Limiting the transmission of vibration from the bass driver to the midrange enclosure. The results speak for themselves. Don’t know what you though I was doing with the sorbothane but it works incredibly in this application. Maybe it wasn’t clear that each driver is in an entirely seperate enclosure. A stack of boxes so to speak.
The bass driver cab vibration either cancels, blurs or reinforces frequencies in the crossover range, best to keep it out of the midrange cab. Bit like keeping your subs from touching your monitors.
i did try solidly coupling the cabinets together, it was good, but not even close to this good.
Btw there are quite a few designs in the market that apply the same principle in various ways. .