mbolddal, my ProAc`s uses dry silver sand instead of lead shot. But I think it does the same thing. Here is what proAc says, "a small amount of sand will give the bass more warmth, adding more sand to the cavity will give a dryer tighter quality, most people will find that a half to two thirds full is optimum in most models".
If you still have your owners manual check it out for your speakers.
Hope this helps,Jim