My first post here, although I have read some of the discussions on this site over the years.

I wanted to share my experience with my Micro Seiki RX-5000 and resonance control of its heavy platter. I have seen posts here before about the bronze platter ringing. Romy suggested that a simple hard rubber mat would be the answer. I tend to agree, but I found another approach that I do not see explicitly written about here. Forgive me if my search failed to turn up this topic already addressed.

The concern is, of course, is that these resonances will color the mechanical pickup of groove modulations by the cartridge. The stylus, which is forced into motion by the music being played imparts opposing forces back into the vinyl and then into the platter. If the platter “answers back” with ringing at specific musical pitches and not at others, the cartridge will pick up these resonances too. You may not hear anything obviously amiss, since all transducers impart resonances, but they are there. Perhaps the best test is to play well-recorded piano which runs up and down the scales. Notes exciting resonances may sound slightly louder, with more smearing and sustain. When resonances are vanquished, the music flows with more ease and naturalness, all music, not only piano. Of course resonance control is valid for more than just platters - tonearms, cartridges, speakers and rooms matter too.

I have heard an argument that the forces imparted into the platter by the stylus must be so weak that they can’t possibly excite the heavy platter. Large heavy objects are moved by tiny forces. The motion is just correspondingly tiny. It’s all about relative proportionality. True, the excitations and resonant responses are very small, but then the cartridge is designed to pick up tiny groove modulations that can be measured in the Angstroms. And we follow that transducer with huge amounts of preamp gain. So, as weak as the excitations are, a phonograph system is equally sensitive in picking up their responses.

If you gently rap a turntable platter (even with a record on top) you can get a sense of its resonant properties. A sharp rap (perhaps with a plastic-tipped object like the handle of a screw driver) can impart a pretty good approximation of an impulse excitation into the object being tested. This impulse (an approximation of the "Dirac delta" function) excites the object equally at all frequencies and therefore excites resonances without having to perform a sine-wave sweep as excitation. With a microphone or an accelerometer and an FFT spectrum analyzer, you can see discrete frequencies representing resonances at the various modes of vibration.

The original gun metal bronze 5000 platter exhibits a primary bell-like resonance at 855 Hz. I’m guessing that this mode is due to the comparatively thin horizontal deck (just under the groove area) acting as a spring and the heavy peripheral ring as the mass. There are other modes too, but they are down much farther in level. The next most significant resonance is a damped one at 2258 Hz. There is nothing unusual here. All platters will exhibit resonances; it’s just the physics of things.

Micro Seiki offered a “copper” mat called the CU-180, which some of you may know about. This 1.8kg device is very popular with the Panasonic SP-10 crowd, but it can be useful with heavyweights like the RX-5000 too. Suspended by itself with something like a screwdriver shaft through its hole so that it is free to move (like a cymbal), it exhibits numerous resonances, at 51, 132, 312, 549, 844, 1182 and 1569 Hz and several spread higher in frequency. Think of it as a flat and thick cymbal. It might not seem promising, but it is.

The magic comes when you place a CU-180 on top of the RX-5000’s gunmetal platter. The pairing is completely devoid of readily measurable resonances. Together they comprise a constrained layer mechanism. The CU-180 must be perfectly flat so that is sits on the 5000 platter with no gaps or rocking. Never drop or bend a CU-180 because you’ll never get it perfectly flat again!

The improvement can be demonstrated easily. If you rap on the bare platter, you’ll clearly hear the pitch of the 855 Hz mode. When you rap on a suspended CU-180, you’ll hear the multiple pitches combining into a sound roughly reminiscent of a cymbal. Now combine the two pieces, and rap on the copper mat. A dead thud. It sounds like knocking on a concrete wall. The two devices have constrained each other from exhibiting their natural resonances.

Next, remove the CU-180, and then place a rubber mat of your choice back onto the patter. Rap again, and you’ll hear the muted, but still quite audible, 855 Hz mode. I have used a Fulton Kinetic Barrier mat, a very thick and well damped rubbery mat. It does reduce the ringing (shortening its duration), but the CU-180 quenches it completely.

Lately I have been playing with a sandwich. First the CU-180 is placed on the platter, then the Fulton mat (or a Micro Seiki leather mat) is placed on top of the CU-180 (minding the VTA adjustments). I have also experimented with the record sitting directly on the CU-180, and weighted down by the 1kg Micro Seiki ST-10 gun metal disc stabilizer . This weight forces the LP to sit on the copper mat’s surface tightly, with no air gaps that could cause buzzing or unchecked resonances. I have not yet formed hard conclusions about which configuration I prefer sound-wise, but I’m leaning toward the CU-180 without any compliant mat at all, in terms of pace and rhythm. One risk of any rubber mat or other compliant mat is that its top surface can shift in the shear mode relative to its bottom surface (without actually sliding) as stylus drag changes with groove modulation. Thus speed is thus slightly modulated by groove modulation, more like in a light platter table. I believe that if the record is held tightly and directly against the heavy platter surface with its high inertial momentum, the speed is less perturbed. More listening needed.

So, I can recommend that other 5000 owners experiment with the CU-180. As always, though, YMMV.

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Chapter Two: Recently I had machinist Mirko Djordjevik make me a new 5000 platter out of 316L stainless steel. As most of you know, the platters on the last mega tables from Micro Seiki were made from stainless steel. The exterior dimensions and appearance are the same as the original 5000, but I had him bevel the inside edge of the peripheral ring to reduce the cantilevering compliance, and also we thickened the horizontal deck (just below the groove area). Mass went from about 16kg in the gunmetal platter to about 22.4kg in the new stainless platter. That’s roughly going from 36 to 49 pounds. We both believe that the spindle bearing can handle the higher mass. The new platter is a beautiful thing to behold, and tarnishing will no longer be a concern. The only resonance I could pick up was a well-damped one at 1667 Hz, which is about one octave higher than in the original platter, but lower in magnitude with little sustain. With the CU-180 on top, even that resonance was squelched entirely, and once again the sandwich is quite quiet. I have yet to spend time auditioning the new platter. > >

Wellington wrote:

Perhaps the best test is to play well-recorded piano which runs up and down the scales. Notes exciting resonances may sound slightly louder, with more smearing and sustain. When resonances are vanquished, the music flows with more ease and naturalness, all music, not only piano. Of course resonance control is valid for more than just platters - tonearms, cartridges, speakers and rooms matter too.

Wellington wrote:

Lately I have been playing with a sandwich. First the CU-180 is placed on the platter, then the Fulton mat (or a Micro Seiki leather mat) is placed on top of the CU-180 (minding the VTA adjustments). I have also experimented with the record sitting directly on the CU-180, and weighted down by the 1kg Micro Seiki ST-10 gun metal disc stabilizer . This weight forces the LP to sit on the copper mat’s surface tightly, with no air gaps that could cause buzzing or unchecked resonances. I have not yet formed hard conclusions about which configuration I prefer sound-wise, but I’m leaning toward the CU-180 without any compliant mat at all, in terms of pace and rhythm. One risk of any rubber mat or other compliant mat is that its top surface can shift in the shear mode relative to its bottom surface (without actually sliding) as stylus drag changes with groove modulation. Thus speed is thus slightly modulated by groove modulation, more like in a light platter table. I believe that if the record is held tightly and directly against the heavy platter surface with its high inertial momentum, the speed is less perturbed. More listening needed.

Wellington wrote:

Chapter Two: Recently I had machinist Mirko Djordjevik make me a new 5000 platter out of 316L stainless steel. As most of you know, the platters on the last mega tables from Micro Seiki were made from stainless steel. The exterior dimensions and appearance are the same as the original 5000, but I had him bevel the inside edge of the peripheral ring to reduce the cantilevering compliance, and also we thickened the horizontal deck (just below the groove area). Mass went from about 16kg in the gunmetal platter to about 22.4kg in the new stainless platter. That’s roughly going from 36 to 49 pounds. We both believe that the spindle bearing can handle the higher mass. The new platter is a beautiful thing to behold, and tarnishing will no longer be a concern. The only resonance I could pick up was a well-damped one at 1667 Hz, which is about one octave higher than in the original platter, but lower in magnitude with little sustain. With the CU-180 on top, even that resonance was squelched entirely, and once again the sandwich is quite quiet. I have yet to spend time auditioning the new platter.

Interesting, but I have to say that does sound a bit problematic in several ways. For one, I’m guessing you meant to say “one mm”, or even “one quarter of an inch”, but not “one inch”. One inch is quite a soup bowl! For another, anti-skating force compensation must pull the arm toward the outside, because skating forces pull it inward toward the spindle. So you’d need an inverted bowl, higher in the center, to use gravity for anti-skating.>>

Perhaps you’re also trying to achieve a tight intimacy between LP and platter, without relying on vacuum clamping (which won’t allow the use of a CU-180 anyway). This reminds me of a simple idea. Decades ago, I bought a SOTA reflex clamp. It included a small rubber washer, which miraculously I still have after all these years. First you slip the washer over the spindle, then the LP and finally the clamp. When you tighten the clamp’s lever, the spindle is gripped and a clamping forced is exerted. So, before the force is applied, the LP is raised slightly higher in the middle by the washer, maybe 1 or 2 mm, with the LP edges drooping down toward the outer edge of the platter (barely visibly). When the clamp is tightened, it pushes down on the outer edges of the label area only, which is between the high spindle washer and the outer edge. The LP is forced to make contact with the platter first at the edges, but then all the way to the label, if you have a washer of the right thickness and the correct clamping force is applied. The idea here is to avoid the cupping problem that can occur with heavy record weights and some soft mats, where the heavy center force causes the outer edges to lift up into a shallow bowl. The SOTA clamp pre-biases the forces with the center lifting washer. BTW, the SOTA clamp works with Micro tables just as well. A simple test is, you guessed it, another rap test, only this time it’s a tap. With a (clean) fingertip, tap around the record’s playing surface while it’s clamped. You can hear any air gaps as “ticks” because the record will momentarily slap the platter when you tap over a void. After a while, I can pretty much determine how much force to exert with having to mishandle my records!>>

Wellington wrote:

Interesting, but I have to say that does sound a bit problematic in several ways. For one, I’m guessing you meant to say “one mm”, or even “one quarter of an inch”, but not “one inch”. One inch is quite a soup bowl! For another, anti-skating force compensation must pull the arm toward the outside, because skating forces pull it inward toward the spindle. So you’d need an inverted bowl, higher in the center, to use gravity for anti-skating.

Wellington wrote:

Sorry, but I have to tell you that you do have it backwards on the skating forces. Just Google for a force diagram. Another way to know is to look at how the anti-skating force is applied in arms using the weight, pulley and monofilament line approach. In the classic SME arms, for example, the weight is on the record side of the arm, but it pulls on a point which is BEHIND the arm's pivot axis; so that the weight pulls the stylus-end of the arm outward. In my Triplanar, the weight is on the opposite side of the arm, away from the record, and is attached to a point on the arm in FRONT of the pivot axis. So it also pulls the arm outward, away from the spindle. Easy to confirm.

Wellington wrote:

I think the notion of NOT having the LP in intimate contact with a well-damped and heavy platter is misguided, in fact terribly misguided. If the LP is forced into contact with a lively, resonant platter (as many are), that's not good either, of course, but it's the platter's problems that need to be fixed. The answer is not to lift the LP free from the platter. Perhaps starting with the Transcriptors turntable of decades past, to the odd Meitner Platterless table, several have tried a platter-less approach, and none have succeeded. Hold a LP freely in your hand in the usual way, and tap the surface. You will hear that plasticy sound. It's a characteristic sound, not neutral at all, not like tapping a concrete wall. Spectrum analysis shows a number of resonant modes especially at lower frequencies, depending on the LP's weight. Those are the sounds that will be underpinning your music if the LP is not forced onto a neutral platter surface. Look at how records are made: Scully and Neumann lathes used massive turntables with vacuum hold down for the lacquer. Early Neumann lathes had 65-pound platters, later ones went as high as 130 pounds, if I recall correctly. No mats, just hard vacuum pull down. Similar to...Micro Seiki!

Romy the Cat wrote:

The anti-skating force pulls arm outward? Sorry, I very much degree. In any arm that I have seen and that makes any sense, including the classic SME arms the anti-skating force pushes arms toward to middle. I think it is not even debatable and I am very surprise that we even talk about

be wrote:

Your circumference force is right, but when viewed from above it work clocwise around the lateral bearing of the arm, therefore the arm wil tend to move inwards :-)

Romy the Cat wrote:

Soory, Be, no matter how I look into it I can’t understand why circumference force would make the arm to move inward. If you spin your platter not at 33 but at let say 45 and pule some light subjects on the platter then they will be thrown off the platter. A needle and a tonearm are the subject of the very same forces and this is why LEFT side of the needle worn more if anticaking is not enough. The platter spins clockwise, so the needle left (the external) side pushed by circumference force press harder to the left side of the groove. It is not a surprise that the left side her more distortions and trucking problem when anti-skating is not enough. When you make a left turn at high spin then your car rolls over it’s right side- or outside of your driving trajectory…. Right?

Romy the Cat wrote:

be wrote: Your circumference force is right, but when viewed from above it work clocwise around the lateral bearing of the arm, therefore the arm wil tend to move inwards :-) Soory, Be, no matter how I look into it I can’t understand why circumference force would make the arm to move inward. If you spin your platter not at 33 but at let say 45 and pule some light subjects on the platter then they will be thrown off the platter. A needle and a tonearm are the subject of the very same forces and this is why LEFT side of the needle worn more if anticaking is not enough. The platter spins clockwise, so the needle left (the external) side pushed by circumference force press harder to the left side of the groove. It is not a surprise that the left side her more distortions and trucking problem when anti-skating is not enough. When you make a left turn at high spin then your car rolls over it’s right side- or outside of your driving trajectory…. Right?

alex wrote:

Sorry Romy,We are talking about pivoted tonearm with overhang. That is the geometry  that creates force to pull the cartridge toward the centre of the record. If you take a moment to observe how anti-scate weight is attached to SME3012 ...you may find that it pools cartridge toward the edge of the record to compensate  force  toward the centre. Right  ?  When we are done with the anti-scate, as a free bonus I can also help you understand how NF EQ works in  EAR834P.

Romy the Cat wrote:

alex wrote: Sorry Romy,We are talking about pivoted tonearm with overhang. That is the geometry  that creates force to pull the cartridge toward the centre of the record. If you take a moment to observe how anti-scate weight is attached to SME3012 ...you may find that it pools cartridge toward the edge of the record to compensate  force  toward the centre. Right  ?  When we are done with the anti-scate, as a free bonus I can also help you understand how NF EQ works in  EAR834P.   Yes, Alex. The overhang’s parallelogram is how the technical papers above explain the “wrong” direction of skating. As I said above I chose to stay with my simplistic circumferential  force, my life with it is more comfortable, pleasurable  and I do not need to admit to myself that I was a Moron for years believing in opposite. I will not take your free bonus. S ince people like you expressed their interest to study EAR834P NF after I pointed to them out that the circuit sounds interesting then I will let other people, the people of my choosing, who explaine to me how EAR834P works. Affectionaly, Romy the Cat