The Strumming of Coils

How does an electric guitar produce sound?

Bohemian Rhapsody plays live, and the whole crowd goes crazy. Lyrics are screamed, and the massive crowd of Queens fans looks like a choppy ocean–waves rising and falling–as each individual jumps and claps. The music echoes, booming into the cloudy sky, and despite the noise, the sweat, and the cramped bodies, the people look overjoyed to be there.

Just as you think the evening has reached its peak, Brian May’s electric guitar solo comes in.

Somehow, cohesively, every single person in the concert stays still. The energy rises, invisible to the eye, and yet you can see it in the way the people hold themselves — poised, anticipatory, waiting for the crescent. The bright, blinding lights illuminate Brian’s grace, his ease with the instrument is almost unbelievable, and through it all the guitar glints as if it knows it’s the true star.

Just as the crowd goes still, they jump back alive; clapping and jumping and screaming. And yet, the electric guitar is louder than all of them–the notes are upbeat, slightly sharp, distorted unlike the sound of an acoustic guitar–as it resonates throughout the enormous arena, seizing each individual. It is impossible for anyone to hold their ground.

One can go on extolling the virtues of the electric guitar, in terms of music. But that’s not all — there’s something in there for physics, too!

Music can be a very intimate and personal affair. From a single person playing an instrument just for the joy of it to a band performing on the roadside, or even a listener humming along with the notes and lyrics, each individual has always connected with music in a unique way, making the experience special for them.

The guitar has had no small history either: even its name, gui-tar, betrays its global origins: tar is the ancient Sanskrit word for string, a term that was bestowed only after the instrument had made a slow evolutionary journey from Persia.

As bands get more famous, there’s the drive to scale up. In the 1880s, large concert halls were becoming increasingly popular as a venue for performances. But this was a problem for a certain small stringed instrument: guitar notes were so soft they could hardly be heard in a gigantic hall.

To address this problem, people started experimenting with ways to amplify the sound — including through electricity.

Most musical instruments can be classified into two categories: acoustic and electric. In both acoustic and electric instruments, the sound is created by a mechanical force — whether it be pressing a piano key or strumming a guitar. What makes electric instruments different is that the sound created from a mechanical force is assisted by electricity.

For example, each key of an electric piano has a programmed sound that gets relayed when you press that key. But for electric string instruments, there are no such programmed sounds for each note.

Before we talk jump into the specifics of an electric guitar, it is important to understand the basics of sound. Unlike light waves, sound waves are mechanical waves which means that they need a medium to travel through. This is why there is no sound in space: sound comes from the medium’s particles hitting other particles. This is very different from light, which doesn’t depend on the interactions between particles.

An electric guitar has six steel strings that run from the headstock of the guitar to the bridge which is toward the lower end of the body. Unlike an acoustic guitar, which has a hollow body to produce sound, the way the electric guitar produces sound is through pickups.

These pickups hear the sound of the steel strings and then send it to the input jack of the guitar. When the guitar is plugged into an amplifier, using a guitar cable, the signal from the pickup is then transferred to the input jack and then goes through the guitar cable, and to the amplifier, thus producing sound.

But how exactly is sound transferred to the pickup?

Want to make someone’s hair stand up? Just rub a balloon on it, and then hover the balloon just overhead to see all the hair reach up towards it!

Hair is normally neutral: it has an equal number of positively-charged protons and negatively-charged electrons. Because of that’ it’s electrically neutral. But when a balloon is rubbed on the hair, some electrons leave the hair and move onto the balloon. The balloon is now negatively charged and the hair is positively charged.

And now, if you were to hover the balloon slightly over the hair, the protons in the hair get attracted to the electrons in the balloon — and so, the hair stands up.

This balloon-on-the-hair trick is an example of induction. Induction is the movement of subatomic particles like the proton and electron based on attraction, and electromagnetic induction is the phenomenon where induction occurs within the presence of a magnetic field. These phenomena can be useful in many ways, such as if you want to mess with your friend’s hair — or if you want to create an electric guitar.

Electromagnetic induction involves two parts: a conductor, and a magnetic field. In our case, the guitar string is the conductor, and the pickup generates the magnetic field. When the conductor moves, that movement changes the behaviour of the magnetic field — which is in turn picked up by (surprise, surprise) the pickup.

These electromagnetic vibrations are sent through the wire, at which point we can start calling them by a more familiar term: electricity. Here, they reach the next important part of the electric-guitar setup: the amplifier, which converts these electromagnetic vibrations into a kinetic vibration of its drivers: that is, a physical vibration you can actually feel.

And finally, the kinetic vibration of the speaker’s drivers compresses air molecules in a specific pattern which then creates sound.

Have you been a concert, such as the one I described in the beginning? Or have you felt the same pull and anticipation while blasting music from your speakers in your room? Well, wherever you heard it, the electric guitar has captured and shaken the entire world.

There is no doubt that the electric guitar affected pop culture. The glory of the electric guitar peaked with guitarists like Jimi Hendrix, Eddie Van Halen, Jimmy Page from Led Zeppelin, and Kirk Hammett from Metallica. These musicians helped define the genre of rock-and-roll and inspired kids like me to pick up the guitar and start learning it.

As one gets to know the instrument better, one realizes there are many different types of electric guitars. And the most important part, the part which influences your instrument’s sound possibly more than anything else, is the guitar pickup.

In some ways, pickups are very funky objects. They are able to create magnetic fields, detect changes in those fields, and pass on the information to amplifiers.

But if you take a closer look, you’ll realize a pickup is basically a copper wire which is wrapped around six magnets — one magnet for each string of the guitar. This wire is wrapped around 4,000 to 14,000 times to increase the magnetic field of the magnets, thus creating an electromagnet.

To get an idea of the scale: if you were to unravel the entire copper wire, the length of it will be about a mile — that’s the size of eighteen football fields! When the guitar is plugged into the amplifier, the magnetic field around the pickup will activate. Since the guitar strings are made out of steel, and the six magnets are made out of a ferromagnetic material, the two are attracted to one another.

When a string is played, it will vibrate causing the magnetic field of the corresponding magnet to oscillate.

If the string is away from the magnet, then the magnetic field will expand, and if the string is closer to the magnet, then the magnetic field will contract. On the subatomic level, the first case  is electrons from the string moving closer to the magnetic field, pulling the magnetic-fields’ protons with them. When the latter occurs, the string’s electrons are moving away from the magnetic field, again pulling the protons of the field with them in the other direction.

This force that is causing the electrons in the string to move closer or farther from the magnet is called the Lorentz force, discovered by Hendrik Lorentz in 1895.

Simple though the setup may be, it can be modified in many ways. To start with, there are two main types of pickups: humbucker, and single-coil. The humbucker pickup  has two coils and creates a nice resonant sound. The single-coil one creates a thinner and more gritty sound.

This is mainly because of the way the signal travels. With a humbucker pickup, the sound goes to the first coil and then to the next. The coils have a set of six magnets, so the second set of magnets — that is, the second coil — alters the sound and gives it more presence.

The way the pickups on a guitar are arranged also matters. When placed in series, the guitar pickup’s signals will stack on top of each other, making for a thicker tone with more resonance. In parallel formation, the pickups’ signals will be side by side, thus creating a thinner but more vibrant sound.

The modern-day electric guitar was designed in the 1930s and popularized in Jazz music by musicians who wanted to play single-note guitar solos in large band performances too — the kind which, when tried with an classical guitar, would be very hard for most of the audience to hear. The instrument has since made its way into most popular music, strongly impacting the culture and even helping create the genre of rock music.

Knowing about things like electromagnetic induction and pickups helps create a better understanding of the electric guitar and its workings. However, this is only the tip of the iceberg. Effects like distortion, delay, reverb, chorus, tremolo, and flange are also incredibly important impacts when it comes to this instrument!

One common question is: how is distortion created, and why is it associated with the electric guitar and the genre of rock-and-roll?

But perhaps that is a story for next time.