Brass tubes and standing waves

According to the band director who gave the low brass their first lesson Tuesday evening, the note that most of them play most easily is an F. When my son played, sometimes it would suddenly drop to a B flat, and the band director told him he could start with either the F or the B flat, whichever seemed easier. But what I kept wondering was, why does it go straight from F to B flat? Why not D, E, or C?

I never played a brass instrument before. I played violin for years, and I tried to learn guitar. I could easily understand how the thickness and length of the string determined the pitch of the note. I also played recorder, and while I never gave a lot of thought to the physics of it, it seemed to make sense that the more holes I covered, the lower the notes were. Longer instruments make lower notes.

I never knew how brass instruments worked, though. I knew that the player’s lip position made a difference, though I never quite knew how. Now that Al is playing one, though, and I am trying to learn it also, I am suddenly very interested in understanding how it works.

It didn’t take me long to find a web site that explained about the important role of harmonics, and another that used the term “standing waves,” but I had to keep looking for a while before I found one that explained this in words I could understand. This article (at a site with a number of helpful article on related subjects) explains first what standing waves are. Next it shows (with helpful diagrams) how the significance of the length of the “container” the waves are in.

I’d never really paid much attention the structure of a brass instrument, but now I have learned that they are all basically long tubes. The tubing curves around, sometimes a lot, but essentially each brass instrument is a long brass tube with a mouthpiece at one end and a bell-shaped opening at the other. How long that tube is determines what is the lowest note that can be played.

Without the valves, the other notes that can be played are also limited by the fixed length of the tube. The lips can be shaped to form higher notes, but only those whose waves fit properly into the length of the tube. I don’t know much about music theory, so that’s about as much of it as I understand, but it makes sense now that I go from an F to a B flat, not a C, D, or E.

I also learned how the valves work. Each one is capable of redirecting the air into an additional length of tubing, which adds to the total length available for the air to vibrate in. (From what I’ve read, some brass instruments are made with ascending valves, where using the valve shortens the total length and raises the tone, but these are less common than descending valves.)

So now I understand a bit better how the instrument makes different sounds when I blow into it. Now if I could just make them sound better…


4 Responses to Brass tubes and standing waves

  1. Margaret says:

    I find sound fascinating. I think I first learned about standing waves in Mr. Rothberg’s physics class, but maybe it was in college. You mentioned in a blog last week that your “sister played a fife for a while,” but that is inaccurate. Your sister blew into a fife for a while, but was unable to produce a single note, and was dismissed from the fife and drum corps (I never tried the drum). I did finally learn to play the piano, and I can produce sounds from a recorder or guitar, but that’s about it.

    • Pauline says:

      I don’t remember learning about sound in Mr. Rothberg’s class at all. We spent most of the year on Newtonian motion, which I enjoyed, then electricity, which I found harder to understand because it was harder to visualize. We finished with a unit on light, which I might have understood better if it hadn’t been the last month of my senior year, and I just didn’t really care about high school anymore.
      We probably used a different textbook than you had. He said they used to use a harder one that required using a lot of math, and they switched so that more students would take physics even if they had only taken basic math classes.
      I remember you being in the fife and drum corps, even though I didn’t remember hearing you play – now I know why.

  2. Paul Wynn says:

    That’s awesome! Maybe a hidden talent will be found reallllll soon.

  3. renaissanceguy says:

    I’m guessing that he is playing the trombone. Is that right.

    I played the trumpet and learned to play the other brass instruments a bit.

    If you think about bugle calls, you will be able to understand audibly what harmonics are. Since a bugle has no valves, it can only play those intervals.

    Traditional trumpet fanfares are the same way. In fact when they first became part of the orchestra, the trumpets could only play fanfares, because they had no valves. They came with sets of interchangeable crooks (bends in the tubing) to be able to play in different keys.

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