I found a bag of some all purpose sand in my garage the other day. I thought I would fill my B&W speaker stands with it to see if mass loading would make a difference in the sound of my CM1s.
I acoustically treated my room but a clap test revealed a ringing that I sourced to the hollow metal stands supporting my speakers. The ringing seemed to be most activated in the upper range of the human voice.
I carefully, with a cup, poured sand into each pillar until all four (two per stand) were full. Rapping on the side of the tubes after filling them produced only a low dead thud. So far so good. After replacing the top plates I clapped loudly and to my satisfaction, there was no ringing or any echo at all. I set the speakers back on top and put on some music I was just listening to earlier. Whoa...
Immediately I noticed everything sounded tighter, especially bass. When the vocals kicked in I was very surprised how much more detail I could hear and how clear the singer's "image" was. High end details were more apparent and defined too.
Basically, everything was clearer, more detailed and more solid sounding. For paying nothing and taking a little time out of my day, I'm very satisfied and recommend anyone with hollow speaker stands (especially metal) to try filling them and hearing your system like new again.