Physics of Guitars By: The Chads

Brief History of Guitars Modern guitars can be traced back to Spain; derived from the Spanish word “Guitarra.” Romans introduced “cithara”; made from wood, connected by ribs, with a tuning bar and strings. This was eventually combined with another instrument called the Oud, a sort of early bass guitar, to create an early predecessor of the modern guitar.

Physics of Acoustic Guitars Acoustic guitars consist of four key components: the body, strings, neck, and sound hole or “air cavity.” Each individual part contributes to the unique sound of acoustic guitars. The body has two plates; the top plate resonates high pitches while the back plate resonates low pitches.

Acoustic Guitars cont. The sound waves resonate from the strings and are transferred in to the body through the bridge. The waves bounce around inside the guitar affecting the air, thus creating the sound we hear coming from the sound hole. You can acquire higher pitches by holding down the string on lower frets, while you get the inverse result on higher frets. This sound is determined by tension on the string while held down on the neck.

Sound wave resonance patterns 2.phys.uaf.edu/211.web.stuff/billington/interference.gif Front plate of the guitar 2.phys.uaf.edu/211.web.stuff/billington/gibson.gif Acoustic Guitars

Several Alvarez acoustic guitars

Physics of Electric Guitars Electric guitars also have crucial components including the pickups, strings, and the body. Electric guitars have electromagnetic pickups that have a coil of wire wrapped around them. The close distance between the strings and pickups make the magnets create north/south poles on the strings. Playing a string changes the magnetic field around the pickup and get transmitted through the wires to the amp.

Electric Guitars cont. String vibrations can be calculated according to basic physics laws including relationships between vel., wavelength, and frequency and equations describing motion of strings fixed at both ends. All the strings use the same range of wavelengths; to make diff. frequencies (pitches), velocity must vary. Velocity can vary by changing mass density and/or tension of strings. It’s preferred to play guitar with uniform tension on all strings.

Electric Guitars Waves/vibrations with bar magnet Waves/vibrations with individual magnets

Electric Guitars

The Actual Physics D=l/1.0595^n ▫ D = distance from neck, l = length of string, n = number of fret starting with 1 V=fλ ▫V = velocity of the wave, f = frequency, lambda (λ) = wavelength V=T/u ▫Wave depends on 2 factors: T = tension and u = mass density of the string

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