Back in 2003 some physicists from Australia (Wolfe, Tarnopolsky, Fletcher, Hollenberg, and Smith) presented at the Stockholm Music Acoustics Conference on research they conducted on the role of the tongue position on didjeridu and the trombone.
Many players of wind instruments talk of the perceived importance of the shape of the mouth on the sound. In the case of the didjeridu, the effect on the timbre is so clear as to be incontestable. Among scientists, however, there is considerable variation in opinion about the effect on pitch [1- 4]. In this paper we report experiments on well-characterised model systems: artificial wind instrument players. Using plausible values of the relevant parameters, these show that vocal tract shapes can have important effects on both pitch and timbre.
Many brass performers and teachers, including myself, have cited Bernoulli’s principle as assisting the air speed as it strikes the vibrating lips for the importance of tongue position while playing. I’ve asked some physics teachers and engineers about this and almost all of them, with some exceptions, have suggested that this might be true. That said, this presentation was focused on the vocal tract impedance (if I understand this correctly, that is how the shape of the vocal tract influence pitch and timbre of a particular pitch).
On the didjeridu the influence was quite strong, perhaps in part due to the larger bore size of the instrument and the much larger vibrating area (there are a lot more of the lips inside the “mouthpiece” of the didjeridu than inside a trombone mouthpiece). They did note that it was an influence on the trombone, however.
The shift in pitch, over the range studied, is typically 20cents: a musically important effect for intonation. Preliminary measurements on experienced brass players showed a comparable shift in pitch when they were asked to lower the tongue, keeping all else constant.
They also noted that a change in tongue position can “cause a transition between different playing register.” In other words, you can shift tongue position and change partials on a brass instrument.
This has some interesting implications for brass performers and teachers. Some folks swear that they keep their tongue position consistent, regardless of what register they play in. This view is in the minority and I suspect that players who claim this aren’t even aware of their shifting tongue position. That said, different people are going to have variations in the size and shape of their mouth and tongue and it would be interesting to compare those players. I’m also curious about the difference between different traditional brass instruments. Do trumpet players change the position of their tongue more or less than tuba players?
Regardless, I think that research like this suggests that tongue position is an important part of playing in tune and with a focused tone on a brass instrument. Players and teachers dealing with intonation issues or poor tone may want to investigate what is happening with the tongue position and work out practice approaches that can help a player learn how to achieve an optimal tongue position according to the register being played.