audioholic
5,000+ posts
not a moderator
What you are probably talking about is external cavities built around the enclosure that were filled with sand to help deaden the enclosure. Its a pretty extreme method for car audio, but home audiophiles often build concrete enclosures for the same reason.I knew a guy named Joe Black that with his Chevy, he had two ProTech 12's and sand in the box. One of the nicest installs and very nice sounding cars of the mid 90s. You could probably google his name and find it.
You cannot simply fill an enclosure with sand. One of the most basic responsibilities of an enclosure is to give the speaker the proper 'air spring' to aid in cone damping, and to tune to the desired frequency response. If you fill the enclosure with sand, you will be altering the internal air volume.
And no, you would never ever want your speaker's motor exposed to sand. You dont even want to leave sawdust in it after being built. I vacuum it out, and then go over all the internal surfaces with a damp cloth. Most subs these days have vented motors, they can and will suck debris in and possibly damage the coil, so you want the enclosure to be thoroughly clean.