Sand filled speakers please help

Sand (which can be combined with lead shot) is a very good vibration damping material (years ago, Wharfedale speakers featured sand-filled cabinets). It's hard to say with precision how your speakers' sound may change with the addition of sand, but it should reduce/eliminate cabinet resonances, and make the low frequencies sound tighter (which may also make the lower-middle frequencies sound clearer). There should no be appreciable change in the high frequencies, but since the sand you add can also be removed, why not experiment to see what you prefer -- sand, or no sand.

If you do decide to load the speakers with sand, make sure it is clean, dry white sand -- not sand from an ocean beach, or sand with a lot of gravel in it. If you put damp sand, or sand that has salt, etc., into the speaker, it will eventually rot the wood and perhaps cause other problems as well. Aquarium sand should work fine, but if you can't find sand that has already been washed, then rinse it several times, and then dry it in a large roasting pan in your oven.

I filled the base compartments of my speakers with steel coated lead shot with a notable improvement in bass control. I can't say that the damping effect it had will be true for the Joseph's but that is the concensus. Therefore I would think it is the most likely outcome. I have not heard that it yields a bright sound.

I thought about putting sand or shot in my KEF Reference Two plinths but am wondering if it's worth the hassle? They are dead solid, basically no vibration even at very load levels. Since they may not vibrate as much as other speakers, will loading the plinths offer even less benefit?