Rock Out to Electric Guitar Physics!

In my younger days, while a student at UCLA, I was in a rock band, and yes, I played the electric guitar. See the photo below?

That’s me, with my brother John on bass and friend Matt on drums. We played shows in Los Angeles and Orange County, and we had a great time. While I still play acoustic and electric guitar for fun (and the odd school talent show), my enduring interest in the guitar is actually physics-related.  Being both a musician and a physicist, I like to think I have some unique insights into the physics of sound and music.

 In addition to the guitar, I also play the piano and the harmonica. Over the years, I have examined the physics behind sound and sound waves, and worked hard to figure out exactly how the electric guitar works. Next time you carry an amp for your friend after a rock show, you might think about “what does amp mean?” When you hear a rock star mention distortion or when you hear distortion at a concert, you might wonder about the cause.

for more info, check out Six String Theories 

The other day, I wrote the script for my video about the physics of the electric guitar. I have not yet filmed this video, but wanted to share with all of you musicians and music-lovers just a little bit of the science behind the electric guitar. And for all of you physics teachers out there, the electric guitar may be just the tool you need to engage a bunch of teenagers in the study of physics!

You can learn more about the history and progression of the Electric Guitar at this Smithsonian website, part of the Lemelson Center for the Study of Invention and Innovation.

The electric guitar, like any guitar, consists of strings that are stretched tight across its neck. When these strings are plucked, they vibrate at various frequencies that are supposed to sound like music. The strings on the electric guitar have different densities and different tensions; for this reason, they vibrate at the frequencies intended by the musician. Tightening the string does not change the length of the string very much, but it will increase the wave speed as the standing wave vibrates up and down across the string. 

In my video, of course, I will be writing equations on the board and explaining them (in addition to demonstrating with an actual electric guitar and showing you demos to use with students), which will give you more information about mass, wavelength, amplitude, and tension and how they relate to the electric guitar. 

How is an electric guitar different from an acoustic guitar?

The electric guitar has a property called sustain. When you pluck a note on acoustic guitar, it fades out pretty quickly. But when you pluck on a note on the electric guitar, it is sustained over a longer period of time. That is because the electric guitar’s strings do not need to waste its energy in the body of the guitar in order to make the sound. A regular acoustic guitar’s entire body vibrates with the pluck of a string. 

Acoustic Guitar(above): 

notice the larger body with space for sound to vibrate inside

Electric Guitar(below):

these can be flatter than acoustic guitars 

Pickups and Electromagnetism

The electric guitar, rather than vibrating its body with the pluck of a string, has its signal picked up by the pickups on the bottom. You can actually choose which pickups to use by flipping a switch.

Can you see the little silver pickup magnets?

A pickup is, in a way, electromagnetic, but in this case, to be precise, we should call it a generator. So, how does a pickup work in the sequence of electric guitar music-making events?

An electric current runs through the coil in the pickup, which magnetizes the string and turns it into a magnet. Then, when a magnet is moved over a coil of copper, it generates electric current which can be amplified and then converted into sound by means of a speaker, sometimes called a transducer.

So far, we have discussed strings that vibrate, generating current which can be amplified and sent through a speaker. However, there is one more thing the electric guitar does that the regular guitar does not--distortion.

How is distortion achieved?

When you amplify the signal beyond what the circuit is capable of handling, you get clipping. This happens with a kazoo. When you talk through a kazoo, it will distort your voice, because its vibrating membrane cannot vibrate with enough amplitude. If you have a kazoo lying around, try this!

The same thing happens when you overcrank the signal going into the circuit that amplifies the electric guitar’s sound. A signal that is too large gets clipped and that distortion = the wonderful sounds of rock music.  

Next time you are rocking out at a concert, next time you contemplate the awesomeness that is the electric guitar, you should thank not only the many people who designed and improved upon the electric guitar--don’t forget to thank the physicists!

If you know the original source of this image, please email me!