Why do my bass drivers shake violently listening to vinyl

My woofers at home are 15" and the speakers are flat to 20Hz. I never have problems with the woofers flopping about. But I am careful to make sure the cartridge isn’t too compliant for the mass of the arm. If it is, as the cartridge negotiates the minor ups and downs of the LP surface, the mass of the arm will take more time to catch up with the cartridge. This causes a lot of low frequency output from the cartridge and its stuff that isn’t on the LP surface.

You can either reduce the mass of the tonearm or decrease the compliance of the cartridge. The former might be done by replacing hardware holding the cartridge in place (or going with a lighter cartridge); the latter is done by replacing the cartridge.

Is this part of the logic behind the Dynavector dv507 arm having a pivot configuration which minimizes vertical moving mass?

Isolation issues can also greatly impact woofer flapping. I had occasional problems when I was using a poor Lovan rack (stackable modules, not very rigid). They completely went away with an upgrade to CMS Maxxum - still using the same kind of table, speakers, cartridge, arm, amps, same positioning, etc.

15" Tannoy drivers here so when the woofers flap at all it is VERY easy to see. Floor here is suspended wood, but old world commercial construction - not nearly as compliant as modern residential suspended floors. Still not like a concrete slab either, though.

Hi all, OP just checking back in. The KAB rumble filter resolved the issue. It would be nice to establish root cause, but for now I'm happy. Speaking of compliance, does anyone know if there would be a compliance issue with my AT VM760SLC mounted on the stock Technics SL1200GR arm? I also may consider purchasing the after market footers KAB sells on their site. Thanks for all the great discussion and happy holidays to all. -Joe

@audionoobie , That should be fine. I do not think the "footers" will add much if anything. Better to have the table on a heavy solid platform. 

@atmasphere , should be and are are two separate issues. I have records the rumble from a poorly maintained lathe is obnoxious. 

The woofer flapping issue is prevalent among people with small woofers that are tuned to go as low as possible. They have to move a lot farther to produce the same results as a large woofer. I have never seen the owner of a 15" woofer complain of this. It is always 10" or below and always with turntables. With many amps going clear down to DC surface irregularities in the vinyl will cause the woofers to flap. They do so in rhythm with the spinning record. This is not necessarily will loud volumes either. But if you do turn it up the problem can become obnoxious. If subwoofers are used and boosted 5 dB like mine you can easily bottom the subwoofer out. Interesting sound for sure. Once digitized it is a simple matter to program in a subsonic filter with a very steep slope sidestepping the issue altogether. If you use subwoofers and play loud using your turntable as the source a subsonic filter is virtually mandatory.

@audionoobie If you're thinking about upgrading the feet, I recommend the feet from MNPCTECH - 

 

They're a little pricey, but it was probably the best upgrade I have made to my SL 1200 MK2.

"The woofer flapping issue is prevalent among people with small woofers that are tuned to go as low as possible. They have to move a lot farther to produce the same results as a large woofer." Only if the bass response is artificially boosted, as in your system. Otherwise, the smaller woofer will just roll off at a higher frequency than a bigger woofer. It’s even possible in some cases that the smaller woofer will be less likely to dance due to upstream perturbation, both because the smaller woofer can't respond and because of the enclosure damping, as in an acoustic suspension cabinet. This was mentioned earlier.

"Once digitized it is a simple matter to program in a subsonic filter with a very steep slope sidestepping the issue altogether." There is no free lunch in audio; fiddling with the signal in the digital domain will have a cost in SQ that some would not tolerate and others would find OK. Anyway, if one wants a subwoofer system, one can build an active low pass filter with a 24-db/octave slope out of discrete components that work in the analog domain, with potentially less of a sonic penalty. 24db/octave should be sufficient for cleaning up the higher frequencies.