It is clean, dry, inexpensive, odor-free, silica-free, lead-free, non-hygroscopic, non-corrosive, ready-to-use, and has a density of .97 g per cubic centimeter, which is dense enough to deaden all resonance in the column(s) of a speaker stand. Anything denser than that is overkill. When I filled mine, each stand weighed an additional 16 Lbs.
A knuckle rap on each column barely yields a sound, as if the entire stand has been sucked into a vacuum inside a black hole of anti-resonance-detail-revealing greatness.
I have tried all the other stuff over the past 20 years, and baking soda works as well of any of them. Obviously, there is some argument to made for using bird shot at the bottom of the stand to make it more bottom-heavy if needed. I used 4 balls of Blue-Tack on the top plate under each speaker to hold them in place.
I just happened to have several bags of baking soda for the pool, and figured I could try it risk-free (still usable in the pool!). It worked just as well as previous, much more elaborate treatments I have used before, with much less effort than drying supposedly "dry" sand in the oven. Just be sure to pack it by whacking the columns with a rubber mallet as you fill them. A "full" column will compress ~3" after a good whacking.
Aw hell... I forgot something. We should all be adding filler a little bit at a time to "tune" our stands to... something... something.
Obviously, ground up PSA Noise Harvesters is the best, but most expensive solution. Think of all the harvested noise!
Anyway this has the be the most hyphens I have ever used in a single post!