The brass player’s lower jaw is an important part of a well functioning embouchure. The player’s use (or misuse) of the jaw can drastically alter the embouchure form. As with other brass playing mechanics, the particular way in which any given player uses the jaw will be personal, but there are some generalities that can be discussed.
One area of some controversy is whether the jaw should be protruded or receded while playing. Some teachers instruct students to protrude the jaw slightly (assuming the player has a normal underbite) so that the teeth are more or less aligned, resulting in a horn angle that is close to straight out. Other teachers will recommend keeping the jaw slightly receded, so the lower teeth are a bit behind the upper teeth and the horn angle is slightly tilted down.
One thing I should note here is that many teachers simply allow their students to do whichever seems to work best for them, without worrying about this. While I agree that all players are unique and need to be treated individually, many don’t consider the jaw position any further as something to be understood and refined as it relates to the player’s overall embouchure form and function.
Some authors have already discussed this at some length. David Hickman covers this in his book, Trumpet Pedagogy, in some detail. He coins players who leave their jaw in a slightly receded position as “fixed-jaw” players and players who align their teeth to be “floating-jaw” players. In my opinion, this sort of jaw division is useful, but fairly incomplete in that it doesn’t account for many different factors that coordinate with the player’s general jaw position. For one thing, some players have a natural overbite and aligning the teeth can be said to be their “fixed-jaw” playing position. Hickman’s ideas about how both of these types of players need to focus muscular effort in different places are interesting, but seem to be largely based on speculation rather than any specific scientific understanding of what muscles get used to play trumpet. While I similarly feel that the jaw position is an important consideration for brass players, I disagree with the specific details and conclusions Hickman draws.
That said, there are definitely some correlations between a brass player’s embouchure type and the player’s general jaw position. Players belonging to the Very High Placement embouchure type tend to have their teeth aligned and a horn angle close to straight out, while the Medium High Placement embouchure type player tends to have a receded jaw position and a horn angle that is tilted slightly down. Low Placement embouchure type players generally have their jaw protruded, but some (such as myself) have a receded jaw position and a slightly lowered horn angle. In fact, exceptions exist for all three embouchure types. In some of these cases the exceptions may improve by adopting a jaw position that is more typical for the player’s particular embouchure type but in other cases the exception is obviously correct for the individual. Consider the embouchure type’s correlation with jaw position to be a useful guide to try first, not as a hard and fast rule.
Beyond the general position of the brass musician’s jaw when playing we also need to consider what, if any, jaw movement is used when playing. The jaw is able to make a wider range of motion than many of us consider. It can move forward/backward, up/down, and left/right in 3 dimensions quite naturally. The next time you get the chance, observe someone chew their food and notice how they don’t just move their jaw up and down, but it also naturally moves in other directions as well. Everyone has at least a little bit of this off-center bite, known as a malocclusion. Playing a brass instrument is no different, as our jaws come into position to play (whether protruded or slightly receded), it also will come to a particular position that may not be perfectly straight forward.
This is important to understand because the jaw position shouldn’t be held rigidly static while playing. Nor should it move huge amounts. When ascending the brass players jaw will typically protrude just a bit more, often with a little side to side motion according to the player’s malocclusion. When descending the jaw then usually comes back slightly, also with the opposition side to side motion, if one is present. Many players will feel this more of a tilting of the instrument angle, for example tilting the bell of the trumpet up and maybe a bit to the right to ascend, but it’s important to understand that any sort of horn angle change happens in conjunction with the slight jaw motion. When the jaw is protruded slightly the horn angle will tend to raise up slightly. If a player has some left and right jaw motion the horn angle will move the left when the jaw moves right and vice versa.
One issue related to the jaw where I go against the mainstream is whether one should drop the jaw to descend. Some teachers actively instruct their students to drop the jaw for the low register, others simply allow it if they don’t notice it causing any problems. Personally, I actively encourage all brass players, regardless of embouchure type and jaw position, to reduce or eliminate the descending jaw drop as much as possible. I can attest from personal experience that this is much more easily said than done, but the goal of a minimal or no jaw drop is worth the effort.
The best argument for instructing students to descend with a jaw drop or allow it is because it tends to work, at least in the low range. When you lower your jaw to descend you lower the lip compression by pulling the whole support structure of the lower lip down and away from the upper lip. An easy demonstration is to hold a middle register pitch and slowly open your jaw while holding out the note. As you drop your jaw the pitch will go flat and maybe even drop down to the next partial or two.
As a general principle, I tend to avoid instructions that encourage the player’s embouchure to function in one range differently than how it functions in the rest. Brass players do not, as a rule, gradually raise the position of their jaw as they ascend into the upper register, so lowering the jaw to descend at a particular point is functionally a different way to play. Speaking anecdotally, I also find there is sometimes a correlation between players with a severe jaw drop and difficulties in other registers. It may be that something about having essentially two embouchures, one for the low range and one for the rest, causes issues in the range where the jaw drop isn’t even present.
Why would this be? If the descending jaw drop works so well, why would it make for problems when the jaw is brought back up into normal playing position? It’s probably because dropping the jaw pulls the entire embouchure formation downward and, depending on the individual player’s specific embouchure type, essentially makes for a reversal in embouchure form. Low Placement and Medium High Placement embouchure type players both have an embouchure motion of pulling the mouthpiece and lips together down to ascend and pushing up to descend. Dropping the jaw essentially pulls the embouchure formation in the opposite direction it wants to go to descend. For Low Placement embouchure type players the jaw drop also risks pulling the mouthpiece placement off the upper lip entirely, as they have so little upper lip inside in the first place. Very High Placement players have the reverse embouchure motion, they pull their mouthpiece and lips together down to descend, but this actually makes them even more prone to pulling the mouthpiece to a lower placement on the upper lip. These players can end up with two separate mouthpiece placements, a little more lower lip inside for the low register but to ascend beyond a certain point they have to reset the mouthpiece higher, closer to the nose.
Before anyone leaves any comments pointing this out, of course you can find lots of great players and teachers advocating for the descending jaw drop. My main point here is to simply show that from the standpoint of how the embouchure functions over the entire range, the less one relies on the jaw drop to descend the more consistent the embouchure form can be for the entire range, including the lower register. At the very least, one way to look at it is that the less the jaw drop is used to descend the less likely to run into the issues I described above. By learning how to coordinate the forward/backward/left/right motion of the jaw along with any accompanying horn angle changes and embouchure motion players can learn how to descend without resorting to an excessive jaw drop and be able to better connect their low register with the rest of the player’s range. Learning how the jaw functions for the entire range can help players open up their sound in the upper register, achieve better flexibility, and in general make playing feel like less effort.