When I was at school, we tried to put things in the bell. Sometimes to mute the instrument, and sometimes to change (neutralize in classical music) the color of the saxophone. Sometimes one need to sound on alto sax more like "viola", sometimes more like "clarinet". Perhaps this insert has such a task.Awesome. At 0:20 (first clip) there is a good view of blue material inside the bell. Is that used to dampen the tone? I have never seen material inside the bell like that.