@perki - The minus K approach would require some engineering based upon some pretty complicated math.
If you’re going to order springs for your speakers, some specifications I have found that may help you. (specific to compression springs)
- springs should have approximately 50% compression under load, this aught to allow for the highest amplitude and frequency range of isolation.
- the diameter being either greater than or equal to the height of the spring under load will help it to deform along it’s length rather than simply twist and collapse under the load.
- the least number of springs (usually three) the better, and use the same spring rate to level the mass supported, move the springs to positions that level the load. Do not change the spring rates to level the load if it can be avoided, move the springs around the center of gravity.
- 4Hz isolation or lower if possible (minus K have some that do 2Hz I think?)
- loads that are tall and skinny (like floor stander speakers) will be able to move when they may be bumped, moving their center or gravity over the base, where gravity will have it’s way with them. Broaden the base so that is much less likely to fall and get damaged
- the substrate supporting the springs is another factor to consider, the more the springs deform to the load’s movement the better
If you consider the speaker cabinet to be somewhat like a very rigid balllon, the lower frequency driver will create a high and lower pressure within the cabinet. This will push and pull at the walls of the cabinet, much like pulling and pushing a post, which at the right frequency with the right amount of force will move back and forth.
These high and low pressures in the enclosure will energise the nodes of the cabinet. Nikola Tesla is an interesting read, and Mythbusters did an excellent episode with a bridge regarding that science. The walls of the enclosure will move in much a similar manner to a balloon. My speakers have been made from composite materials, lined with steel plates, and they move, their nodes can be heard by wrapping my knuckles on them.
Instead of thinking of a speaker enclosure as an entirely rigid structure, consider it to be an ever morphing shape energised by the drivers during playback, especially when played loudly. So instead of it moving on it’s base, the idea of springs is to keep the center of gravity as virtually stationary as possible, trying to keep the drivers held in relative space to the listener.
