Yesterday I decided to repeat a tweak I applied to my JBL L-96 back in those days (remember?)
In short I added a thin layer of silicone rubber on the inner edge of the woofer. The purpose is to isolate the woofer from the cabinets, so fewer vibrations escape to the cab itself. See the pic below.
The speakers I have today are much smaller than the L-96's, but are somewhat plagued by cabinet vibrations due to a not too solidly built cabinet. Long time ago I added 1