JackD201.....
Have been thinking about that, thats another way to go.
Sympathetic resonance is if you have wood floor on the second floor, reading the manual right now.

But I do belive It's better to decouple the speaker directly with spikes to the concrete. Dead resonance than that coulden't be better.
I had that in mind with my floor, but I have to drill small holes in the wooden floor and put the spike directly on the concrete, but it woulden't look nice if I had to sell my house sometime and then I'm stuck with that position, not a good idea

Thanks