In this blog post, we’ll explore the scientific principles of electromagnetic induction and the pickup—the key component that produces the electric guitar’s diverse sounds—and examine how the electric guitar creates such a rich tonal palette.
Have you ever listened closely to the subtle, warm sound of a guitar while enjoying some mellow jazz? If so, what about the lively, crisp guitar sound you hear in upbeat rock music? If you listen to heavier heavy metal music, you’ll likely feel the overflowing energy in the deep, intense guitar sound. In this way, the electric guitar produces a wide range of tones and plays an indispensable role in modern music. Unlike most acoustic guitars, electric guitars do not have a soundbox. Of course, there are semi-hollow and hollow-body electric guitars that do have soundboxes, but they do not produce the rich resonance typical of standard acoustic guitars. Therefore, unless an electric guitar is plugged into an amplifier, it produces only a very soft and faint sound. However, the moment the guitar is plugged into an amplifier, a wide variety of tones come vividly to life. So how does an electric guitar produce such a loud sound without a soundbox? The secret lies in the guitar’s pickups and the scientific principle of electromagnetic induction.
Electromagnetic induction refers to the phenomenon in which an electric current is generated by a changing magnetic field. For example, imagine a coil and a magnet. Magnetic field lines from the magnet pass through the coil, forming a constant magnetic field. When the magnet is moved into the coil, the number of magnetic field lines passing through the coil increases, causing the strength of the magnetic field to change; as a result, an electric current is generated in the coil. When the magnet stops moving, the change in the magnetic field ceases, and no current flows. Conversely, when the magnet is moved out of the coil, the strength of the magnetic field changes again, generating an electric current. This phenomenon is called electromagnetic induction. This principle is explained by “Faraday’s Law,” established by the British physicist Michael Faraday, and later, Heinrich Lenz proposed “Lenz’s Law,” which states that the induced current flows in a direction that opposes the change in the magnetic field.
A prime example of a device utilizing the principle of electromagnetic induction is the guitar pickup. A pickup typically consists of six magnets surrounded by very fine coils; it is positioned beneath the guitar strings, where it forms a magnetic field together with the magnetic metal strings. When a musician plucks a guitar string, the metal string vibrates, causing the magnetic field around the pickup to change. This change in the magnetic field induces a current in the coil, and this induced current is converted into an electrical signal that is transmitted to an amplifier via a cable.
So how does the electrical signal accurately convey the pitch of the sound? Every sound we hear has its own unique frequency. For example, the reference pitch “A4” has a frequency of 440 Hz, meaning it vibrates 440 times per second. When a musician plays the note “A,” the guitar string also vibrates 440 times per second, and the magnetic field around the pickup changes at the same frequency. According to Lenz’s law, the induced current flows in a direction that counteracts this change in the magnetic field, so it has the same frequency as the changing magnetic field. In other words, since the frequency of the guitar string is directly reflected in the frequency of the electrical signal, the pitch is accurately preserved as it is transmitted to the amplifier.
The electrical signal generated in this way is transmitted to the amplifier via a cable, where it is converted back into sound by the amplifier’s speaker and heard by our ears. Furthermore, as the signal passes through various electronic circuits and effects pedals during this process, its form changes, creating a wide range of tones. The rough, distorted guitar sounds heard in rock music are also produced through this signal processing.
Before the advent of the electric guitar, a guitar without a soundbox was like a singer without vocal cords. Consequently, most guitars had to be equipped with large soundboxes to achieve sufficient resonance, and there were certain limitations to the tones they could produce. However, the scientific principle of electromagnetic induction—and the pickups that utilize it—have become the “artificial vocal cords” of the electric guitar, enabling diverse designs and a wide range of tones. From now on, whenever you listen to music featuring guitar playing, try to imagine the process through which that sound is created. Then, you’ll be able to appreciate not only the beauty of the music the guitar produces but also the beauty of the science behind it.
