Turntable Causes Speaker Cones To Excessively Move Rapidly

Just speculating based upon the picture of your room -- it could be the combination of where you placed the turntable, the dust cover and/or cartridge/tonearm setup.

At this point you don't need an audiophile type equipment rack, but you do need to make sure the furniture the turntable is sitting on is stable and preferably has some mass to it.  You may have placed the turntable in a spot that reinforces bass energy which is then fed back into the turntable by the dust cover and/or cartridge tonearm.

I would start by taking off the dust cover and see what happens.  If the problem still persists then reinstall your cartridge.  Make sure the resonance is within the proper range.  Finally move the turntable to a different location.

Try what I have suggested before spending money on isolation devices and equipment racks.  They might solve the issue.

Question -- does the Technics tonearm have dampening?

I had the same problem years ago using a DD deck on an unstable stand on a suspended floor. Switched to a belt drive and the issue stopped.

I am currently using a lesser Technics DD deck (SLQ2) and a shimmed, for VTA, AT 440 MLA cartridge on a concrete floor. I never leave the dustcover on during play. No pumping from Velodyne sub or from 6.5” midbass drivers. Also using entry level NAD pp2e phono pre.

Remove dust cover, place the player on isoacoustics zazen 2 or equivalent. That's what I did

If you can, put the TT on the floor to test as it is most likely the stand it's on.

Hello Dman777,

I had that same experience with my Rel subwoofers cavitating rather violently when playing analog only. Most of the recommendations I received focused on isolating my turntable. After doing all the isolation options, upgrading my tonearm, changing phono cartridges, upgrading the subs, changing the turntable platter bearing it turned out to be a turntable motor issue where the screws affixing the motor to the plinth had somehow not been tightened. 

Make sure your turntable assembly is torqued down properly. Hope this helps you.