Hi Raul . . . were you able to get any comparisons of stylus drag between a modulated and an unmodulated groove? I think that's one of the central points of most of the discussion of stylus drag. |
I'll second the motion for some discussion on these topics . . . regardless of where we stand as individuals, the enthusiast audio industry these days is very much threateaned by the stagnation of ideas, and open discussions are an excellent way to combat it (or each other:)). |
Dan_ed, I think Lewm is talking about inner tracks vs. outer tracks on the disc. This will of course vary the amount of stylus drag torque that is applied to the platter, by a simple difference in leverage. |
I heard in the last 15 years more average sounding units than I wanted to. Some are good looking, some are heavy, some are extremely expensive but at the end of day, well you know...average. Couldn't have said it better myself. And I think that one of the reasons why the audio community tends to make deities and martyrs out of certain designers is because their dream of making i.e. the ultimate turntable is something we can all respect, love, and identify with. And yes, the story behind a product is a very powerful (and legitimate) incentive to buy . . . but whether or not the dreams have actually been realized in the product is of course another question entirely. And there's also the question of what are exactly the objectives of a turntable "done right"? The story that Dertonarm tells of his ultimate turntable pursuit would be a frustrating one for me, because after that amount of work . . . I would personally want to see more than 15 people able to enjoy the pleasure of owning one. I think a truly successful product should put just as much innovation and excellence into the effecient use of materials and resources, and the financial model that allows it to be produced, purchased, and enjoyed to a significant degree. But anyway, I'd like to steer the discussion more toward what we think are the biggest weaknesses in most current high-end turntables, in a general sense across the industry. Personally, I feel that the suspension/isolation systems are the huge weak spot, along with the proper control and dissipation of resonant energy between the platter and tonearm mount. |
That implies that the suspension should go as low as 0.5 Hz to ensure isolation from building resonance. I'm not so sure on this -- after all, at 0.5 Hz the relative stylus-to-record motion *should* be fairly well attenuated simply due to the fact that it's now several octaves below the basic cartridge/tonearm resonance, which is acting as a 12dB/oct high-pass filter. From emperical evidence, the cartridge/tonearm resonance envelope definately affects the sensitivity of a boingy suspended turntable system to foot-falls and such. So I'm thinking that the primary suspension mechanism of importance is its Q, and flatness through its transition region . . . so it doesn't add any additional peaking to the tonearm/cartridge resonant peak . . . the exact rolloff point for the suspension simply needs to be a bit (an octave should easily do) below the that of the tonearm/cartridge. The best results will then be acheived because the slope of the attenuation (provided by both the suspension and tonearm/cartridge working together) is smoothly increased, without increasing the peaking, and the ultimate attenuation at very-low frequencies could be similar to the system you describe. Another huge issue is how the suspension behaves with horizontal shock, in addition to its vertical behavior. I think that this is THE main flaw in the Linn/AR suspension, and just about every turntable suspension that uses compression springs. In these systems, since the mass of the subchassis sits above its support points, it's inherently unstable with regard to external horizontal motion. This fits with the long-time Linn recommendation of the Sound Org stand for floorstanding applications . . . something will minimise the addition of horizontal energy, yet cleanly transfers vertical energy to the turntable, where the suspension does its job the best. Ideally, it seems that the subchassis should be underhung with respect to the fixed chassis, resulting in a stable, predictable horizontal resonance . . . and there's probably some perfect relationship between the horizontal and vertical resonant frequencies that would allow horizontal shock to be converted to vertical spring deflection (through pendulum action). |
Thanks for the info, Dertonarm . . . I enjoyed reading about these products.
But it's not a matter of "re-inventing the wheel", its a matter of understanding the exact requirements so as to make sure we understand how well the solution fits the application, and the problems we're trying to solve. Because (to use a silly example), putting your tomato plants in the finest laboratory glassware doesn't mean their fruit will taste any better.
Most of these off-the-shelf devices (i.e. the MK26) appear to have a low-pass characteristic that somewhat resembles a Chebyshev response, which trades some pass-band ripple or peaking for increased performance in the stop-band . . . I'd speculate that this is an excellent trade-off for most of the laboratory applications for which they're sold. But for a turntable, the low-frequency peaking of these products may indeed cause some problems. I'm sure they still sound excellent . . .
. . . but if you truly want to do a turntable "right" as you say, then simply sticking i.e. an RX5000 on an off-the-shelf Minus-K platform doesn't cut in my book. Using existing laboratory-instrument technology might be a good approach . . . but if you want the BEST performance like you say . . . a custom-designed product that had its stopband/passband performance tailored specifically to a turntable application is what you should be after. |
Wow, thanks for the picture, Syntax. Very, very cool work, Dertonarm. Since we're hitting on the subject of "how do we pursue perfection" . . . this is of course a difficult question, both in the defining and the persuing. I think that there are several of us here who are frequently travel on this obsessive road in one way or another, and it seems to be ultimately a reflection of one's concept of their own mortality. And I've always enjoyed how much audio and music parallel each other in this capacity. But to lighten up a bit (I attended a funeral yesterday), there are always a couple of big obstacles in the pursuit of "perfection", the first of which I'll call the "Hubble telescope phenomonon" . . . where a focus on the tiniest of minute details causes one to completely miss the end goal -- that is, a telescope mirror with an amazing level of polish on a micro-level, and a huge macro-level flaw that goes completely unnoticed. Dertonarm metioned the Eminent tonearm, and I'll use this as an example -- great low friction, but horribly excessive horizontal mass (not to mention dirt-sensitive). The other common problem occurs with high-budget, limited-production projects. . . where from a true perfectionist standpoint, the contribution of every single design, material, and manufacturing decision must contribute maximally to the performance of the end unit. But the "cost no object" attitude actually can work against this, as there's the temptation simply to throw money at a given problem, because after all . . . what's mere money when perfection (and ultimately immortality) is at stake? And in reality, the assumption frequently gets made that simply because a problem has received great financial attention, that it is therefore solved. Thus, the input of cash has distracted the builders/designers from the required process of analyzing its contribution. Both of these are what I feel are some of the currents that drive up the cost of our hobby, without necessarily driving up the quality of the experience . . . and that's very much away from what I'd consider perfection to be. As Dylan Thomas said: The force that through the white thread drives the platter
takes my green dollar; that blasts my bank account
Is my destroyer. |
I wasn't on a field campain just to bring as many troops as possible on the battlefield as to crush the enemy by simply overwhelming him by sheer number and brute force.
From the plain dimensions this may look as just another gigantic egomatic turntable where weight and money were the driving forces and the brain was replaced by the big wallet. I didn't mean to insinuate that these were at all your motivations, my apologies if it came across that way. I was simply trying to give a little counterpoint to the general discussion, and make the point that the consideration of cost isn't necessarily anathema to the pursuit of perfection. Lewm did bring up the string . . . I'd appreciate it if you could explain some of the dynamics involved here, as I don't have much experience with thread-drive turntables. While the mid-1980s Micros and such are designs I've always admired and enjoyed listening to . . . I've always been a bit mystified as to how such a thing as the alignment of the pulleys, the tautness of the string, etc. (which strike me as critical parameters) were left up to the end-user to get right, when there was obviously so much effort into removing variability from so many other aspects of the mechanical design. Also seems really inconsistent with regards to temperature, and wear/stretching of the string itself. Are these significant factors, and does it ever bug you that maybe with sub-optimum setup and maintainance, your designs over the course of the years may not be delivering the performance you designed them to have? |
So this futzing-about with various types of belt media and such . . . I take it that this is pretty much "de rigueur" to get the best from any turntable that uses the thread-drive approach? What did i.e. Micro Seiki originally intend for the RX/RY-5000 system? |
Fascinating stuff . . . great thread (pun intended).
I will admit that I'm having a conceptual problem with the whole "controlled slippage" approach to filtering the motor vibrations from the platter. I can see how it would work brilliantly if all the conditions were carefully balanced . . . it just seems really inconsistent in terms of day-to-day usage, and likely to require very frequent tune-ups at least in terms the thread tension. But I will admit that I am comparatively ignorant of the real-world characteristics of these actual materials in this application.
Just a couple thoughts on the drive-system subject - first, how much data is available on the characteristics of the rotational vibration produced by the motors themselves? It seems to me that the relative strength and spectrum of this energy would be of paramount importance to determining the amount of slippage, the tensile flexibility of the belt or thread, and the necessary mass of the platter (and inertial flywheel device). Second, there is actually one more slippage mechanism -- that between the rotating magnetic force vector produced by the motor's stator, and the speed of the armature. It would seem that it's the interaction of these two time constants (or three if there's an inertial flywheel thingey) that ultimately determine how effective the motor/platter isolation can be.
Also, Dertonarm brings up the point of clamping and the record/platter interface, and I agree that it's undeniable that the platter must be of sufficient mass to effectively sink the vibrational energy of the record. But as far as the proper way to make the record-platter interface, that's another issue. There seem to be obvious drawbacks with clamping (tolerances in record dimensions, flexibilty, and condition), vacuum hold-down (complexity, noise and reverse-side dirt-bonding), and mere gravity (poor coupling). I confess that I don't really have an opinion as to what the "ultimate" solution has to be . . . maybe we just play lacquers! Issue solved! :) |
Please explain why pulley material would be audible when used with a 70 lbs. platter. I don't have a clue what physics are involved for this case. Well, assuming that this is a thread-drive system with "controlled slippage", and assuming that you're talking about the motor pulley . . . . the first thing to look at would be the effect of the pulley material on the coefficient of friction on the belt material, both in terms of the material itself, and the resulting surface finish from a given machining process. Second, looking at some pulley designs (again using the Micro RY-5000 for reference) I'd guess that it *could* exhibit different resonant characteristics when made of different materials. And of course, if changing the pulley material changes its mass . . . But the effects of these criteria are going to be highly dependent on the actual vibrational energy coming from the motor in the first place. And when they reach the platter . . . just because it weighs 70 lbs doesn't mean that it doesn't resonate, and that vibrational energy can't move through it. And yes, this is all speculation . . . but from speculation comes hypothesis (not theory) . . . which is generally the first step in good science. As Raul pointed out, it's not that basic Newtonian physics doesn't apply, it's just a matter of having the time, money, and common sense to find out how. |
I believe some models of Jeep/Chrysler used hydraulic cooling fan motors powered by the P/S pump due to the fact they are quieter. I would speculate that the main reason for using a hydraulic motor is more to do with the high-temperature environment in which the fan motor must operate, especially if used on the back side of the radiator. At these temperatures, copper conductors get pretty lossy, and when running a 12V motor (drawing 20-30 amps), they start to really add up . . . in windings, commutators, brush leads, wiring, relay contacts, etc. And then you've got make up for those losses in power generation . . . and when a cooling fan is most important is when the vehicle isn't moving, hence engine speeds are low, and the alternator suffers from poor effeciency. In this application . . . hydraulic makes lots of sense. But for a turntable, both air-vane and fluid-vane motors are far from vibration-free and cogless (go to an auto-body shop and listen to their air-vane-powered tools) . . . so there will be similar challanges as electric magnetic motors. Maybe an expanding-chamber screw-type armature fed by high-pressure hydraulic fluid? Then the problem is that you've got NO speed feedback, not even the fixed-frequency rotating magnetic field in an electric motor, and there's been disapproval voiced for a feedback speed control system. Believe me, I'm not completely poo-poo'ing the idea, but rather will be extremely impressed if these challanges (and all of the others that I've not thought of) are able to be solved. And of course I'll want to read all about it, so do keep us posted. |
