Sunfire True Subwoofer Hard Wood cures

A friend of mine has a Sunfire True on hardwood floors and has complained about vibrations (his words, not mine). Any suggestions as to how to cure his problem. Thanks. Richard
Try a granite stone!
There are stands made that fit the sub... They help... I will make the call to a local dealer to find out the specifics -- give me an E-MAIL if you want me to call for you..