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Why are my woofers pumping?

The other day, with sunlight direct from the side, I noticed that the woofers in my speakers are pumping in and out, much more than I was aware of, when the stylus is in the groove, even between tracks (no music).  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. 

I’ve read that the typical reason for woofer pumping is that the cartridge / arm resonance is too low.  I tested, with my Hifi News test record, and yes, the lateral test puts the resonance at 7 hz or so – too low (but I’ve seen some doubts about the results from that test record).  It is strange, since the combo I use – Lyra Atlas cartridge and  SME V arm (on a Hanss T-30 player) is supposed to work well. I tried to strip my arm of extras, cleaned the damping trough, etc – but it did not help much.

Anyone has an idea, why it happens, or what to do about it?  


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o_holter OP
977 posts
 
Ct0517 you are right - i’ve installed two beams in the cellar under the rack - I hammered them into place, a horizontal plank on top of each - it makes a lot of difference - i can jump in front of the player without mistracking. This, and separate el to the system, are among my "no looking back" mods / tweaks.
stringreen's avatar
stringreen
6,475 posts
 
Have you tried solidifying your support table to the wall with an appropriate piece of wood wedged there??  
atmasphere's avatar
atmasphere
11,874 posts
 
Since degree of pumping varies with the LP and repeats precisely with the record's revolution, drive problems probably is not much involved - confirmed by cleaning belts and adjusting the player - no big difference.
This comment really suggests an issue with the turntable despite the belt cleaning (which would not address something like this).
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o_holter OP
977 posts
 
Back home, some more testing on main system:

Audiotomb suggested an arm bearing test. I set the SME V so that the arm floats, zero weight and zero anti-skate, can I lift it with a light feather? Yes. Movement is vertical, not slanted? Yes. Can I drop a 1 cm square piece of paper on the top of the cart, and the arm sinks? Yes. Can I blow the arm vertical and lateral? Yes. Can I  wiggle the arm base, is there any slack? No. Conclusion: arm bearings probably OK.

Stingreen - support is a heavy stone rack, but sure, I can try a wedge.

Atmasphere - I guess you mean that there could be a turntable issue even if the pumping is more evident on some LPs than others. I have ordered the tool to tighten the bearing shaft/housing on the Hanss, but have not received it yet. So I have no way to check directly. Come to think of it, I could try to find some DSD recordings made with the same cart and arm, on the VPI HW19 player that I used before - this should clarify the issue. If it is a turntable issue, I shouldn't have pumping on recordings from the VPI - right? (But my inner audiophile says: if things were that simple...)

atmasphere's avatar
atmasphere
11,874 posts
 
I would grease the platter bearing and see if that makes a difference. If it helps, I would consider replacement of the bearing unless grease is an acceptable lubricant.

The fact that its happening in time with the rotation of the platter (as you stated earlier) points to the platter bearing.
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