A spring is an energy store, a bit like a capacitor, so where does that energy go?.. Either back into the loudspeaker or into the floor. So the problem hasn't really been dealt with by using a spring on it's own, it will need further engineering or tuning to ensure the energy is dissipated benignly. If you end up spending a lot of time or money trying to fix the problems introduced by your 'solution' then there's a good chance you
didn't choose the right one in the first place.
Compliant materials like acoustic foam etc. are more like resistors - they are designed to transfer most of the energy into heat and so don't require any further 'tuning'. They don't always look great and they're difficult for manufacturers to make a big profit on (because everyone knows they're just buying slabs of material), but they do the job just fine. However there may be a problem with stability if your speakers have a high centre of gravity.
didn't choose the right one in the first place.
Compliant materials like acoustic foam etc. are more like resistors - they are designed to transfer most of the energy into heat and so don't require any further 'tuning'. They don't always look great and they're difficult for manufacturers to make a big profit on (because everyone knows they're just buying slabs of material), but they do the job just fine. However there may be a problem with stability if your speakers have a high centre of gravity.