Guitar Strings and Physics

Allen A. Rodriguez

Probably everybody in this world knows what a guitar is and probably everybody knows how it sounds. It’s a really interesting and beautiful instrument but surely not everybody knows how the sound in the guitar works. As every phenomenon in this world, the sound n the guitar surely has an explanation in the world of physics. Why does all the classical and acoustic guitars have the same form or similar? Why the structure in the inside has to be specific? Why the tools in the guitar changes if the material of the string change?  All of these questions may arise to the user or just to an admirer, and as purpose of this work we’ll try to explain it in a new world of vision… physics.

Guitars are made mostly from wood. Wood, apart from giving a great image to the guitar, creates a chamber of resonance that makes the sound wave of the guitar even clearer. It all depends on the wood, that’s why the best the wood, the more expensive the guitar. We’ll focus on how everything in the guitar has to do with the sound of it. They’re two types of strings, the metal strings and the nylon string. The first one is clearly metal and the second one is a synthesized polymer, is “plastic”. Structure on guitar may vary according to the type of string because when tension is applied to both of the strings, metal exerts more force than nylon. This means that if we put metal strings into a nylon guitar, the guitar will break up, because tension was creating excessive pressure to the bridge of the guitar. Now that we’re related to basic materials let’s jump to how is all combined to make the guitar sound.

Guitar has six strings all of them with frequencies of: 82 Hz, 110 Hz, 147 Hz, 196 Hz, 247 Hz and 330 Hz. Strings, depending on material, are stretched in the guitar in order to produce the sound waves that moves into the body of the guitar. Inside they set up an internal resonance in the chamber made up by the body of the guitar which creates vibrations inside of the body that makes compression of air and eventually go out in for of sounds to our ears. Inside the body, if we take a closer look to the internal structure, the guitar has an empty space and some of them have “columns” of wood. This structure is completely on purpose, it’s made up in order to create more vibrations and make a clearer sound. The sound, which is transfer to the wood via the bridge, creates a pattern on the face of the guitar and that’s were sounds propagate. This is when wood roles an important paper, because of the propagation of sound, the sound propagates differently through materials of different densities. If the material is too dense, the sound is transmitted with less energy. 

But an interesting observation could be made and furthermore a theory can be extracted. When the strings are exposed to tension, the process of tuning begins.  As the tension is applied to the string the sound becomes more and more sharp and acute. This is exactly what happens when we take a rubber and stretched it, if we touch it, it will sound and the sound will be acuter if we stretch it even more. So we can establish that: Then sound in a string is directly proportional to the tension applied and inversely proportional to the length of the string. This we can see it in the string of a guitar vs. a rubber. Sound is attached to the tension that is applied to it. That’s what we call tuning of a guitar. 

All of the components in a guitar are important in the role of the sound but tension is what puts everything on work. Tension is the magnitude of the pulling force, which is exactly what we see in the structure of the guitar. The guitar pin is what exerts the force and the string is what experiences the tension. The more tension, the more steady the string and a more acute sound. It’s important to also remind that every string has its maximum tension capacity, even the sound is directly proportional to the tension, tension applied to the cord has to be within the accepted range of tension. This behavior is also known as the module of elasticity. When the string or cord reaches the maximum tension capable, it will break.  It’s really interesting to know how this entire system works. But guitars aren’t the only instruments with strings; there is lots of other instrument that have strings such as violins, Chellos, harps and a lot’s of other. 

It’s very cool to know how to use one of these instruments, but is amazing knowing hoy does the instrument work in the world of science, specially physics. It’s like Frank Wilczek said once: “In physics, you don’t have to go around making trouble for yourself – nature does it for you”.

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Sources Cited:

1. Billington, I. “The physics of the guitar”. http://ffden-2.phys.uaf.edu. Physics 211x. 1999. Web