Speaker vibration isolation

specifically the ones that replace the spikes as opposed to the stands?

Always spike into a cement slab floor, especially if it’s laid on mother earth.

Good test if you can feel through your bare feet drop something heavy dropped on the floor, if not spike into it, if you can feel it don’t spike (couple), as the floor will become a sound board for the bass notes and muddy the bass.

Best in this situation is to isolate (decouple) the speaker from the floor, numerous ways, cheapest I found without being ripped off by "audiophile products" is with heavy duty "Sorbothane" pads like these, there many if you search, 4 of these "70 duro" will take a 52kg speaker.
https://www.ebay.com/itm/NEW-SRM-TECH-SORBOTHANE-ISOLATION-RINGS-HEAVY-DUTY-70-DURO-4-PACK/332856500...

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313.TR2.TRC0.A0.H0.Xsorbothane...

Whatever you do DON"T put your speakers on springs, they'll wobble around like jelly, and your image will be shot to hell. 

Cheers George

For starters, getting back to reality for a moment, Vibrapods are not (rpt not) designed to support objects with high centers of gravity. You know, like speakers. They the Vibrapods don’t have enough lateral support. That’s why you see a lot of designs for speakers with the capability for obtaining very wide footprints. It’s to get the necessary lateral support. Otherwise the speakers would just flop over.

@georgehifi   My speakers are sitting on plush carpet with pad over a "floating concrete slab". I too believed that coupling (spiking) them through the carpet to the slab would be the way to go...until it wasn't.

After decoupling there is no going back. Cleaner, clearer sound.

I too believed that coupling (spiking) them through the carpet to the slab would be the way to go...until it wasn't.

If it was a proper building slab of concrete some 2ft thick around the edge and some 6'-8" thick for the rest, if this wasn't best, then something else is at play.
https://s.hswstatic.com/gif/house-slab.gif

Cheers George

I feel it’s only fair to interject that whilst cement slabs do have their advantages they are nevertheless subject to the very low frequency vibration produced by the motion of the Earth’s crust, which pushes the cement slab just a tad. That is why mass on spring isolation is effective on cement slabs.