Filling speaker cavities with cat litter

I have Skylan speaker stands and cat litter was the recommended fill material. I chose playground sand, however, for more mass loading.

Use led shot or silica sand HELLO!!!

Cat litter is PURE GARBADGE!!!

what speaker cavities?  
hopefully you mean speaker stands.  

my old proac response 3.5's have a lower area of the cabinet (below the drivers) that allow the user to sand fill

stuart tyler said in the manual to use dry sand for mass loading

but for my skylan stands i use landscaping gravel or rice as the grains are larger and will not leak through the tiny seams