How to isolate turntable from footstep shake or vibration

@cleeds , that is right, flat to 20 hz at 1 meter. There is no full range loudspeaker I know of capable of reproducing the bottom two octaves in your average room at realistic levels. You have to be able to have separate control of that part of the spectrum. Your average room requires at least two 15" or four 12" subwoofer drivers to do the job. Room control and a lot of power help. To get the sensations of a live performance you have to be able to boost the low end 5 to 10 dB  sloping up from 100 Hz  to 18 Hz. Smaller drivers have to take overly long excursions to do this and distortion levels are much higher. 
At any rate, adding a bad subwoofer system is worse than no subwoofer at all so I can understand why many people do not.

mijostyn

@cleeds , that is right, flat to 20 hz at 1 meter. There is no full range loudspeaker I know of capable of reproducing the bottom two octaves in your average room at realistic levels ...

You obviously never heard an Infinity IRS Beta system. Essentially flat in my room to below 20 hZ. No Band-Aid "rumble filter" or heroic digital DSP required.

@cleeds, not a tone arm resonance problem at all. It is set perfectly at 8 Hz (horizontal. vertical is a little higher 9-10 Hz.) The cartridge is reading irregularities in the records surface. No record is absolutely flat. Unfiltered the subwoofers will gladly try to reproduce this. They are not projecting any "sound" into the room. They are no where near large enough to produce those frequencies but, if there is an electrical signal at 8 Hz they will gladly flap around at 8 Hz adding distortion to the sound you want to hear. In my case each subwoofer has 1800 Class AB watts behind it that will amplify right down to DC. Filtering all this garbage below 18 Hz cleans up the signal very audibly. You would have absolutely no problem hearing it. 

mijostyn

... Unfiltered the subwoofers will gladly try to reproduce this. They are not projecting any "sound" into the room. They are no where near large enough to produce those frequencies but, if there is an electrical signal at 8 Hz they will gladly flap around at 8 Hz adding distortion to the sound you want to hear ...

I can assure you that your LPs have no electrical signal at 8 hZ. You obviously have a rumble issue and use essentially a rumble filter to resolve it. That works!

Thank you for all your suggestions! I’ve double checked the suspension. And it appeared that the right tonearm side needed a stiffer spring as the aluminum housing was so low that it touched the base. It was simply sitting on the turnable instead of "floating in air". I have replaced the spring with the stiffer one and viola! The effect was instant. The footsteps rattle is gone. Even with the maximum subwoofer volume it is dead silent. It doesn’t even respond to me jumping in a room or shutting the door. It feels like I’ve got a free upgrade as it appears it sounds better!