Physics in Low Brass!

Now, while you might possibly be thinking that low brass instruments usually only serve as metronomes for the rest of the band with very few chances at the melody, that's not entirely true. Although we do find ourselves playing only eighth-notes on down beats more often than the flutes, clarinets, and trumpets do, we often have glory parts of our own (for a good example, listen to "Overture to Colas Breugnon." Go sixteenth-notes!). Or if you want to hear something really different, come to "Merry TubaChristmas," featuring euphoniums(/baritones/me!) and tubas only! I went to a rehearsal for this on Saturday, so along with our awesome lab on Friday, I feel like analyzing the Physics involved in this glorious section of the band.

Now among the various low brass intruments, there are pleny of examples of physics in closed tubes, as our intruments are made of metal tubes and our lips close one end as well as provide sound vibrations. All of these instruments work using the same physics concepts as well. Although the trombone uses a slide instead of valves, as the tuba and baritone do, all three of these instruments legnthen their curly "tube" to create different pitches(however, tuning them to the correct pitches is another story :-) ). Since these instruments are "closed tubes," the harmonics can be calculated using the equation Fn=(2n-1)F1, or (2n-1)(v/2L). For my particular instrument playing the f below middle c, first harmonic present is about 190 Hz, with the other harmonics being twice and three times that. As the valves are pressed, or the slide is lowered, the tube gets longer, increasing L and therefore decreasing the fundamental frequency and all subsequent frequencies, lowering the pitch. But, as we learned in class, these instruments will only let one's lips vibrate at a certain frequency (which explains a lot, especially why I have lots of difficulty "lipping up" my rather flat e flat). When the lip position is tightened to vibrate at the next "open" frequency, the lips vibrate faster, thus resulting in a faster frequency of sound waves and a higher pitch. And over the weekend at TubaChristmas rehersal (an hour and a half of glorious baritone and tuba sound!), I discovered once again that having my lips constantly vibrate at a high frequency is not only difficult to maintain, it hurts! I'm not sure how much it had to do with the frequency and how much had to do with muscle fatigue, but about an hour in I didn't want to play the first part anymore. :-)

Although I'm a devoted baritone player, I have tried trombone as well. Yet in both my attempts to find the correct pitches and listening to our outstanding Band 4 trombonists, I've found that even though the tube of a trombone seems much shorter than the winding ones of a baritone, they have relatively the same sound, as does the small-tubed "valve trombone" I play during Marching Band (except baritones sound prettier. Sorry trombonists, I love my instrument). I wonder if the diameter of the tubes has anything to do with it, because we use the same mouthpieces and our music is interchangable, except for the sound. An interesting question to look into. :-)

By the way, that's me with my baritone in its case and my uncle's trombone, plus the mouthpiece I use for both in my right hand. Isn't my shirt cool? :-)