Why are my woofers pumping?

It should be easy to test here on Audiogon. If you have a cart-arm combination with resonance around 7hz, you should be able to see the pumping. (Put weight of arm and cart, and cart compliance, into the vinylengine resonance calculator, and/or test with the HFN test record, lateral compliance track).

Testing Jefferson Airplane Volunteers, the new 45 rpm Mofi edition. Not much clear woofer pumping in the outro. But clear in the intro, before We should be together.

The subsonic woofer pumping seems inherent in the recording itself, picked up by my cart-arm combination. It is not due to vinyl warps or turntable problems. But more, due to recording issues, engineers’ decisions. Sometimes the recording goes way low - sometimes it doesn’t.

I associate the records with pumping with "quite good sound", or even very good sound (especially in low energy music, like on Pink Floyd’s Echoes, in the subdued sections). Not "bad sound". Pumping records maybe go a bit further down in the bass, with an overall improvement factor. Even if I suspect that the pumping is not so good for the music.

It is quite bewildering - testing LPs - Elvis Costello: This year’s model - intro yes, between tracks no, outro yes. JA Volunteers mofi side 3, intro yes, between tracks some, outro some. Liz Phair: Exile side A - some, but rather little. A Parsons: I robot, Classic, intro yes, mid track yes, outro yes - with note "great sound".

@o_holter Very interesting, your last few posts.  I have noticed on some LPs there can be a hum in the runout grooves and have always supposed it was on the record.  I don't see why there could not also be subsonic signals in the runout grooves that would cause woofer pumping also.  Unless the woofer pumping is extreme I'd be inclined to congratulate my self on a great resolving system and ignore the pumping.  If it is bothering you, I suppose you could use a subsonic filter as some here have suggested.  I personally don't like filters because you are just placing additional things in the signal path and more "stuff" you put in the signal path the greater the opportunity to degrade your sound quality.

Dear @o_holter : I think you own a Clavis DC too. Do you already tested with?

Characteristics are almost the same as the Atlas regarding resonance frequency calculations. 
I think you have to test it because you " think " problem is that resoannce frequency tonearm/cartridge behavior.

R.