why spikes under speakers???

Eldartford is correct. No decently made cabinet is going to be moved by a lightweight little driver. Vibrated/resonated, yes, but pumped back and forth by a driver...no way. Eldartford's experiment is the perfect way to prove that and to clarify what he said: Idiots who don't know why they sell spikes disagree.

S7horton, that cell phone on vibrate isn't moving in response to a driver since in vibrate mode it isn't connected to one. It's moving in response to a small electric motor with its driveshaft connected to one side of a small weight, purposely creating an unbalanced rotation. Take one apart, if you doubt me. Ever had sore muscles? It's the exact same system used to make a massager.

Some spikes are more cone shaped than others. Cones run one way when it comes to vibration. They 'drain' vibration from the speaker cabinet and dont permit vibration from traveling up from the floor. Thats why with cones under components and stands you get less vibration.
As for speakers moving, I have seen speakers and subs "walk". Its the vibration of the cabinet that you are trying to reduce. A drivers motion will be more precise if its 'working against' a solid stationary baffle to start and stop from , as opposed to a vibrating baffle. Spikes ususally improve the sound by giving the drivers a less resonant platform so they work better and also by reducing the sound you may hear from the cabinet itself.

Blkadr...The notion that a mechanical structure (cone) can transmit vibration one way, and not the other has no basis in fact. Vibration, by its nature, is a back-and-forth motion.

Vibration of enclosure walls can be a significant sound source. It is minimized by solid construction, with internal braces, curved panels, and damping material. Except for the bottom panel of the enclosure, where the spikes/floor may serve as a brace, spikes don't help.

Suspending a speaker by ropes is the same as using spikes. You just validated my point. You are using points to keep the speaker up, just like you are when you use spikes. A cell phone is a fine example. In both situations, you have two enclosures that have moving parts inside. Whether off balance or not isn't the point. This is simple physics taught in high school. Whether the movement is significant or not, is another discussion entirely. The point is, there is movement.

S7horton...Your "simple physics taught in high school" must mean Newton's Law of Action and Reaction forces. But you evidently missed the second class where we learned how to calculate how much motion a force produces.

The suspended speaker motion test was done with a single rope, so it isn't like spikes.

Ttrhp has a good reason.