Stillpoints Ultra SS vs spikes on concrete

Pretty hard to get solid concrete to vibrate in the first place. Are you worried about itty, bitty, tiny-tiney micro vibrations that only bats might notice? Speakers by there very nature are designed to work in their respective environment. The spikes IMO, if properly set-up should be most sufficient. Save your money and make sure that your source and pre are well isolated from unwanted vibes.

I would make sure your spikes are actually penetrating the carpet and sitting directly on the concrete. I used a sharp pointed X-acto hobby knife to make a small "X" so the spike actually sits on concrete. It made an obvious improvement.

Like the SS Ultras, have a set under my speakers, and they were a real improvement coming from spikes on a suspended wooden floor (with granite in between). That said, a good solid spike into concrete is a real solid (pun intended) solution. I'd be a lot less quick to assume that the Stillpoints would be an improvement under your circumstances (and, personally, I likely wouldn't have bothered had I concrete to spike to in the first place). At root, they provide a fundamentally different approach -- coupling and mass-loading v. isolation -- and which might work better in your particular setup may be unknowable absent some experimentation. If you're really itching to find out, try a set from an outfit with a lending or return policy (used The Cable Co for mine, ended up keeping them) and send'em back if they don't do it for you. The ultras are mighty spendy for a footer, makes good sense to try them out first if you can. If they can't convince you, consider yourself lucky and spike away with confidence and abandon. No?