Crossing the break, or the transition between your lower and middle registers of the clarinet, can be challenging, especially if you're just starting out with learning how to play the clarinet.
In this video demonstrating the registers of the clarinet, the "break" that we'll be talking about occurs between the chalumeau and the clarinet registers:
You can hear that there's a big difference in timbre (tone quality) between the two registers. When you go up to the middle register, you put down you register key, which raises the pitch of a note that has the same fingering minus the register key up a 12th, or an octave plus a 5th (i.e. low E + register key = middle B)
Scales are a good example of something you'll have to go over the break to play. If you're playing your G Major scale, between throat A and the B above it you over the break. In the F scale, between throat B-flat and C you have to go over the break as well.
A good way to start going over the break is to practice simply going from your lower chalumeau to your middle clarion registers. Make sure you can comfortably play a low note and put down your register key to make a higher note.
Going over the break from the throat tones can be challenging at first. Have you ever tried to play with just the top half of the clarinet? If you have, maybe you've noticed that the throat tones sound exactly the same whether or not you have the bottom joint and bell attached or not. That's because throat tones like open G, A, and B-flat only use the top half of the clarinet. Notes like B and C in the clarion register, however, require ALL of the length of the clarinet because all of the holes are covered. Going over the break involves the transition between an open note and a closed note.
These tips will help you in crossing the break. They will focus on the transition from A to B, but you can use these tips for other note combinations as well, such as A to C, B-flat to B, B-flat to C, and others.
Tips for Crossing the Break