[jtcf]

These platforms have been more effective than I'd hoped for my bottom ported Zu Omen Defs to eliminate floor vibrations. They were (I think) developed originally for studio monitors that sat on desks and consoles.They are available in multiple sizes and consist of two inches of polyurethane foam, a heavy steel plinth,and neoprene rubber on top (non skid grip).The 17" x17" I bought were $299 each.For those on a strict budget you could fashion a close facsimile except for the steel. Substituting mdf wouldn't prevent the recoil 100% as well as the steel that curves around the front.
 My listening space is the living room in a very old home with wood walls,wood floor over a basement, and even wood ceilings. I do have GIK room treatments and foam decorative tiles on the ceiling.
 What I was hoping for was to tighten the bass and eliminate a lot of the vibration that transfers to the floor. What I got was so much more. Not only did the bass tighten up significantly, the entire frequency spectrum cleaned up and became clearer. The only way I can describe it is like all of my music has been remastered and cleaned of noise. I'm now thinking seriously of purchasing more for my subs,which would've been the best place to start but I knew the bottom ports on the ZUs needed to be addressed sooner or later.
  The music I listened to isn't really significant as everything was simply clearer and cleaner no matter what instrument or vocalist.My best CDs from Analogue Productions and MoFi  - Otis Spann,Janis Ian,Pink Floyd, along with the old blues and rock that I love - James Gang,BB King,Hot Tuna. 
 System: Cambridge transport, Audio Mirror Dac
                 Rogue RP1 preamp
                 Aric Audio Transcend amp
                 ZenWave cables
                 Custom rack RusticIndustrialMi
                 GIK room treatments

[Letitroll98]

They're sold on the Sweetwater site, $145 for the 11" x 15" size that would fit my floorstanders just fine.  The 9.5" x 11.5" size for my stand mounts are $115.  On that site they're called monitor isolation pads, not recoil stabilizers, but the construction is exactly as you describe.  https://www.sweetwater.com/store/detail/RX5f--primacoustic-rx5-monitor-isolation-pad-7.5-inch-by-9.5-inch-flat.

The ones from Auralex on the same side are exactly the same, except they substitute an MDF plate for the steel plate, and are on sale for $33 for the stand mount size.  I think it would be hard to buy the materials at HD for that price, so the Auralex model would be my go to if looking for the cheaper option.  Right now I have a sheet of neoprene under the stand mounts (Celestion 7 mkII) that seems to do a lot of what you describe, but perhaps I might go a little further with one of these.

One caveat that came from my situation, they don't appear suitable for carpeted floors.  Not the intended use I'm sure so not their fault.  I'm thinking that could be solved with a solid sheet on the carpet, anything from a MDF shelving flat to a concrete paving stone.

[jtcf]

I think the steel plate would be a plus for lighter cabinets especially to reduce the back and forth motion.Also better than mdf for bottom ports like my ZUs or down firing subs.
 My subs are heavy and front firing so I've been researching and have a materials list that replicates the Primacoustics using 3/4 mdf,two inches of foam,1/4 neoprene.I can build three platforms for $100.I'll order three Primacoustics and compare since they are returnable. My wallet will be happy if the homemade platforms work even 90% as well.
   I do think they would work on carpet if the speakers had  leveling feet or yes,something flat underneath.
 

[jtcf]

Here's a video that got me thinking about vibration control alternatives. I couldn't remember the company name but someone posted it on another thread and I've recaptured it:-) Platforms vs granite vs outriggers vs spikes to help speakers interact better with your room.If it doesn't post correctly it's Credo Audio on YouTube.http://https://m.youtube.com/watch?v=5ihzvD3urc4&embeds_euri=https%3A%2F%2Fif-cdn.com%2F&feature=emb_imp_woyt

[jtcf]

I decided to scrap the DIY and ordered some wood/foam/neoprene from Amazon. The results are interesting. First up was a platform under the SVS sub.No matter what music was playing there was a nasty glare introduced. Removed that one!Next were two platforms under the HSU sub to my left so all four feet were on on them.Same result,but when I removed one and positioned it in the center bottom between the feet that did the trick. The only anomaly is the midrange came forward noticeably but without the glare but the bass became pleasantly even tighter and clearer. Hmm...It seems the ratio of equipment weight to foam(or probably any type of footer) is as important as claimed by various manufacturers. I'm sure it's measurable also but it was easy to hear.Third and last was the other HSU located close to the right front wall corner.Not a huge difference between two or one platform. All of the subs are crossed over where the ZUs begin rolling off at 42hz and are placed after doing the 'subwoofer crawl'.Time to fiddle with the settings and see if the mids will get back in balance. Today I'm wishing that the HSUs had the app like the SVS to skip the back and forth to change the dials by hand.
  One other thing I could try is a pair of IsoAcoustics Aperta speaker isolators that I have stored away. Wouldn't hurt to try I suppose, but the subs would be up about four inches above the floor.That company has two products specifically for subs but they are lower.Perhaps the only reason is for aesthetics though.I think I've just talked myself into it

[jtcf]

Finally have everything sorted The IsoAcoustics Apertas which I had low expectations of are perfect under the HSUs.The glare disappeared and everything sounds great. As an afterthought I popped a 'vibe boss' $49 platform from one of the HSUs under the SVS and I swear the soundstage widened.It's a couple inches larger on all sides so it apparently needed more mass  in order to decouple.I'm relieved that I don't need to fiddle with the settings too.Also relieved not having to purchase three more Primacoustics. No regrets at all having them under the ZUs though. To my ears they are amazing.

[jtcf]

Not being able to leave well enough alone,I ordered two more Primacoustics to try under the HSUs.Last night not wanting to power lift them,I put one under the smaller SVS(with equalizer)I wasn't expecting a big change but Damn!The articulation is twice as good. Tonight I'll wrestle an HSU on the other one,see what happens,and may order another one.Whomever reads this think about saving a few $ and refraining from *top of the line* subs.For $100 - $300 (as opposed to $1,000s) these recoil platforms give the subs that are built to a price point,the weight, structure, and vibration control of the more expensive offerings of your favorite company. Just my opinion of course, but they are returnable so there's no risk.
 My subs are fortunately able to be placed in their optimal spots in my room. If aesthetics prevent optimal placement YMMV.No affiliation with the company.