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How brass instruments work

What gives the trumpet its clarion ring and the tuba its gut-shaking “omm pah pah?” And what makes the trombone so jazzy? The answer lies not in the brass these instruments are made of, but in the journey air takes from the musician’s lungs to the instrument’s bell. Like any sound, music consists of vibrations traveling through air. Instruments are classified based on how those vibrations are produced. Percussion instruments are struck. String instruments are plucked or bowed. Woodwinds have air blown against a reed or sharp edge. For brass instruments, however, the vibration come directly from the musician’s mouth.

One of the first things a brass player must learn is to breathe in deeply, until every possible particle of air is crammed into the lungs. Once all that air is inside, it must come out through the mouth, but there, an internal battle takes place as the musician simultaneously tries to hold their lips firmly closed while blowing enough air to force them open. The escaping air meets resistance from the lip muscles, forms an opening called the aperture and creates the vibration that brass players call “the buzz.” When a mouthpiece is held up to those vibrating lips, it slightly refines the buzz, amplifying the vibration at certain frequencies.

But things get really interesting depending on what instrument is attached to that mouthpiece. A brass instrument’s body is essentially a tube that resonates with the air column blowing through it. The way that sound waves travel through this column forms a limited pattern of pitches known as the harmonic series, with notes spaced far apart at the lower end, but coming closer together as the pitch increases. The musician can alter the pitch of the note through slight contractions of the lips and alterations to air volume and speed.

Slower, warm sighing air produces lower pitches, and faster, cool, flowing air produces higher pitches in the series. But any single harmonic series has gaps where pitches are missing and the versatility of brass instruments lies in their ability to switch between multiple series. On instruments like the trumpet, valves can be lowered to increase the length of tubing the air travels through, while on a trombone, this is done by extending its slide. Lengthening the tube stretches the vibrating air column, reducing the frequency of vibrations and resulting in a lower pitch.

This is why the tuba, the largest brass instrument, is also the one capable of playing the lowest notes. So changing the instrument length shifts its harmonic series, while slight variations of the air flow and the player’s lips produce the different notes within it.

And those notes finally emerge through the flared bell opening at the end. What started as a deep breath and a vibrating buzz on the lips has now been transformed into a bold and brassy tune. The musician’s skillful manipulation of every part of the process from lungs, to lips, to the mouthpiece, to the instrument itself creates an amazing palette of pitches that can be heard in musical genres across the globe

. By harnessing the power of natural resonance in a flexible and controllable way, brass instruments are great examples of the fusion of human creativity with the physics of our world.

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