I am trying to adapt this from work. We used electric motors and bolted them to a concrete base. The mass of the base was 3-5X the mass of the motor. The same would hold true for a driver and the enclosure. If the speaker cabinet is vibrating then that is the resonant frequency. An accelerometer placed on the cabinet would also tell you what that frequency is. Another way is to hit the cabinet with a rubber mallet while the accelerometer is attached. If weight is added to a certain portion of the speaker enclosure that would help but would not solve the resonant frequency for the entire cabinet, I don't think. It got more complicated with motors if they were mounted on springs, which I think is what you have with a speaker driver. But in general weight is good, unless you want to move them.
