For sub users with carpet over concrete (or any well-supported floor), spikes are championed for doing the exact opposite of what Ed states the SVS feet (Sorbothane) were designed to do. Ed suggests his feet "isolate" the sub from the floor. What you actually want feet to do (and spikes do it very well, though, sorry, I can't "prove" it here, so feel free to dismiss this) is "couple" the enclosure to the floor, so that it doesn't move backwards in reaction to the cone moving forward. If the box is an immovable object, the driver's output should be, all things being equal, closer to the signal, with less (in audiophile terms...don't gag yet) smearing, having instead more resolution. If this sounds farfetched to you, it's a commonly understood phenomenon in photography, hence the tripod and the cable shutter-release. No fairy dust there.