what do you put under your sub?

12"X 12" landscaping pavers.

I was laying on the floor next to one of my subs while the music was playing and could feel vibrations from my janis subs. Also the cables are directed out of the bottom of my sub. A quick check of the Soundanchor website and Alberporter revealed that they have stock stands for subs and also make cutom stands.
I contacted them. Sent them the measurements for my speakers. Sometime later a set of stands arrived via UPS.
Problem solved. Carpet no longer vibrates and the sub is no longer sitting on the cables. The bass has tightend up considerably.
BTW I support and encourage DIY solutions to problems like this.

I have two solutions. Under my VSA sub in my HT room, the sub which is a downshooter sits on spikes on a 2" maple block from Mapleshade. The block rests on four (4) Isoblocks (cork and rubber also from Mapleshade) which rest on the floor. This is a suspended wood floor which is hollow underneath since there is no slab. Bass is tight and there is no boominess through the floor.

In my two channel room upstairs, the MJ Acoustics sub (also a downshooter) sits on Nordost spikes, which in turn sit on an Auralex SubDude. Check this out, Auralex developed this design for roadies to use to isolate their speaker cabinets from hollow temporary arena stages. Inexpensive and very effective - bass is tight and there is no annoying thump through downstairs.

I have ASC Subtrap under my Velodyne DD-15.

Depends on your floor (and what you're trying to achieve).
If you have a suspended wood floor, and you want to hear the sub's bass output, not the room and floor rattling, use something that isolates. The Auralex SubDude is a nice option. A cheap, but not quite as effective, alternative is $1 hockey pucks. And then there's everything from isopods to sandboxes.
If you want to hear your room rattle and feel your chair vibrate, as some ( esp home theater guys) do, then couple the sub to the floor with spikes, etc.

If your floor is concrete slab, then the effects of either won't be as pronounced, and I think most find cones appropriate here, though isolation has been said to reduce floor vibration a bit here too. Again, depends what you want.

I've tried the pucks and DH cones and Pulsar points and even Aurios under my RBH subs. They all helped in slightly different ways, but I'm using the inexpensive pucks at present. I may try the SubDude next. Then again, I like bass that's extended and tight and non-intrusive, and I also use a Tact to equalize and eliminate room nodes.

I had an audiophile friend over a while back and he thought my bass was anemic. He didn't like it. The bass was too flat. Me, I thought it sounded great, but it takes a while to get used to flat bass as we're so accustomed to the extra room-induced boom.