Under speaker metal SPIKES ...what is the point ?

Speakers vibrate when they play. Spikes "couple" the speaker to the floor such that vibrations are shunted from the speaker and into the floor. This usually has the effect of tightening up the bass, which makes the mid-range and treble more clear. And as the bass is "faster" or more articulate, pace, rhythm, and timing are also often improved (PRaT).

Of course the effect depends on many things such as type of floor, type of music, how loud it's played, type of spikes, etc. The opposite of "coupling" the speakers to the floor would be using rubber feet or footers which usually has the effect of "de-coupling" the speakers from the floor.

De-coupling is more often used with other stero components such as pre-amps and front ends. And sometimes the two techniques can be effectively used together, ie McCormack amps do both-- they have a coupling spike at the bottom rear, and sorbothane feet at the front for de-coupling.

All of this has to do with vibration management, and there are many old threads on the subject. Cheers. Craig.

Well first it ruins your carpet or hardwood floor. In theory, all the weight of the speaker being on a tiny little point increases the pressure on the floor at its contact point and better couples the speaker to the room and prevents it from vibrating or rocking in minute increments. That's what I understand is the theory. Does it make a difference? Who knows. It's like chicken soup when you have a cold, it can't hurt, except for the floor covering. Someone in Sensible Sound has explained that the physics of it all are somewhat flawed. Again, if the spikes are free and you or your significant other (what a terrible expression, I only hope it's politically correct, 'cause I sure ain't) don't mind the collateral floor damage, go for it. Maybe you will be able to hear a difference, I doubt it. I sure as hell have not, but hey, my ears are only gold plated.

Also bear in mind that the limited surface area at the tips of the spikes presents little surface area for the vibrations from the floor to travel up into the speaker cabinets or stands. The broader the surface area exposed to the floor the more likely the cabinets will act as floor vibration antennae. Added bonus - the spikes keep the speakers from dancing across the room.

Speaker spikes serve ascentially two purposes. The first being they provide a contact point w/ considerably less surface area thus increasing the stability of your speakers.

One might ask why is this important? Think of your tweeters speakers w/ small piston areas designed to move only a few thousands of an inch any movement of the cabinet will alter the sound.

The second purpose of spikes is to allow a focal point for resonance energy. That being secondary vibrations from the cabinet after the speaker initionally pulsates. By mating the spikes w/ the speakers this energy travels from the large part of the cone to the point (or moving from greatest resistance to least) in wich it is disopated into the floor.