DIY speaker isolation base for a wood floor

I want a firm solid foundation closer to concrete. We may be over thinking this. A bouncy spring on a bouncy wooden suspended floor? Nothing that gives is going to firm up the bass. Muscle is what is needed to control the woofer. Right? No movement. My platform is not perfect. Would it be better if I place a 36x36 inch slab of granite directly on the floor? 

Two things. Even through the cement slab is very thick and stiff it still moves right along with the movement of the ground due to traffic 🚗 🚙 , subways 🚊 trains 🚞 ocean waves 🌊 on the shore, Earth 🌍 crust motion. The entire house moves. And it moves in 6 directions! 🔛 🔝Springs under components are not “bouncy” as you are imagining them - they actually don’t move visibly when in operation. It’s the combination of mass + springs that provides the mechanical low pass filter. So the object being isolated moves much less with springs under it than without springs. It’s like springs (shock absorbers) on car wheels - they provide a smoother ride, not a rougher ride on solid road surfaces. The more things you isolate with springs the better the bass performance becomes. More dynamic, more slam, lower in frequency and more detailed.

Springs and shock absorbers are completely different beasts. If you have just the spring and not the absorber you can get oscillation at the resonant frequency.


Are there any tests w.r.t. frequency response, distortion, impulse response of a speaker on/off an isolation platform to characterize the improvement? 

Shock absorbers are air springs or gas springs. They’re springs. You say no, I say yes, you say hello, I say goodbye. Goodbye!

A vehicle suspension consists of a spring element AND a shock absorber. The shock absorber portion is not a spring. It moves typically fluid between sections through small channels converting motion to heat. A little research may be in order for you.