Physics of Music

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Fluid Behaviors of Sound Waves

Sound is capable of being produced only if a medium is present. By this, I mean that, for there to be sound, there must be air. For a sound wave to be emitted by an instrument and be received by a listener, the instrument must excite the air around it and propagate its energy through the air, in the form of compression/longitudinal waves. When received by the listener, the waves pulse the eardrums with the same varying frequencies as they were emitted.

An instrument shakes to produce its tone

In instruments, air is excited and set into oscillation by vibrations. Instruments use such mechanisms as strings (violin and guitar), bars or rods (marimba and chimes and reeds), membranes (drum heads), plates or shells (cymbals or gongs), air in tubes (woodwinds and brass), or volumes of air enclosed in vessels (drum and string bodies) to produce vibrations.

Sound oscillations are created as the oscillating instrument vibrates a column of air and “bumps” the air that is within immediate proximity. This bump sends out a compression, also called longitudinal, waves in all directions.

The tone of a brass instrument is produced as a player contracts their embouchure and expels a jet of air in order to vibrate their lips, and thereby vibrate the air in the tubing of their horn.

The tone of reed instruments (single or double) is produced by holding a reed rigid and forcing air over, or through. When this happens, the reed vibrates, creating an oscillation.

The tone of flute instruments is produced when air blown over the mouthpiece hole excites surrounding particles. When the vibrations of these surrounding particles match the natural frequency of the instrument, the column of air inside the ins...

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...requency higher and into a higher row of harmonics.

How Does Any of this Relate to Music?

Okay, so I just spent the last several pages expressing fluid, energy, and math properties of how sound is put through air. But this essay is dedicated to the physics of music! Simply, none of the attributes of sound, as I have described them in the other pages in terms of physics, are not in any way musical. Music and physics really only have one point of connection, that music is made by manipulating the mechanics of air oscillations--how the signals are emitted by the instruments and received by the listeners. Music itself, however, is made by how the listener interprets or experiences those signals.

As stated in Levarie and Levy's, Tone, A study in Musical Acoustics, "Music is not 'something that happens in the air.' It is something that happens in the soul."

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