it is relatively easy to machine and is inexpensive. However, aluminum is poorly damped and subject to resonance. So it was imperative that other materials are used such as steel,lead,bronze and many others to numerous.I am guessing also the availability and easy to work with then say acrylics...I am sure their are more reasons to using it as a chosen metal.
Why Use Aluminum for a TT Platter?
Mass I am told is a good thing when it comes to TT platters. Lloyd Walker for one extolls it's virtues and as a rule some of the better turntables like to brag about their big ..Platters. Why then would aluminum, known for it's light weight (low density) turn up as frequently as it does as a platter material. I know it is easily machined but isn't there anything better and much denser.
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I was under the impression the weight of the platter was more for maintaining a steady constant speed thru inertia so the motor is less taxed in the quotient. I never understood aluminum either, is it not a quality of the platter to allow the vibrations to be drained and not reflected back at the stylus interfearing with its purpose that one would want. Many people call any platter not metal, acrylic which is not a true description. The platters infused with carbon and nylon known as Derlan are as the manufacturers claim closer to that of the vynil itself. Maybe your question is really the answer to what material has not been tried for a record mat and why. Cheers |
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The idea of "big" or extremely heavy platters is mostly for use with belt drive tables which I believe, in terms of speed accuracy, are clearly inferior to properly implemented direct drive tables. And yes, when it comes to belt drive, it is about inertia. "An object in motion remains in motion unless acted upon by an outside force". |
Just look at the platter of the relatively inexpensive ($2k) Nottingham Spacedeck. It's a minimalist design table, and I bet that the platter alone costs at least half, probably more. I have no idea what it is made of but the thing is quite heavy. As I understand, that's what mostly makes Nottinghams sound the way they do - the platter. Cooper with lead and steel in a sandwich style sounds good to me. And a beer please. |
I just know in direct comparisons in the same system between VPI tables: Aries 3, Aries 1, Classic 1, and Classic 2 it appeared consistently whether with or without a mat that the new aluminum VPI platters ring like a bell compared to the VPI super platter and acrylic platters. Resonance, noise, and brightness were in abundance compared to the others. |
Let me restate that. ;-) The mass is not there for inertia. That flywheel affect that folks like to think about when high mass platters are mentioned with belt drives would only matter when the platter is accelerating or decelerating. Once the platter is up to speed the mass would make any sudden changes in platter speed near impossible. This is also why so many DD tables have light-weight platters. The motor on a DD is designed to directly manipulate the platter in order to correct speed. The platter is supposed to have it's acceleration constantly manipulated. |
02-09-11: Wntrmute2 wrote: "Belt drives...in terms of speed accuracy, are clearly inferior to properly implemented direct drive tables." Humm, proof, evidence to back this up? ----- I was going to ask this as well, until I realized who the author was. Although I must ask - who's making a properly implemented dd nowdays? I recall people liking the Goldmund DD. |
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I think the key to an aluminum TT platter is to properly damp the aluminum to reduce resonance. This is often done within the platter and/or on top of the platter as in the case of SME. Mass does matter depending on the drive system and what problem the designer is attempting to solve. Regarding the whole belt vs. DD discussion here, I agree with Dan ed, though this is far too complex a topic to discuss on this thread and I think we should stay away from gross generalizations regarding TT drive systems. It's how its implemented that counts. |
Aluminum is used for several reasons. The first is that it is non-magnetic. This keeps it from messing with the cartridge. Aluminum is also relatively cheap, as it is one of the most abundant metals. Its also easy to machine. An aluminum platter should be damped in some fashion for best results. If this is done it will keep up with any other material with no worries. |
i think the reason why direct drive tables tend to have light-weight platters is for fast acceleration. club dj's are among the most enthusiastic users of direct drive turntables. when you are a club dj you want to be able to cue up the record and have it accelerate to speed as quickly as possible on the break. one of the drawbacks of direct drive turntables is the possibility that vibrations from the motor would couple into the turntable and get picked up at the cartridge. since the vibrations would likely be relatively low frequency, it would likely be in the frequency range that gets amplified in the phono stage. so a higher mass platter would require a more powerful motor, which i would think, would increase the likelihood of vibration. |
I am in the process of building a turntable made entirely of Delrin which I understand is as close to a metal as you can get in a polyvinyl product. Fabricators love it because it machines so well, and holds its shape under load. Enought that you can use it for a bearing surface without a sleeve. I hope to see what a turntable with a Delrin plinth and platter sound like compared to a similar ridgid deck. However, a 3" thick piece of Delrin is about $250 per square foot. Dont want to make too many false cuts or holes in that. |
Paperw8: "one of the drawbacks of direct drive turntables is the possibility that vibrations from the motor would couple into the turntable and get picked up at the cartridge. since the vibrations would likely be relatively low frequency, it would likely be in the frequency range that gets amplified in the phono stage." You're talking about half Hertz at 33rpm. That frequency exists in ALL turntables. Direct-drive is as quiet as anything. Unless the bearing is bad quality, there is very little or no noise in DD, just like belt-drive. I would say it's even quieter than belt-drive. The motor turns at 33rpm, the same amount of rotations as the platter of a belt-drive or idler-drive, WITHOUT the fast spinning motor in a BD or ID that sometimes spins at 1800rpm, and that's 30Hz! Now, the DD platter is spinning at 33rpm by magnetic force and please tell me where the stereotype DD motor noise is coming from? The second people think the motor is underneath the platter, they immediately think it's noisy. Go take a look at the assembly of a DD table, it's a platter with a ring magnet underneath and wrapped around or above a series of coils centered by the bearing well. That's it, nothing is touching the platter, unlike the belt in BD or idler wheel in ID. It's "magnetic drive" - though I hate the use of that term in commercial products. You can criticize DD having cogging issue but not noise. Noise in DD is the last thing I worry about. Oops, this thread is about platter material. Sorry. ____ |
When VPI's Harry was asked that question he said it was all about cost related to the platter and less torque on the motor. Remember Harry went from lead/rubber, to acrylic to aluminum. If one is not very cynical, profit would be the answer. I've heard them all and still think the original TNT platter is best. |
you can't hear 2Hz so obviously i was not referring to any 2Hz rumble. in the real world, nothing is machined to perfect balance, so when it rotates there will be some vibration. if you can hear sound from a drive motor, then obviously the frequency is within the audible range. a cartridge can pick that up and if it does, it is likely going to be in the part of the frequncy range that is amplified in a phono stage. as to the magnetic drive to which you refer, a rotating magnetic force field (which is what you need to turn the platter) doesn't just happen by magic: there has to be some motor that turns a rotor (e.g. an induction motor) that creates the time varying magnetic field that could turn a platter by lorentz force. there will be *some* vibration in that motor. if it is a reasonably well made turntable you probably won't be able to hear it, especially if you use a large signal cartridge. |
"there has to be some motor that turns a rotor (e.g. an induction motor) that creates the time varying magnetic field that could turn a platter by lorentz force. there will be *some* vibration in that motor." The rotor is PART of the motor, propelled by the stator coils. There's NO extra motor to turn the rotor. The platter and the motor shares the same bearing, hence "direct drive." NOTHING is physically touch the platter outside of the bearing and rotor, no belt, no idler wheel. You can argue the magnetic force to spin the rotor creates a reverse torque energy (vibration) on the stator. But that's still a lot less vibration from other means of spinning the platter such as belt-drive and idler-drive. Of course there will ALWAYS be some vibration, so is planet earth. Let's not nitpick here. All I am saying is that people seem to be brainwashed by the stereotype that just because there's a motor underneath the platter of a direct-drive turntable there will automatically more vibration than a belt-drive turntable. Simply not true. To get a better illustration, take a look at the mechanical simplicity of a, say, Brinkmann Bardo DD turntable and its coreless mtor: http://www.onahighernote.com/images/product_categories/Bardo_Magnetic_Drive_small.jpg [url]http://www.onahighernote.com/brinkmann/?c=2>http://www.brinkmann-audio.de/inhalt/bilder/bardo2.jpg[/ur] [url]http://www.onahighernote.com/brinkmann/?c=2 People can argue all they want about cogging and speed hunting, etc... which are true issues. Noise, again, is the last thing I worry about in a direct-drive turntable with quality bearing, which holds true for ANY turntable. If you have noisy bearing, you have a noisy turntable, not just a DD table. I own all genres of turntables, BD, DD, and ID. They all can sound good and I like them all. DD gets a bad rep so I am compelled to comment. That's all. Happy listening! ____ |
Aluminum (or aluminum alloy) were chosen many decades ago for a number of reasons depending on the company and its intentions. Aluminum is non-magnetic and easy to machine, shape, and balance. Copper or bronze is heavier, but is also more expensive, would take longer to spin up, and is more likely to bend out of shape. And get this straight: The direct drive turntables were not designed for the DJ market; they were designed for the high end home audio market. Adjusted for inflation, the SL1200 was $300, equivalent to $1200 today. Most "nice" turntables at the time were $200-300. The SL1200 was designed around the SME 309 tonearm, and the SL120 version came with an SME armboard instead of a tonearm. DJs adopted SL1200s gradually because they're rugged and spin up to speed quickly. In the '70s, a 4-to-5 lb. platter was considered a heavy platter. There are many things to commend an aluminum alloy platter, some from a design standpoint and several from a manufacturing standpoint. To control ringing Technics dampened the underside with a thick rubbery coating, and furnished a 17-oz 1/4" thick turntable mat to dampen the topside. This was later dropped to half the weight and thickness because the DJ market favored it. I have a heavy Oracle Groove Isolator sorbothane mat and it quieted my SL1210 M5G nicely. Before belt drive really took off, aluminum was the platter of choice, inherited from the rim drive 'tables of Garrard and Dual. As mentioned before, it was easy to mill, balance and shape. It also has plenty of tensile strength for creating a thin rim to accommodate the pressure of the motor's idler wheel. Acrylic, MDF, and glass would not make a good platter material for an inner rim drive as implemented by Dual and Garrard. So most of the reasons for aluminum are historical. If Technics had continued making turntables for the high end home audio market, they might have come up with an acrylic platter and better damping and isolation, but they didn't, so economy of scale dictated that they stay with the original design and materials and shift their market to the dance clubs. |
As a former club dj and as current employee for one of the worlds largest aluminum companies here is my two cents worth. First regarding DJs and direct drive tables when you are a club dj you want to be able to cue up the record and have it accelerate to speed as quickly as possible on the break. This is not true unless you are a bad dj and don't know how to mix. DJ's are attracted to the SL1200 for its ability to accurately adjust and maintain a steady speed with the pitch adjust. As a dj you want to mix the music such that the BPM's of the next track are in synch with the one playing so the change from one to the next does not disrupt the dancing of the crowd. Second, upon purchase of a new table by a dj, the rubber mat that is provided is thrown out along with the rest of the useless packaging, then a felt mat is used to allow the platter to spin beneath the record such that the racord can be held in place or pulled back during the cueing process without disrupting the movement of the platter (it act as sort of a coupling). If you are scratch DJ you may even chose to add teflon record sleeve cut into a round shape between the felt and platter just to be sure there is no sticking. Now that this is cleared up, high inertia could be benefitial for DJs provided the performance of the slip mat "felt coupling" can prevent the fly-wheel from slowing. So far the direct-drive quartz speed adjust is more reliable. Aluminum or Aluminium, not much to add other then to confirm what has already been mentioned, it is relatively inexpensive, non-magnetic, easy to machine, cast, or forge and readily available in wide variety of sizes and formats. Copper has become extremely expensive. Steel is cheap but difficult to machine, magnetic and will it rust unless protected, bronze contains copper so it is also relatively expensive. Finally lead, is toxic. There also magnesium, berylium and titanium, these are expensive, difficult to machine (specialy for Mg, which the chips are flammable and potentially explosive) and toxic in the case of beryllium. So in terms of metals Al is pretty easy choice. As for other materials such a plastic, carbon fiber or wood, I can't comment, but I would image they could be good choices for the given application. |
things have probably changed quite a bit since the days when i used to go to clubs. in the 1980's disco scratching, mixing &c were much the rage. |
"In the '70s, a 4-to-5 lb. platter was considered a heavy platter. " Considered heavy by who? Certainly not any of the dealers or audiophiles I hung out with. "The SL1200 was designed around the SME 309 tonearm" I'm thinkin' the SL1200 was designed and brought to market before the 309 existed. Anybody know? I have sent an inquiry to SME. Y'all be cool, Robert |
In my experience aluminum is not the best platter material. But there are good reasons that it is common and popular. It is easy to machine, reasonably inexpensive and when layered with another material or at least a good mat it performs quite well. Brass is a far better sounding platter material than aluminum, but costs 4 to 6x as much as aluminum. So as good as brass is, it's not a great value. I find that paper based phenolic, like Garolite XX, makes an exceptionally good sounding platter. The discussion about vibration from motors is missing the most important point. It is not vibration that degrades sound but cogging. Motors with a lot of cogging usually, but not always have detectable vibration. Because of the isolation afforded by the belt, most belt drive motors have a lot of cogging. Because DD motors have no isolation they must be designed to have dramatically less cogging or they would sound terrible. Cheap DD implementations often have mediocre motors that have too much cogging (still far less than belt drive motors) and hence sound ragged. It's not that DD is bad but it's that a poor implementation of any sort will sound bad. I find that DD has the potential for goodness that cannot be matched by even the best belt drive implementations, but bring your wallet because it is both expensive and difficult to get right. |
i used to have a dual turntable, which was a fairly popular, and reasonably well-regarded, brand at that time (at the time it was better regarded than panasonic, but that might be a matter of who your circle was). i believe that the platter was in that range. |
02-09-11: RobobI was a dealer at an audiophile store in 1975 when the SL1200 and relatives came out. The SL1200 platter was heavier than the platters on Garrards and Duals of the time, and heavier than platters on the Rabco, Philips, and B&O turntables, and at least as heavy as a Thorens platter, all upscale from the Dual. The really heavy platters started coming along with the Micro-Seiki and similar massive belt-drive turntables and showed up soon but were not as widely known. But compared to other 200-300 turntables of 1975, the platter of the SL1200 was pretty heavy. I oughtta know; I held most of these platters in my hands as we assembled them for demo models. Sorry. I meant the SME 3009, which existed before the Technics DD 'tables appeared. It has a J-shaped tonearm with standard detachable headshell. The SL120 was an armless DD turntable with a calibrated SME 3009 cutout. In fact, the Technics tonearm on the SL1200 variants has an effective mass of 12.5g, the same as a SME 3009 Series II. |
If you use enough aluminum, it can get pretty heavy. It is a lot easier to work, and a lot cheaper than using stainless steel, bronze, brass, copper, feric alloys, etc. When you are trying to mass produce (and keep in mind, in the 70s, companies made turntables like today they make ipods), ease/speed of creating the shiny metal piece was paramount for many. Moving off-track... There are DD tables with heavy platters. I have a couple with platters which weigh 20+lbs. Not all DD motors are built to instantaneously bring the platter to speed if there is the slightest speed variation. Some are built to bring back to speed more slowly. Cogging is an artifact of certain motor types (generally, those with iron cores). Not all motors cog. The top brushless, slotless, coreless motors by Pioneer, Yamaha, Denon, and others are (generally) extremely smooth (zero cogging). They'd be a bear to make again in some cases. In general, these motors will have less torque than slotted motors like Technics. From what I can tell, the first really heavy platter came on a belt drive Melco. Micro copied soon afterwards. That said, DD platters gradually got heavier on the high-torque motors. The Sony PS-X9 of 1976 has a decently heavy platter which is very wide (more inertia). The Technics SP-10Mk2 platter is not light. The Yamaha PX-1 of 1978 is also a decently heavy platter, and the higher- end tables from Exclusive, Onkyo, Lo-D, and others from the early 80s mostly had high-mass platters even though they were DD tables (they all had coreless linear motors too). The lighter platters on high-end tables came on Denon, JVC, and most other Sony tables, which operated with substantially lower torque than other high-end tables. |
T_bone, very good post. This DD sub-topic came about after some general comments about dd/bd and mass, and thus my own generalized comments. It is most definitely a much more complicated discussion. I think if Chris starts talking about eddy current braking and such we'd soon leave the dj talk behind. ;-) |
Livemusic, Yes Cocobolo is still the best platter material I have heard, but Garolite sounds nearly identical and is far less expensive. Tbone, Coreless, slotless motors have very low cogging, but it is not zero. A top quality DD table is remarkably sensitive to even extraordinarily small amounts of cogging. I have no first hand experience with the fine motors you cite, but suspect that the very low cogging they exhibit is still audible. Higher platter mass generally translates into better sound. But as is often the case with audio there is no consensus. Heavy platters sound different than light platters. Most but not all prefer the sound of heavier platters. I have experimented with platters up to 75 lbs. For my tastes I found that heavier was always better and never found a point of diminishing returns. But anything beyond 75 lbs starts getting very impractical. An interesting discovery was that both belt drive and DD implementations seemed to benefit from heavier platters. But with DD the benefit from a heavier platter was significantly less than with belt drive. |
I had a Technics SL-1100. I think it had the distinction of being the first DD machine made. It also had the heaviest platter of any DD machine, including the SP-10 and certainly heavier than any Dual, Garrard, Thorens, or the like. The 'cogging' thing is not an issue on the better DD 'tables. However I should point out that this is a problem with any servo-controlled motor (often found on belt-drive machines) if the servo is not designed properly. The result can be that if you graph the overall speed of the table over time, the result will be something that looks like a sine wave, centered around 33.33 rpm. The slower the sine wave and the less amplitude it has the better. Subtle speed variations like this are heard as a loss of focus in the sound stage due to variable skating forces on the arm. This is why a belt drive, using an AC synchronous motor, might be preferred over some of the cheaper DD machines. But to assume that all DD machines have this problem would be a mistake. |
"But compared to other 200-300 turntables of 1975, the platter of the SL1200 was pretty heavy." That may be but I remember thinking something like a 12 pound platter was heavy. "Sorry. I meant the SME 3009" I should have thought of that. Response from SME: Regarding the SME 300 Series we can confirm production began in 1988 as an addition to the SV range which of course includes the SME SIV. The 309 arm remains much the same apart the introduction of magnesium arm tube approximately 11/12 years ago. This change was to bring the arm tube into standard production alongside the SV and IV but clearly is also an upgrade to the 309. The 309 today is one of our most popular arms and provides many of the sonic benefits so often referred to in HiFi press of the SV tone arm. |
Chris/Teres, My understanding of the technical term for cogging means either slots or cores are required (though I could imagine where badly-designed slotless coreless motors could have other iron present. I assume that the 'cogging' issues you mention on slotless AND ironless motors comes from the fact the stators are not infinitely small. Does it also come from coil material saturation/resistance of some kind (i.e. Induction is not perfect because of materials issues)? Is there something else I am missing? I completely agree that in the end it comes down to execution. |
Cogging is measured as torque ripple. It is the amount of variation in the developed torque as the motor rotates. A single phase AC motor by definition has 100% torque ripple since at the zero crossing of the waveform no toque is generated. DC motors have much more constant torque and typically will have torque ripple values of 10 to 15%. The motors used in DD tables have multiple overlapping phases that dramatically reduce torque ripple. In theory a three phase motor will have less than 1% torque ripple. But that is only if they are perfectly constructed and driven with perfect waveforms. But even a crappy three phase motor will have relatively low cogging compared to a single phase AC or DC motor. Typical motors will have windings wrapped around a laminated iron core. This focuses the magnetic field and makes the motor more efficient. Core-less motors (AC or DC) have copper windings that are formed without a core. They have less cogging because there is no attraction between the magnets in and the iron cores. Cogging can also be reduced by angling the cores so that they have equal attraction between the magnets and the cores as the motor is rotated. You can tell how much the cores affect cogging by turning the motor by hand without power. Core-less motors are less powerful, more expensive and usually have less cogging. |
Copper is the best for platter top! There are problems with any metal for being the top of a platter. The top of the platter should be available as a means of damping the vinyl as it is tracked by the tone arm. Metal is ill-suited to this task. Copper is a special condition that likely should be avoided. In the presence of a magnetic field (perhaps the one in the cartridge itself), the spinning copper will form a sort of primitive generator, and could easily be responsible for extra noise in the playback. |
I wonder if Cocobolo is such a good sounding wood if one can't invent a cheaper Cocobolo plywood. I guess the glue and compression would have an effect. Other alternatives are the numerous sandwich type composites where the upper most layer being your favored material with the easily machined, cheap but invariably aircraft grade aluminum, that is bragged over is used as the center then something like another dense wood or composite like paka or tank wood. I personally don't think that well encased lead does not pose danger once it is properly manufactured. How about concentric brass rings embedded in the bottom layer. Perhaps a contest with the few remaining lucrative TT companies sponsoring the best platter material yet. I noted that no one suggested melamine. There is an asphaltic roofing tile that might be good if it could be made hard enough stabalised and used as a center layer. You get the idea. It's like any recipe contest. |
