DIY speaker isolation base for a wood floor

Thanks for offering Geof.

Right. So there are two issues here, the speaker vibrating and the floor acting as a sounding board. In geoFFkait's example he is isolating the floor from everything above 1 Hz. So the floor is being isolated nicely. But, unfortunately the speaker is free to vibrate at all frequencies above 1Hz. Any vibration of the speaker is distortion. Some new designs like the Kef Blades and Magico subwoofers use drivers on opposite sides of very stiff enclosures so their forces cancel. This prevents the enclosure from vibrating as a whole. The best way for us to deal with both problems is to have a stiff well dampened floor. Concrete is ideal. A wood floor has to be very stiff then dampened with padding and carpet. The best way to keep the enclosure from vibrating is to spike it to a stiff well dampened floor. Force cancelling woofers like in the Kef Blades are ideal. 
Good work geoFFkait you have succeeded in making a bass distortion machine.

On the advice of Dr. Edgar I built a pair of sand boxes slightly larger than the bottom of my Fitzmaurice HT Tuba subs.  Each box contains 100 pounds of fine white sand with the subs sitting directly on the sand.  I think this addresses both issues nicely.