How does one isolate the speakers from a "suspended" floor ? Thought that’s what the spikes are for .
Many get this confused, spikes couple the speaker or stand to the floor, this is fine for cement slab floors, and the best.
But with any suspended floor the speaker or stand should be de-coupled from it to get the best bass response, as the manufacturer would have voiced it. As they would have been crazy to voice it spiked into a suspended floor acting as a sound board to any bass notes from the speaker.
To de-couple from a suspended floor you need to use an isolating puck or device like a sorbothane filled disc. Like these which you can still use your spikes with
"Cone/Spike Decoupling Glider" that are half way down the page.
http://herbiesaudiolab.net/spkrfeet.htm
Or you can substitute your spikes for these "Threaded Stud Glider " a bit further down the page.
Cheers George