What your choice speakers with spikes or speakers with a vibration isolation device?

I always decouple, no matter the floor..No spikes ever...I dampen the enclosure, as much I can. If you can get the KNOCH factor to green concrete, you've done a good job...

I go by the pound..about 60 lb a foot for monitors, bass lowriders or bass columns.

I'd hang the darn things if I could figure a way without turning the room into looking like the Big Top at Barnum and Bailey's..

@ 60 lb a foot, that's over a ton hanging from the rafters, with just 4, columns. There are 8 enclosures in there.

Hanging is out, spikes are out. 

Adjustable spring mounts and silicone.
A spring suspension and different viscous ratings for the rubber, from staying liquid (like an accumulator, or a shock), to a VERY hard dry material.
Hospital generators, and power plants in floating structures use them.. Where I got the idea from 40 years ago. ZERO harmonics, as long as the dampeners would stay charged, (no leaks from the bladders) with nitrogen

There is NOT a better way to control harmonics...

Vibration = distortion, simple...

Regards

Anyway the evidence, what there is, seems to come in the form of baffle accelerometer readings which heavily favour any compliant feet over any spikes.

Your speaking of spectral decay rates within the enclosure. A good enclosure there is really no need for that spec.

A lot of speaker repair people chime in with, decay rates, when it is such a simple fix.. Green concrete. If the enclosure sounds like green concrete it is good. Decay rates are important, for VERY old amps with no dampening ability, and poorly designed enclosures.

Undampened.. You’ll keep hearing it until tomorrow.

Same with phase shift, you or I are not going to notice the 20 hz PS, you can’t. It’s sub, you’ll feel it, or not depending. I like correction before it hits the speaker cable, not after.

A servo amp with a feed back correction circuit, is probably the fastest, to STOP, not correct the overshoot of the cone, and decay rate are once again, not an issue.. It’s an old spec. that in real world NEW SPEAKER application doesn’t matter.. Sound walls, yes, speakers NO.

Second, a speaker, mounted to the side of a taller, narrow baffle, that is deep, can rock side to side. I’ve seen it. It’s actually an upgrade on certain speakers I use. Remove the side firing woofer, and plug the space. They use to replace the woofer with a passive radiator, it still rocked the cabinet, ever so slightly.

Isolate the cabinet, decrease the vibration, and decrease the distortion, everywhere...

Think air ride, and a tractor trailer rig.. Think 100 foot jump off a building, into an air bag. and Walk away.. Green concrete and air, everything in between is an issue...

Regards

They have smaller ones for individual components, do you see a problem with floating a CD player in the air?

The magnetic field? How will that influence things... I'm always a little careful, with magnets.. Hard drives, eproms, tape decks, Reel to Reels
The steel plate in my head, my hip, my knee, my leg, my jaw, and the two screws lose in my head.. 

Bing.... Eyes Cross..

Regard

If i had a wooden suspended floor I might consider isolating the stands from the floor- it might provide the best possible sound but would be a compromise compared to a more solidly mounted system on a solid floor.  

The best all around for a room is solid, no doubt. I have a few way I can go, including outside in the summer months. Raised floors are probably the hardest to control.  I've found large soft decoupling silicone isolators work very well too.  I'm just a decouple guy... From my primary LP playing days, and still do, just a lot of streaming, servers, CD, a little Reel to Reel. There is no need for AS much vibration control.. as before.

For me it's bass distortion more than vibration control, NOW..

Regards