How to isolate turntable from footstep shake or vibration

mijostyn4,740 posts07-22-2021 8:37am"user510, there are well designed turntables suspensions and not so well designed suspensions. Suspended turntables that have their sub chassis sitting on springs like the AR XA, LP 12 and Thorens turntables are inherently unstable and they tend to oscillate laterally when aggravated. They will skip with footfalls sometimes even more readily than unsuspended turntables. Suspended turntables that have their sub chassis hanging from the springs are inherently stable and want to maintain their resting positions. This category includes SME, some Basis and Sota turntables. They will not skip with footfalls. You can put them on a collapsible card table and they will operate fine without any audible consequence.  "

Agree that some suspended subchassis type turntables are more stable than are others.  Also agree that the  lighter Thorens models are definitely prone toward footfall.  And this is inherent in the design.  Particularly the  models such as the TD150 and TD16x/TD14x.
However the AR-XA was originally quite stable and able to effectively isolate from physical disturbances such as foot fall, or being bumped into, or even have a fist hit the top of the cabinet while the thing was playing a record.....and not skip.  This was one of their advertised abilities.  And it was proven time after time in public demonstrations.

I think I understand why the AR isolated well while the Thorens or Ariston RD-11 or LP-12 did not.  It had to do with a combination of things including the mass of the suspended parts as well as stiffness of that suspended subchassis.  The Thorens models, along with the LP12 models did suffer some chassis flex when being disturbed into motion.  This chassis flex altered distance between platter bearing and the tonearm mounting, effectively causing the stylus to jump out of the groove.  Only later, some several decades later, has Linn addressed this issue with the Sole subchassis. 

Thorens addressed it with their heavier TD125 and TD126 models which have cast aluminum subchassis that are stout enough not to flex while in oscillation.  But they knew what they had back in their earliest versions.

https://www.theanalogdept.com/td150_history.htm

That said, and it is an interesting discussion, I wonder if anyone has actually solved the issue described in the OP.-Steve

I had an AR which I could rap in the the top with my knuckle and it would not skip or have the sound transmitted to the speakers. It did what it was designed to do. When I walked by it would skip every time. The solution was simple, a wall rack… that is the solution for suspended floors.

user510, I have intimate experience with both the AR XA and I have owned 2 LP 12s. They are both potentially unstable and do not handle footfalls well just as ghdprentice indicates. A Sota you can rap on the surface and dance the jig on springy floor and it will not care. It is all about the self centering stability of the suspension that count.

@williewonka , Those feet do not offer isolation. Those center posts used to stabilize the magnets ruin any isolation the feet provide except in the perfectly vertical axis. 

ghdprentice509 posts07-23-2021 3:18pmI had an AR which I could rap in the the top with my knuckle and it would not skip or have the sound transmitted to the speakers. It did what it was designed to do. When I walked by it would skip every time. The solution was simple, a wall rack… that is the solution for suspended floors.

mijostyn4,747 posts07-23-2021 3:34pmuser510, I have intimate experience with both the AR XA and I have owned 2 LP 12s. They are both potentially unstable and do not handle footfalls well just as ghdprentice indicates. A Sota you can rap on the surface and dance the jig on springy floor and it will not care. It is all about the self centering stability of the suspension that count.

good feedback and I don't mind being contradicted with factual evidence.  There definitely are other suspended subchassis designs which isolate well...and I think mjostyn's suggestion that the "hungie" type of suspension proves to be more stable than is the "sprungie".  Where the hungie tends to find center while the sprungie tends to never quite find it.  Although you can get close in those adjustment sessions but those conical coil springs always point their load in one direction, which needs to be steered...and the drive belt imposes a horizontal pull which will yank the lighter subchassis in a direction we don't want it to go.
Ime with a Td126-III i can say that this design suffers far less from footfall. Even though it is a "sprungie" and needs to be adjusted in order to obtain a vertical oscillation action, it does resist the pull of the belt far better with its larger mass.  And the cast chassis does indeed not flex. 

Btw, I can prove chassis flex on the TD150/TD160.  Having checked this using a dial indicator,to see that just the addition of the platter mass alone will cause the subchassis to flex.  Now if you put this into a dynamic situation where footfall ripples the suspended floor, which causes the floor supported audio rack to teeter just a little bit and that is enough to put the turntable in motion which excites the suspension components within and then we see even greater chassis flex due to the dynamics of the compression/extension action.  And that alters the distance between platter bearing center and pivot center of the tonearm, which skips the needle out of the groove.
https://www.theanalogdept.com/subchassis_rigidity.htm

-StevePs: have we solved the issues described by the OP yet?