Subwoofer resonance isolation platform vs footers.

I live on the second floor in an apt. I use a concrete patio block 2" thick, 20" square. With the sub on rubber bottle stoppers on the slab, then the slab on top of toptoes
Totally cuts the vibes into the floor.

Rubber bottle stoppers! I remember those (circa 1955) as little plunger devices to keep the fizz in a 16 oz. Pepsi 'cause I was too young to drink the whole thing.

To the point, I use 4 sorbothane "pucks" under my SVS Ultra13 on a flagstone hearth. It was certainly an audible tweak.

Others swear by an Auralex product called the "sub dude". It's a platform with nothing but rave reviews.

I use threaded Audio Points from Star Sound with my REL Stadium subs. I am on concrete and they still helped. I used the 2" but the 1.5" might even have been better.