The throat Bb is a very problematic tone on many clarinets because the tone hole used to create it has dual functions. It should work as a tone hole when you play the Bb and as a register hole when you play the upper register. These are two completely different things. As a tone hole, it should be placed at a different position and be much bigger. As a register hole, it should have a different shape. Additionally, the register tube sticks into the bore, which causes problems for the air column.
There are many solutions to this problem. From different shaped register tubes to a variety of different mechanisms. We offer solutions to solve this problem.