Why are my woofers pumping?

Thank you, vpi. I have no indication that the pumping happens only with flawed or warped records. I think your hypothesis 2) is correct, that is, first the low resonance plus a superb cart picks up subsonics, and next, the system is very resolving and sends it all to the speakers. Note, however, that even my modest cottage system was able to reproduce the pumping.

I don't have test instruments to test if the pumping is exactly in sync. I can only say that the pattern repeats ca once per revolution. This is easiest to test in the outro of a record with pumping. There is a click once per revolution when the lead-out groove meets the circular groove at the end, and I can see (and touch) the woofers pump in a regular pattern between each click. So it seems roughly in sync. Which would be the case with most records I would guess? 

Examples of records with subsonic woofer pumping:Pink Floyd Meddle (UK orig), Rickie Lee Jones: Evening of the best day of my life, Byrds: Untitled (US orig), Byrds: The Columbia hits (Sundazed).

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".