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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?  


Ag insider logo xs@2xo_holter
stereo5's avatar
stereo5
6,430 posts
 
+1 miner42

Just a thought, what if you used RCA to XLR adapters? BAT makes some excellent ones. I have an original Harvest first pressing of DSOTM and the bass is very taut and very deep with no woofer pumping.  I also have a MFSL pressing which for some reason is much lower in volume with no pumping.   I wish you lived close by, I would let you borrow my KAB filter to try.
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o_holter OP
977 posts
 
Thank you miner42 and stereo5. It may take some time, but i wish to try your suggestions. Although changing the arm or the cart might be optimal, no one so far knows for sure what works best in my system. 
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o_holter OP
977 posts
 
I already know that using single ended outputs from my phono stage curbs the pumping compared to using balanced outputs. But it also sounds much poorer! So to give the KAB a fair chance it would need an xlr to rca adapter (thanks, stereo5). Not sure if an additional adapter is needed to the Einstein preamp it seems xlr and rca inputs sound the same.
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o_holter OP
977 posts
 
Listening to vinyl rips from main system, on my cottage system. No pumping of course - the Aurum Cantus speakers only go down to 40 hz or so. So music is limited but it also sounds nicely peaceful. No harm done - sins of omission not commision in the bass.

I think beyond the low cart-arm resonance we need to add the very fullscale speaker system in my main system. Four speaker Audiokinesis. Lots of woofer power. - Maybe other speakers is why some users and reviewers dont experience much problem.
atmasphere's avatar
atmasphere
11,874 posts
 
Electronics bandwidth is an issue too- your amps are full power to 1Hz. Most tube amps can't go anywhere near that low.

But I have similar bandwidth with both the amps and speakers at home, yet don't experience this issue. I am using a Triplanar, which allows for a bit of adjustment of the mechanical resonance by using multiple weights for the counterbalance. My 'table is different too.

Its true that some lathes can impart low frequencies to the LP, but that usually occurs between tracks and also at the end, where the carriage for the cutter head is advanced at a higher rate than during a cut. It sounds like you are getting this pumping during cuts on the LP, so I would rule out the LP as the source.

I would try applying a light grease to the platter bearing, to see if it shuts it up. If so, I would be thinking that the platter bearing is worn as normally a light oil is used.
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