About a month ago I posted a bit of info and some of my interpretations of the effect that the size and shape of the oral cavity and vocal tract have on intonation while playing a brass instrument. Today I will finally get around to expanding a little bit on this post, again with the help of Vincent Freour, a PhD candidate in acoustics at McGill University and a trombonist. Vincent has given me permission to quote his email to me, which I will do at length since he’s a much better authority in physics than me.
First, Vincent confirmed that I at least had one aspect of my discussion correct. When we play a brass instrument our lips are directly responding to the “acoustic wave” of the vibrating column of air inside the instrument. When we play a pedal B flat on the trombone, for example, the vibrations travel inside the instrument towards the bell, where some of the energy is reflected back until it reaches the lips. This helps to support the vibrating lips and makes the pitch slot. By increasing the muscular contraction of the lips we form “node points” and the vibrating column of air will split into two, three, or more sections. This is why brass instruments play along the, familiar to brass performers, harmonic series. For a little more info about this, check out this article here.
Where I started to go wrong is in eliminating the influence the oral cavity and vocal tract can have at the same time. I wrote earlier, “Traditional brass pedagogy emphasizes playing with as open a throat as possible, which greatly lowers the resonance of the oral cavity as much more of the sound gets absorbed by the porous lungs.”
I’ll quote Vincent, who explains it better than I can.
On the other sides of the lips, we find the vocal tract whose shape and length (in some extent) can be adjusted by the player. In this side of the lips, the same phenomenon occurs, the acoustic wave produced by the vibration of the lips propagates toward the trachea and is reflected around the glottis. Furthermore, like the horn, the vocal tract is a tube (much shorter) that has some resonances: 3 main resonances called formant. The amplitude (ability to emphasize a vibration) and frequency of these resonances can be adjusted by the player by modifying the shape and vertical position of the tongue. Therefore, appropriate adjustments of the vocal tract are likely to support lip vibration and to influence their frequency of vibration that would explain why two different players will have to tune the same horn differently.
My research and performing experience make me quite sure about what I wrote above. Furthermore, I have some comments about what Wolfe mentions when he refers to the approximation of the vocal folds when playing.
First, because it might be true that dissipation in the lungs may reduce the influence of vocal-tract resonance on the support of lip vibration.
Second, because I used to work with a trumpet player that used to make me sing while I was playing. My voice was going in low pitch (the concern was not to control voice pitch) and this exercise really helped: I could reach the higher register on the trombone really easily as if my voice was helping. Technically speaking, I m not sure whether the vocal folds vibration was actually helping supporting lip vibration or not, on the other hand, I’m quite sure that fact the vocal fold were almost closed helped emphasizing vocal-tract resonance effect.
Finally, I perfectly agree that brass player always try to “open the throat” and avoid create any “constriction” in this area. However I’m always trying to convince people that constricting the throat does not mean closing the vocal folds! YES, the vocal folds are located in the glottis, situated in the larynx. YES, I believe it is possible to constrict the larynx without closing the vocal folds and vice versa. NO, we usually don’t feel anything when we close the vocal folds, except that we cannot breath anymore. Bottom line: the sensation we try to create by “opening the throat” has nothing to say with the position of the vocal folds! Therefore, it is totally possible that an “optimum control” of trombone performance goes through an approximation of the vocal folds when playing.
So I stand corrected. As an aside, Vincent and I also corresponded a bit about how after a certain range (Vincent suggested D above high B flat on trombone) the instrument begins to function more like a megaphone. Below that register, the acoustic resonance of the instrument are strong enough that the vocal tract influence is quite low in comparison. Around this high D, however, the vocal tract influence may become much more necessary for the player.
Curiously, it’s been my experience (and that of others, like Donald Reinhardt) that brass players who have an issue with their embouchure form, such as playing on the incorrect embouchure type for their anatomy or playing with too loose an embouchure formation, will have a range cap that is somewhere around the same high D. In my personal case, playing with a Medium High Placement up through grad school, I could play the C# just below it, but couldn’t squeak out a high D to save my life. Changing my embouchure type to a Low Placement type allowed me to break past this range cap. Perhaps there’s something to the acoustical properties of playing above this pitch that make this range cap so common for players with either embouchure issues or not altering their vocal tract accordingly.