to the afore mentioned conditions no one yet has demonstrated that this so far unmeasurable speed variation is responsible for the effects they are hearing. If the speed measures stable with a strobe then what pitch related anomaly can be heard? When John hears better bass extension and dynamics with his idler compared to belt but both systems are showing no deviation in speed perhaps its not speed shift that he is hearing.

If the speed measures stable with a strobe then what pitch related anomaly can be heard?

1. Any pitch-related anomaly whose time duration from delay through recovery is shorter than the time that passes between two marks on the strobe disc. This would be a greater risk with low resolution strobes (ie, fewer marks per circumference).

2. Any pitch-related anomaly which slows the platter by precisely one (or any other whole number) strobe mark in 1/60th of a second (1/50 in some other countries). This would be a greater risk with high resolution strobes (ie, more marks per circumference).

A strobe isn't perfect. It's a an unnumbered, circular yardstick with markings giving it one very specific resolution. Changes that are completed below that resolution won't be detected. Changes that cause a whole number shift in mark position won't be detected.

You haven't responded to Mosin's or my suggestion: listen to a good quality belt drive table properly set up with a variety of belts. Hear the differences. Supply some explanation other than speed variation for the differences you'll certainly hear.

"listen to a good quality belt drive table properly set up with a variety of belts. Hear the differences."
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.
Thankyou for the fun dialogue Ill sum up by saying "if you dont know what it is you dont know what it isnt" and in that spirit Ill be researching this much farther and will report back on any ground breaking discoveries

This is a shining example of what I was talking about in one of my earlier threads, "The High end and Glubglub". Lifted from a discussions in logical argument and philosophy:

"What he (the skeptic) wants it is logically impossible to supply. But doesn't the logical impossibility of the skeptic's demand defeat his cause? If he raises a logically impossible demand, can we be expected to fulfill it? He says we have no evidence, but whatever we adduce he refuses to count as evidence. At least we know what we would count as evidence, and we show him what it is. But he only shakes his head and says it isn't evidence. But then surely he is using the word "evidence" in a very peculiar way (a meaningless way?), so that nothing whatever would count as a case of it...Might he not just as well say, "There is no glubglub?"" In short, a waste of time.

"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.

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.

Johnnantais,
In a thread about belt stretch due to stylus drag you added the information above to the discussion, but either I or you are confused. You seem to think that the force seen by the belt and/or motor is something great, like 340lb/sq. inch. That is not the case.

A simple experiment (that you should not do!) is to put a 1"x1" block of wood on your TT, place a 340lb weight on top of it, hold it in place, and turn on the TT. Of course it's not going to turn at all. The pressures you noted above (if the calculations are correct) are only seen by the vinyl and stylus but never by the belt or motor. The forces needed to overcome the friction of stylus drag are minimal.

Here's an experiment that will be hard to implement but easy to think about. Imagine a cartridge attached to your finger with a string, tracking an LP that's turning on a TT. The cartridge would have to stay up somehow, of course. Use your imagination. Because there is no counterweight, also imagine that the 8 gram cartridge is not going to destroy its suspension and cantilever. How much force do you think you are going to have to use to keep your hand in one spot? You probably aren't even going to feel a pull on your finger... and that's with 8 grams of tracking force. Belts and motors don't see as much drag as you think.

FWIW, I don't disbelieve that belt stretch and rebound occur, I just think this is good discussion :) I do think that it's not as serious as some believe, though.

I find this thread very interesting. I thought I would throw a monkey in the wrench so to speak. We know for a fact that for a certain amount of mass, a belt that has a specific amount of elasticity and proper torque to spin such mass, we can produce a specified speed according to the accuracy of the drive source, albeit; digital control speed controllers or DD quartz reference. The monkey is how much more accurate does a belt drive system become when you multiply the amount of motors with a specific torque factor to spin the platter? We must also account for the amount of belt elasticity and compute that into any formulas for an accurate answer.

I would like to use this example, my Transrotor has three motors with three belts to spin a fairly heavy 80MM platter. With one motor, it could be done, however, I did notice a lot slower start up and some belt slippage at start up. With 3 motors and 3 belts, the belt slippage at start up is minimized and the platter is spun up to speed fairly quick. The speed maintained fairly accurate readinds, but the belt wore out faster, Note, I do use a quartz controlled speed controller motor assembly that I check with the Clearaudio 300MHZ stroboscope for accuracy. From my experience, the belts over a period of time will wear out and the diminished amount of belt elasticity will cause the turntable to flucuate out of speed tolerance and will eventually need to be adjusted via the speed controller. The formula for torque is: T = r x F. The other formulas needed to find the rest of the story can be easily looked up. Basically, if we have three seperate effects of torque acting on a stationalry mass that becomes rotational, it is easier to transfer said torque or power if you want to convert to power and cause the movement of the mass than with one moment of torque. The caveat is if the initial amount of torque with one motor is the same as the same with 3 motors, most likely not for a turntable. If manufacturers published their torque specs for the seperate motor assemblies in either newton meter or torque specs we could calculate the amount of torque that is applied to the mass and see how that would effect our perfect 33.3 rotational speed.

The talk about the belt stretch vs. DD is going down the tubes so to speak, much good information about both types of drive systems, though, many hard core audiophiles. I would state that whatever you like, just like it, and not worry about anything else. Just listen to the music.

We can get down into the weeds of this, I have not seen anyone speak about the effect of rotational torque with additional motors vs one on a platter and how that would help speed consistency with a turntable. Their are so many ways and methods manufacturers are using to get to the means to the end, it is making my head spin.

V/r
Audioquest4life

John, you have offered no measurable explanation and per Ketchups post misinterpreted the data. If thats your version of logic I doubt we'd gree on anything. My mind is open to the possibility of these effects but I dont think enough testing has been done to prove the point. Ill concede Im very much a believer in blind listening and measurable performance. I do alot of comparative listening. Ill add that consumer audio is dominated by myth and conjecture as well as the magnitude of effects being grossly exaggerated. I think that kind of thinking does a disservice to the hobby at large and so when I hear performance claims being attributed to specific systems I want to know that they are on the right track. Does that sound logical?
Mosin, Thats a very good point. I think the core question is what amount of speed deviation is audible, how can it be measured and what are the effects (dynamics feq response image ect) I think its a question worth pursuing and will be experimenting with it in great depth. Thanks for your input.

In defense of Rccc

Amazing how stylus drag can make a belt stretch even when the platter mass exceeds 10, 20 or even 30 pounds, yet somehow unclamped LPs on felt mat do not slip on the platter!

So funny how the direct drive folks boast about speed stability, but when you see their rigs many (if not most) do not use clamps. They seemingly find it easier to believe a 10 pound platter and belt drive has less rotational force than a 120gram LP coupled to a felt mat by gravity only. Mmmm.

I did an experiment some time ago. (http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1181854929&openflup&74&4#74) From my own observation LP slippage (unclamped + felt mat) for 20 min of play amounted to only 9.235e-5 % - less than 1/64 of an inch after approx. 16,920 inches of grooves.

I’m not saying folks don’t hear differences between direct, rim and belt drives, but something else is at play.

Regards
Paul

Thanks Paul I was startin to get lonely.