I have risers for my Forte, but after considerable research, am not going to use them.
Don't get me wrong, sand or lead fill will improve things by adding mass. The mass, makes it harder for the vibrations to travel downward. But there are far more elegant and particularly effective solutions to "decouple" your speakers from the floor and room.
To start, if you go to audioasylum.com's Tweak forum, do some searches on "Svelte". You will find several discussions on how to build a DIY version of the Symposium Svelte platform (and save yourself some big $$). Most people agree, this is a far more effective way of "decoupling" a speaker than sand bases or spikes. This technique is sometimes called "constrained layer" resonance damping. By using different materials with different resonance charecteristics, you basically "drain" away the vibrations. The Svelte is only 1.5" thick, yet accomplishes more than the 3 3/4" riser on my forte, which essentially does nothing but shake the floors in my room. The "magic sauce" of the Svelte involves a thin aluminum layer, a PE (polyethylene foam) layer and then another alluminum layer. For that, they charge, $259 per Svelte - $499/pair. If you did it yourself, you can do it for much less. Much less. PE Foam costs next to nothing.
From there, you can look into more elaborate solutions which involve suspending the speakers either on ball bearings, inner tubes or poly balls (but done in an aesthetic manner). These are called "floating" methods of resonance damping. These are a little more involved. A lot of guidance and "how-to's" is available on AA.
Just something to consider anyways. If you feel like adding mass and weight, like the look of risers, then adding sand is better than nothing to the status quo. A "sand pit" would even be better, whereby the speakers would sit in a sand pit. You then remove vibrations occuring both in the horizontal and vertical planes. That is the key, and why PE foam and hip joint tungsten balls, are so effective. They remove vibrations because they react in both planes.
Based on what the engineering types on AA have said ... I believe you can do better than just adding weight to tbe bottom of your speakers.
Think about what you are trying to achieve, and poke around and do some research. There is more than one way to decouple your Chorus' so as to minimize resonances and improve sound. People now know a lot more on the subject than ten years ago.
