I don’t remember exactly how I happened across this, but I while ago I found interesting discussion of air pockets by trumpet player Tim Morrison. According to this link, Tim Morrison plays intentionally with some air pockets under his lips.
The primary pocketing spot is the upper lip and cheek area above the corners. It’s important to keep corners and cheeks firm, but to allow the air pockets to form. I’ve found this dramatically reduces counter-productive embouchure stress, yet keeps strength where you need it, which is in the corners and through the middle of the cheeks. One more thing. There is always air present under the upper lip/cheek area and even more noticeably when playing in the lower register. This is paramount in getting the “trombone effect” in lower register playing. As you ascend, the facial muscles come more into play and the air pockets become less noticeable, but are still present.
Take a look at this video of Tim Morrison and look at his upper lip. The resolution is a little low, unfortunately, but I think I can see his air pockets. Also, I have to say how much I loved watching the composer, Joe Hisaishi, conduct this piece. It’s unusual for an orchestral conductor to not use a baton, but he is a very expressive conductor.
While I’m at it, I’ll play “Guess the Embouchure Type.” Take a look and I’ll have my guess after the break.
My best guess for Morrison’s embouchure type is the “medium high placement” type. His placement seems to be just a bit more upper lip inside the mouthpiece and he also appears to have the correct embouchure motion for that type. His horn angle is close to straight out, though, which isn’t typical for this embouchure type. Still, I have seen some very fine players belonging to this embouchure type with the same straight out horn angle, so it isn’t necessarily wrong for these players.
Donald Reinhardt wrote a little about the air pockets.
Sometimes a little puff will form under the upper lip while playing at great volume in the upper register. This, however, is of little consequence as long as it does not interfere with the mouthcorners. Never permit a puff to form under the lower lip regardless of the performer’s physical type; this fault makes a trumpet sound like a cornet, a cornet like a flugelhorn, a trombone like a baritone, etc.
– Donald Reinhardt, Encyclopedia of the Pivot System p. 220
Both Morrison and Reinhardt agree to keep the air pockets away from the mouth corners. Reinhardt did have some specific exercises he used that intentionally required cheek puffing, but did not encourage his students to perform this way. He used cheek puffing as either a diagnostic tool or correctional procedure at times.
In general, I feel it’s best to reduce any air pockets when possible, but it does seem to be helpful for some players and may be necessary at certain stages of development. It’s probably best to keep any air pockets away from the mouth corners, unless you’re being guided by a teacher who understands how to keep it from hindering your playing.