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Wednesday, November 4, 2015

Wave Velocity of String Vibrations

As I move away from the human perception of sound, I'm beginning to look at the physics of sound that are directly applied to musical instruments in order to prepare for my culminating project of the semester. The first thing I'm studying in this context is the wave velocity of strings, a topic essential to understanding how string instruments (piano, violin, guitar) work.

In a previous post, I established that the frequency of a string is proportional to the square of the tension divided by the mass. This makes sense at a basic level to anyone who is familiar with the tuning of a string instrument, such as a guitar. Increasing the tension of a string causes it to create a sound of higher pitch, and increasing the mass of a string causes it to create a sound of lower pitch. This ties into the idea of wave velocity, the speed at which a wave is able to travel on the string. A faster wave has a higher frequency and thus a higher pitch. The opposite is true for a slower wave.

I've established that the pitch of a string is dependent on its tension and its mass density. Linear mass density is defined as mass divided by length for a string. From this definition, we can see that changing mass of a string will affect its pitch.

With an understanding of wave velocity, an instrument creator has three ways to set the pitch of a string instrument. It should already be known that pitch is related to the length of a string, so one can change the length of the string. However, only being able to adjust string length does not grant much freedom for creativity in instrument design. Luckily, one can change the tension on a string and the linear mass density of the string in order to tune it. This is a fundamental idea in a guitar. While the strings of a guitar are similar in length, they clearly differ in thickness, which allows them to produce sounds of different pitches. A guitar player also knows that he or she can adjust the pitch of strings by making them more or less tense by turning the tuning keys.

Works Cited:
1.  Gunther, Leon. The Physics of Music and Color. New York, New York: Springer, 2012.

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