Why are my woofers pumping?

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

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.

@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,

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.

>>>>>> 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.