How Guitars Work
Guitars look fairly simple. A body and neck hold a set of taut strings and the musician clamps the string down at different points and strums or picks. Out comes music. But there’s more to the story…
In order to make sound, any sound, air molecules have to vibrate. But to make music, just wiggling isn’t enough.
The air molecules have to oscillate in a pattern. That pattern is produced by a combination of factors in a guitar - the strings, the top, the cavity (in an acoustic guitar) and several other contributing components. In an electric guitar, the strings’ vibrations are transmitted to a pickup that electrically transforms and transfers them to an amplifier.
In order for those patterns to emerge, the vibrating strings - which vibrate the top, then the cavity inside - have to exist in regular intervals. They have to produce something called ’standing waves’.
Flutes, clarinets and other instruments exhibit the idea more clearly. Even a soda bottle would do. The length of the air column makes it possible for waves of a certain length to fit inside.
Picture a rope you wiggle.
You can wiggle it over all in one wave, or you can have someone hold the center and wiggle both sections. That gives you the idea of waves with different lengths. The length is directly related to the pitch you hear. As you shorten the guitar string by pressing it against a fret, you’re changing the length of that ‘rope’, causing different pitches.
Another major factor is the tension on the string itself. The string is secured at both ends, by the nut and the saddle/bridge, and the tuning peg can change the tension along its length. As you tighten it, the string vibrates faster, which causes a higher pitch. The strings, in order, are: E-A-D-G-B-E, from the lowest pitch to the highest. So the B string near the high end has more tension than the G string below it.
When those strings vibrate they set up vibrations on the top, which oscillates the air inside the cavity. Inside, something similar to the air vibrating in a flute happens. But because of the irregular shape, the pattern inside is much more complicated.
The final result of all these vibrations is a complex, overlapping series of different ‘resonances’ that combine in the air of your ear, which vibrates your eardrums. The result you perceive is all those waves overlapping, like different-sized ripples around the piers at the beach coming from many angles.
Describing all those waves, and their interactions, in detail is a fantastically complex undertaking. But you translate all that complication without apparent effort and hear music - the sweet music of a fine guitar.