Belt stretch


OK Im out to start an argument here. Im flattly stating that stylus drag and the effects of belt stretch on belt drive tt's is pure BS. Unless the motor was grossly underpowered there is no way there are any audible effects (even to a dog) related to belt stretching. Im not saying that there is no measureable speed fluctuation but Im saying that even if you have something sensitive enough to measure it you still cant hear it. So there
rccc
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.