Best vibration isolation for speakers on carpet?

Carlsbad,

you got that wrong, the podiums isolate vibration down to three Hertz so the speaker is not vibrating at all that would defeat the purpose it stops the vibration from going into the floor and then coming back up into the speakers and shaking it and it also stops the constant Earth vibration that shakes your speakers all the time. one of the most significant upgrades I've ever made.

I concur with a number of folks on here but my formula is a little different. I use IsoAcoustics Gaia footers under my speakers but instead of the carpet spikes, which are a pain to move the speakers around to tweak positioning, or a butcher block which I find raises the speaker height too much after combining with IsoAcoustics, I put the speakers with IsoAcoustics footers on 16x20x3/4” marble pastry boards from Sur La Table (I believe Amazon and World Market may have cheaper but perhaps lower quality alternatives). This adds additional mass while keeping it low profile, and offers additional decoupling with the use of the footers. 

https://isoacoustics.com/home-audio-isolation-products/gaia-series/gaia-iii/

https://www.surlatable.com/white-marble-pastry-board-1634-x-2034/PRO-535591.html

I had really bad coupling to the floor, producing boomy bass. It was unlistenable. Did careful comparison of isoacoustic Gaia and the Herbie’s gliders. The isoacoustic was a tad more effective but both were fine. On hardwood the Gaia was good because it has a suction cup that sticks to the floor. Worked on carpet too. The Herbie’s was way more convenient because it has Teflon or something like it on the bottom. Even for heavy speakers you can just slide the speakers around to find the best position, or move them out of the way for parties or whatever. Went with the Herbie’s and find the ability to move the speakers very useful. 

Mapleshade makes brass cones especially for carpet...

You could use 3 spikes instead of 4.  Use 2 stock ones on the speaker and buy one aftermarket cone of the same size and use a spot of Blu Tak to hold it on the center of the opposite side.  That will keep everything level, assuming your floor is level.