Why are my woofers pumping?

stereo5: I don't diss the KAB. I am only saying, single-ended cables from my balanced phono stage to my balanced preamp sound much poorer in my system, compared to balanced cables. So a filter, to become a plausible option, would have to be balanced. The KAB, in the current configuration, is only single-ended (RCA connectors). OK?

I have been in contact with KAB and another filter maker suggested earlier in this thread. They have responded very well and informatively. 

Two camps appear: the "purist" who say: fix the problem, and the "lowly ones" (plebeians) who suggest a filter "to be done with it".

You keep coming back to the KAB, then diss it.  Why not get one and try it?  If you don't like it you can send it back.  I use one in my system and my 3 audiophile friends and I could tell no difference with or without it other than absolutely no woofer pumping.  The Turntable is a VPI Prime with a ZU-Dl103mc cartridge, VPI interconnects going to a 7K McIntosh tube preamp.  Speakers are GE Triton Reference.  Like I said, problem solved and I can sleep at night.

Status: I enjoy my SME V / Atlas combo, even with some woofer pumping and - maybe - possible distortion. Yesterday I tested Kula Shaker: K2, on LP vs Tidal digital. Result: digital = no clear woofing (as before), but poorer sound. Distortion - some, very evident in loud music passages, from both sources, but overall more "grunge" in the digital. The contest was a bit more even, than I remember - analog does not totally outcompete digital, but still, no doubt. I should probably consider a better DAC. But if it has real "grunt" (like the Aesthetix Io) maybe this includes some woofer pumping ;-  If you cut low frequency it easily hurts ambience, overtones, etc. I think this is why Pink Floyd's Echoes has woofer pumping. Everything down below is recorded. The vinyl is taxed to the maximum. You can hear this deeper tonality also in the high frequencies (Richard Wright playing light organ touches). With today's resolving systems, we are able to reproduce such pioneer enginering efforts and should be grateful for it.

One more test. Changing the connectors from the Aesthetix Io phono stage to the Einstein preamp from balanced to single-ended. Result; much less woofing with single-ended. But much poorer sound too! More flat, congested, less involving. Even when I turn the volume up, to get the equivalent decibel level (which I have to do, for the single-ended connection), there is less "here-ness" to the music. I have a semi-balanced phono stage - balanced from the second amplification section through the output. The balanced outputs sound way better than the SE / RCA outputs. Conclusion: a single ended filter like the KAB probably will not work for me. Running the phono signal single ended, or through a single ended tape loop, will degrade it.
Cables used for testing: 1) balanced - JPS Superconductor 3 (very good xlr cable); 2) single ended - Kimber KCAG (very good in some applications but not here).

vpi, and others - two camps in this thread, "fix the cause" or "fix the problem" - if I want to fix the cause, and change the tonearm, keeping the Atlas, although I dont have the financing to do it now - what would be a good match, with a resonance around 10 hz? That sounds good with the cart?

Some more testing. The woofer pumping problem is still there, maybe a bit reduced, but not fully solved (sorry for too general statements above - I thought it was solved). It is very dependent on the record - some LPs have more, some have less. I am investigating whether a filter could be an idea, using a laptop and a sound card to see what goes on in the low hz region (through the program Audacity).

Thank you vpi. Always something new to learn.

@o_holter The studder you are seeing in the spindle is typical af asynchronous motors and not a malfunction.  Download and read the manual for the VPI HW-19 MK 4.  There is a paragraph that explains this.

If your woofer pumping returns do not use a filter.  You would just be covering up the problem instead of solving it.

in the meantime, enjoy the music.

Since this thread is getting over and finished - the woofer pumping has stopped - I will only update if I find some clue, what the problem was. So far, I have not been able to recreate it. Maybe it was caused by a troubled spindle - not quite in place - or other drive problems, as suggested by vpi and others, above. Obviously, the slight leeway between the spindle housing and the plinth, which I need to tighten, may play a role, but in practice I don't think so, since due to the 10 kg platter weight, it settles quite solid anyway, and I cannot reproduce pumping by pushing the platter (or plinth).

I note an interesting thing, checking the player, and cleaning the belts, pulleys and platter. The Hanss uses two very silent motors, not vibrating much. But when I touch the top pulleys, slightly with fingertips, the vibrations are more notable. Sometimes it seems as if the motors develop a "trouble" position with the pulleys straining and vibrating. I can reduce the vibrations just by moving them a tiny bit. This is a behavior I recognize from my VPI HW-19. The motor / pulley does not quite "stall", but a combination of energies has made it stressed. Anyone who recognizes this pattern?

Some of you have suggested that acoustic feedback may have played a role for my "woofing" or woofer pumping.

This is relevant not least in a four speaker system, like mine, where some drivers are pointed towards the back wall  (with the record player).

I tested a bit more, playing the new 2 x 45 rpm Jefferson Airplane: Volunteers. Volume: loud. This is a very good remaster, quality pressing, low vinyl noise. I hear this on the grooves between the tracks. When the tracks / music played, I used my stetoscope on top of the different parts of the player.

The results were interesting, more varied than I would have thought. The top of the maglev feet had next to no feedback, the sound was dead. The plinth, and also the motors, had more feedback, although I did not hear clearly "wrong" or exaggerated sound. I tried to "hold on" to the plinth, firmly, as suggested in the thread above. It made no difference.

I would like to test the platter and the record clamp, but since this rotates, I can’t do it with a stetoscope. Anyone knows of a phone app to test for rumble or noise, laying on the platter?

Hi Raul, thanks, I reread your former post, where you wrote: "even at 100hz the Atlat compliance and effective mass puts the resonat frequency in a " solid " 8hz."  I get results closer to 7hz (arm mass 10.5, screws 0.5, cart 11.6g). It all depends on what we assume is the 10hz measured compliance (supposed to be x 1.5 to x 2 of the 100hz measure - 12 in the Atlas case). I have to assume a compliance of 17 to get above 8hz. I have found no exact Lyra specification. So this is really "blind", especially if we assume - as some do - that small variations in resonant frequency play a role, at the margins at least. I get confused by all the web debate on this, "fundamentalists" who say resonance is of key importance, some who say it varies with the type of arm, player, and what not, and some who simply dont believe in it (at least not with modern fairly "medium" cart/arm combos).

Likewise, I can find no objective measure of how much the resonance increases, by adjusting the static counterweight so it does all the lifting on the SME V, compared to using the dynamic spring mechanism (but a lot of debate about how the dynamic may sound best and be more kind to the cartridge). I do see the point of Lyra including light weight alu screws (among several types). Regardless of their problems, both the Hifi record test and the calculators indicate that the arm could be lighter.

So - back to the ears? Only listening can really be the judge? Test records not correct, calculators failing to take into account important parameters  - like the arm stiffness - you name it.   

Correction: the Atlas has a 121 ohm load (not 100) - and sounds fine.
Replacing belts - yes, new ones ordered.
I will give the spindle a drop of oil, and fasten the spindle housing when I get the right tool.
BTW, reading up on the Hifi News test record shows that people find a lot of problems with it. On the lateral resonance test the actual test tones are different from those stated. I know from before that the record's anti-skating test is not good, in my case at least.
Some years ago Michael Fremer reviewed the Kuzma 4-point with his Lyra Titan i cartridge, pronouncing it the best arm he had heard so far. But using the calculators, resonance is down to ca 7.2 hz. Even more problematic than with the SME V (ca 7.5), since the 4-point weighs a bit more. Yet it wasn't a problem, to his ears.

Almarg 4-24-2018
... given the unusual design of the turntable’s drive mechanism (comprising six belts, three of them driven by what is apparently a synchronous motor on one side of the table, and three of them driven at a different height by a similar motor on the other side of the table) ... the platter might be being driven in a slightly uneven and/or not perfectly level manner. Perhaps simply due to the condition of the drive belts differing slightly between the two sides.

And I note from your system description thread that the table appears to be around five years old. Perhaps all that is needed to resolve the problem is a new set of belts?


Cleeds 4-28-2018
That actually sounds very much like a drive problem, such as a bearing issue or bad belt.


Atmasphere 4-30-2018
Boy, that sure sounds like a drive issue to me!

Consider replacing the belts!

Best regards,
-- Al

@o_holter : Again:

https://forum.audiogon.com/discussions/why-are-my-woofers-pumping/post?postid=1551771#1551771

With all respect to those gentlemans that insist on the KAB filter or the like please ask you: who of them owns the Atlas or even listen that kind of very high quality performance levels?

Seems to me that no one of them because they are not taking in count what really means: quality level performance at the Atlas levels- They say that with the filter they almost did not listen degradation and this just makes no sense.

R.

I own the KAB Rumble Filter and I am one of the ones that claim otherwise.  (No change in the sound!)

@o_holter

It sounds as though your setup adjustments might have reduced some cartidge resonance. I’m thinking that was likely part of the problem.

And in answer to one of your questions, yes, sometimes subsonic noise is actually pressed right into the grooves. It can result from multiple steps of the vinyl manufacturing process. It can also result from warps but that is a problem more often associated with stable balance tonearms, such as some uni-pivots, as their tracking force changes when they traverse the warps.

So there’s many factors that can lead to woofer pumping, but only one ironclad solution: a rumble filter. It will only be a detriment to the sound if that is your expectation. For every one who claims they alter the sound, there’s probably a dozen who claim otherwise.

I think it was the KAB filter....or something similar to that.

I'm not saying its not a good product....it just didn't work for me.

The interesting thing is: it happens at certain intervals per revolution of the record (playing silent grooves between tracks). If I turn up speed to 45, the pattern is repeated, only faster. This seems to indicate that player rumble or drive problems are NOT the main issue.

Boy, that sure sounds like a drive issue to me!

But it sounds like this is mostly solved :)   I would put a drop of oil on the platter bearing for good measure...

The Atlas sounds real good, now, with 100 ohm loading (+1 to Atmasphere). Playing Nik Bartsch: Continuum (great sound) for example, but also older overlooked classics like Joe Walsh: No peace in the city. I love this cartridge. The woofers are energetic, yes, but I cannot see much pumping.
 
Toddc2 - this reminds me of all the tweaking I did with my VPI HW19 - every little bit helped - sand box - ceramic cones - name it. I will take you up on your kindly offer to try the filter, if the pumping persists.

krelldog - I see what you mean - and I also position my speakers quite far into the room. I think best practice is to move the whole stero system away from the wall behind the speakers but thats not very possible, in my case. Which filter did you try?

I've had that same issue. I bought the rumble filter....it degraded the sound and didn't cure the problem either.
I actually had a post on these forums and someone recommended moving the turntable away from the speakers.
I moved my speakers out into the room as much as I could and the problem was solved. I now rarely get this to happen....and when it does I lower the volume a couple notches and it goes away.
I'm convinced that if I could move the turntable completely away from my my speakers...there would be no issues.
The issue is with your cartridge and speakers. That's my opinion.

@o_holter

I too had reduced my woofer pumping with each of the following steps:

1. Cartridge setup tweaked by my VPI dealer
2. Replaced my cartridge
3. Added a Symposium Seque ISO platform
4. Added Symposium VPI footers
5. Added a custom 2" walnut platform sitting on RollerBlock Jr’s under the Seque
6. Swapped my Quadraspire Q4 Evo rack with a Massif Audio Design rack (no obvious change)
7. I have an older Classic 3 and tried damping the arm with VPI damping oil, that didn’t help...

Each of these changes reduced the pumping (well, more or less) and a couple of times I thought my issue was resolved. I think your intuition is probably correct in that this problem might not be resolved.

PM me if the problem returns, I might be open to sending my filter out for you to try.

Todd

Since the problem is mainly gone, the thread should end soon. But it would be nice with a conclusion. I had woofer pumping, I changed some things in my system, and then the pumping (or most of it) went away. Why? Not clear.

Maybe the most likely reason - for now - is that I took out the platter and reinstalled it, with a little change of the ball and spindle position, making the drive work a bit more smoothly.

However my "audio intuition" is not quite satisfied with this explanation. The pumping error seems more like a yes/no proposition, as if you throw a switch - it is there, or not there - maybe mainly resonance-related (or even electric, e g could it even be influenced by static electricity?). So far I have not been able to reproduce the error. So I dont know exactly what makes the woofers start pumping. But it seems fairly clear that if it was only the drive, or player imperfections, the pumping / rumble problems would have been much more constant. 

Resonance - a red herring? If so, reducing effective mass on the SME V may not be a good idea (+1 to Atmasphere, and others, for setting me on this track).

Therefore I thought, OK, let me go back to a normal setup of the arm. I screwed the upper bridge back on and adjusted the counterweight back so the spring weight does the job alone, tuning it to the 1.72g recommended for the Atlas. Then I checked, using the runout on R L Jones The evening..., on the same very high volume level as before. Did I see more subsonic cone movement / pumping? NO. Slightly more energy, touching the cones? MAYBE but not much. What strikes me is that the "tone" of the vinyl noise has gone down a bit, it reaches lower in frequency. (Usually a good sign, says my audio intuition).

This test result does not rule out a "demanding" combo that can easily pick up too much lowest-low frequency. Maybe there is a herring. But its not red?

Tighten the center shaft - meaning: the housing of the spindle.

cleeds - thank you, yes I bought the Atlas new and it shows no obvious signs of wear so far.  You are right, it may be a spindle / bearing problem. So I want to eliminate this factor. I have a friend with a T-60 who may help me fix it, soon.

Before going on, I need to tighten the center shaft (with the magnets) to the plinth on my Hanss T-30. It is fastened by four screws from the underside of the plinth. Does anyone know the type and dimension? The screws are very hard to see unless the player is placed on the side. Thats a heavy and somewhat risky job, so when I do it, I need to have the right tool. The Hanss manual does not specify the type of screw, but they have confirmed that the shaft should sit tight. ("shaft" maybe not the correct term - I mean the cylinder that the spindle sits in.)

o_holter

Some more pumping and woofer cone vibration testing today ... still noticeable on very high volume. There is some subsonic pumping ... it happens at certain intervals per revolution of the record (playing silent grooves between tracks). If I turn up speed to 45, the pattern is repeated, only faster. This seems to indicate that player rumble or drive problems are NOT the main issue.

That actually sounds very much like a drive problem, such as a bearing issue or bad belt

.... Could this “inherent vinyl noise” be most strong down around the resonance frequency, at ca 7 herz?

I don't think what you're experiencing is “inherent vinyl noise.” I agree with @stringreen - it would be a good idea to start at square one and have Lyra check that cartridge. Did you buy it used? If so, it's immediately suspect, even if it isn't your only problem.

Han_n - yes I will test this more. The "low cut" option may be what I lack.
Toddc2 - thanks, I have followed up.

I mailed an audio tech the other day, is it likely my woofers are getting worn out? Even if I don't hear clear problems? Answer: after five years no - it is not likely.

Some more pumping and woofer cone vibration testing today.

Pattern confirmed: the misbehaviour is less than before, but still noticeable on very high volume. There is some subsonic pumping (I can see it but not hear it).

The interesting thing is: it happens at certain intervals per revolution of the record (playing silent grooves between tracks). If I turn up speed to 45, the pattern is repeated, only faster. This seems to indicate that player rumble or drive problems are NOT the main issue. The platter on the Hanss T-30 is perfectly levelled and revolves smoothly – the pitch is steady, there is no sign of imbalance or distress, and almost no perceptible vibration noise touching or stetoscoping the plinth.

So if the player is mainly fine, the answer must be that the cart/arm combo picks up “vinyl noise”. Please correct me if I am wrong!

Could this “inherent vinyl noise” be most strong down around the resonance frequency, at ca 7 herz?

I am investigating different filter options, with helpful answers from KAB and Satoni, thanks to your advice. Since I have invested in a balanced system (from the phono stage to the amps) I am not so keen to go back to single ended connections from the phono to the preamp, although this would be the easiest (and cheapest) way to know if I am on the right course – if a rumble filter would help.  

Please note that woofer pumping is not only caused by the cartridge/arm. Some CD's cause pumping as well. Hopefully you have a "low-cut" option. Use it only when needed.

@o_holter - You mentioned earlier in the thread about an XLR filter. I was struggling with the same woofer pumping problem and finally commissioned Dan Satoni at DTS electronics to build a custom balanced high pass filter for me. Problem solved with no obvious loss of sonic performance. I know Dan has a minimum board order of 5 units so I am pretty sure he can quickly build another one for you if interested. It wasn't exactly cheap ($550 CAD) but I feel it was an exceptional value at that price.

Todd

VPI Classic 3 w/Lyra Delos -> Whest PS.RDT30 SE -> Custom Filter -> ARC Ref2 MkII -> ARC VT100 MkIII -> Magico S1

Thanks, all! I think we can conclude that

1) the Atlas / SME V combo is very “receptive” in the lowest frequencies, and that in some resolving systems this may give unwanted effects like woofer pumping.

2) this is mainly a resonance problem, not a rumble or player noise problem (it does not change much, with different platter mats, damping or stabilizing the turntable, etc), and the first measure is to try to move the resonant frequency up - reduce the effective mass of the arm. This is only slightly possible on the SME V, but even small changes may help

3) the somewhat "over-eager" reception at the lowest frequencies of the Lyra/SME combo makes it even more important to correct any residual system noise, drive noise or rumble.

4) if the problem persists, try a rumble filter.

I will now try to decrease system noise – check the turntable, bearing, oil, feet, etc.

I wonder, even if the pumping is already reduced, would a filter be an idea anyway? Are my woofers straining too much, in the lowest bass? Is this prone to happen more, when the suspension of the cartridge is more worn?

+1 tkr and stereo5! A well designed subsonic filter (KAB) will do wonders for bass in your system! 

Whatever you do, don’t get a subsonic filter, unless of course you want to kill good sound.

This is nonsense. I use the cheap DB Systems filters and the loss in fidelity is barely perceptible.

I also discovered that, indeed, "silent" record grooves are not the same.

You discovered that subsonic noise is often cut into the grooves. This is why you're not getting pumping in the runout grooves. I once believed warps were the major culprit. They’re not. It’s usually acoustic feedback and poor album cuts

Read some of the reviews on these:

http://store.acousticsounds.com/d/60042/DB_Systems-DB_Systems_Subsonic_Filter-Turntable_Accessories

At only $20, it can’t hurt to try them. If you like the result, consider investing in the DB-12 or KAB filter.

Does your turntable have an attached cover? If yes, it catches low frequency audio like a sail catches wind. See if removing it reduces the feedback. If yes but you still  want to keep the cover attached, rotate it perpendicular to the speakers to at least reduce the pickup. Worked for me! Just a thought. - Andy

>>>>>> I can see it, even if I don’t hear it. Why does it happen? The woofers behave normally (no pumping) with digital music, and when the stylus it lifted from the groove, so it is not the speakers, amps, preamp or phono stage. <<<<<<

In the day of phono only they had a button sometimes labeled "Rumble filter."  That's what you got.  Others may say "Low filter."  Interaction between the cartridge, tonearm and record cause ir.

If I were you, I'd start from square 1....make sure the cartridge suspension and stylus is ok.   I'd send it back to Lyra for a checkup.  They probably won'r even charge you to look at it.  The Atlas is one of my favorite cartridges....I've heard it in  V with a high end system with powerful low end and no woofer pumping.

@o_holter Reading over these posts I'd lean toward motor, pulley or bearing as the source of the problem.  By way of example, a couple years ago I noticed excessive woofer pumping in my speakers.  It was extreme to the point where I could hear chugging from my subwoofer.  I have a VPI HW-19 Mark IV with a very early SAMA.  The early SAMAs came with a flywheel that was a large stainless steel washer that just slipped over the motor shaft.  Upon examination I noticed that this "flywheel" was wobbling while the motor was running.  I removed the flywheel and the problem was solved.  I later learned that VPI eventually realized the flywheel was causing more problems than benefit and discontinued using it.

Since you observed much less pumping after removing your platter it sounds like either your platter was out of balance on the bearing or the bearing was not properly seated.  I would clean the bearing shaft with long qtips and reoil the bearing shaft with a high quality oil.  I use sewing machine oil.  Second, I'd examine the pulleys and motor shaft for any wobble.
Cheers,

Based on Atmasphere's advice, I also tried higher loading, going from 475 ohm to 121 ohm (not so easy on the Io, changing a jumper at the back). Result? Musicality: great. "Echoes" sounds a bit sweeter, more mellow. I realize, I am moved by the music - always a good sign. Is it also a bit duller, rolled off, or contracted? Not sure. Maybe a little. I will have to try the middle setting (243 ohm). Testing with the Hifi news record, I did not find any change in the resonance frequency, it is still down at ca 7.5Hz.

Loading should not affect the tonality of the cartridge, as essentially the loading is to prevent a resonance at very high frequencies from occurring by detuning it. If it made for an improvement, it means that the phono section is sensitive to RFI at its input and may have stability problems (but not the sort that cause woofer pumping).

In an ideal situation, the cartridge should be loaded by 47K. With low load resistances (like 100 ohms) the cartridge has to do more work, and that energy coming from the stylus motion means that the cantilever has to be stiffer as well. JCarr and I talked about this at Munich a few years ago.

Now you mentioned that you examined the platter bearing- did you lubricate it? If the platter bearing was dry, the simple act of removing the platter and reinstalling it may have gotten enough lubricant in place to result in the reduced woofer pumping. So the arm and cartridge combo not being ideal might be a complete red herring.

Like I said in a earlier post, just buy the KAB rumble filter and be done with it!  I tried everything mentioned in this thread at one time or another and only the KAB filter worked with no loss in bass quality or quantity.  I am using it with a VPT Prime and a ZU/Denon Dl103mc.  My woofers would oscilate so much I thought they were going to come right out of the cabinets.  With the KAB, nothing, nada and perfect pitched

OP. This is all bunk. Just enjoy the music. 

There must be other Lyra cartridge / SME V owners out there, who have or don't have woofer pumping - ? Would be nice to hear from you! And maybe J Carr from Lyra could give a comment?

Atmasphere's advice reminded me of the old trick with the SME V to reduce effective mass: put the spring-loaded weight scale at zero, and then adjust the counterweight closer to the bearing of the arm. I use an electronic weight to get it exact at 1.72 g.

Based on Atmasphere's advice, I also tried higher loading, going from 475 ohm to 121 ohm (not so easy on the Io, changing a jumper at the back). Result? Musicality: great. "Echoes" sounds a bit sweeter, more mellow. I realize, I am moved by the music - always a good sign. Is it also a bit duller, rolled off, or contracted? Not sure. Maybe a little. I will have to try the middle setting (243 ohm). Testing with the Hifi news record, I did not find any change in the resonance frequency, it is still down at ca 7.5Hz.

More precisely: I can hear the test tone starting to quiver at 8Hz, increasing down to 7Hz, and then I can see the cantilever vibrating badly at 7-6Hz. So the effect of my various measures to raise the resonance seems rather small, and yet, the woofers have mainly stopped pumping. Why? Something else I did? Just changing the position of the player and spindle, a little? Is it the position of the sun (as was suggested)? The collective psyche of Audiogon members? I wish I could report some more hard facts. But whatever the case, I am mainly happy with the outcome. Even with NOS tubes in the first gain stage, the Io's noise level is mostly below the average groove noise level.  

Invictus005: I've tried your suggestion now, holding the plinth, but it makes no difference. This is a very heavy player (83 lbs). I used the runout on the Hifi News test record. And noticed, once more, that the woofer pumping is much reduced, compared to some days ago. In fact, it now looks/feels more like normal vibrations. And this is with the volume very loud (95+ db when playing music). So, where did the pumping go? I have a prolapsis so testing takes a bit of time. I wish I could tell you more exact what has caused the reduction of the problem. Besides reducing the effective mass, I did take off the platter, checked the spindle and moved the steel ball a little.

I also discovered that, indeed, "silent" record grooves are not the same. I have a UK original of Pink Floyd: Meddle, that plays amazing, especially side B (Echoes), with "HTM" in the deadwax, which means Harry T Moss "cutter extraordinaire at EMI UK" from what I read. In the silent-to-quiet opening of Echoes, the woofers pump a lot (on high volume). Is it a problem? Rather, I get the impression, this was intended by Mr Moss, to get the absolute best from the recording. As the music gets louder, I don't see the pumping (since the musical energy now grabs the woofers), although it may be there, in the background. This is what I suspect, and the reason I wanted to improve the situation in the first place. I think that this relates to a more "tense" or "disturbed" sound, and also, to a bit of break-up of the woofers at high volume (in sum - creating more listening fatigue). Btw the woofers are Acoustic Elegance TD10X (four of them in my system).

Testing again, with the HiFi News record side B band 6: Unmodulated groove (check residual system noise). Not much pumping even at unrealistic high volume. Even this track is not fully silent (what record is?) and the cone movement is in line with what I hear, indicating - I think - that indeed, the cartridge/arm combo has become less over-eager down at 5-6 Hz. I tested the runout on some other high quality records also - MFSL, ECM - same result.

Why don't you try what I posted...

tzh21y - yes I think the same. Maybe even small things help, getting the resonance up. Stripping the arm of all extra mass and changing the counterweight position, like Atmasphere suggested.
Invictus, Almarg - I don’t think the player is the problem, behaves much better than my former VPI. The plinth is dead stable as it is. Belts - maybe new ones would be better, but this is not the main cause.
Somehow, the pumping has decreased a bit over the last days. Not sure which of my modifications that made the change.
The pumping is now very evident when I turn the volume up to 92-96 db from the listener position - measured when playing music. Going down to 88-90, where I usually listen, it is not so notable. I must test this more, trying to find "silent" vinyl grooves.
Atmasphere - I was not aware that loading could influence the resonance - ? I load the Atlas at 475 Ohm, but could go down to 100, have not tried yet.

Still even though it still falls within the 8hz range, I believe the ideal range would be closer to 10hz.  so if you buy a cartridge that you think has a compliance of 12 and it is really closer to between 16 and eighteen, i would think that would be audible at some frequencies which could be bothersome for some people.  its kind of deceiving as I did not even notice the whole 100 hertz thing until after I bought my cartridge.  It still sounds good but it is not what I thought I was getting.  for instance when I bought a benz cartridge and its compliance was 16, it was 16.

Your problem is most likely a combination of ununiform belt thickness, not precise pulleys, motor rumble, not precise bearing. They all combine and create a mechanical shimmer in the turntable's suspension. 

While playing the runout groove and watching the woofers move in and out. Gently, but firmly place your hands on the plinth and try to very carefully hold it in place. The woofers should move in and out less.

Dear @o_holter : According your self research looks like the rpoblem is developed by the TT and not a mistmatch between cartridge/tonearm because even at 100hz the Atlat compliance and effective mass puts the resonat frequency in a " solid " 8hz.

The cartridge is a very sensitive " microphone "/transducer and it's picking up " something that is happening somewhere in the TT.

Normally when  a some kind of resonance/vibration are exiting/coincide with the cartridge/ tonearm resonance frequency in between the pick up jumps more than make a noise.

Before you go for the filter try to " figure " what could be happens in your TT. You are the one that know it, even contact the TT manufacturer and ask for its advice.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

O_Holter, while it indeed sounds like the problem is a consequence of the arm/cartridge resonant frequency being too low, I’ve been thinking about what might be exciting that resonance, since based on what you’ve said it seems that the excitation is probably unrelated to record warps. And the one thing that occurs to me, given the unusual design of the turntable’s drive mechanism (comprising six belts, three of them driven by what is apparently a synchronous motor on one side of the table, and three of them driven at a different height by a similar motor on the other side of the table), is that the platter might be being driven in a slightly uneven and/or not perfectly level manner. Perhaps simply due to the condition of the drive belts differing slightly between the two sides.

And I note from your system description thread that the table appears to be around five years old. Perhaps all that is needed to resolve the problem is a new set of belts?

Regards,
-- Al

OK... what do you want to know?

@atmasphere All of it...

@invictus005 To which part do you address the 'huh'?