At what vol level do you get rumble / flutter?

Tobes,

The existence of woofer pumping is not a debatable issue and I didn't claim you tried to dispute it. But I do disagree, at least somewhat, with your proposition that "[t]he sub-sonic frequencies are generated by the playback process but probably not by music content." It is not that it is done intentionally, but my understanding is that it occurs during the lathe cutting process. So it's not "recorded" but imparted during the cutting of the master disk. I'm not sure whether my example was clear enough or whether you gave it any thought, but given the differences in the degree of woofer excursion with perfectly flat records, I simply do not see how you can argue that the subsonic frequency is not present in the recording itself (well, in the vinyl to be more precise). How else would you explain the difference?

I certainly agree that it can be caused by the mismatch or acoustic feedback, or can be exacerbated depending on certain characteristic of the cartridge itself. Or turntable placement. I just think the phenomenon is more complex that many make it out to be.

By the way, I really enjoy your audio page. The pictures are superb, and there is lots of great information. I especially enjoyed your account of the making of the sand box. Well done.

Actusreus,

I do see your point, I probably didn't read your post above.
Like you say, it is probably a combination of factors at work here.
From memory the cartridges i mentioned above produced 'nervous' woofer pumping even on nominally flat records. They were verging on out of control with any ripple like warps near the start of the record - hence I found them unusable in that setup (and I returned them).
I suspect, for whatever reason, they had very pronounced resonance which was 'set off' by any subsonic content.

BTW, thanks for your kind words on my audio page, not sure its as deserving as you make out, but thanks.

I meant to mention it in my last post - if anyone saw Fremer's "21st Century Vinyl" DVD, there was a great segment shot at Stirling Sound in NYC, and interview with the recently deceased, great George Marino. (What a loss to the community, by the way. Left us way prematurely. RIP George.)

Stirling uses a Neumann lathe to cut the master disc, and Marino was explaining the importance of isolating the lathe as it's essentially a turntable with a cutting "stylus," and any extrinsic noise can easily get transferred through the cutter and be embedded in the disc together with the recorded sound. They have the lathe on a slab of concrete and spring suspended. Even with this, I'm not sure you can isolate anything in Midtown Manhattan where Stirling is located, and it is certainly possible that many cutting lathes are not perfectly isolated and thus some of that unwanted low frequency noise does make its way into the vinyl.

@johnny, my table is at my dealer now. It has the lighter 65g counterweight for cartridges between 4-7 grams. How do I calculate the effective tonearm mass with this lighter counterweight (10g lighter that the factory 75g for 7-12g cartridges). I might have him put in a pair of 1 gram brass screws to bring the weight up a little.