When I purchased the speakers five years ago I noticed they seemed a bit heavier than the spec'd 56 lbs. I decided to weigh them and they tipped the scale at 85 lbs. I noticed they had plywood flush and screwed into the base. I began to remove the plywood out of curiosity and found it was sealed with caulk. After doing a search at the Klipsch website, I found pictures and details on the mod. It appears that I own the speakers that were pictured on the website. Funny thing - the seller apparently had no idea. I picked them up locally and while he and I loaded them in the car, we both commented on how heavy they were.
Since I have no comparison with the speakers prior to this mod, I can only assume that it has helped with bass response.