All told, my stance on this is that isolation is very situational-dependent.
a few thoughts.
the trampoline suspended floor would likely do the opposite. It would likely not send vibrations through the rest of the house as it is decoupled from it. In your example, the term trampoline might evoke what happens to the frame of a trampoline when a person jumps on it. But the mass of that frame is less than the mass of the moving object. In this case it’s massively in the other direction. So a trampoline is a decoupled by nature.
it would actually be the more rigid floor of low mass that is sending vibrations everywhere and shaking things. A typical timber floor would fit this. The more rigid it is made the worse it would be.
as for absorbing. There are two issues to deal with. If the mass and rigidity of the floor is so great that the difference between it and the speaker is huge, there will be an impedance difference at the interface. The vibrations won’t transfer into the floor then. They just bounce back. Now we are in the same boat as before. You can graduate the interface to reduce the probability that the vibration bounces back. The easier solution is to change the impedance mismatch. Such as with adding a suspended floor over the concrete.
in any case, I feel like I can make a case for any of these scenarios. Without really first understanding the more desirable state, I am not sure where to land. What if the energy in the cabinet is of no audible consequence, then this may be for nothing.
I use the analogy of a trampoline because of how a footfall on one part of the floor will send vibrations through the whole floor. Perhaps trampoline is a poor word choice I settled on because of the springiness, rather think of it as ripples on the surface of a pond, perhaps, or the way solid ground and even concrete can ripple in an earthquake.
Regardless, I grew up on suspended wood floors which did not behave as the flooring in our home now. This house is “special” with this “half-story” section is much springier than the other section. I have yet to explore the
underverse (crawl space) of the house to see how our landlord actually built the flooring in terms of joist spacing, but my thought process based on a knowledge of basic architecture is that he chose a wider-than-standard joist spacing or a non-standard material for the floorboard.
Either way, my suspicion bore out in the months I had my Subwoofers operating without utilizing any isolation technique with them (the outriggers I was going to use with my Sub platforms were mis-shipped, then delayed).
My experience using the stock feet (two-part assembly terminated by rubber cones) on the carpeted floor was that I could feel and hear excess vibrations throughout the room.
Once I knew the right Outriggers were coming, I started playing with the Subs, some. First I laid down the concrete pads and put the sub with stock feet on top. The pad compressed the medium-pile carpet and vibrations could still easily be felt and heard. It was an improvement over just having the Sub on the floor.
I then tried the Soundpath Feet, first without, then with the concrete pad in place. Each was different still and each was better than the Subs’ stock feet in either situation.
The only aspect I can grok reasonably then about the difference in putting the concrete platform on the outriggers with spikes is that I dramatically changed the surface area in contact with the flooring, considering the Platform alone was compressing the carpet into a very minimal layer still capable of transferring some of the mechanical energy.
As you said, it would require a level of study and measurement that I am not capable of performing. In my mind, isolating and measuring the actual mechanical energy of the Sub would be the first step, followed by wiring the floor and walls with accelerometers, or lasers...
Of course, then there is the syntax conversation of how a person can reasonably describe the effect of what is happening when a change in energy transference is observed. Frankly, I despise the "audiophile" lingo for this as I've hinted previously. The performance of the Speaker as an isolated object is one thing (e.g. anechoic FR, cabinet resonance, etc), whereas the more complex system of the Speaker-Room interaction is different.
(I've seen many references to how a designer, for example, will go to great lengths to take the room out of the equation when listening to a new speaker and voicing it. This furthers my understanding that the Speaker exists as its own entity separate from any room interaction prior to being placed in any room. Likewise, we continuously discuss the interaction of any Speaker in any room with no two situations being exactly the same and how to deal with the acoustic concerns that arise, recognizing how some speakers aren't really meant to be used in certain rooms such as a RTJ 'Mega Stack' or Perlisten Tower in my 11x15' room, or perhaps a BMR Monitor in a 20' x50' room. (And while the Speakers themselves will still perform, what would the resulting interactions in terms of efficacious enjoyment?)).
I am intrigued at the notion that somehow an Isolation Product would transfer mechanical energy back into the Speaker as a potentially detrimental effect on performance. Likewise, I had not previously heard that Isolation can negatively impact Low Frequencies.
Hopefully, we can see something cool in the measurements you suggested being able to take as in room before and after with the Software you mentioned. It would be interesting indeed to see if there is any measurable difference considering a direct in room blind test is pretty much unrealistic.