Me and my brother got this problem too, didnt think much of it I just shoved it up the hilt until it wouldent move. My brothers was more difficult, heres the solution we came up with:
1)get either a toilet roll or paper towel roll (the cardboard bit)
2)Cut to desired length (probably about 2or 2 and a half inches (not sure I measure stuff in metric)
3) cut a peice out downwards (on the "face" of the tube)
4) put board/ speaker into saber and push in and insert cardboard tube
5)screw in pommel and viola!
PS: the lengh probably varies from saber to saber experiment a bit until you find the right length