A few months ago I wrote this about the clarinet:
If breath support, embouchure, and voicing are correctly established, then Crossing the Dreaded Break ceases to be a Thing. It’s just another note: a moment ago you were playing B-flat, and now you are playing B-natural. As long as your fingers get where they are supposed to go, then that’s all there is to it. Personally, I don’t even use the word “break” with a beginning student—there’s no need to get them all uptight about what really is a non-event.
My point was that crossing a register break is merely a fingering issue, and shouldn’t be turned into a big to-do about embouchures and equipment purchases and so forth. And I stand by that, but there is something I glossed over a bit that perhaps ought to be revisited in more detail, and that applies to register break crossings on all woodwind instruments.
The point that I want to return to is that of breath support. If it, and some other basic tone-production matters, are “correctly established,” then break-crossing is indeed nothing more than a new fingering or two. But assuming that breath support is 100% correct with a student just reaching the break-crossing stage is often a mistake.
Each note on the clarinet (and on any woodwind) has a certain level of resistance—that is to say, it requires a certain amount of air pressure to get the air column vibrating. Some notes are more resistant, and some are less resistant. As a sort of general oversimplification, we might assume that a long-tube note (with more toneholes closed) is more resistant than a short-tube note (with more toneholes open). Other factors do apply, of course: the size of the toneholes, whether the fingering is a “forked” fingering, and more, but let’s isolate tube length for the moment. So for the clarinet, having a break between A-sharp and B, we would expect to see this kind of resistance change while crossing the break:
(Note that the bar graphs here are strictly illustrative and not based on any real measurements.)
A beginner who is accustomed to the lower resistance of a few chalumeau-register notes might have intuitively developed just enough breath support to make those notes respond. When he or she attempts to cross the break, the breath support isn’t enough to overcome the increased resistance:
The breath support needs to be high enough to power the most resistant notes, and the less-resistant ones certainly do not suffer from it; on the contrary, their tone and pitch stability are improved by the additional support:
My college-level clarinet students have mostly mastered this, though sometimes they slip a bit. More of them still struggle a little with the transition across the higher break into the clarinet’s altissimo register, especially if they are timid about squeaking and tend to reduce airflow as they approach the high notes. My other reed-playing students sometimes have similar problems: oboists’ and saxophonists’ fourth-line D is sluggish (D-flat too, for oboists). With the bassoon, resistance throughout the instrument’s “beginner” range is generally fairly low and response isn’t as much of an issue, but lazy breath support manifests itself in a big way as pitch instability.
So crossing the break is not specifically a breath support issue; breath support needs to be powerful enough and constantly applied, to improve response across the break but also to improve virtually every aspect of woodwind tone production.