Another misconception: "depends on the spring rate and the mass": that is called a SWINGER for good reason. at resonance frequency, amplitude will be infinite. Try driving your car with spring only.
That is were the DAMPER comes in. Now you have a system of spring, damper and mass, and can be tuned to KILL vibrations.
This has NOTHING to do with the vibrations the emitted sound is producing ('will vibrate even if suspend the speaker in the air'). It has to do with the vibration the mass off the speaker is COUPLING to the floor (not those of the soundwave).