Why do my bass drivers shake violently listening to vinyl

@lewm

I generally prefer to go from the simple to the complex, in trying to solve any problem. Simple is to either move your turntable in your listening room or suspend it, or both. Complex is to add a subsonic filter

I agree wholeheartedly with this approach

FYI: Japanese cartridge specs are rated at 100hz not 10hz. You have to multiply by 1.7 and the resonance frequency is not 11.12 it is 8.53. That is a fine figure and will not cause the problem of woofer pumping! 

"Working" from home today so I moved the TT from within the dormer area on the Pangea shelf to outside of the dormer on a much more stable IKEA Kallax shelf. (see Audionoobie's system pics) Was pic 4, now is pic 3. 

Same problem....

Seems like I'll be looking for a rumble filter.

That's very interesting.  You mentioned you are using a 1200GR turntable.  Do you own or can you borrow a different TT, just to see if the problem is the same with a different source TT?  I am wondering whether there is some sort of defect in your 1200GR.  That seems very unlikely, given that Technics make thousands of them and have vast experience building TTs with a very low error rate, but unlikely events do occur.  If you own a stethoscope, place the bell on the plinth and listen for excessive noise; that might be an indicator of a problem. (It's also interesting that a Pangea shelf is not as stable as an IKEA product not even made to support a TT.)

Sorry noob that you had to read through all the bad advice before finally lewm helped you out. It is not the record or the turntable or arm or cartridge or anything to do with compliance or any of that. Sorry you have been so misinformed. What you are seeing is the mechanical vibration being transmitted up from the floor, rack, and shelf into the turntable. 

This happens because the signal cut into the vinyl goes through RIAA equalization that turns the lowest frequencies down 20dB. That is a lot. When playing back the phono stage has to amplify that 20dB back to sound flat. Only problem, no way of knowing what low frequency vibration is signal and what is noise. Even the tiniest vibration amplified 20dB is gonna be quite loud. Which is exactly what you are seeing. Only it is too low frequency for your speakers to reproduce audibly, but it is there and so you see it. This is the grain of truth in some of the bad advice above.

The solution lewm has in mind is to put the turntable on something more stable. There are several ways of doing this, which one will work best in your situation is hard to say. But the good news is these are tried and true simple and easy and cheap to do.

Easiest/cheapest will probably be Nobsound springs. Put the correct number of springs under each footer, will be a big improvement and might just solve your problem in one fell swoop. For $30. If not no worries they will be an improvement for sure you just might need to go further.

A nice thick butcher block shelf works well. Another one is to build a sand box. Anything the right size you can fill with an inch or two of sand. Mix the sand with just enough mineral oil to eliminate dust, pack it down, put the butcher block on top, turntable on top of that. Nobsound between butcher block and turntable. Premium isolation for cheap.

Any one or two of these will probably do the trick, and not just eliminate your woofer pumping but improve sound quality a lot in the process.