The Science of String Vibration: How Guitar Strings Produce Sound

The Science of String Vibration: How Guitar Strings Produce Sound

Playing guitar is seen by many people as an art form — and with good reason. It takes some serious creativity and passion to make music that inspires, moves and enlightens others. You can’t imagine the Stairway to Heaven solo being put together in a laboratory, right?

But the reality is that, although white coats and microscopes may not be involved, there is a lot of science behind how a guitar makes sound — and it starts with the guitar strings. Understanding some of that science will help you understand how string gauge and body size change the guitar’s tone. You don’t need a Ph.D., either! (Although some guitarists like Brian May and Dexter Holland went and got them anyway.) The artsy scientists — or is it science-y artists? — at Strings and Beyond decided to break down the physics of strings for guitarists who want a little extra knowledge to give them an extra edge when they play.

Good Vibrations: Guitar String Waves

First, we need to understand how sound works. At its core, sound is all about vibrations. Anyone who has ever placed their hand on a loudspeaker or a grand piano has likely felt the vibrations coming from it as the music plays. If a club has the music turned up loud, you might even feel vibrations from the floor.

Here’s the basic explanation: when you strike an object — whether a guitar string, a piano key or your desk — it produces vibrations that cause the surrounding air molecules (or water molecules if you’re underwater) to compress and collide in a chain reaction. This air disturbance creates a pressurized sound wave as it travels. Your eardrum senses those vibrations and translates them to audio. A speaker driver or pickup can also sense sound vibrations. In the case of the speaker, it has a cone that pulls or pushes the air around it based on the vibrations it feels to turn them into sound waves.

So while it may seem like a Beach Boys pun, it’s true that your guitar is picking up good vibrations when you play — guitar vibrations, as it were. Science World has a great resource center explaining the fundamentals of sound in more detail. But how do those vibrations become the specific notes you’re trying to play? Let’s continue.

Guitar String Pitch

The sound you ultimately hear depends on how fast the vibrations are from the source. This is known as the frequency — the higher the frequency, the higher the note. Human ears can detect sound frequencies from roughly 20 to 20,000 vibrations per second, aka 20 to 20,000 hertz (Hz) That’s certainly a large range, but many animals have even larger ranges. Dogs have a hearing range of 67 to 45,000 Hz and cats can hear 45 to 64,000 Hz. This is how dog whistles work: they generate a sound frequency higher than what humans can hear but is still within a dog’s range.

Anyway, while we’re certain your pets love listening to you play, let’s get back to guitar strings. The note of a guitar string — also known as the pitch — is directly related to the sound frequency. Here are the frequencies of each string on a standard-tuned guitar along with the corresponding orchestral note:

• Low-E: 82 Hz (E2)
• A: 110 Hz (A2)
• D: 147 Hz (D3)
• G: 196 Hz (G3)
• B: 247 Hz (B3)
• High-E: 330 Hz (E4)

We should also point out that the A4 note — the fifth fret on the high-E string — is 440 Hz. This is relevant because, before electronic tuners, people used tuning forks to tune their instruments. Over time, the accepted Western standard for the tuning fork became 440 Hz. So a guitarist would start by getting their A4 to match the 440 Hz tuning fork, then do the other tuning based on that. The British Standards Institute made it the official international tuning standard in 1939.

Factors That Affect String Pitch

So how is it that placing your finger on the fifth fret changes the E4 to an A4? And why is that that after changing to drop-D tuning, your now low-D string feels so floppy? Four factors work in tandem to determine the frequency of a guitar string: mass, tension, length and vibration mode. Let’s examine each factor in more detail:

Guitar String Mass

The larger and heavier a string is, the slower it vibrates. This is why steel strings get thicker as you move from the high-E to a low-E, and it’s why the strings on a bass guitar are so big compared to a standard guitar. On nylon string guitars, the three low strings (E-A-D) are often denser than the three high strings (G-B-E), which allows them to be closer in diameter.

Guitar String Tension

The more tension you have in the string, the faster it vibrates. When you up-tune a guitar, you add tension to the strings; when you down-tune, you remove tension. This is a big reason why medium-gauge strings are harder to play and put more strain on the guitar neck than light-gauge strings — you need to add more tension to counterbalance the larger mass.

Guitar String Length

Longer strings vibrate slower than faster strings. When you place your finger on the fretboard, you shorten the string and thus make the pitch higher. The height of the bridge saddle also affects the string length. Bassists experience this principle as well with bass guitars that have different scale lengths. A longer scale length requires longer strings, so the strings need to be lighter and/or have more tension to account for the slower vibrations.

String Vibration Mode

There are three ways you can play a string, and each makes it vibrate differently. Plucking a string, with a plectrum or finger-picking, causes a sound wave where the high frequencies fade rather quickly so the sound mellows out. Bowing a string, such as with a violin or standup bass, offers a more continuous and uniform motion to maintain all aspects of the frequency longer.

Striking a string — think Eddie Van Halen’s famous finger-tapping — creates two different vibrations: one from the hammer finger to the bridge and the other from the hammer to the nut (open string) or your stopping finger (closed string). This produces a piano-style overtone sound, though the latter vibration tends to override the former.

So How Does a Guitar Make Sound?

We can already hear some of you: “Yeah, so strings vibrate, But if I just pluck a string by itself, it doesn’t sound like much of anything. What gives?” It’s a valid point. The answer goes back to the explanation of how sound works. The bigger the disturbance in the air is, the bigger the sound is — and a string by itself just doesn’t disturb the air that much. Even the lower strings tend to glide through the air without much trouble.

This is where the rest of the guitar comes in. It’s what takes the relatively low-disturbance string vibrations and turns them into the beautiful sounds you’re trying to make. By transmitting the vibrations through the guitar itself, it accentuates them, increasing the air disturbance and thus the volume.

There are three main guitar designs: acoustic, electric and acoustic-electric. Each of them converts string vibrations to audible sound in a different way, and knowing how they do it will help you fine-tune your existing setup or shop for a new one.

Acoustic Guitars

As we’ve discussed, the non-electrified guitar has origins going back centuries. The principles of how it generates sound remain unchanged after all this time. When the strings vibrate, the guitar bridge and saddle transfer those frequencies to the soundboard (aka the front plate), made of a vibration-friendly springy wood. Braces on the inside reinforce the soundboard and customize how it vibrates.

Those vibrations then travel through the air inside the body, with the resonation and oscillation increasing the sound energy before it escapes from the sound hole. Although the sides and back of the guitar also give off some sound, it is nowhere near as much as the front plate — especially since the back is typically pressed against your body as you play, which absorbs the vibrations.

Barring any other source of amplification, the size of the body on an acoustic guitar will be the primary limiting factor for the volume. The larger the body, the more air it holds and the more vibrations can resonate; thus the volume will be louder. You can also change the tone by adjusting the guitar action, which is how high the strings sit above the fretboard. Higher action increases resonance for more sustain and openness. On the other hand, it will be harder to press down on the strings, and they’ll also be longer, the effects we discussed above.

Acoustic-Electric Guitars

Also known as hollow-body electric guitars, semi-acoustic guitars or AEGs, these were the first attempt at amplifying a guitar’s volume beyond the limits of the body size. The earliest efforts in the 1920s and 1930s consisted of an acoustic guitar with a pickup attached to it. The pickup has a coil that detects string vibrations and turns them into electrical signals. Those signals then pass through a cable into an amplifier, pre-amp or speaker.

You can still buy these basic “amplified acoustic” guitars today, with many of them using electromagnetic pickups to help induce the needed electrical current. Another popular acoustic-electric option is the F-body guitar. This looks more like a modern electric guitar but has a hollow body with two F-shaped sound holes on either side of the strings for playing acoustically, though it won’t be as loud as a true acoustic. An F-body is common for jazz and other music where you want a warm, well-rounded tone.

One common issue with AEGs is that they are more likely to have unwanted feedback and unfocused low-end frequencies, especially at high gain. This is because the sound vibrations from the natural acoustics interfere with the pickup coils, resulting in a “sonic overload.” One solution was the development of the semi-hollow body guitar, which has a piece of solid wood beneath the pickups and strings. This lowers the acoustic volume but also lowers the feedback, so the amplified sound is cleaner and more focused.

Electric Guitars

When you play a modern electric guitar, it’s very quiet — and there’s a reason for that. Like AEGs, electric-only guitars have built-in electromagnetic pickups to sense and convert the string vibrations for amplification. However, they have a solid wood body without any hollowing out. This design minimizes the natural acoustic resonance and blocks out more of the secondary frequencies, giving the pickups a cleaner and purer signal.

Since the pickups now have less information to deal with, they can give more focus to the primary string vibrations. As a result, true electric guitars produce a brighter, cleaner and tighter sound with less feedback. The denser solid body also increases the sustain, letting you hold all frequencies much longer than on an acoustic guitar.

The difference in how the vibrations create sound also accounts for the difference in string materials between acoustic and electric guitars. While most steel string acoustic guitars use 80/20 bronze or phosphor bronze string wrappings, electric guitars use materials like nickel, steel and stainless steel. These metals have more magnetic output than bronze, making it easier for electromagnetic pickups to detect them.

Choose Your Strings With Science

We hope this guitar string science lesson helps you select the right guitar strings for your next work of art. If you’re looking for other information about how guitar strings affect your sound, check out more entries in the Strings and Beyond blog or call us at (877) 830-0722.