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.
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!
