THE HIGH REGISTER
Over many years of playing and teaching, I have found the management of the altissimo register i.e. the notes above high C (c''' or thumb/register key) are those which, because of various reasons, are unstable and very much unwelcome in the repertoire of fingerings of young players. It is not enough to have a teacher provide the correct fingering or the student searching for it in an excellent fingering chart. In addition to the finger position, the most important element in stabilizing these altissimo notes is EMBOUCHURE. Assuming a good reed and mouthpiece are to be had and are in good working order, it is first the embouchure followed by proper breath support that creates the stability and color of all the notes above high C. This is not to preclude the fact that one supports properly in other registers as well. (See chapter on Clarinet Embouchure.)
Good breath support alone does not secure the altissimo register. Adequate breath support in addition to over-gripping (pinching) the mouthpiece will net poor results and a very sore lip. I can remember the words of my band director in high school . . ."pinch harder for the high notes." He was a fine trumpeter but didn't know very much about the clarinet. I pinched, I cut my lip, and I played out of tune. These symptoms most assuredly do not apply solely to me, but to hundreds of young high clarinetists who have not been properly instructed in how to play the high register. If one keeps squeezing (biting) harder on the mouthpiece and reed, the muscles used in gripping the mouthpiece grow fatigued provide little support; we then bite even harder to sustain the tone, and then the reed collapses. The next step toward self-destruction is finding a harder reed to play on and this is where the trouble really begins. The harder reed gives a heavy, airy tone, and the player has to bit even harder to sustain it. This situation now becomes a vicious circle of events which defeat all reasons and artistic goals for playing the clarinet - making music.
I would be remiss not to include a final point concerning the upper register, and that is the position of the tongue and throat. Many teachers do not emphasize the fact that the throat must be kept open at all times, and the tongue in a raised position. Since I am rather emphatic about using a syllable for articulation, (i.e. dah, nu, lu or other variables) to keep the tongue stroke consistent, it is necessary to mention the change of syllable when playing the high register. Using 'dah' in the upper register pulls the tongue down and creates an unsupported throaty sound. Even though urged not to pinch in the upper register, the player must create a narrower focus keeping the tongue high and the syllable to an 'ee' sound. What is high? With the mouthpiece positioned in the mouth and the tip of the tongue placed on the tip of the reed ready to play, withdrawing the tongue slightly away from the reed creates a rather basic tongue position. Lowering the tip and dropping the back of the tongue loses the proper 'tone center,' tongue position, and the high notes become almost impossible to control.
The bottom line is simply this. Besides the visual aspects of teaching clarinet viz a viz clarinet angle, hand position, embouchure etc., one must use the ear critically, and play 'twenty questions' in order to determine what the problem is, and how to solve it. Don't hesitate to pose questions to the student as to what he/she is doing in respect to oral configurations within the mouth. They sometimes just can't tell what is going on and how to define it. Four ears are better than two. Questions are not an admission of incompetence, but a necessary part of effective teaching, and a sure way of amassing an important set criteria for future use.