I like to remind readers from time to time that I’m not a scientist, I’m a science fan. So when I’m reviewing a paper published in a science journal, you need to take my interpretation with a grain of salt. Particularly in the physics domain, I’m self taught. I’ve been called out before for misunderstanding the physics of how we play and will probably be called out again.
Back in April of 2025 the Journal of Applied Physics published an article written by Michael T. Strauss called “A lip vibration model using mechanical properties of flesh.” The problem Strauss and his team were investigating was:
The mechanics of brass instrument playing extend beyond simple lip tension. While the mechanical properties of human lips vary between relaxed and fully contracted states, these properties alone cannot explain the extensive pitch range achieved by professional brass players.
Strauss wanted to look at the existing models of brass acoustics and try to come to a better understanding of how the playing system and instrument interact with each other. The lips are often described in acoustics of brass instruments as a mass and spring system. In this model the lips serve as a flexible spring that move back and forth and set up a harmonic motion. At its most basic level, the “spring” of the lips bounce back and forth.
However, this model is too simplistic to account for the full range of pitches that professional brass musicians are required to play. Looking purely at measurements of how other muscles in the human body react and extrapolating how lip muscles might work, the authors conclude that if the lips were to function solely as a mass and spring system the maximum range of a brass instrument would fall somewhere around 2-3 octaves, well short of the 5 octave or more range that professional brass musicians play. This simplified system would require the player to have an elasticity ratio in the lips that is 16 times greater than the biceps. “This is unlikely,” as the paper says.
Strauss then looked at how actual musicians play and how that compares to what some brass pedagogy texts say. For example, in “The Art of Brass Playing” Phillip Farkas states that the lips should line up so that neither lip slides behind or in front of the other and the air stream should be blown straight forward into the mouthpiece. Strauss notes what I and many others have commented on here, “Interestingly, while Farkas advocates this method, none of the photographs of himself or other Chicago Symphony brass players included in his book demonstrate it.” Regardless, following this description Strauss modeled the lips as “two flat semi-circular vibrating plates.” Combining this concept with instructions by Arban, he added increasing mouthpiece pressure to play higher and reducing mouthpiece pressure to play lower. Then using Leno’s film showing brass embouchures functioning in slow motion Strauss notes that brass players’ lips don’t show any nodal lines inside the mouthpiece while playing. In other words, the lips vibrate in a single pattern and don’t segment into independently vibrating sections the way a string would for harmonics.
Using the Farkas-Arban-Leno model gets closer to reality than the simple mass and spring model, but only extends if from a 3 octave range to a 4 octave range. So there must be some other factors that come into play in order to allow brass musicians to play the entire range of the instrument. In order to investigate this, Strauss used a trombone that attached pickup microphones and pressure sensors at various points in the instrument as well as a pressure sensor that was positioned inside the player’s mouth. This allowed Strauss to confirm that the oral cavity is used by brass musicians as a Helmholtz resonator. As the air is blown into and out of the oral cavity the air inside the mouth will vibrate at a frequency that is tuned by the musician’s tongue arch and jaw position. The level of the tongue arch is an important part of brass musicians’ technique and this is another line of evidence that demonstrates that it does directly influence range.
The other mechanism Strauss found brass musicians use is the way players modify the vibrating mass of the lips. In other words, he found that brass musicians position the mouthpiece so that one lip or another predominates inside the cup and the player blows the air upstream or downstream. Brass musicians are able to reduce aperture length by positioning the mouthpiece with more than one lip inside (also off center), one lip gets clamped with the mouthpiece rim against the teeth more (the lip with less inside) while the other lip presses into and slightly overlaps the clamped lip.
One element of brass technique that isn’t mentioned in the article is the embouchure motion. All brass musicians use an embouchure motion to some degree and while many (perhaps most) are unaware of this phenomenon, it is a necessary part of efficient brass embouchure technique. It would be interesting to see what physicists have to say about the embouchure motion and how it actually helps players change register with less effort. It would also be interesting to learn why one of the basic downstream embouchure types push up to ascend and the other downstream embouchure type pulls down to ascend. I have some speculation, but I would love to read what someone who knows more about the acoustic principals can say about how the embouchure motion works the way it does.
The article is available here if you want to go straight to the source. Let me know if I got any of my summary wrong in the comments.
