Loading speaker stands with?

@mofimadness Thanks, I started my search there, but didn't see anything about lightweight packing foam

@ghdprentice I think uranium pellets are an interesting suggestion since "Unlike materials with specific acoustic resonances, the radioactive decay and radiation emitted by uranium (alpha, beta, and gamma rays) are physically silent." But unless the speaker stands are made of lead, I don't think I would want that in my listening room. And if the stands are lead, I probably wouldn't need filler.

I use cleaned and dried sand from a pet store, usually used in fish tanks. if you prefer crushed rock, they have that too. lead is dead as they say, if it’s not encapsulated don't use it. 

Agree with @ghdprentice about the steel shot.  Look for S110, which is about 1/4 of a mm in diameter, or the even smaller S70.  You can mix with silica sand (the white sandbox stuff) if desired. One vendor in Kansas (link).

Lightweight packing foam may dampen ringing of the metal stand itself, but will probably not add to the overall vibration resistance.  The weight from shot and/or sand should help lower the natural frequency of the combined components and stand system.

Yeah there are a few choices....I have a pair of speakers on hollow stands and have never filled them and the sound is aok.

   I have a pair of Sound Anchor 3 leg stands that weigh about 50 lbs Ea. This is what the internet says -  “Sound Anchor stands are factory-filled with a mix of heavy granular materials, primarily heavy sand and specialized steel shot, which are bound together by a hardened, proprietary epoxy/damping foam. This combination of mass and dense packing eliminates hollow tube ringing and isolates speaker vibrations.” What I’d also look at is some form of decoupling to either the speaker or the entire stand / speaker combo. Happy Listening, Mike B.